Paper: Recent investigations on trypanosomiasis in British West Africa

(The previous number of these Transactions, Vol. 49, No. 2, was published on 28th March, 1955.)

ORDINARY

MEETING

of the ROYAL SOCIETY"OF TROPICAL MEDICINE AND HYGIENE, held

at

Manson

House,

26, Portland Place, London,

W.,

on T h u r s d a y , 17th F e b r u a r y , 1955, at 7.30 p . m . The President, F. NORMAN WHITE,C.I.E., M.D., in the Chair.

PAPER

RECENT

INVESTIGATIONS

ON

TRYPANOSOMIASIS

IN

BRITISH

WEST

AFRICA BY

H. W. MULLIGAN,* c.~.G., M.D., B.SC. In 1945, the recently formed Tsetse-Fly and Trypanosomiasis Committee set up in L o n d o n by the Secretary of State for the Colonies invited Professor T. H. DAVEY of the Liverpool School of Tropical Medicine to proceed to British West Africa to examine and report upon the trypanosomiasis problem, and inter alia to formulate proposals for research on this subject. After making an extended fact-finding tour of West Africa, Professor DAWY advised that a regional research organization should be established to serve the needs of the four British West African t e r r i t o r i e s - Nigeria, the Gold Coast, Sierra Leone and the Gambia - - and stressed the essential unity of research on human and animal trypanosomiasis. It was subsequently arranged that the funds necessary to finance an ambitious regional research scheme would be provided jointly by the Colonial Welfare and Development F u n d and by the four West African Governments. A sum of approximately £350,000 was made available to meet estimated capital and recurrent expenditure during the formative stages of the West African Institute for Trypanosomiasis Research. Later, a new scheme, financed on similar lines, was made to provide for the maintenance of the Institute at a level of approximately £75,000 per annum. I had the good fortune to be invited to become the Director of the proposed new Institute and I arrived in West Africa in October, 1947, with terms of reference which gave me that degree of freedom which is essential to the rapid development of any project of this kind. It was decided that the Institute should be located in Nigeria, partly because it is the largest of the West African Colonies in area and population, but mainly because Nigeria provides a much wider variety of conditions connected with tsetse-fly and trypanosomiasis than any of the other West African territories. Furthermore, it is possible to find in Nigeria a close parallel for most of the major trypanosomiasis problems affecting West Africa. No single locality could be found in Nigeria which satisfied * Formerly Director of the West African Institute for Trypanosomiasis Research and presently Head of the Biological Division, Wellcome Research Laboratories, Beckenham, Kent.

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all r e q u i r e m e n t s for t h e p r o g r a m m e of research to be u n d e r t a k e n . It was essential t h a t p a r t of t h e work s h o u l d be d o n e in a n area w h e r e h u m a n a n d a n i m a l t r y p a n o s o m i a s i s was e n d e m i c a n d enzootic, respectively, a n d p a r t in a locality w h e r e cyclical t r a n s m i s s i o n of t h e disease d i d n o t occur u n d e r n a t u r a l conditions. T h e only accessible tsetse-free area w h e r e a suitable site could b e o b t a i n e d was at V o m on t h e h i g h plateau of N o r t h e r n Nigeria, a n d two sections of t h e I n s t i t u t e were e s t a b l i s h e d there. T h e o t h e r two sections were located in the t o w n s h i p of K a d u n a , capital of t h e N o r t h e r n Provinces, w h e r e t r y p a n o s o m i a s i s is e n d e m i c . C o n s t r u c t i o n was c o m m e n c e d i n S e p t e m b e r , 1948, a n d was virtually c o m p l e t e two years later. T h e I n s t i t u t e b u i l d i n g s at t h e two m a i n centres p r o v i d e spacious l a b o r a t o r y a c c o m m o d a t i o n including, in each section, space for a visiting scientist. T h e laboratories are of s i m p l e design a n d are readily a d a p t a b l e to a l m o s t any p u r p o s e ; a m p l e r o o m has b e e n left for expansion. T h e I n s t i t u t e is adequately, t h o u g h n o t lavishly, e q u i p p e d for t h e type of r e s e a r c h work u n d e r t a k e n . S u b s i d i a r y b u i l d i n g s include stores, workshops, a n d a n i m a l houses ; in all, it is possible to m a i n t a i n m a n y t h o u s a n d s of small l a b o r a t o r y a n i m a l s a n d u p to 100 h e a d of cattle or o t h e r large m a m m a l s for r e s e a r c h p u r p o s e s . A t t h e c o m m e n c e m e n t of the scheme, t h e I n s t i t u t e was a d m i n i s t e r e d b y t h e N i g e r i a n G o v e r n m e n t , b u t it soon b e c a m e a p p a r e n t t h a t t h e a d m i n i s t r a t i o n of a n i n t e r - t e r r i t o r i a l r e s e a r c h organization b y a n y one of t h e p a r t i c i p a t i n g G o v e r n m e n t s was u n w i e l d y and, in r e s p o n s e to r e p r e s e n t a t i o n s , t h e I n s t i t u t e was set u p as a b o d y corporate w i t h its o w n S t a t u t o r y M a n a g i n g C o m m i t t e e c o m p o s e d of representatives of all t h e c o n t r i b u t i n g G o v e r n m e n t s . T h e I n s t i t u t e accepts n o responsibility for t h e actual c o n d u c t of t r y p a n o s o m i a s i s control, b u t it serves as a clearing h o u s e for i n f o r m a t i o n a b o u t trypanosomiasis, as a n advisory bureau, a n d as a centre for t h e t r a i n i n g of expert t e c h n i c a l personnel. T h e I n s t i t u t e is organized in f o u r sectibns dealing, respectively, w i t h E n t o m o l o g y , Epidemiology, Protozoology a n d V e t e r i n a r y .Trypanosomiasis. N o h a r d a n d fast line can b e d r a w n b e t w e e n t h e f u n c t i o n s of t h e various sections b u t each is r e q u i r e d to u n d e r t a k e i n v e s t i g a t i o n s for w h i c h t h e t r a i n i n g a n d experience of its staff m a k e it b e s t suited.

The account of the work which is given below represents the combined efforts of a team of investigators and, in presenting this paper, I wish to stress that I make no claim to any personal contribution other than that ordinarily made by the person responsible for the initiation and direction of research. RESEARCH WORK ENTOMOLOGY.

The ecology of Glossina palpalis. Shortly after my arrival in West Africa, Dr. T. A. M. NASH, Medical Entomologist of the Nigerian Sleeping Sickness Service, joined the staff as Chief Entomologist, bringing with him a nucleus of trained technical staff and field assistants. Dr. NASH continued investigations on the ecology of G. palpalis which he had recently begun at a small Field Station near Kaduna and these investigations were intensified and extended as additional scientific staff became available. In all, this investigation was continued over a period of 6 years and the results obtained have recently been published (NAsH and PAGE, 1953) ; the brief account which follows covers the most important of their observations. I n t h e s a v a n n a h zones of W e s t Africa, G. palpalis is confined to t h e vicinity of rivers a n d s t r e a m s a n d its p e r m a n e n t h a b i t a t s are to b e f o u n d in t h e dense f r i n g i n g forest w h i c h contrasts so strikingly w i t h t h e open w o o d l a n d s a v a n n a h , O v e r a p e r i o d of 6 consecutive years, a detailed s t u d y was m a d e of t h e G. palpalis p o p u l a t i o n along 2,400 yards of a selected s t r e a m - b e d n e a r K a d u n a w h i c h is close to t h e e x t r e m e n o r t h e r n limit of this species' distribution. T h e m e t h o d s of investigation i n c l u d e d the r e g u l a r catching, m a r k i n g a n d liberation of adult flies, t h e regular collection of p u p a e a n d the m a i n t e n a n c e of captive fly p o p u l a t i o n s w i t h i n t h e species' n a t u r a l habitats. Meteorological stations set u p w i t h i n t h e fi-inging forest of t h e s t r e a m a n d in t h e adjacent o p e n w o o d l a n d revealed the o c c u r r e n c e w i t h i n t h e f r i n g i n g forest of a n ecoelimate w h i c h is m u c h m o r e equable t h a n t h e general climate of t h e w o o d l a n d . O f two meteorological stations set u p w i t h i n the f r i n g i n g forest, one was sited o n a r e a c h of t h e s t r e a m - b e d w h i c h was k n o w n to b e c o m e waterless d u r i n g t h e d r y season a n d t h e o t h e r in a s t r e t c h w h i c h was k n o w n to c o n t a i n pools of w a t e r t h r o u g h o u t t h e

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d r y season. N o appreciable differences were o b s e r v e d b e t w e e n t h e recordings in these two stations in the wet season but, in t h e late d r y season, t h e ecoclimate n e a r t h e p e r m a n e n t pools was m u c h less extreme. D e s p i t e considerable a n n u a l variations in t h e severity of t h e late d r y season the microclimatic conditions r e m a i n e d r e m a r k a b l y c o n s t a n t f r o m year to year. T h e extent of t h e e q u a b l e m i c r o c l i m a t e available v a r i e d f r o m year to year, b e i n g m o s t restricted in severe dry seasons w h e n t h e w a t e r table was at a low level following a b n o r m a l l y low rainfall. I t was repeatedly o b s e r v e d that, as climatic conditions b e c o m e inimical to G. palpalis, this species t e n d s to c o n c e n t r a t e in those reaches of t h e s t r e a m - b e d w h e r e an e q u a b l e m i c r o c l i m a t e is to b e f o u n d a n d t h a t t h e m o r e severe the d r y season t h e m o r e r e s t r i c t e d are t h e e q u a b l e m i c r o c l i m a t e s a n d t h e greater t h e degree of fly c o n c e n t r a t i o n . I n years in w h i c h m a x i m a l c o n c e n t r a t i o n of G. palpalis was observed, this species was restricted to the i m m e d i a t e vicinity of a few p e r m a n e n t pools. T h i s o b s e r v a t i o n has a n i m p o r t a n t epidemiological significance in t h a t villages in N o r t h e r n Nigeria are sited n e a r p e r m a n e n t pools a n d hence, i n d r y seasons of exceptional severity, G. palpalis is c o n c e n t r a t e d in t h e closest p r o x i m i t y to m a n . I n s u c h c i r c u m s t a n c e s wells have dried u p so t h a t m a n a n d fly b e c o m e d e p e n d e n t for t h e i r existence o n t h e same w a t e r holes. T h i s e x t r e m e l y close association b e t w e e n m a n a n d fly, c o u p l e d w i t h t h e h i g h t e m peratures t h e n prevailing, is believed to afford o p t i m u m c o n d i t i o n s for t h e t r a n s m i s s i o n of sleeping sickness. W i t h the a d v e n t of t h e r a i n y season, conditions again b e c o m e favourable for free m o v e m e n t of the fly a n d dispersal along t h e s t r e a m - b e d t e n d s to b r i n g infected flies into contact w i t h o t h e r villages. T h e r e is good reason to believe, therefore, t h a t t h e m a x i m u m c o n c e n t r a t i o n of G. palpalis w h i c h occurs in d r y seasons of exceptional severity m a y b e m o r e d a n g e r o u s f r o m t h e p o i n t of view of t h e t r a n s m i s s i o n of h u m a n t r y p a n o s o m i a s i s t h a n less severe d r y seasons w h e n w a t e r is m o r e a b u n d a n t ; in t h e latter case, G. palpalis is u b i q u i t o u s along t h e s t r e a m s a n d m a n - f l y contact is m o r e i m p e r s o n a l b o t h o n account of t h e lesser degree of fly c o n c e n t r a t i o n a n d t h e greater d e p e n d e n c e of m a n o n wells t h a n o n s t r e a m - b e d w a t e r holes. T h e season w h e n G. palpalis is m o s t h i g h l y c o n c e n t r a t e d a n d m o s t restricted in its m o v e m e n t s covers t h e latter p a r t of t h e d r y season a n d t h e c o m m e n c e m e n t of t h e wet season, a n d it seems p r o b a b l e that, in N o r t h e r n Nigeria, it is at this season t h a t t h e b u l k of h u m a n t r y p a n o s o m i a s i s is t r a n s mitted. O n t h e o t h e r h a n d , t h e d a n g e r to cattle grazing o n t h e n e w grass along miles of s t r e a m - b e d infested w i t h tsetse w o u l d be greater in d r y seasons of lesser severity t h a n in dry seasons of e x t r e m e severity w h e n fly are h i g h l y c o n c e n t r a t e d at focal points.

