Observations on wuchereria bancrofti and acanthocheilonema perstans in Tanganyika

460 TRANSACTIONSOF THE ROYAL SOCIETYOF TROPICAL MEDICINE AND HYGIENE. Vo1. 49. No. 5. September, 1955.

ON WUCHERERIA BANCROFTI AND ACANTHOCHEILONEMA PERSTANS IN TANGANYIKA

OBSERVATIONS

BY

PETER JORDAN *

(From the East African Medical Survey, Mwanza, Tanganyika.) This paper is based on the results of surveys made b y the Filariasis Research Unit and East African Medical Survey organizations of the East Africa H i g h Commission. T h e work was carried out over a period of 3 years between 1951 and 1954. Interim Reports have been published elsewhere, (Filariasis Research Unit Annual Reports, 1952, 1953 and 1954 ; JORDAN, 1953, 1954a). METHODS AND MATERIALS Nearly 150 villages in Tanganyika were visited in the course of investigations designed to determine the incidence and distribution of infection with W. bancrofti and with .4. perstans in the Territory. Before the arrival of the investigating t e a m at each village surveyed, the Administrative Authorities informed the people of our work, indicating that we were investigating elephantiasis. I t was explained that since this disease is due to a w o r m which can be found in the blood only at night, it was necessary for t h e m to allow blood to be taken during the hours of darkness. I n this way and with the aid of a film show, an a t t e m p t was made to overcome the suspicions and fears of the Africans. I n some tribes the taking of blood - especially when this is done at n i g h t - is associated with witchcraft, and unless the local chiefs or village elders were persuaded that our visit was for the good of the villagers, then our time was wasted because few people came forward to have their blood taken at night. T h i s was the case in some places. I n others, 500 or more people volunteered to have their blood examined. While blood was being taken f r o m a finger tip, a note was made of the sex and approximate age of each person, and their extremities were examined for elephantiasis. Wherever possible the scrotum of the males was examined in order to determine the incidence of genital filariasis. T h i s procedure was sometimes approved of, but in other places it proved to be unpopular and was stopped. Over 30,000 blood specimens were obtained during the course of these investigations. Since the people were informed that elephantiasis was to be investigated, the incidence * Acknowledgements are made to the Administrator, East Africa High Commission, for permission to publish this paper ; to Lt.-Col. W. Laurie, late Director, East African Medical Survey and Filariasis Research Unit, for his help ; to the African laboratory assistants who assisted throughout the work reported here ; and to the numerous Medical and Administrative Officers of the Tanganyika Government without whose co-operation this survey would have been impossible.

PETER JORDAN

461

o f this disease as d e t e r m i n e d b y a n e x a m i n a t i o n o f t h e v o l u n t e e r s c a n n o t b e r e g a r d e d as t r u l y i n d i c a t i v e of t h e p r e v a l e n c e o f t h e c o n d i t i o n . T h e o b s e r v e d i n c i d e n c e o f genital filariasis is t h o u g h t to b e m o r e a c c u r a t e b e c a u s e e l e p h a n t i a s i s of t h e legs a n d h y d r o c o e l e are n o t g e n e r a l l y associated w i t h e a c h o t h e r b y t h e A f r i c a n . P r o b a b l y t h e m o s t a c c u r a t e m e t h o d o f d e t e r m i n i n g t h e i n c i d e n c e o f IV. bancrofti a n d A . perstans i n f e c t i o n s is to e x a m i n e b l o o d s a m p l e s t a k e n w h e n m i c r o f i l a r i a e o f W. bancrofti are likely to b e in t h e p e r i p h e r a l c i r c u l a t i o n . T h e results of t h e p r e s e n t series o f s u r v e y s were b a s e d o n t h e e x a m i n a t i o n of a single t h i c k d r o p p r e p a r a t i o n o f b l o o d o b t a i n e d b e t w e e n t h e h o u r s o f 8 p . m . a n d 10 p . m . , i.e. well b e f o r e t h e p e a k of t h e m i c r o f i l a r i a l t i d e in t h e case o f W. bancrofti. I f m o r e b l o o d h a d b e e n e x a m i n e d at a later h o u r it is t h o u g h t t h a t a h i g h e r i n c i d e n c e o f p o s i t i v e b l o o d s - - viz. b l o o d s in w h i c h m i c r o f i l a r i a e o f W. bancofti were f o u n d --would have been obtained. B l o o d slides w e r e s t a i n e d w i t h h a e m a t o x y l i n a n d eosin in t h e field a n d e x a m i n e d in t h e laboratory by trained Africans working under European supervision. A l t h o u g h t h e results of t h e s u r v e y w e r e b a s e d on t h e e x a m i n a t i o n of v o l u n t e e r s , ( a d m i t t e d l y statistically i n c o r r e c t ) , t h e n e c e s s i t y of w o r k i n g at night, a n d t h e w i d e l y s c a t t e r e d a r r a n g e m e n t of m o s t of t h e villages, p r e v e n t e d o t h e r m o r e a c c u r a t e a n d t i m e - c o n s u m i n g m e t h o d s b e i n g e m p l o y e d . N e v e r t h e l e s s t h e results o b t a i n e d are t h o u g h t to give a fairly a c c u r a t e i n d i c a t i o n o f t h e i n c i d e n c e of t h e s e t w o f o r m s of filariasis in t h e T e r r i t o r y . T h e f o l l o w i n g t e r m s h a v e b e e n u s e d in t h e p r e s e n t c o m m u n i c a t i o n : - -