Dispersal. T h e season of l o n g - r a n g e travel or dispersal of G. paIpalis c o m m e n c e s at t h e b e g i n n i n g of t h e h e a v y rains (June), reaches a peak at t h e e n d of t h e h e a v y rains (October), a n d t h e n persists on a d i m i n i s h i n g scale t h r o u g h t h e d r y season u n t i l t e r m i n a t e d b y h i g h t e m p e r a t u r e a n d low h u m i d i t y ; t h e season of l o n g - r a n g e travel lasts in all a b o u t 9 m o n t h s . B o t h sexes indulge equally in l o n g - r a n g e dispersal ; it has b e e n o b s e r v e d t h a t flies f r e q u e n t l y travel as far as 1,000 yards w i t h i n 24 h o u r s a n d even distances of 2,0G0 y a r d s are n o t u n c o m m o n . T h e longest distance o b s e r v e d for a fly to travel along t h e s t r e a m in one day was two miles a n d the longest distance of k n o w n travel was t h r e e miles. T w o flies were o b s e r v e d to have travelled a distance of one mile across o p e n w o o d l a n d to r e a c h a n o t h e r s t r e a m system.

Influence of temperature on survival. O b s e r v a t i o n s o n captive flies k e p t in the s t r e a m - b e d d u r i n g t h e latter p a r t of a severe dry season s e r v e d as a check o n t h e s t u d y of t h e wild fly p o p u l a t i o n d u r i n g this season of exceptional stress. O v e r 10-day periods, an average m a x i m u m t e m p e r a t u r e of 88°F was associated w i t h h i g h fly m o r t a l i t y in b o t h sexes ; male flies are seriously affected b y an average m a x i m u m t e m p e r a t u r e of 84°F while females are n o t equally affected u n t i l t h e average m a x i m u m tel~qperature reaches 91°F. A t average m a x i m u m t e m p e r a t u r e s of 93 ° to 95°F t h e fly p o p u l a t i o n is e x t e r m i n a t e d . It m a y be c o n c l u d e d f r o m these observations t h a t t h e reason w h y t h e wild fly p o p u l a t i o n evacuates the waterless stretches of a s t r e a m at this season is t h a t failure to do so w o u l d result in its virtual e x t e r m i n a t i o n d u e to extremes of t e m p e r a t u r e a n d s a t u r a t i o n deficit.

Expectation of life. It has b e e n possible on t h e basis of t h e r e c a p t u r e of m a r k e d wild flies to m a k e a conservative estimate of t h e expectation of life of G. palpalis. A t t h e very e n d of t h e rainy season the expectation of life of b o t h sexes is t e m p o r a r i l y h i g h h u t it falls rapidly to b e c o m e m i n i m a l b y t h e m i d d l e of the d r y season because the a p p r o a c h i n g rigours of t h e late d r y season will d i s c r i m i n a t e against t h e older flies, m a k i n g t h e a t t a i n m e n t of old age impossible. E x p e c t a t i o n of life is greatest at the c o m m e n c e m e n t of the rainy season because the s u r v i v i n g p o p u l a t i o n consists m a i n l y of y o u n g flies a n d t h e r e are some m o n t h s of v e r y favourable conditions ahead. E x p e c t a t i o n of life d i m i n i s h e s slightly b u t steadily d u r i n g the season of heaviest rainfall b u t this t e n d e n c y is a b r u p t l y reversed w h e n t h e rains abate. T h e s e

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observations have epidemiological significance to both human and animal trypanosomiasis. From the point of view of transmission of the bovine disease the maximum expectation of life at the beginning of the rainy season coincides with the northward migration of nomadic cattle and the high expectation of life at the beginning of the dry season coincides with their southward migration. From the standpoint of human trypanosomiasis the maximum expectation of life of G. palpalis coincides with the period when man and fly are brought into the most intimate association. T h e minimal expectation of life among the flies found in the cold mid-dry season, suggests that these flies would be of relatively little danger to man or animals.

Longevity. On the basis of recapture of wild flies, the average age of female flies has been conservatively estimated to vary from 6 to 15 weeks and of male flies from 4 to 8 weeks, according to the season. In experiments of this kind it is not possible to ascertain the date of emergence and death of wild flies. In order, therefore, to estimate the potential longevity of G. palpalis, captive flies were kept in the stream-bed near permanent pools during the dry seasons of two mild years, that is, in conditions which were believed to be very favourable for their survival. After a period of high initial mortality, females survived a period (20 to 60 days) with few deaths but about half of them died between the 60th and 140th days and the remainder by the 233rd day. A similar trend was observed among male flies but about half the deaths occurred between the 20th and 80th days and the remainder died by the 168th day. T h e extremes of age attained by G. palpalis were observed to be 6 months for wild female flies and 8 months for captive flies ; the corresponding extremes for male flies were 5 months for wild flies and 5½ months for captive flies.

Breeding season. Observations on the breeding of G. palpalis based on pupal collections and pregnancy dissections of wild flies have shown that, in the drier parts of its range, this species breeds throughout the year. Laboratory experiments have suggested that the rate of reproduction in the field would be retarded by the low temperatures prevailing during most of the dry season and accelerated by the high temperatures occurring in the late dry season and early rains.

Larviposition. In the season of heavy rainfall, G. palpalis does not appear to larviposit in the open woodland but in many scattered sites along the higher ground forming the boundary between fringing forest and woodland ; here the pupae are safe from inundation except in years of excessive precipitation.

Seasonal density. A well-defined seasonal fluctuation in the density of G. palpalis has been observed. From a peak density at the height of the rains, the fly population decreases rapidly as the rainy season is coming to an end and gradually declines through the dry season to become minimal at the commencement of the following wet season. This period of progressive reduction lasts from October until April or May and is followed by a period of recovery which results in maximum density in August or September. Seasonal fluctuations in fly density have been correlated with temperature and humidity which also affect the longevity of adult flies and their reproduction rate. Longevity is reduced at high and very low saturation deficits and increased at intermediate points, while the breeding rate is increased at high temperatures.

Infection rates. Among the thousands of wild flies collected from streams in the Kaduna-Katabu area, and dissected, 3.3 per cent. showed mature trypanosome infections o f which the vast majority belonged to the T. vivax group.

Food supply. As regards food supply, it has been shown that G. palpalis can maintain itself when the only available sources of blood are baboon, duiker, monitor lizard and possibly also monkey ; the blood of larger game animals is not essential to the survival of this species. From the results of this investigation it has been possible to define the conditions necessary for the permanent and temporary habitats of G. palpalis in the savannah zone of Northern Nigeria.

Habitats. A permanent habitat requires the presence of good lateral and vertical insulation provided by evergreen vegetation and a free flight-line along the stream-bed or through the fringing forest so that the

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fly may be able to travel from dense shelter to its feeding grounds. If the fringing forest is narrow, the presence of permanent pools of water is essential to the fly's survival at certain seasons ; even here the essential microclimate may be dissipated by the wind unless the stream banks are steep and sharply defined. Where, however, the fringing forest is extensive and well insulated these latter features are not essential. Favourable temporary habitats of G. palpalis are of great importance in that, following a period of low fly-density, they enable the fly to re-establish a high density. Such temporary habitats are characterized by continuous vertical insulation leading to suppressed undergrowth and good visibility thus providing extensive feeding grounds for the fly during the season when the grass is long. Lateral insulation is usually absent but small thickets provide temporary breeding sites until extreme conditions render them untenable. The vegetation is usually of a mixed deciduous type.

Laboratory studies on behaviour. An extended investigation was undertaken in the laboratory to determine the factors governing the selection of sites by female G. palpalis for the deposition of larvae. This investigation was suggested by the repeated failure of field observations to provide conclusive evidence as to the whereabouts of this species' breeding places during the wet season. It is not possible to summarize the results of these interesting and enlightening experiments carried out by Mr. PARKER,except to say that it has been conclusively shown that the gravid female does in fact select the sites in which she deposits her larvae independent of their proximity to favoured resting places.

A new method for the eradication of G. palpalis. One important result of the ecological studies on G. palpalis described above was the conception of an entirely new method for the eradication of this species from certain of its riverine habitats. Wherever the fringing forest is demarcated by a wall of shrubs and climbers and is roofed over by a canopy consisting of the creeper-covered crowns of medium-sized trees, it appeared that by felling the trees of the canopy so as to block the stream-bed and by sparing the shrubs, thickets, climbers and giant emergents, the stream-bed would become so choked by low thicket that G. palpalis would be unable to travel within the ecoclimate essential to its survival at certain seasons and would therefore disappear. " Obstructive clearing," the name given to this novel method, might be expected to be of value in the savannah zones wherever climber and thicket species of vegetation are common components of the fringing forest ; if successful, the method would result in an enormous reduction in cost as compared with partial clearance and its subsequent maintenance. A special grant of approximately £10,000 was made to defray the cost of a pilot scheme to put this new method to practical test. Work was commenced in 1953 and the results so far obtained have been most encouraging. A typical stream system near Kaduna was selected for the pilot scheme and, after it had been kept under observation for a preliminary period, a stretch of two miles was isolated by mile-long ruthless barrier clearings. T h e section of stream thus isolated was cleared by the new obstructive clearing technique during the dry season. T h e initial effect was to cause a dramatic reduction in the fly population. When the rains came, fly-density on the control stream rose enormously, as is usual, but, in the experimental stream, fly-density was reduced to a very low level. It is highly probable that total eradication of fly would have been achieved but for an occasional fly crossing the barrier clearings. It was observed that flies were taken only at the extremities of the experimental stretch and it was confirmed by liberating marked flies in the control stream that flies were actually crossing the barriers. These are now being increased in length. No complaints were made by the local cultivators and the use of the new method gave rise to no undesirable

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consequences such as flooding. Initial cost worked out at a fraction of that for ordinary partial clearing and there are, of course, no maintenance costs to consider.

High forest tsetse-flies. T h e extensive investigation of the ecology of G. palpalis which has been very briefly summarized above has yielded results of great value in relation to both the epidemiology and the epizoology of trypanosomiasis and in pointing the way to improved methods of tsetse control. It was felt that, for the present, sufficient information about the ecology of G. palpalis in the savannah zones of West Africa had been obtained to enable practical control measures to be undertaken on a sound scientific basis, and that the time had come to direct attention to the investigation of tsetse species of the high forest belt concerning which very little is known. No appreciable amount of research had hitherto been done either on the fusca group of tsetse which is restricted to the forest belt, or on G. longipalpis which occurs in patches of savannah within this belt. Likewise the ecology of G. palpalis has been little studied in areas of high rainfall where conditions are vastly different from those pertaining near the northern limit of this species' distribution. It was decided, therefore, to establish a Field Station in an area that would provide easy access to the maximum number of high forest tsetse species, as well as those common to both forest and savannah. After two extensive surveys had been made, a suitable site for this Field Station was selected at Ugbobiga in the Benin Province of Southern Nigeria. Eight different species of tsetse have been found within a radius of" a few miles of Ugbobiga namely, G. fusca, G. nigrofusca, G. tabaniformis, G. medicorum, G. longipalpis, G. palpalis, G. tachinoides and G. pallicera. An investigation similar to that completed on G. palpalis in Northern Nigeria has been commenced, and it is already apparent that the ecology of this species in the much wetter conditions of Benin Province is entirely different from that in the arid zones at the northern limit of this species' distribution. A field investigation of G. longipalpis (the southern representative of G. morsitans) has also been commenced. This species is likely to be of considerable veterinary importance since dissection of over 600 flies yielded an infection rate of 23 per cent. ; the majority of the fly infections were with trypanosomes of the T. vivax group.

A new survey method. T h e time-honoured method of catching tsetse-flies is to attract them to man or baitanimals or to specially designed traps. Since these methods had failed in high forest areas, Dr. NASH resorted to direct searching of natural tsetse resting-places with great success. Using this new survey method he has shown that certain high forest species hitherto regarded as extremely rare are not only prevalent but are potential vectors of trypanosomiasis. The direct searching method has since been extended to the study of other species of tsetse-fly and has yielded information of considerable interest and importance in relation to their behaviour.

Erosion in relation to tsetse clearing. Another long-term experiment is worthy of brief mention. This was commenced in 1949 with the primary object of ascertaining whether the common practice of clearing streambed vegetation for the purpose of tsetse eradication leads, as has often been alleged, to a greatly accelerated rate of erosion. So far as this experiment has gone, it has shown that the

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degree of normal erosion which takes place is not alarming and there is no significant increase in erosion following ruthless clearing of riverine vegetation. On the contrary, a certain amount of silt is deposited and grasses invade the water-course in cleared sections of the stream-bed.

Systematic studies. Apart from the field studies described above, considerable attention has been paid to the laboratory investigation of tsetse. Dr. NASH and Mr. PARKER compiled a TsetseDistribution Map of West Africa from data already available or supplied by the British, French and Portuguese territories. This map has been incorporated in the All-Africa Tsetse Map. Since the inception of the Institute, tsetse surveys have been made over the greater part of the British Cameroons and the species collected have been accurately identified by genitalia dissections. Many of these species belong to the fusca group, and the large number of permanent preparations made will be invaluable in attempting the identification of some unusual specimens. One new species has been discovered, but has not yet been described.

Laboratory rearing of G. palpalis. An essential pre-requisite to the work of all sections of the Institute is a constant supply of adequate numbers of " clean " tsetse flies for experimental purposes. This need was foreseen when the Institute was planned and a large fly-breeding room was provided, although at that time, large-scale production of tsetse in the laboratory had not been achieved and exact requirements were unknown. Persistent efforts have been made to establish a simple and reliable fly-breeding routine requiring the minimum of highly skilled supervision. Although the position cannot yet be said to be satisfactory in all respects, a large measure of success has been achieved in the large-scale rearing of G. palpalis in the laboratory. A breeding stock of about 4,000 fertilized female flies can now be maintained throughout the year and the output of pupae is of the order of 50,000 per annum. This result has been achieved only after a great deal of research. It has been shown, for example, that male flies are not fully potent until they are a week old, and that female flies are most readily fertilized on the 3rd and 4th days of life. It is uneconomical to keep females over the age of 100 days. Other factors of importance are the proportion of male and female fliesplaced in the mating cage, the size of the cage, and the length of time the sexes are left together. EPIDEMIOLOGY.

It is a remarkable fact that, by comparison with the vast amount of work which has been done on tsetse-flies and trypanosomes, co-ordinated studies on the epidemiology of trypanosomiasis, human or animal, have been carried out on only a very limited scale. The many isolated observations made in the past have not been adequately correlated so as to give a clear picture of the epidemiology of the disease. Recognizing the need for repairing this deficiency an early decision was taken to set up a special section of the Institute to undertake epidemiological studies.

Epidemiology of human trypanosomiasis. Pending the provision of facilities for a fresh approach to this problem, Dr. DUGGAN,

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and later Dr. HUTCHINSON,applied themselves to unearthing previous records, subjecting these to critical analyses and reconstructing the history of epidemics of human trypanosomiasis in Nigeria. In this way a great deal of valuable information, much of it buried and forgotten in inaccessible files, was brought to light, and from this critical examination an enlightening picture of the genesis of epidemics of sleeping sickness in Northern Nigeria was obtained. Regardless of what the incidence of sleeping sickness may have been in earlier times, a highly pathogenic form of the disease is known to have spread far and wide through Northern Nigeria during the present century. It is difficult to escape the conclusion that the circumstances which made this possible were connected with the British occupation of the country. The continual state of strife which prevailed prior to the British occupation confined the population to walled towns and villages and restricted agriculture and fuel collecting to the immediate environs of them, thereby effectively eliminating tsetse-haunts in close proximity to human habitations. Among those who ventured abroad to hunt or to pillage, man-fly contact was sufficiently " impersonal " to reduce opportunities for the transmission of trypanosomiasis to negligible proportions. It can scarcely be doubted that, in the country at large, tsetse were as ubiquitous and as prevalent as they are today. The political changes which occurred during the early part of this century were closely followed by striking sociological changes. The population, no longer confined within walls, began to move freely about the country and to apply themselves to peaceful avocations. The opening up of roads and railways enormously increased facilities for trade and travel and soon the old trans-Sahara route was largely superseded by new routes to the coast. Farming was no longer restricted to the immediate environs of walled towns and villages and new industries developed. The net result was that large sections of the population were brought into much more intimate contact with tsetse and it remained ofily to introduce a reservoir of infection to complete the set of circumstances necessary to precipitate serious outbreaks of the disease. It was not long before this was provided. Strong evidence has been produced to show that, while the greater part of Northern Nigeria was, until recently, virtually free from human trypanosomiasis, two separate endemic loci had existed for many years. One of these had apparently been smouldering in the region of the Niger-Benue confluence from early times and was probably derived orig:nally from spread of the disease down the Niger. The nature of the infection appeared to be typical of classical T. gambiense infection. The other endemic focus existed in the Lake Chad basin, and here the infection appears to have been of a more virulent type, in some respects resembling T. rhodesiense. It has been possible to trace the spread of the disease northwards from the Niger-Benue focus and southwards from the Lake Chad focus until the two met and intermingled somewhere in the vicinity of Anchau in Zaria Province. There is here a probable explanation for some puzzling discrepancies in the manifestations of the disease which formerly perplexed clinical observers in Northern Nigeria. It has been possible to :nap out with a considerable degree of accuracy, the main routes along which the disease spread, and 'to fix the approximate dates when various localities became affected. From small beginnings in the early part of the century, sleeping sickness epidemics occurred in increasing frequency and magnitude until, within a period of some 20 years, their incidence and severity reached the proportions of a pandemic which called for energetic control measures. It is not known to what extent the disease might have continued to spread had it been allowed to proceed unchecked. Some of the more important factors .in the causation of this series Of explosive epidemics

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will be briefly outlined. The first introduction of the disease to non-endemic areas was almost certainly effected by troop movements, but this source of infection is believed to have been insignificant in comparison with the part played by labour forces employed on the opening up of road and rail communications. Infections introduced in this way were soon carried a stage further by travellers and traders traversing the newly developed lines of communication, and eventually foci of infection became established along hundreds of miles of these newly opened routes from which, in due course, the disease filtered through to the remoter areas. Once a reservoir of infection had been introduced, the altered mode of life of the community created ideal conditions for the spread of sleeping sickness. Where the majority of the peasants adhered to farming as their means of livelihood extensive areas were brought under cultivation along the tsetse-infested streams draining into the Niger and Lake Chad systems. Villages sprang up where farming was practised and man-fly contact became increasingly close. The epidemics of sleeping sickness which inevitably followed often so decimated the stricken villages that the surviving inhabitants, some of them already infected, dispersed and carried with them the seeds of fresh epidemics. Elsewhere, the development of the tin-mining industry created conditions which were, if anything, more favourable for the dissemination of the disease. The method of tin mining employed necessitated the use of hundreds of tsetse-infested streams to wash the mineral deposits with the result that man-fly contact along these streams became most intimate. The labourers were at great risk and, in due course, infection rates among them reached alarming proportions. Unfortunately, labour was continually shifting, so that fresh localities became infected, including many isolated pagan villages in and around which tsetse already abounded. The results were devastating. For a time sleeping sickness was almost an occupational disease of the traveller, the mine labourer and the cultivator, but it continued to spread until practically every member of the community was at risk. Everyday domestic activities such as marketing, fetching water and washing brought unsuspecting victims within the range of infected tsetse. It is clear that the most potent factor in the causation of the widespread epidemics of sleeping sickness which have occurred throughout Northern Nigeria during the past 30 to 40 years was the dispersal of infected persons. There is no evidence to suggest that extended distribution or increased prevalence of tsetse played any appreciable part in the production of these widespread epidemics, though these factors may sometimes have been of local importance. So far as is at present known, the incidence of sleeping sickness in the high forest zones of Southern Nigeria is very slight though endemic foci are known to exist. Recent surveys have shown that, in some localities at least, tsetse may be prevalent and widely distributed where the disease does not occur, or occurs in such low-grade form that its presence has escaped unnoticed. The reasons for the scarcity or apparent absence of the human disease in these localities, where animal trypanosomiasis is highly enzootic, remain unexplored and unexplained.

(a) Epidemiologyof human trypanosomiasis in the Gambia. An intensive investigation of the epidemiology of sleeping sickness in the Gambia was undertaken by Dr. HVTCmNSON in 1951-52. In the course of this survey over 55,000 persons were examined. The Upper River Division was surveyed in greatest detail but spot surveys were made in all representative parts of the territory.

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The diagnosis of trypanosomiasis was established by both blood examination and lymphgland puncture and, in some cases also, by examination of the cerebro-spinal fluid. The survey revealed an over-all incidence of sleeping sickness of 0.65 per cent. of the population. The incidence of the disease was found to vary within very wide limits being completely absent in some localities and present in endemic or highly endemic form in others. The disease, in all cases caused by T. gambiense, is clinically of a mild type in the local inhabitants. Glandular enlargement is an early and prominent symptom of the Gambian disease, and since it is recognized by the local inhabitants, subjects tend to report for treatment at an early date. There is no doubt that hospital and dispensary treatment, which is widely available, plays an important part in limiting the incidence and effects of the disease in the Gambia. Sleeping sickness is widely distributed but about two-thirds of the cases are reported from the maritime Western Division. Elsewhere, the incidence of the disease in restricted localities may be as high as, or even higher than, in the maritime villages. As the human disease occurs only where G. palpalis is present, and is absent where this species does not occur but where G. morsitans may be prevalent, there can be no reasonable doubt but that G. palpalis is the sole vector. A study of the habits and distribution of G. palpalis in relation to human habitations and occupations has clearly shown that the incidence of the disease is directly correlated with the intimacy and continuity of contact between man and fly. This, in turn, is governed partly by prevailing climatic conditions which favour or restrict fly movements and partly by the situation of villages and the occupations of their inhabitants. Rainfall in the Gambia is relatively low, averaging only about 44 inches per annum. There is a long dry season during which prevailing relative humidities are very low, except in the maritime zone. In March, for example, the saturation deficit in the maritimeregion rarely exceeds 20 millibars whereas 250 miles inland it may be as much as 50 millibars. G. palpalis in the Gambia, as elsewhere in West Africa, is essentially a riverine species whose permanent habitats and breeding grounds are restricted to the vicinity of watercourses. Since the territory is traversed throughout its entire length by the Gambia River it follows that G. palpalis is restricted to the vicinity of the main river and to the relatively few tributaries and lateral creeks or depressions which drain into it. From the point of view of the epidemiology of sleeping sickness the Gambia may be divided into three main regions : (i) the Maritime Region extending from the coast for 30 miles up the main river, (ii) the River Flats Region lying between 30 and 130 miles from the coast, and (iii) the Fresh Water Region lying between 130 and 280 miles from the coast. (i) The Maritime Region. On the north bank of the Gambia Rivers G. palpalis is widespread in an extensive oil-palm forest, which lies behind the mangroves bordering the river, and close to which there are numerous villages. On the south bank, G. palpalis is widely distributed throughout the heavy woodland within which thickets are numerous. Owing to the close proximity to the sea and to the wide estuary of the river, prevailing relative humidity is high and this permits the fly to travel widely ; it is commonly found within villages. But, although contact between man and fly is close and sustained, it is relatively impersonal owing to the wandering habits of the fly. Sleeping sickness is widely distributed but occurs only at low to moderate endemicity. Infection rates in individual villages were found to vary from 0 to 5 per cent., the high incidence being found in closest proximity to permanent fly habitats. One feature of exceptional interest in this region is the relatively