Microfilaraemia rate of a v i l l a g e - the percentage of adult males over the age of 16 years, showing microfilariae in their blood. In most cases these persons were free from obvious clinical filariasis (i.e. genital filariasis or elephantiasis of the limbs). Hydrocoele rate - - the percentage of adult males with hydrocoele, lymph scrotum or elephantiasis of the scrotum. (These three conditions are sometimes referred to as genital filariasis). Elephantiasis r a t e - the percentage of adults with elephantiasis of the legs. T h e incidence of A. perstans was determined from an examination of the night blood specimens. GENERAL DESCRIPTION OF THE AREA SURVEYED Tal~ganyika, lying between latitudes l ° S - 12°S and longitudes 3 0 ° E - 39°E, is bounded to the north by Kenya and Uganda, to the west by the Belgian Congo, and to the south by Northern Rhodesia and Portuguese East Africa. T h e Indian Ocean forms the eastern seaboard. T h e country covers nearly a third of a million square miles. Apart from the Coastal Plain and the river valleys, most of the country is more than 3,000 feet above sea level. Higher ground extends from Lake Nyasa in a north-easterly direction forming the eastern edge of the Central Plateau. In the north of the Territory, the Serengeti Plain, the Mbulu Highlands, Ngorongoro Crater, Mounts Meru and Kilimanjaro and the Pare and Usambara Mountains rise to heights varying between 5,000 and 19,000 feet. Over such a vast area varying climatic conditions are experienced. An extensive area in the centre o f the Territory has, on an average, less than 30 inches of rain a year while the area i m m e d i a t e l y to the north of Lake Nyasa has over 100 inches a year. Most of the remainder of the Territory averages between 30 and 50 inches, with rather more occurring in the highland areas. The mean maximum temperature is between 80°F - - 85°F. In the highland areas it is 75°F - 80°F or less, and the eastern coastal strip averages over 85°F. The mean minimum temperature for most of the Territory is 600F - - 65°F with lower temperatures in the highland areas and a higher minimum temperature towards the coast. E x t e n s i v e areas o f Tanganyika are uninhabited o w i n g to the presence o f tsetse fly and lack o f water. T h e seven million p o p u l a t i o n are concentrated m a i n l y along the coast, round the great lakes and in the highland areas.

462

Wuchererla bancrofti AND Acanthocheilonema perstans IN TANGANYIKA

RESULTS As a result of surveys carried Out as indicated above, the incidence of microfilaraemia in children, adult males and females was determined. T h e incidence of genital filariasis and elephantiasis was also established for most places. T h e meteorological data for each village visited was noted. Bancroftian infection in Tanganyika was found in three main loci. An extensive coastal area of infection extends up the main river valleys and covers most of the low lying Southern Province of the Territory. In this focus, areas with very high infection rates were found and it is considered that in these areas the disease must be of importance. A second area extends southwards from the southern end of Lake Victoria, and thirdly, there is a small but heavily infected, isolated focus at the northern end of Lake Nyasa. Villages having similar microfilaraemia rates were grouped t o g e t h e r - villages with adult male microfilaraemia rates of 0 - 5 per cent., 6 - 30 per cent. and over 30 per cent. were thus combined - - and the mean meteorological data for these three groups calculated together with the over-all microfilaraemia rates, the hydrocoele and elephantiasis rates (Table I.) TABLE I. Relationship between bancroftian microfilaraemia rates, hydrocoele and elephantiasis rates in different village groups, and the mean climatic conditions there. (Means of climatic data to nearest whole number).