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high incidence of sleeping sickness among those engaged in the cultivation of rice, an occupation which brings the cultivators into the closest contact with fly at certain seasons. Only women engage in rice cultivation and it was observed that, in areas where rice is grown, the incidence of the disease was five times greater in women than in men, whereas elsewhere in the maritime region the incidende was equal in both sexes. (ii) The River Flats Region. In this region the Gambia River is bordered by a thick belt of giant mangroves which provides a permanent habitat and breeding ground for G. palpalis but owing to the drier atmospheric conditions the fly's range of dispersal during the greater part of the year is restricted. Behind the mangrove belt there is a wide zone of marsh and open river flats which is more or less devoid of trees. Villages are situated on the rising ground separated from the main river by marshes and flats and for the greater part of the year at least are beyond the range of G. palpalis whose permanent habitat is in the riverside mangroves. There is, however, a discontinuous belt of oil palm and thicket on the higher ground, parts of which provide suitable habitats for the fly. The incidence of sleeping sickness in the villages in this region was found to vary from 0 to 9 per cent., and was directly correlated with the proximity of individual villages to oil palms and thicket where G. palpalis was established. (iii) The Freshwater Region. A gradual transition takes place on proceeding upstream. Mangroves give place to swamp forest and after 60 miles the main river is confined between high banks which, in the upper reaches, may be as much as 30 feet above river level in the dry season. As a rule, at this season, the riverside vegetation no longer provides suitable haunts for G. palpalis so that the fly is often compelled to evacuate the main river and to concentrate in the fringing vegetation of the side creeks and drainage depressions where permanent pools persist and fringing vegetation is dense ; conditions here are favourable for the survival and breeding of G. palpalis throughout the year. Sleeping sickness in this region is almost entirely confined to villages adjacent to the freshwater creeks and in some of them a high incidence (5 to 12 per cent.) of the disease was observed. Man-fly contact in the creekside villages is close, sustained and personal and is greatest during the wet season when fly spreads readily into the villages. Elsewhere in this region the villages are virtually free from infection being beyond the range of G. palpalis which, owing to the low relative humidity prevailing during the greater part of the year, is severely restricted in its movements. Rice is cultivated by women in the drainage depressions but among those residing in nearby villages the incidence of sleeping sickness is no greater than among the men. When, however, women from more distant villages in which the disease does not occur, engage in rice cultivation it becomes an exceptional occupational risk. With some important exceptions, such as the creekside villages of the freshwater region and the cultivation of rice in the maritime region, the social, economic and geographical structure of the Gambia is such as to keep man largely isolated from the most dangerous haunts of G. palpalis. Where prevailing high relative humidity permits, the fly ranges widely and gives rise to a low or moderate degree of endemicity but elsewhere fly-movements are severely restricted during the greater part of the year by prevailing low relative humidity. Consequently the population of all villages, except those in the maritime region, is at little or no risk except where villages are situated in close proximity to permanent fly habitats, or where such occupations as rice cultivation or the fetching of water bring the inhabitants into close contact with the fly. It is a noteworthy feature of the Gambia that human pursuits are, with rare exceptions,

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such that man is not brought into close contact with the foci of greatest fly concentration. Thus, the prevalence of wells absolves man from the necessity of visiting fly-haunts to fetch water, while the absence of a fishing industry on the main river, and the very limited use of local craft for water transport, are factors mitigating against the spread of the disease. The tendency of the river to flood compels the inhabitants to site their villages on the higher ground far removed from the main foci of fly-concentration. It is fortunate also that G. tachinoides does not occur in the Gambia since this species is capable of withstanding a greater degree of desiccation than G. palpalis. Were it not for these favourable features the population would be at very serious risk. As it is, there appears to be no reason to fear an extension of the disease in epidemic form. So far as the Upper River Division is concerned there is little doubt that the clearance of permanent fly habitats bordel"ing the limited number of lateral freshwater creeks would result in the total elimination of sleeping sickness in this Division.

(b) Epidemiology of human trypanosomiasis in Sierra Leone. After completing his investigation in the Gambia, Dr. HVTCHINSON re-visited Sierra Leone where he had for four years taken a prominent part in controlling a very severe epidemic of sleeping sickness in the Kissi Chiefdoms. The epidemiology of human trypanosomiasis in Sierra Leone presents a striking contrast to the findings in the Gambia. Rainfall is heavy and varies from 160 inches on the coast to 90 inches in the hinterland. A mangrove belt in the coastal area gives place to a large area of rain forest (mostly secondary) which, in turn, is replaced by savannah woodland ; there is a well-defined transitional zone between forest and savannah. Owing to the steep rise of the contours, mangroves seldom extend for more than 30 miles up the larger rivers; the whole territory including the savannah zone is intersected by numerous rivers and streams. As compared with the Gambia maximum temperatures are lower, relative humidities are higher and the dry season is much shorter.

G. palpalis is the sole vector of human trypanosomiasis. In the rain forest belt it occurs mainly along the coastal swamps and the main rivers but is rarely found elsewhere. This species is, however, very widely distributed along the numerous rivers and streams of the savannah zone and in the transitional zone between forest and savannah. In contrast to the Gambia, G. palpalis in Sierra Leone is less prevalent and does not show the same tendency to concentrate in selected habitats. It was repeatedly observed that G. palpalis was absent from small streams which were choked with dense vegetation, an observation which lends support to Dr. NASH'S conception of " obstructive clearing " to which reference has been made above. Except for scattered endemic foci, the incidence of sleeping sickness in the rain forest belt of Sierra Leone is negligible, and owing to the scarcity of G. palpalis is likely to remain so. In the transitional and savannah zones, however, there is good reason to believe that the introduction of a focus of infection would facilitate the rapid and serious spread of the disease on a scale comparable to the vast epidemics which have occurred elsewhere in West Africa during the present century. There is, in fact, definite proof that this danger is a very real one for, with the introduction of the disease into the Kissi tongue which protrudes between French Guinea and Liberia, an epidemic of exceptional severity has actually occurred within recent years. Fortunately, the outbreak in the Kissi and adjacent Fuero area has so far been the only major epidemic with which Sierra Leone has had to contend.

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In the Kissi area the vegetation is transitional between forest and savannah, the population density is exceptionally high (over 100 per sq. mile), and the villages are sited along numerous streams which harbour G. palpalis, and on which the local inhabitants are entirely dependent for their water supplies. Because of close, personal and sustained contact between man and fly and the prevailing fa;courable conditions for the cyclical transmission of T. gambiense, the disease, once introduced, spreads rapidly along the streams linking village to village. In 1939, the over-all infection rate in the three Kissi Chiefdoms had reached 20 per cent., while the indices in individual villages were sometimes considerably in excess of this figure. The disease was of an exceptionally severe type, possibly because of its rapid spread through a non-immune population in whom signs of malnutrition were much in evidence at the time. About the same time sleeping sickness also broke out in the small Fuero area some 30 miles northwest of Kissi where epidemiological conditions appeared to be very similar, and where the disease is believed to have been introduced from the same source. At Fuero the manifestations of the disease were originally similar to those observed in the Kissi area but at a later stage of the epidemic the disease assumed a much milder form. Clinical symptoms and enlargement of cervical glands" were so often absent that 90 per cent. of the cases were detected by blood examination. Despite the large numbers of trypanosomes present in the blood, the disease ran a mild course among the local inhabitants, yet a European definitely known to have been infected at Fuero developed a virulent infection. Sleeping sickness has never established itself permanently in the rain-forest zone of Sierra Leone although G. palpalis is commonly found along the larger rivers. Owing to the liability to flooding, villages are not sited near the larger water-courses but are situated along the smaller tributary streams which are often so choked with dense vegetation as to be unsuitable habitats for G. palpalis. Should farm clearings along such streams convert them to suitable fly-haunts and should a reservoir of infection be introduced, local sporadic outbreaks of sleeping sickness would almost certainly occur. One such outbreak is known to have occurred in 1948 and involved three chiefdoms in the secondary forest zone. The severe epidemics which affected the Kissi and Fuero areas but a few years ago, were brought under control by the prompt and efficient application of control measures. Had this action been deferred or less rigidly applied there is every liklihood that the disease would have spread widely through the savannah and transitional zones of Sierra Leone. At the present time human trypanosomiasis is not a major health problem in the territory but the potential for the occurrence of devastating epidemics has been clearly demonstrated and the need for continued efforts to contain the disease cannot be over-emphasized.

Epizoology of veterinary lrypanosomiasis. The epizoology of trypanosomiasis as it occurs in cattle and other domestic animals has received even less attention in the past than the epidemiology of the human disease. Indeed, until very recently, it was not known which species of trypanosome was the most prevalent or the most virulent for the important Zebu cattle of West Africa. In the course of various experiments on cattle carried out at the Institute and in the field over a period of several years, Dr. UNSWORTH observed that T. vivax was by far the most prevalent of the pathogenic trypanosomes of Zebu cattle, and that the infections caused by this species were nearly always fatal. This proved to be the case when Zebu cattle were exposed to natural infection by tsetse-bite in widely separated localities in Nigeria, or to the

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bites of naturally infected tsetse collected in the field and transported to the laboratory. In the majority of cases, death was observed to occur in 3 to 4 months after infection but instances of rapidly fatal infections were occasionally seen. T. vivax is now regarded as the species of greatest economic importance in West Africa. These observations are at variance with the findings in East Africa where T. vivax is generally regarded as a parasite of low virulence in cattle, although the occasional occurrence of highly virulent strains has been reported from certain localities. By making comparative morphological studies on strains of T. vivax from different parts of Africa, as well as from Mauritius and Panama, Dr. FAIRBAIRN has shown that, with the exception of a virulent strain from East Africa, the mean lengths of strains from West Africa and Panama were significantly shorter than those for strains from East Africa and Mauritius. The available evidence suggests that there are two distinct types or subspecies of T. vivax which differ in virulence and in morphology, the shorter and more virulent type being that commonly found in West Africa, whereas the longer and less virulent type is that usually encountered in Eastern Africa.

Tolerance of indigenous cattle to trypanosomiasis. One of the first problems to engage attention was the reported tolerance or resistance to trypanosomiasis of certain small indigenous breeds of cattle in West Africa. Cattle of the Ndama breed were singled out for preliminary investigation. Ndama cattle maintained for prolonged periods in the presence of tsetse (G. palpalis and G. morsitans) in Northern Nigeria remained in excellent condition, despite the presence in some animals of low-grade trypanosome infections, whereas Zebu cattle maintained under identical conditions developed heavy and ultimately fatal trypanosome infections. First cross Zebu x Ndama also succumbed, albeit from infections of less intensity than those observed in pure Zebu and after a somewhat longer period of infection. Ndama cattle maintained in a tsetse-free locality and repeatedly exposed to infection with a wide variety of strains of both T. vivax and T. congolense (transmitted by tsetse-bite as well as by blood inoculation) remained in excellent condition, although low-grade infections sometimes developed. Further observations were made in the laboratory on the nature of the tolerance shown by Ndama cattle, including observations on Ndamas which had not previously been exposed to trypanosome infection and which had been maintained in a tsetse-free locality since birth. The results of all observations so far made on Ndama cattle support the belief that this breed possesses a remarkable degree of tolerance to the pathogenic effects of infection with a number of strains, of different geographical origin, of both T. vivax and T. congolense. This tolerance did not break down when the cattle were worked or exposed to adverse conditions. First cross Zebu x Ndama adults have been shown to occupy an intermediate position in that they are more susceptible to the pathogenic effects of trypanosome infections than Ndama cattle, but less susceptible than pure Zebu cattle. It is difficult to escape the conclusion that tolerance to trypanosome infections is an inherent quality of the Ndama breed. It was not possible to demonstrate natural immunity in Ndama cattle by serological tests, but it was clearly shown that specific antibodies are elaborated in these cattle as a result of infection. These antibodies appear to be species, but not strain, specific ; but there is no proof that the strains of each species investigated, although of different geographical origin, were antigenically distinct. The occurrence of specific antibodies in response to

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infection has been shown, in some animals, to be associated with a heightened degree of tolerance, and it seems reasonable to conclude that the inherent natural resistance of Ndama cattle may be enhanced or reinforced by a degree of acquired immunity. Only practical experience will show whether the tolerance observed in Ndama cattle will prove to be effective under various conditions in the field in West Africa, but the experimental evidence is suflqciently convincing to justify the limited use of Ndama cattle in tsetse areas in West Africa. A policy of establishing Ndama breeding centres is now in progress. PROTOZOOLOGY.