Microfilaraen ia rates (%)

Mean temperatures Max.°F Min. °F

0-5

Over-all incider

of :

Mean rainfall in inches

Mean vapour pressure in millibars

Children

Males

Females

81-61

42

18

0.3%

0.8%

0.2%

0.7%

0.3%

6 - 30

83-64

40

21

2.7%

13.4%

9.9%

10.4%

0.5%

31--

84--67

43

23

11.5%

40.6%

26.8%

27.0%

1.5%

Microfilaraemia

Hydrocoele

Elephantiasis

It is apparent that the lower microfilaraemia and clinical rates occur with the lowest temperature and vapour pressure recordings, whereas the high rates are associated with high temperatures and vapour pressures. T h e r e does not appear to be any direct relationship between the rainfall and the incidence of bancroftian filariasis in the different groups.

DISCUSSION (A) BANCROFTIANMICROFILARAEMIA

(1)

Variation in microfilaraemia rates.

T h e correlation between high temperature and vapour pressure and high infection rates shown above, is, of course, a generalization. In many places a high or low microfilaraemia rate was found although, from a consideration of the recorded climatic data, less or more filariasis would be expected. It is thought that this may be due to the fact that meteorological data utilized in the present investigations were obtained from maps covering the whole of Tanganyika. In such maps local variations in ecoclimate produced by hill

P~'t~n JOin)AN

463

features, different types of natural and cultivated vegetation, artificial dams, water holes, ponds and streams and, no doubt, numerous other factors, are not shown. These factors, and details such as force and direction of the prevailing wind (O'CONNOR and HULSE, 1935), combine to produce conditions which facilitate or hinder the propagation and activity of the different mosquito vectors and will be largely responsible for the varying microfilaraemia rates which have been found to occur in endemic areas. Probably the most important factor on the human side of the filarial cycle which will influence the infection rate in an area is the density of population at risk, and the application or otherwise of anti-mosquito measures. The observations regarding meteorological data discussed above will no doubt partly explain anomalies in infection rates, but it is unlikely that this type of finding will be explained satisfactorily until detailed meteorological and entomological studies have been carried out in the different areas. In Tanganyika bancroftian filariasis was rarely found in places above 4,000 - - 4,500 feet above sea level. At these altitudes climatic conditions were generally unsuitable for the mosquito or, if the mosquito become infected, the conditions would be unsuitable for the completion of the filarial cycle in the insect. In the small focus at the northern end of Lake Nyasa very high infection rates were found. It is of interest to compare this with the low rates found on the eastern side of the lake. The mean annual rainfall of the two places is over 100 inches, and 50-60 inches, respectively. As the altitude is the same at each place and the temperatures are almost the same, it is considered likely that the greater rainfall in the north produces a dense mosquito population which will facilitate the transmission of the disease. The environment here is also probably more conducive to mosquito breeding and filarial transmission, since the focus is densely populated, flat and poorly drained, with the Africans carrying on intensive banana and rice cultivation. On the other side of the lake, however, there is a narrow well-drained lakeside strip where the population density is considerably less than in the north.

Microfilaraemia in the two sexes. From Tables I, II and III it is seen that in both W. bancrofti and A. perstans infections males are more frequently infected than females. In both infections the difference in the infection rates between the two sexes is statistically significant. (2)

TABLE II.

Incidence of infection with W. bancrofti (W.B.) and .4. perstans (A.P.) in children, adult males and adult females. Number examined in infected villages

% infected

Children

W.B. A.P.

6011 1034

4.4 16.9

Males

W.B. A.P.

8772 1785

19.6 37.8

Females

W.B. A.P.