Although the need for laboratory studies to supplement field investigations had been recognized from the start, t h e extreme importance of laboratory work was emphasized when it became apparent that investigations in the field, however carefully carried out, lacked the precision necessary for the proper elucidation of many of the problems encountered.

Studies on T. gambiense. T. gambiense is believed to be the only species responsible for human trypanosomiasis in West Africa, and at an early stage, Dr. GALL attempted to establish in laboratory animals strains which would be suitable for studies on the cyclical transmission of this species through tsetse, on the pathology of the disease, and on the value of chemotherapeutic and chemoprophylactic agents for human use. Considerable difficulties were experienced in establishing virulent laboratory strains of T. gambiense and, although good progress has been made, it would be premature to claim that this problem has been satisfactorily solved. In attempting to establish strains of T. gambiense, the use of large inocula of infected blood and of unweaned nursing rats has been of great value. It is important also to obtain infected blood at a stage of infection when trypanosomes are increasing in number rather than when the parasitaemia is on the decline. At the present time some eight different strains of T. gambiense are being maintained in small laboratory animals including monkeys, rabbits, rats and mice. Two of these strains were obtained from a very remote locality where it is highly improbable that any form of treatment had hitherto been available to the local population. In adult rats and mice, most of the strains produced a consistent pattern of infection characterized by the development within a few days of a massive parasitaemia ending either in the death of the host, or in a short-lived negative phase followed by a recrudescence of intense parasitaemia. T. gambiense has been successfully transmitted from rat to rat through G. palpalis on several occasions but no satisfactory routine for experimental cyclical transmission has so far been established. Attention is now being directed to ascertaining the optinmm conditions for tsetse transmission of T. gambiense, including observations on the temperatures necessary for the incubation of tsetse pupae and the maintenance of adult flies as well as the stage of infection in the vertebrate host which yields the highest percentage of infected flies. Apart from improvement in laboratory procedures, investigations of this kind are of obvious importance in relation to the epidemiology of human trypanosomiasis. Studies on T. vivax. Drs. DESOWITZ, WATSON and UNSWORTH have paid special attention to the study of T. vivax because of its prime importance as the main cause of cattle trypanosomiasis in Nigeria

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and probably elsewhere in West Africa. Little experimental work had hitherto been attempted on this species, presumably because of the repeated failure to establish strains in any suitable laboratory animal. No difficulty was experienced in infecting white rats with T. vivax when relatively large doses of blood from sheep were inoculated, provided the blood was taken in the early stages of infection. The resultant infections were heavy in most cases and persisted in some rats for as long as 20 days. Several instances of relapse were observed. When further attempts were made to maintain this strain in rats by serial sub-passage (blood inoculation) it was found impossible to maintain the strain beyond the second rat-to-rat sub-passage. Reasoning that the successful inoculation of rats from sheep might be due to some factor associated with sheep's blood per se, attempts were made to maintain serial sub-passages in rats by administering " clean " sheep's blood to the rats within 24 hours of inoculating with infected rat's blood. It was found that, in this way, T. vivax could be passed from rat to rat by blood inoculation with ease and regularity. The resultant infections in rats were heavy, showed several peaks of parasitaemia, relapsed on several occasions, and persisted for as long as 26 days. It was observed that blood taken for sub-inoculation during the primary attack was more liable to produce an infection in rats than blood taken during a relapse of infection. After prolonged sub-passage in rats, one strain of T. vivax became so well adapted to the rat host that it was possible to maintain it by direct blood inoculation without the use of " clean " sheep-serum supplement. This strain has now been maintained in rats for over 3 years and has been sub-passaged nearly 500 times. The course of infection in rats altered considerably after repeated sub-passages to become characterized by an intense parasitaemia persisting for 4 to 6 days after inoculation and ending fatally in over 90 per cent. of cases. The character of this infection in the rat, as judged by infectivity and virulence, now appears to be stabilized since no further change has been observed during the last 12 months. This strain was found to be transmissible through G. palpalis after 459 serial passages in the rat by blood inoculation. The peculiar property of " clean " sheep-blood in facilitating the infection of white rats with T. vivax (supplement), has been the subject of considerable investigation. It was quickly established that the supplementary action of " c l e a n " sheep-blood was a property of the fluid and not the cellular elements ; serum or plasma proved as effective as whole blood. It was further shown that bovine serum was as active in this respect as sheep serum, but that the sera of other animals including man, monkey, rabbit, guinea-pig, rat and mouse possessed no such activity. It may be significant that the sera of animals that are refractory to infection with T. vivax are devoid of supplementary action, while the sera of susceptible animals, such as sheep and oxen, possess this quality. Through the kindness of the Lister Institute of Preventive Medicine, London, and of the Armour Laboratories, Chicago, fractions of normal bovine serum were made available for the further study of the component of serum responsible for supplementary action. The results obtained indicate that the active substance in plasma or serum which facilitates the infection of T. vivax in the white rat, is protein. The possibility cannot be excluded that the essential factor is a trace element present as an impurity in the fractions used, though this seems unlikely when it is remembered that some of the plasma fractions employed were of high purity. Satisfactory supplementary action was given by such diverse types of protein as albumin, gamma-globulin and fribrinogen. Beta-globulin gave negative results but this may be due to the relative insolubility of the beta-globulin fraction used.

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The degree of parasitaemia which occurs in the rat after the injection of plasma protein is directly proportional to the amount of protein given. Any one of the active fractions serves as well as a mixture of fractions provided the total quantity of protein administered is the same. Some interesting observations have been made in the course of these studies. Specific antibodies are produced in the blood of sheep infected with T. vivax. Trypanicidal antibodies are developed about the 8th day after the first appearance of trypanosomes in the blood and agglutinating antibodies about the l l t h day. These antibodies exert no demonstrable effect on the co-existing trypanosomes in the blood of sheep, but serum obtained from this host has a powerful trypanolytic or agglutinating action on trypanosomes present in the blood of infected rats or on sheep trypanosomes which have been washed three times in Ringer solution. The serum of sheep containing these specific antibodies has been found to be ineffective in facilitating infection of the white rat with T. vivax but, after full saturation with ammonium sulphate, the precipitate obtained (when re-dissolved in normal saline solution) acts in the same manner as " clean " sheep-serum, or as serum taken early in the infection before antibodies are developed. Blood taken early in an infection with T. vivax in the sheep has been shown to be more liable to produce infection in the white rat than blood taken in the later stages of infection when specific antibodies have developed. Groups of rats which received supplementary inoculations o f " clean " sheep-serum developed heavy infections, whereas comparable groups of rats which received no supplementary inoculation or which received supplementary inoculations of immune sheep serum remained refractory, or developed only transient tow-grade infections. White rats infected with T. vivax are capable of producing specific antibodies, at a high titre, against this infection. From these and other observations it would appear that there is some substance in sheep serum which is capable of protecting trypanosomes against the action of specific antibody. It is presumably this " antibody protective factor " which is operative when sheep serum is given as " supplement " to facilitate the infection of white rats with T. vivax.

Transmission of T. vivax through G. palpalis. Although G. palpalis can be readily infected by feeding on rats harbouring a strain of T. vivax, and although it has so far proved impossible to infect " clean " rats by cyclical transmission through G. palpalis, no difficulty has been experienced i n infecting sheep through the bites of tsetse infected by feeding on rats. Significant differences have been noted in the percentage of flies infected after feeding on rats at different stages of the infection, the percentage increasing from about 8 per cent. at 24 hours to over 60 per cent. at 72 hours. The factors governing the transmission of T. vivax by G. palpalis have been the subject of intensive investigation in the laboratory. This work has been beset by considerable difficulties since a number of variable factors are involved, including the temperature to which tsetse pupae are exposed, the temperatures at which adult flies are maintained after taking an infective blood-meal and the prevalence and morphology of the trypanosomes present in the blood of the host at the time of the infective feed. Mean trypanosome length appears to be a factor of major importance in determining the infection rate with T. vivax in G. palpalis. The infection rate has been observed to increase as mean trypanosome length increases, being only about 5 per cent. at 20~, and increasing progressively to over 80 per cent. at 24~, when other variables are kept as constant as possible. The influence of pupal- and flymaintenance temperature on the infection rate of T. vivax with G. palpalis has not yet been

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precisely determined, but the work so far carried out suggests that the optimum temperature lies between 24 ° and 28°C. Similar studies are being made on the transmission of T. congolense through G. palpalis, and although it has been possible to maintain a strain of T. congolense in sheep by cyclical transmission, it seems probable that this fly may need lower pupaland fly-maintenance temperatures for the transmission of T. congolense than for the transmission of T. vivax.

The influence of milk diet on the course of T. vivax infections in rats. Following the reported suppressive action of a diet of milk and vitamins on infections with Plasmodium berghei in rats and P. cynomolgi in monkeys, the effect of a similar diet on the course of infection with T. vivax in rats was investigated. It was found that milk diet, with or without added vitamins, had no suppressive effect on T. vivax infections in rats. Studies on T. simiae. Wild-caught G. morsitans, collected from an area where wart-hog were prevalent, were fed on two domestic pigs both of which developed severe and rapidly fatal infections with T. simiae. Blood from one of these infected pigs was inoculated into sheep, rabbits, guineapigs, rats and mice. The three latter species were completely refractory to infection, even when splenectomized, but the sheep developed a transient low-grade infection and rabbits developed infections of very variable intensity. A more uniform type of infection occurred in splenectomized rabbits in which T. simiae caused intense parasitaemia culminating in a fatal termination. The strain was maintained by serial passage in splenectomized rabbits without difficulty. It was observed that, after rabbit passage, T. simiae lost much of its virulence for the pig. PATHOLOGY. /

Histological studies. Detailed studies of the morbid histology of both human and animal trypanosomiasis are very badly needed. Every opportunity has been taken to collect tissues in cases of infection in man, both at biopsy or at postmortem. There is already available a large collection of tissues taken from animals at all stages of infection with T. vivax. Diagnostic methods. Attention has been given to improved procedures for the culture of trypanosomes in vitro but no satisfactory method has so far been devised. Estimation of the protein content of cerebro-spinal fluid is one of the most valuable single tests for the assessment of the sleeping sickness case. The Sicard and Cantaloube method is that commonly used in making these estimations but it has been shown that there are certain errors inherent in this method. For example, wide variations in readings occur depending upon the bore of the tube used ; wide bores give high readings and narrow bores low readings. If the method is to be relied upon, and if results from different sources are to be comparable, it will be necessary to standardize the bore of the tubes used. A sulphosalicylic acid precipitation method is at present under investigation and promises to be more accurate than the Sicard and Cantaloube method, as well as having the advantages of requiring smaller quantities of cerebro-spinal fluid and of being readable within 5 minutes.