5313 999

13.0 21.4

A higher incidence of infection with W. bancrofti var. pacifica has been reported in males from Fiji, Ellice and Tokelau Islands, from Rarotonga, Aititaki and Tonga by various workers,

464

Wuchereria bancrofti AND Acanthocheilonema perstans IN TANGANYIKA

quoted by BUXTON (1928). Similar findings were reported in Wuchereria malayi infection by POYNTON and HODGKIN (1938), though RAO (1936) in India found no marked difference in the infection rates in the two sexes with either W. bancrofti or W. malayi. MCFADZEAN (1954) found higher infection rates in males in both W. bancrofti and A. perstans in the Gambia. In Kenya, MCMAHON (1940) and BUCKLEY(1949) found males more frequently infected with Onchoeerca volvulus in one tribe but not in another. In general, the reason given for the difference in sex incidence in filariasis has been, that women are exposed less to infection than are their menfolk, and JACHOWSKIand OTTO (1952) have shown that on one Pacific Island males are bitten and infected as they leave their villages on the way to their work ; women, remaining near to their houses, are bitten less frequently. In East Africa, this cannot be the explanation of the higher male incidence. There are very few villages where the houses are built round a village square (as in the Pacific) or at all close to each other. Dwelling places tend to be separated by considerable distances, and a "village" may cover several square miles. In addition, it is often the females who do most of the work on the land. On Ukara Island in Lake Victoria, a higher incidence of infection was found in males, although SMITH (1953) has shown that Anopheles gambiae and Anopheles funestus - - biting at night - - are the main vectors. In view of this finding one might suppose that both sexes, being similarly exposed to infection, would show similar infection rates, but the differential biting habits of certain species of mosquito (MuIRHEAD-THoMSON, 1951) may partly account for the different rates of infection noted above. In view, however, of the almost universal finding of a higher incidence of filarial infection in males, it is suggested that they are more susceptible to filariasis than females. In some cases the difference may be affected by greater or lesser opportunities for infection occurring in one or other of the sexes. (3)

Microfilaraemia in infants.

It will be seen from Tables I and II that the incidence of infection with W. bancrofti is considerably less in children than in adults. Various attempts have been made to explain such low rates of microfilaraemia in infants. Although American Service personnel in the Pacific suffered from a symptom complex similar to " mumu " within 6 months of arriving in hyperendemic filarial areas, no microfilariae were found in the blood at that time. In spite of this early development of symptoms the earliest report of microfilariae in infants in the Pacific area is by LOWMAN (1944) who found microfilariae in the blood of an infant of 14 months. JORDAN(1952) reported from Tanganyika two infants in their first year of life with microfilariae. In spite of these findings, embryos are unusual before about 6 years of age after which time they are more frequently found. MACGREGOR and SMITH (1952) suggested that the low incidence of microfilaraemia in infants may be associated with recurrent malarial fever suffered by infants in the first few years of life. This factor may be involved, since JORDAN (1954b) has shown that hospital patients suffering with fever have a very low microfilarial incidence, and MANSON in 1877 observed the disappearance of microfilariae from the blood of a patient with typhoid fever during the height of the illness (O'CONNOR, 1923). The reason for this is not known. Fundamentally, however, probably the main factor in infection is the frequency with which the individual is bitten by infected mosquitoes.

PETER JORDAN

465

It is of interest to note that MUIRHEAD-THoMSON(1951) found that some species of mosquito were less attracted to children than to adults, and he considers this to be an important factor in the age distribution of filariasis, (MuIRHEAD-THoMPSON, 1954). SMITH(1953) has noted that the children of the Wakara (people from Ukara Island in Lake Victoria) are given some protection against mosquito bites by the blankets of their parents with whom they sleep. After the age of about six, the children usually sleep by themselves and have no protection against mosquitoes. By a combination of such factors, together possibly with factors at present unknown, children may suffer insufficient bites to become heavily inoculated with infective larvae until this age of relative immunity from mosquito bites has passed. The incidence of infected bites thereafter rapidly increases, with the result that adult worms are more likely to establish themselves in the individual. But, before microfilariae appear in the blood of an infected person, a female adult worm must be fertilized by a male. As there are numerous sites in the body in which adult worms have been found (O'CONNORand HULSE, 1935) it is feasible to suppose that a considerable number of infective larvae are required to enter the body before a male and female adult worm develop in the same lymphatic tissue. This may take a number of years, and during this time no microfilariae will be seen in the circulation. Tables II and III indicate that in A. perstans infection, microfilaraemia is more frequent in children than in the case of W. bancrofti infection. Nothing is known of the biting habits of Culicoides grahami and C. austeni (vectors of A. perstans) but it is interesting to speculate that it may be easier for male and female adult A. perstans to find each other and mate in the peritoneal cavity of the infected person, than it is for adult bancroftian worms in the widespread lymphatic tissue of the host. If this is indeed so, then it may explain the appearance of microfilariae in the blood of persons at an earlier age than in bancroftian infection. (B) CLINICALMANIFESTATIONS OF BANCROFTIAN INFECTION The clinical manifestations of bancroftian infection as seen during the survey work in Tanganyika are discussed below under the following sub-heads : (1) (2)