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The erythrocyte sedimentation rate. It has been amply confirmed that the erythrocyte sedimentation rate is greatly increased in cases of human trypanosomiasis. Numerous observations have been made not only on sleeping sickness cases but on " normal " subjects (European and African) in West Africa. The Westergren method is preferred since, by comparison with Wintrobe's method, it has been found to be more sensitive, less liable to error and better suited to field conditions. The most important figure to be obtained is the maximum velocity of fall of the red blood corpuscles. The measured fall in one hour is not considered to be a true index of the rate of fall of erythrocytes as, in many cases, there is already considerable gravity packing of the red cells when readings are taken after one hour. It has been shown that there is good correlation between the 30-minute reading and the velocity of fall. Although a wide scatter occurs in various groups of " normal " subjects, the erythrocyte sedimentation rate is often strong confirmatory evidence of trypanosomiasis, though it cannot be regarded as a rigid diagnostic test. Clinically, the highest erythrocyte sedimentation rates occur in early, rather than in later or chronic cases. Changes in the blood proteins. Of the major blood proteins (albumin, globulin and fibrinogen), only the latter two are normally associated with changes in the sedimentation rate. It has been shown that there is a distinct positive correlation between the amount of gamma globulin present and the sedimentation rate. One observation of particular interest is the great increase of gamma globulin which occurs in sleeping sickness cases ; there is no appreciable change in the alpha- or betaglobulins. There is some evidence to suggest that the greatly increased gamma globulin which occurs in sleeping sickness may not be entirely normal gamma globulin, since critical electrophoretograms produced by the Tiselius apparatus are strongly suggestive of an abnormal component between the beta- and gamma-globulin peaks. The significance of the gamma globulin increase in sleeping sickness remains to be investigated. CHEMOTHERAPY OF HUMAN TRYPANOSOMIASIS

In the conduct of trials with drugs for the prevention and cure Of human trypanosomiasis, Dr. DUGGAN, and later Dr. HUTCHINSON, worked in the closest co-operation with the Nigerian Sleeping Sickness Service. Early work with various drugs and combinations of drugs yielded results of considerable importance in the treatment of T. gambiense infections. Pentamidine alone gave good results in early cases and better results than expected in cases which showed changes in the cerebrospinal fluid. Combined pentamidine-tryparsamide treatment gave results at least as good as any other tryparsamide combination. Of the Friedheim group of drugs, melarsen itself appeared to be most worthy of further trial. Further large-scale trials were undertaken with a standardized batch of melarsen, but the long-term follow-up on this series has not yet been completed. The clinical impressions of melarsen treatment have been favourable. The drug is easy to give and is generally well tolerated. The indications are that melarsen may become the drug of choice for the treatment of both early subjects and those already showing changes in the cerebro-spinal fluid, but final assessment of its value must await the outcome of the 2-year follow-up period.

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Mel B has been found to be of value in the treatment of certain advanced cases of sleeping sickness but has the disadvantage of causing toxic reactions, the severity of which appears to be greatest in the most advanced cases. C H E M O P R O P H Y L A X I S OF H U M A N T R Y P A N O S O M I A S I S .

In 1952, in collaboration with the Nigerian Sleeping Sickness Service, prophylactic pentamidine was used to protect the population of a circumscribed locality in Northern Nigeria where no measures for the prevention of sleeping sickness, other than survey and treatment of cases, were being taken. The circumstances were such as to provide the near equivalent of a controlled experiment. Observations were continued over a period of 3 years and have provided confirmatory evidence of the high value of pentamidine prophylaxis. Mass treatment with pentamidine (involving about 70 per cent. of the population), given on two or three occasions at intervals of 6 to 9 months reduced the incidence of sleeping sickness to negligible proportions. With the exception of one clinically suspicious case in which trypanosomes could not be found, no case of sleeping sickness occurred among approximately 3,000 persons who had received pentamidine and even among those who escaped injection, the incidence had dropped to a very low level, probably on account of the lowering of the reservoir of infection in the community. In the light of recently acquired evidence as to the seasonal liability to infection, it is believed that, in this locality, routine administration of pentamidine in the month of February would afford virtually complete protection for a full year. Regular administration has now been discontinued, and thesituation is being carefully watched in order to determine the period during which sleeping sickness will remain at a negligible level. Dr. GALL made a careful study of all published work on the use of the prophylactic diamidines in Africa, and concluded that the drug of choice is pentamidine (as diisethionate or dimethyl sulphonate) administered intramuscularly in doses of 3 to 4 mg. per kg. body weight of pentamidine base, at intervals of 6 to 12 months. The toxic effects of pentamidine are mostly immediate and inconsequential. Failure of prophylaxis occurs in about 0.1 per cent. of those treated, and it is believed that these failures represent persons infected before administration of the prophylactic dose who have escaped detection and treatment at the preliminary survey. It is clear that we have in pentamidine a relatively cheap drug of which a single non-toxic dose will protect the individual from sleeping sickness for at least several months. CHEMOTHERAPY OF ANIMALTRYPANOSOMIASIS. In work on the chemotherapy and chemoprophylaxis of animal trypanosomiasis, Drs. UNSWORTHand CHANDLERco-operated closely with the Nigerian Veterinary Service.

Antrycide. The discovery of antrycide was announced when the Institute was in its earliest stages of development. Facilities were not yet available for the conduct of controlled laboratory experiments, but it was possible to initiate field trials with antrycide prophylactic (later marketed as " prosalt ") almost immediately. In later work at the Institute, antrycide methyl sulphate was used on a considerable scale in the treatment of animals infected, both by tsetse-bite and by blood inoculation,

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with a number of different strains of both T. vivax and T. congolense. Complete cure was effected in all cases in which the drug was administered in the standard recommended dosage of 5 mg./kg, and often at lower doses. The immediate success which followed the use of antrycide methyl sulphate for the treatment of infections of both T . vivax and T. congolense led to its being used on a large scale for curative purposes in the West African colonies. In many cases diagnosis was made on clinical grounds only and in most instances long-term follow-up of treated cases was not possible. An attempt was made to collect and analyse all the results obtained by the use of antrycide methyl sulphate in West Africa, as a result of which it was concluded that this drug effected cure in almost all cases of cattle trypanosomiasis and gave uniformly good results in the treatment of trypanosomiasis in most other domestic animals. Local reactions following the use of antrycide methyl sulphate are generally of little consequence. Immediate toxic reactions are sometimes seen, especially in horses. In cattle, a single dose is sufficient to effect radical cure but in other animals such as dogs, and especially pigs infected with T. simiae, two or even three doses may be required to produce radical cure. The success of curative antrycide led to trials with this drug for the periodical treatment of cattle in areas where the trypanosome challenge was believed to be light. The procedure adopted was to treat cattle as and when they became infected. It was found, however, that treatment and re-treatment was required somewhat more frequently than was foreseen, and it was suspected that the repeated use of antrycide methyl sulphate was producing antrycide-resistant strains. One strain of T. vivax, recovered from an area in which periodical treatment of infected animals was being carried out, was tested in the laboratory and was found to be resistant to treatment with this drug in doses exceeding the maximum recommended dosage. In view of the more satisfactory results obtained with antrycide prosalt for the protection of cattle maintained in areas where the trypanosome challenge is light, the use of antrycide methyl sulphate for the periodical treatment of cattle maintained under such conditions was discontinued. The introduction of antrycide methyl sulphate undoubtedly represents an immense advance in the chemotherapy of animal trypanosomiasis and has quickly become extremely popular among stock owners.

Phenanthridinium compounds. In 1951, Dr. L. G. GOODWlN of the Wellcome Laboratories of Tropical Medicine, worked at the Institute for 6 months on the therapeutic and prophylactic value of four new phenanthridinium compounds. The trials in the laboratory and in the field showed that two of these compounds had a satisfactory curative action against cyclically transmitted strains of T. vivax in Zebu cattle ; although local reactions were more severe than those produced by antrycide, no evidence of generalized dermatitis or photosensitization was observed under local conditions. One of these compounds (150 C 47) was shown to have a powerful prophylactic action, but was found to be highly toxic to cattle in the doses given. " 528 " Chloride. In 1951, Dr. E. M. LOURIE and his co-workers announced the preparation of a new trypanicidal compound provisionally designated " 528 " which had been shown to possess a high curative value against T. congolense in mice. This new drug was subjected to trials in cattle tinder carefully controlled laboratory conditions using two different strains of T.

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vivax and two strains of T. congolense. Although " 528 " chloride proved to be an extremely effective curative agent against T. congolense at doses well below the acceptable limit of toxicity, this drug failed to cure T. vivax infections even when pushed to, or over, this limit. Since T. vivax is the most prevalent and the most pathogenic trypanosome infection of cattle in West Africa, it was clear that " 528 " chloride could not be regarded as a suitable trypanicide for general use in the field under West African conditions. In this respect it fell far short of antrycide methyl sulphate.

Ethidium bromide. Research work carried out in the United Kingdom had shown that compounds obtained by alteration of the quarternizing group of dimidium bromide possessed enhanced trypanicidal properties against T. congolense and other species. One of these compounds, known as ethidium bromide, was found to have an exceptionally high curative value when tested against T. congolense in laboratory animals in the United Kingdom and, later, against natural infections with T. congolense in Zebu cattle in East Africa. Dr. UNSWORTHsubjected this drug to carefully controlled laboratory experiments in Zebu cattle infected, both by tsetse bite and by blood inoculation, with local strains of T. vivax in West Africa. These trials have shown that ethidium bromide can be relied upon to effect radical cure of T. vivax in Zebu cattle when administered in doses of 1 mg./kg, or above. At a dose level of 1 mg./kg, ethidium bromide produced no general toxic effects, and such local reactions as were encountered were of little significance. The curative value of ethidium bromide against West African strains of T. congolense has not yet been investigated but it has been reported to be effective against natural T. congolense infections in Zebu cattle in East Africa. CHEMOPROPHYLAXIS OF ANIMAL TRYPANOSOMIASIS.

The prophylactic value of antrycide prosalt. The value of antrycide prosalt in the protection of cattle has been the subject of intensive investigation over the past 5 years. It has been concluded that the use of prosalt administered in the recommended dosage and repeated at intervals not exceeding 70 days, permits susceptible cattle to be kept continuously in areas where the trypanosome challenge is not excessive, that is, in areas where cattle are exposed to the risk of infection from riverine tsetse only. In localities where the trypanosome challenge is great, as in areas where G. morsitans occurs, antrycide prosalt provides only partial protection. Cattle under the protection of antrycide prosalt have been kept in selected areas for periods up to 3 years without any evidence of infection. These cattle were exposed to the risk of infection from riverine tsetse only, and the drug was administered at regular intervals of 2 months. Under such conditions, the risk of the development of antrycide-resistant strains is considered to be negligible. When, however, cattle are exposed to the greater challenge in areas in which G. morsitans occurs, parasites frequently appear in the blood of protected cattle and the risk of developing antrycide-resistant strains is believed to be considerable. Antrycide prosalt has proved to be of great value for the protection of trade cattle on their long journeys through tsetse-infested country on their way from the cattle-raising areas .in the North of Nigeria to markets in Southern Nigeria. In journeys af about 6 weeks'

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duration, protected cattle have been shown to remain completely free from infection, even when G. morsitans areas have been traversed. It seemed possible that cattle maintained in the presence of riverine tsetse under the protection of antrycide prosalt might, as a result of repeated exposure to infection, develop some degree of immunity. In order to investigate the possible r61e of this hypothetical immunity, two groups of Zebu cattle were observed over a period of nearly 1 year. Antrycide prosalt in the recommended dosage was administered to both groups and, thereafter, the cattle of one group was exposed to homologous reinfection with T. congolense at weekly intervals, with the object of stimulating an immune response, while the other group was not so exposed. Both groups were subjected to a heavy challenge at intervals of approximately 3 months so that the degree and duration of the protection afforded in the two groups could be compared. It was necessary to terminate this experiment after 10 months ; no clear-cut result was obtained because none of the cattle in either group became infected from any of the assault challenges to which they had been subjected. All animals in both groups received a final challenge with a heterologous strain of T. congolense which had been rendered strongly resistant to antrycide. All became infected within an incubation period of a few days, but no differences were apparent in the pathogenicity of this strain for the cattle in the two groups. Throughout the course of these experiments serological tests were carried out on the cattle of the two groups. In the group that was repeatedly exposed to infection at regular, short intervals, the presence of specific antibodies was detected in most cases, whereas in the other group, not so exposed, no antibodies were detected at any stage of the experiment except in two cattle which had received two assault challenges. These observations indicated that the administration of antrycide prosalt does not prevent the development of a specific immune response, even when the trypanosomes inoculated fail to produce infection in the protected bovine host, that the production of antibodies is increased in proportion to the amount of antigenic stimulation to which the host is subjected, and that the titre of such antibodies declines when antigenic stimulation is suspended for a relatively short time. The original antibody titre is, however, quickly regained when antigenic stimulation is resumed.