(3) (1)

Bancroftian elephantiasis. Genital filariasis. (a) Hydrocoele. (b) Elephantiasis of the scrotum. (c) Lymph scrotum. Lymphadenopathy.

Bancroftian elephantiasis.

Prior to our visiting the African villages, the inhabitants were told that we were investigating elephantiasis. In view of this the incidence of the disease as determined in our surveys is biased. Yet one can say that in most areas in which bancroftian microfilariaemia was found elephantiasis was also seen. In some areas, however, in the absense of bancroftian microfilaraemia, elephantiasis appeared to be not uncommon. These cases of non-bancroftian elephantiasis have been described elsewhere (JORDAN, TRANT and LAURIE, in press). Since it was found impossible to differentiate between the bancroftian and non-bancroftian types of elephantiasis, it is apparently unwise to assess the occurrence of bancroftian infection simply on the presence of elephantiasis in an area.

Wuchereria bancr ofti AND Axanthocheilonema perstans IN TANG~YIKA

466

Night blood samples were taken from 259 subjects of elephantiasis of the lower limbs in b o t h sexes. Of 83 males and 61 females suffering from unilateral disease, microfilariae were present in five and three cases respectively, or in 5.6 per cent. of the total. In the 115 cases of bilateral disease, one of the 64 males and two of the 51 females had microfilariae, or 2.6 per cent. of the total. T h e age incidence in the cases is shown below •

Nos. of cases % of cases

20 under

21-30

31 - 40

41 - 50

51 - 60

61 - 70

71

15

30

68

74

50

19

3

6

12

26

28

19

8

1

The cases in this series are from areas in which microfilariae of W. bancrofti were found. Elephantiasis of the arm was seen in seven cases, of which six were in males, three of whom had bilateral hydrocoele. All these cases were seen in areas having a high microfilaraemia rate. Genital filariasis, of one form or another, was associated with elephantiasis of the leg in a number of cases, but there was no difference in the incidence of scrotal disease with unilateral or bilateral elephantiasis (42 per cent. and 45 per cent. respectively). T h e cases of elephantiasis seen during the survey work were not usually very severe and the condition rarely extended above the knee. Lymphostasis verrucosis was present in some. (2)

Genital filariasis.

In Table I the hydrocoele rate in the different village groups is given. It is seen that as the microfilaraemia rate increases so does the hydrocoele rate. This relationship between the two rates was demonstrated in a further paper (JORDAN, 1955) in which it was also shown that the incidence of high counts was greater in villages with high microfilaraemia rates, and evidence was produced suggesting that hydrocoeles may be related to heavy infestation with

W. bancrofti. (a) Hydrocoeles.

Elephantiasis is usually considered to be the most important late manifestations of bancroftian infection, but survey work in Tanganyika indicates that in this Territory it is of little importance when compared with the very high incidence of hydrocoele that was recorded in some places. This is recognized by the Territorial Medical Department, since in the Annual Reports of 1949, 1950 and 1951 it is stated that " operations for hydrocoele and hernia form the bulk of surgical work thoughout the T e r r i t o r y , " - - t h i s is in spite of large areas of the Territory being free of bancroftian infection. Night bloods were obtained in 517 cases of unilateral hydrocoele, and in 148, or 29 per cent., the blood was positive. Of the 440 subjects of bilateral hydrocoele seen, 91, or 20 per cent., had microfilariae in their blood. A further 59 cases of hydrocoele were seen associated with elephantiasis of the legs. Only two of these had microfilariae in the night blood (3 per cent.). This very low incidence compared with the 25 per cent. incidence of microfilariae in uncomplicated hydrocoeles will be discussed in a further paper. Of the 59 cases of hydrocoele complicating elephantiasis, 33 were bilateral, 21 were unilateral. No note was made of the remaining five. (b) Elephantiasis of the scrotum. This condition was seen 16 times during the survey.

PETER joan~'q

467

It appeared to be more prevalent in areas where a high incidence of filarial infection was recorded. The condition was associated with elephantiasis of the leg in four cases. Little attempt was made to investigate the presence of hydrocoele in the elephantoid scrotal mass, since the condition of the scrotal wall invariably made accurate palpation of the contents impossible. Attempts. to investigate the presence of hydrocoele by aspiration were frequently unsuccessful owing to the thickness of the scrotal wall. During operations on elephantiasis of the scrotum, however, testes have been found to be almost normal macroscopically, with no hydrocoele even in the presence of gross elephantiasis of the scrotal wall. The penis in these cases may or may not be involved. In some cases the weight of the scrotum causes the penis to disappear within the scrotal mass. More rarely, the penis alone is involved in elephantoid changes. (c) Lymph scrotum. This is comparatively rare in Tanganyika, only three cases were seen in survey work. It is of interest to note that all these cases were seen at one village, Muheza, near the coast at Tanga. Such a localization of certain filarial conditions to restricted areas has been noted by BUXTON (1928) and BRYGOO (1951), and no satisfactory explanation has, as yet, been given. Lymph scrotum is considered by ACTON and RAO (1930) to develop after the removal of the sac of filarial hydrocoeles, but since the lymph drainage of the scrotal contents and scrotal wall is different it is difficult to understand the mechanism of this. (3)

Filarial lymphadenopathy.

Since the lymphatic system is the main site for adult bancroftian worms, it would be expected that evidence of filarial infection would show itself in the lymph glands or vessels. In this respect, BUXTON (1928) has drawn attention to the correlation between enlargement of the epitrochlear glands and the presence of microfilariae in the bloodstream, and in addition, he has shown that the incidence of epitrochlear adenopathy was higher in men with elephantiasis below the waist than in men of the same age-groups without elephantiasis. These observations were made in the South Pacific where W. bancrofti var. pacifica is the common filarial infection: BUXTON considers that epitrochlear lymphadenopathy provides a satisfactory measure of filarial infection in a community. The same authority found a steady increase in the incidence of inguinal and femoral glandular enlargement with age corresponding to the increase in the incidence of microfilariaemia with age. During investigations in East Africa the opportunity was taken to examine the glandular condition of Africans with different filarial conditions. Six such groups have been examined as enumerated below • (1) (2) (3) (4) (5) (6)

Cases of microfilaraemia. Cases of microfilaraemia with hydrocoele. Cases of hydrocoele with negative bloods. Cases of elephantiasis with negative bloods. Control from endemic area. Control from non-endemic area.

Two control groups have been used - - a group of Africans apparently free of filariasis from an endemic filarial area, and a group from an area in which bancroftian infection does not occur. Both control series leave much to be desired but it is difficult to obtain an entirely satisfactory control group. Any criteria for assessing enlargement of a gland must be essentially dependent on the

468

Wuchereria bancrofti AND Acanthocheilonema perstans IN TANCANYIKA

examiner's conception of what is normal and what abnormal. In the present investigation, any gland considered by the examiner to be larger than normal has been included. Cases of scabies with secondary infection of the skin or tropical ulcers, or any other obvious disease associated with lymphadenopathy - - either local or generalized - - have been excluded from the present series. The findings reported here and shown in the nomograms are generally in agreement with BUXTON'S work. Although a high incidence of epitrochlear glandular enlargement has been noted in persons with microfilaraemia and in elephantiasis, it is not considered that the finding is sufficiently conclusive to give a satisfactory indication of the incidence of filariasis in East Africa, particularly since the prevalence of spirochaetal infection is liable to confuse any such findings based on epitrochlear adenopathy.