Antrycide resistance. It is believed that antrycide-resistant strains of trypanosomes may develop in certain circumstances as, for example, where antrycide methyl sulphate is used for treatment and re-treatment at relatively frequent intervals, or where the challenge to protection with prosalt is sufficiently great for " break-throughs " to occur. In such circumstances the use of antrycide is not recommended. When antrycide methyl sulphate is used for the occasional treatment of trypanosome infections or when antrycide prosalt is regularly administered at intervals not exceeding 70 days for the protection of cattle exposed to a relatively light trypanosome challenge, the risk of developing antrycide-resistant strains is believed to be remote. No difficulty was experienced in producing an antrycide-resistal strain of T. congolense in the laboratory by serial passage of a strain in rats given sub-curative doses of antrycide methyl sulphate. By the procedure adopted, one strain of T. congolense was rendered resistant to 15 times the original curative dose in 3½ months ; it is probable that this result could have been achieved even more quickly. Work on the " fading " of this resistance to antrycide has not yet been completed.

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BIBLIOGRAPHY. CHANDLER, t~. L. (1952).

T h e c o m p a r a t i v e tolerance of W e s t A f r i c a n N d a m a cattle to trypanosomiasis.

Ann. trop. Med. Parasit., 46, 127. DESOWITZ, R. S. (1954). Studies o n Trypanosoma vivax.

Part X--The activity of some b l o o d fractions in facilitating i n f e c t i o n in t h e w h i t e rat. Ibid., 48, 142. - - - - - - • WATSON, H . J. C. (1951). Studies on Trypanosoma vivax. P a r t I - - Susceptibility of w h i t e rats to infection. Ibid., 45, 207. ---& - (1951). Studies o n Trypanosoma vivax. P a r t I I I - - T h e m a i n t e n a n c e of strain i n w h i t e rats. Ibid., 46, 92. & - (1953). Studies o n Trypanosoma vivax. P a r t I V - T h e m a i n t e n a n c e of a strain in w h i t e rats w i t h o u t s h e e p - s e r u m s u p p l e m e n t . Ibid., 47, 62. - & - (1953). Studies o n Trypanosoma vivax. P a r t V I - - T h e o c c u r r e n c e of a n t i b o d i e s i n t h e sera of sheep a n d w h i t e rats a n d t h e i r influence o n t h e course of infection in w h i t e rats. Ibid., 47, 247. ---& - (1953). Studies o n Trypanosoma vivax. P a r t V I I - - O b s e r v a t i o n s o n t h e effect of a diet of cow's m i l k w i t h a d d e d v i t a m i n s o n t h e course of infection in w h i t e rats. Ibid., 47~ 258. - &- (1953). T h e m a i n t e n a n c e of a s t r a i n of T. simiae in r a b b i t s : T h e effect of s p l e n e c t o m y o n the course of infection. Ibid., 47, 324. DUGGAN, A. J. & HUTCHINSON, M . P. (1951). " T h e emcacy of certain t r y p a n o c i d a l c o m p o u n d s against T. gambiense infections i n m a n . " Trans. R. Soc. trop. Med. Hyg., 44, 535. FAIRBAIRN, H . (1953). Studies o n Trypanosoma vivax. P a r t I X - - M o r p h o l o g i c a l differences in strains in relation to p a t h o g e n i c i t y . Ann. trop. Med. Parasit., 47, 394. GALL, DAVID (1954). T h e c h e m o p r o p h y l a x i s of sleeping sickness w i t h t h e diamidines. Ibid., 48, 242. GOODWIN, L. G. & CHANDLER, R. L. (1952). T h e c h e m o t h e r a p e u t i c action of p h e n a n t h r i d i n i u m c o m p o u n d s . P a r t V I - - T h e p r o p h y l a c t i c a n d toxic actions of 2 : 7 - d i a m i n o - 9 - p - a m i n o p h e n y l - 10 - m e t h y l p h e n a n t h r i d i n i u m chloride (150C47) a n d iodide. Brit. J. Pharmacol., 7, 591. - & UNSWORTH, K. (1952). T h e c h e m o t h e r a p e u t i c action of p h e n a n t h r i d i n i u m c o m p o u n d s . P a r t V - T h e effect of four n e w p h e n a n t h r i d i n i u m derivatives u p o n fly t r a n s m i t t e d T. vivax infections in cattle. Ibid., 7, 581. HUTCHINSON, M. P. (1953). T h e epidemiology of h u m a n t r y p a n o s o m i a s i s in British W e s t Africa. P a r t I - T h e G a m b i a w i t h special reference to U p p e r R i v e r Division. Ann. trop. Med. Parasit., 47, 156. (1953). T h e e p i d e m i o l o g y of h u m a n t r y p a n o s o m i a s i s in B r i t i s h W e s t Africa. P a r t I I T h e G a m b i a (concluded). Ibid., 47, 169. (1954). T h e epidemiology of h u m a n trypanosorniasis in B r i t i s h W e s t Africa. P a r t I I I Sierra Leone. Ibid., 48, 75. KITCHEN, W . H. & GALL, D. (1953). A controlled h u m i d i f i e r for insect b r e e d i n g rooms. Bull. ent. Res., 44, 367. MULLIGAN, H. W. (1952). West African Institute for Trypanosomiasis Research. Annual Report for 1951. Gaskiya C o r p o r a t i o n Zaria. (1953). West African Institute for Trypanosomiasis Research. Annual Report 1952. Gaskiya C o r p o r a t i o n , Zaria. (1954). West African Imtitute for Trypanosomiasis Research. Annual Report 1953. Gaskiya C o r p o r a t i o n , Zaria. NASH, T . A. M. (1948). Tsetse-Flies in British West Africa. L o n d o n : H . M . S . O . (1951). A n o t e o n t h e effects of h i g h t e m p e r a t u r e o n t h e p u p a l stages of G l o s s i n a in relation to t h e t r a n s m i s s i o n rate of t r y p a n o s o m e s . Ann. trop. Med. Parasit., 42, 30. - (1951). T h e eradication of G. morsitans b y t h e p l a n n e d d e v e l o p m e n t of a territory. Farm and Forest, 10, 24. ---(1952). S o m e o b s e r v a t i o n s o n resting tsetse-fly populations. Bull. ent. Res., 43, 33. & DAVEY, J. T . (1951). N o t e s o n t h e r e s t i n g h a b i t s of G. fusca, G. medicorum a n d G. longipalpis. Ibid., 4 1 , 153. & PAGE, W. A. (1953). T h e ecology of G. palpalis in N o r t h e r n Nigeria. Trans. R. ent. Soe., 1 0 4 ,

71.

A n o u t b r e a k of T. simiae infection in pigs in N i g e r i a a n d its a t t e m p t e d control u s i n g antrycide m e t h y l s u l p h a t e : Vet. Rec., 64, 353. (1953). Studies o n Trypanosoma vivax. P a r t V - - T h e m a i n t e n a n c e of a strain in w h i t e mice. Ann. trop. Med. Parasit., 47, 232. (1953). Studies on Trypanosoma vivax. P a r t V I I I - - I n c i d e n c e a n d p a t h o g e n i c i t y in Z e b u cattle. Ibid., 47, 361.

UNSWORTH, K. (1952). -

-

-

-

DISCUSSION UNSWORTI:I, K. (1954).

O b s e r v a t i o n s o n a n t r y c i d e - f a s t strains of Trypanosoma

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congolense a n d T.

vivax. Ibid., 48, 178. -------

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• BIRKETT, J. D . (1952). T h e use of a n t r y c i d e p r o - s a l t in p r o t e c t i n g cattle against t r y p a n o s o miasis w h e n i n t r a n s i t t h r o u g h tsetse areas. Vet. Rec., 64, 351. & CHANDLER, R. L. (1952). Field trials w i t h p r o p h y l a c t i c a n t r y c i d e in W e s t Africa. Ann. trop. Med. Parasit., 46, 240. , & NESBITT, P. E. (1952). Studies o n Trypanosoma vivax. P a r t I I T h e m a i n t e n a n c e of a s t r a i n in rabbits. Ibid., 46, 85.

DISCUSSION Professor T, H. D a v e y : It is now less than eight years since Colonel Mulligan was appointed the first Director of the West African Institute for Trypanosomiasis Research. I think it would be fair to say that his knowledge of the disease and the trypanosome was then about the level which enabled him to pass his D.T.M. examination many years previously. His qualifications for the post were a sound basic knowledge of protozoology as indicated by his work on malaria, and his experience of initiating and running a large research organization in India. It has been said of members of the Cabinet that if one of them makes an outstanding success of his Ministry he is immediately removed to another, presumably to discover his defects. Colonel Mulligan switched from his work in India to work on trypanosomiasis in West Africa, and no defect has been revealed. This evening he has given abundant proof of his ability to organize and direct research in a field that was new to him. It was a phenomenal accomplishment to supervise the planning and building of the laboratories, to recruit staff and to supply the drive and direction for the large volume of research, remarkable for its quality and scope, which has appeared from the laboratory under his direction in the last few years. In the field of entomology Dr. Nash's long and detailed study of the ecology of Glossina palpalis has provided data that will be of great practical value in control. His method of obstructive clearing appears already to be a success, and by its cheapness it will enable this species to be controlled in many places where, on grounds of cost, previous methods were precluded. There is one question I should like to ask Colonel Mulligan : Have any observations been made on the effect of obstructive clearing on aquatic vectors of disease ? It might be important to know whether the slowing of the stream and the dense shade encouraged mosquitoes such as Anopheles funestus, or provided suitable conditions above or below the obstruction for the propagation of snail vectors of schistosomiasis. Clearly, many of the foci in which this method might be applicable would attract not merely the tsetse which could not survive elsewhere, but also man who would be dependent on the water for survival. It would be important to know that this very promising control method did not enhance the risk of malaria oi" schistosomiasis in the human population in the immediate vicinity. The very interesting report on the epidemiological investigations in the West African Colonies must be attributed specifically to the Institute, for in the territorial sleeping sickness services no individual worker had the time or facilities for a special epidemiological study. Much that was puzzling about the distribution of the disease in human communities has now been clarified, and it is interesting to note not only that the three territories studied have all shown marked differences in epidemiology but that great differences exist between different areas of the same territory. The rapid spread of human trypanosomiasis during the second and third decades of this century resulted from the great increase in communications and