~C ~o 0ZLt.I n3;

~2o uz tc

H34 FEMORAL

G

i I

E PITROCHLEAR

Normogram showing the incidence of femoral, inguinal and epitrochlear adenopathy in different filarial conditions. (1- microfilaraemia ; 2- microfilaraemia and hydrocele ; 3- hydroceles with negative bloods ; 4 - elephantiasis with negative bloods ; 5 - control from endemic area ; 6 - control from non-endemic area.) Although pathological changes in lymph glands are usually associated with adult filarial worms it has been shown recently (Baas and Jo~, 1953) that in some cases of (?) W. malayi infection small eosinophilic abscesses found in lymph glands were due to the presence of microfilariae in the gland, and MEYERS and KOUW~NAAR (1939) have described a syndrome in which generalized lymph-adenopathy is the main feature. It is considered to be of filarial origin and it seems possible that it is the result of an allergic-type reaction. MICHAEL (1944) from histological studies of tissues from American Service personnel, considers that the lymphangitis and lymphadenitis characteristic of the early stage of filarial infection is an allergic response to adult worms elsewhere, and that many of these early pathological changes are reversible. The epitrochlear lymphadenopathy reported in Africans, associated with the stage of the disease in which microfilaraemia is present, may be a remote manifestation of the allergic response to the adult worm situated in the spermatic cord or elsewhere. T h e high incidence of lymphadenopathy in elephantiasis cases may again be due to an allergic reaction as a result of the death of adult worms which may occur with, or be responsible for, the development of elephantiasis.

PETER JORDAN (C)

469

ACANTHOCHEILONEMAPERSTANS

T h e incidence of this infection has been determined throughout Tanganyika during the series of investigations reported here. T h e results indicate a more extensive distribution particularly in the Southern Province - - than had previously been recorded by HAWKING (1940). In this Province large numbers of persons were found to be infected with both A. perstans and W. bancrofti, and it has been shown that the n u m b e r with the double infection is greater than would be expected to occur by chance (JORDAN, 1955). HAWKING (1940) considers that the climatic conditions suitable for one of these conditions are probably not acceptable to the other, but the findings reported here disprove this. In addition to the focus of infection in the Southern Province, A. perstans was found in the area between Lakes Tanganyika and Victoria. As long ago as 1903, CHRISTY noted the occurrence of A. perstans in areas where bananas were grown. T h e reason for this fact was apparent after SHARPE (1928) showed the vector to be Culicoides sp., and HOPKINS (1952) reported decaying banana trees to be a suitable environment for the breeding of this fly. MCFADZEAN (1954) however, failed to find any correlation between the incidence of A. perstans and the numbers of banana trees in a village. In Tanganyika bananas form an important part of the diet of some of the tribes living in the area between Lakes Tanganyika and V i c t o r i a - an area in which A. perstans has been found, but in the heavily infected parts of the Southern Province bananas play only a very small part in the diet of the local people. Other areas where bananas form the staple diet of the African are the locations round Mounts M e r u and Kilamanjaro and in the Pare, Usambara and Uluguru Mountain Ranges. In the area to the north of Lake Nyasa, where bancroftian infection is hyperendemic, bananas are grown in abundance, but acanthocheilonemiasis does not occur in any of these areas. It is at first difficult to explain the absence of this infection from these areas where abundant bananas are grown, and where a suitable environment for the vector apparently exists. In an attempt to investigate this, the villages with A. perstans infection were grouped together according to the infection rates in adult males as was done for W. bancrofti infection. T h r e e groups were utilized - - villages with rates of less than 20, 21 to 40 per cent. and those with rates of 41 per cent. and over. T h e over-all infection rates for children, adult males and females and the means of the meteorological recordings of each village were calculated for each group and the results are shown in Table III. TABLE III.

Relationship between A. perstans rates in different village groups and the mean climatic recordings there. (Means of climatic data to nearest whole number).