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population movement following the Pax Britannica. This same result of population movement had been observed in the High Volta and Gold Coast about 1900 when Samory, the slave raider, spread the disease in his wake. Increase of communications did not, however, explain why one village was attacked and another not, or why one sex in a community suffered more than another. The investigations of Drs. Duggan and Hutchinson have now made it clear that epidemic spread is likely to occur only when a particular group of people is in constant contact with a particular fly population. Where contact is fortuitous, sporadic cases only will occur. The effect of close contact between specific small populations of man and fly was brought home to me in Sierra Leone when carrying out a survey of the epidemic in 1939. Few fly were seen during our trek through the epidemic area, and at one village where fly-boys were posted at a variety of places only five Glossina were collected by six boys in 3 hours, and these were taken at frequented areas on the stream near the village. Nevertheless, the villagers showed an incidence of about 30 per cent., the result of the same people being bitten day after day by the same flies. In other areas where fly were very numerous no cases of the disease were known. Passing down a creek in a launch on one occasion I estimated that there was roughly one Glossina per square foot of the launch, yet enquiry revealed no cases of sleeping sickness although the disease was known to the people. I am still not clear how, in circumstances such as these, sporadic cases may continue to appear only every 2 or 3 years as they do in some places. How does the parasite survive between cases ? I should also like to ask Colonel Mulligan whether he can add anything to the statement that malnutrition was a possible cause of the severity of the epidemic amongst the Kissi in Sierra Leone. Is there good evidence that malnutrition enhances virulence ? Some records in the Gambia state that fulminating cases of the disease tended to occur more commonly during the " hungry months " of the early rains. Turning to trypanosomiasis in cattle, it is obvious that the disease is now receiving the attention it merits. Disease of domestic stock, in which trypanosomiasis is very important, is one of the major factors holding up progress in tropical Africa. It is a much more serious problem than sleeping sickness in man which can be rapidly and relatively cheaply brought under control by several means. In the case of cattle there is difficulty in organizing and obtaining the co-operation of the people in regular prophylaxis, and the costs of fly control in areas where each beast requires a grazing area of as much as 12 acres per year would be quite prohibitive. On this account it is very interesting that the economic importance of T. vivax in West Africa has been established and that the organism can now be maintained and studied in laboratory animals. This is a major advance, and the Trypanosomiasis Institute is to be congratulated on having solved a problem which had baffled so many previous workers. In other diseases the problems of treatment and control have often remained unsolved until the infection could be studied in laboratory animals. I think we may expect that T. vivax infection in West Africa will soon cease to be the great problem it has been. I am particularly glad to see that the resistance of Ndama cattle to trypanosomes has been corroborated and that it is probably an inherent quality of the breed. I am doubtful as to the wisdom of the policy of cross-breeding Ndama cattle with susceptible breeds. General Van Hoof told me of their experience of cross-breeding in the Belgian Congo. The local resistant stock was bred with high-quality imported stock. Apparently it took nearly 30 years of breeding back to the local stock to regain an economic degree of resistance, by

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which time the qualities of the imported strain had been lost. I hope that by selective breeding the Ndama stock may be up-graded to produce a more valuable beast as regards work, milk and meat. In regard to chemotherapy, the studies on melarsen are very valuable and it is of great interest to learn that it is well tolerated. Mel B does not appear to be the answer to the problem of the late-stage case. I wonder would Colonel Mulligan give us his opinion as to the value of pentamidine prophylaxis as a means of eradicating T. gambiense. Some French workers appear to believe that prophylaxis using this drug continued over a number of years will completely eliminate the disease. Possibly the occurrence of a low incidence of cryptic cases may deter British workers from attempting large-scale control by this method. In this connection it is obvious that improved techniques of diagnosis must be available so that cryptic cases become so rare as to be of negligible importance. I see that some attention is being paid to diagnostic methods. I wonder whether any study has been made of antibody formation in human infections, comparable to the studies being made in animals. I should like again to thank Colonel Mulligan for his lucid and comprehensive review of the very interesting work which has been carried out under his direction in the West African Institute for Trypanosomiasis Research.

Dr. A. J. D u g g a n said that he had the good fortune to be associated with the West African Institute for Trypanosomiasis Research during its development. Although he had seen it rise from the wilderness into a complete scientific research organization, he still felt astonished that so much had been achieved by Colonel Mulligan and his staff in so short a time. By instigating the intensive study of sleeping sickness among small communities, Colonel Mulligan had shown the importance to transmission of man's behaviour in relation to his environment. One of the early studies, among the Rukuba of Northern Nigeria, revealed that their exogamous marriage system, whereby infected women married into a separate and previously unaffected section of the tribe, had caused a serious extension of a hitherto limited outbreak. After two decades of mass treatment a type of sleeping sickness has emerged in Northern Nigeria which does not respond satisfactorily to tryparsamide. Hence the appearance of the melarsen drugs is not untimely. Melarsen could be used as a substitute for tryparsamide in treating new cases, and Mel B could be used under hospital conditions for relapses with a grave prognosis. The cause of a considerable proportion of the deaths from T. gambiense sleeping sickness is still a matter of conjecture. Until more postmortem material was obtainable this state of affairs would continue. Could a modified form of autopsy be devised that would be acceptable to native law and custom ? By his obstructive clearing technique, Dr. Nash appears to have shown that the same botanical genera provide G. palpalis with a home on one hand and a graveyard on the other. But does densification produce only a change of form, or does it cause the development of new vegetational species ?

Dr. C. A. H o a r e : As a protozoologist with a vested interest in trypanosomiasis I have closely followed the work of the West African Institute, and am full of admiration for the

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advances made during the short period of its existence. One of the most important achievements, in my opinion, was the successful adaptation of Trypanosoma vivax and T. simiae to rodents, which opens for the first time a promising field for researches on these infections under laboratory conditions. In this connection, it may be mentioned that my colleagues at the Wellcome Laboratories have succeeded in adapting one of the strains of T. vivax, kindly supplied by Colonel Mulligan, to mice, in which this trypanosome has now been maintained without supplement for 2 years. Colonel Mulligan has referred to a comparative investigation on East and West African strains of T. vivax, in whichit is claimed that differences in the virulence of this species observed in these areas are correlated with differences in the mean lengths of the trypanosomes. However, the data advanced in support of this theory are not sufficiently convincing. Thus, if the mean measurements given by Fairbairn (1953) for the East and West African bovine strains of T. vivax are arranged in the ascending order and compared, it will be seen that, although on the whole eastern strains are longer than western ones, there is a considerable overlap in the ranges, showing that at least some of the strains differing i n virulence cannot be distinguished on the basis of their mean lengths. It has also been established that, in West Africa, strains which cause acute disease in Zebu cattle are innocuous to the Ndama breed. It would be interesting therefore to know whether there is a corresponding difference in the lengths of the trypanosomes in these two breeds. As it is, the available evidence seems to indicate that in West Africa the virulence of T. vivax depends on the degree of susceptibility of the host. Hence it may be argued that the mild course of the disease in East Africa might likewise be due to a greater tolerance of local cattle. Finally, it is suggested that the eastern and western strains of T. vivax represent distinct subspecies, separable by their dimensions. However there are no valid grounds for this assumption, since comparable differences have been found by me in the case of camel surra in the Sudan, where the mean lengths of T. evansi in a number of populations of one and the same s t r a i n - which could not possibly be attributed to distinct s u b s p e c i e s - varied as widely as in T. vivax. In conclusion, it can be said that the figures obtained for T. vivax and for T. evansi serve to emphasize once more that the statistical significance of mensural data cannot always be interpreted in terms of taxonomic and biological significance. REFERENCE FAIRBAIRN, H. (1953). Ann. trop. Med. Parasit. 47, 394. Dr. C. C. C h e s t e r m a n : This paper is full of most interesting observations and suggestions. Having recently had the privilege of visiting the Institute at Kaduna I should like to record my tribute to the work done by Colonel Mulligan and his colleagues. I will confine my remarks to one observation and one question. The discovery of an " antibody protective factor " in sheep's serum acting in favour of trypanosomes seems to me to be of great interest. With the modern methods of separation of the various serum protein fractions, it is to be hoped that further work will be done in an attempt to identify this factor, and thus show some light on the refractoriness of Ndama cattle to infection and possibly the reason why human serum is trypanolytic to T. brucei. My question i s : Is forest gallery clearance really necessary ? I view with dismay the possible destruction of these attractive little parks in what is otherwise a monotonous and featureless country-side. Is not our best hope in the statement made later by the speaker,

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that " It is believed that in this locality, routine administration of pentamidine in the month of February would afford virtually complete protection for a full year "? Workers in other areas are increasingly hopeful of this method and a study of the reports o f " residual infections" following pentamidine prophylaxis suggest that, like sporadic cases in untreated populations, the answer is " cherchez la femme," (ou l'homme). It has been my experience that human beings are easier to control than tsetse-flies.

Colonel Mulligan (in reply) said it should be clearly understood that the obstructive clearing technique was still an experiment and not a widely used control measure. If it proved to be a successful method for the control of riverine tsetse, consideration would have to be given to its effects on the vectors of other diseases such as malaria and schistosomiasis which were endemic in Northern Nigeria. In the Discussion, one speaker referred to dense shade as an anti-mosquito measure in Malaya and, of course, this measure had been exploited in other countries also. The Nigerian Malaria Service under Dr. Chwatt would be most interested in the effects of the new method on anopheline breeding. Dr. Chesterman regretted interference with the beautiful gallery forests. It was as yet too early to observe the end result of obstructive clearing but it was felt that, aesthetically, it would prove to be a distinct advance on either ruthless or partial clearing as practised hitherto. While Dr. Chesterman's remarks were appreciated, it would scarcely be desirable to encourage the local population to use tsetse-infested streams as pleasure parks. Dr. Nash was very much alive to the need for studying vegetational changes following obstructive clearing and had endeavoured to enlist the active interest of experts in forestry and botany in these changes. Dr. Nash was himself a very good amateur botanist and the matter was receiving his attention. Regarding the cost of drugs, the view held by local Veterinary Officers was that the Fulani cattle owners had been very quick to recognize the curative and prophylactic value of antrycide and would be more than willing to meet the cost of treatment. Curative antrycide was already immensly popular with stock owners. It seemed unlikely that either human or animal trypanosomiasis would ultimately be eradicated by any single control measure. Elimination of the tsetse-fly was more likely to be accomplished by proper land utilization and this would involve intelligent planning from many different angles. There was obvious advantage in developing a number of different lines of attack, and it was for that reason that the work of the West African Institute was so broadly based. The up-grading of resistant breeds of cattle might prove a very useful measure but even first-crosses with susceptible breeds lacked sufficient tolerance to withstand exposure to a relatively light challenge from riverine tsetse. Pentamidine prophylaxis had not, perhaps, been sufficiently exploited in British territories in the past but it had been used on a considerable scale, and with excellent results, both in Sierra Leone and in Nigeria. Dr. Gall had recently published a very valuable paper reviewing all work done in Africa with the prophylactic diamidines. The incidence of human trypanosomiasis had often been reduced to a very low level but it was doubtful whether complete eradication had ever been achieved by chemoprophylaxis. One speaker expressed doubt about the absence of sleeping sickness over the greater part of Northern Nigeria prior to the British occupation. The investigation which had been briefly outlined had been a thorough one. It was known that tWO endemic foci had existed for many y e a r s - one near the Niger-Benue confluence and the other in the Lake Chad b a s i n - but there was no reasonable doubt that the greater part of Northern Nigeria had

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been free from human trypanosomiasis prior to the British occupation. The changed mode of life of the population in the earlier part of this century permitted the spread of the disease from these two endemic foci. Several speakers had expressed interest in antibody responses in human trypanosomiasis. So far, studies of this kind had been made chiefly on T. vivax but much information of a fundamental nature had been obtained and this might be expected to be of value in future work on T. gambiense. Dr. Duggan had kindly answered the question about blindness following tryparsamide therapy. A number of cases had occurred in one treatment series many years ago, probably due to faulty injection solution, but in his experience the acute form of blindness occurring after a single injection was rare. When visual symptoms are of gradual onset, tryparsamide treatment should be stopped before blindness occurs. In conclusion, Colonel Mulligan stressed the unparalleled opportunities for original research on trypanosomiasis now available in both East and West Africa. Each of the four sections of the Institute in West Africa had excellent facilities to offer to visiting scientists. Several distinguished workers had already availed themselves of these opportunities and he hoped that even greater use of them would be made in future.