Mean Mean Microfilaria temperatures rainfall VIax°F Min°F in inches rates (%)

Infection rates

Mean vapour pressure in millibars

Children

Males

Females

0 - 20

82 - 64

46

19

2.1%

7.3%

2.9%

21 - 40

70 - 64

40

20

13.2%

32.0%

28.0%

41--

80 - 65

37

20

52.4%

36.7%

22.9%

It is seen that the mean temperatures and vapour pressures show no consistant variation in the three village groups, but that the mean rainfall figures decrease steadily with the higher

470

Wuchreeria bancrofti AND Acanthocheilonema perstans IN TANGANYmA

microfilaraemia rates. This suggests that one of the reasons for the absence of A . perstans from some of the areas where apparently suitable conditions prevail (i.e. those areas where bananas are extensively grown), may be that in these areas the rainfall may be excessive. This is certainly the case in the dense banana area at the northern end of Lake Nyasa, where over 100 inches of rain per year are recorded. Similarly high readings are recorded in the mountainous areas mentioned above where bananas are extensively grown, but no data are available relating to the incidence of Culicoides sp. in these areas. In the two areas where A . perstans was found to be prevalent, tsetse fly were found in varying densities and it was considered possible that these may sometimes be vectors. Accordingly a number of flies were dissected and one out of 33 tsetse flies (species unknown) from the inter-lake focus was found to contain a filarial worm in the abdomen. It was impossible to identify the species, but no larval forms were found in over 200 Glossina morsitans from the Southern Province. The possibility that A . perstans may be a cause of elephantiasis has been discussed elsewhere (JoRom,I, TRANT and LAURIE, in press). SUMMARY (1) A general outline of the methods employed during the filarial survey of Tanganyika is given. The limitations of these methods is recognized. (2) The low-lying coastal plain together with an extensive area in the Southern Province, the area to the north of Lake Nyasa and the region to the south of Lake Victoria, are the three main foci of W. bancrofti infection in Tanganyika. These areas correspond closely to the areas in which transmission of malaria occurs throughout the year. (3) The microfilaraemia rate is shown to be high in places having high temperatures and high vapour pressures. (4) It is suggested that differences in the ecoclimate of neighbouring villages may account for differences in infection rates. (S) The almost universal finding that males are more frequently infected than females with different types of filariasis is noted, and it is suggested that for some reason or other females are less susceptible to filarial infections than are males. (6) It is suggested that the low incidence of bancroftian infection in children may be due to the difficulty that male and female filariae may have in meeting and mating in the widespread lymphatic system in the body. (7) Microfilariae were found in 5.6 per cent of the unilateral, and in 2.5 per cent. of the bilateral, elephantiasis cases. (8) The incidence of genital filariasis was the same in unilateral and bilateral cases of elephantiasis of the legs. (9) The hydrocoele rate was found to increase with an increase in the microfilaraemia rate. (10) In 29 per cent. cases of unilateral and in 20 per cent. of bilateral hydrocoele, the night blood was positive. (11) In 59 subjects of hydrocoele complicating elephantiasis of the leg only two (or 3 per cent.) had microfilariae. (12) Elephantiasis 'of the scrotum and lymph scrotum was not as frequently seen in the Territory as was simple hydrocoele. (13) Nomograms show the incidence of lymphadenopathy in different clinical conditions : 35 - 45 per cent. of persons with microfilaraemia and 41 per cent. of those with

PETER

JORDAN

471

elephantiasis have epitrochlear adenopathy. I t is suggested that this may be due to an allergic response. (14) A . perstans was found over an extensive area of the Southern Province of T a n g a n yika and in the area between Lakes Tanganyika and Victoria. (15) T h e relationship b e t w e e n A . perstans and bananas is discussed. (16) I t is suggested that the tsetse fly m a y act as a vector of A . perstans. REFERENCES ACTON, H. W. & RAo, S. S. (1930). Indian med. Gaz., 65, 54. BAsu, B. C. & RAO, S. S. (1949), Indian J. reed. Res., 27, 233. BRAS, G. & JOE, L. K. (1951). Docum. neer. Indones. Morb. trop., 3, 289. BRYGOO,E. R. (1951). S. Pacific Commission. Conference of Experts on Filariasis and Elephantiasis, Sept., 1951. (Mimeographed summary of proceedings) p. 7. BUCKLEY, J. J. C. (1949). J. Helminth., 23, 1. BUXTON, P. A. (1928). Mem. SeT. Lond. Sch. Hyg. trop. Med., No. 2. CHRISTY, C. (1903). Rep. Sleep. Sickn. Comm. roy. Soc., 2, EAST AFRICA H m a COMMISSION (1952, 1953 & 1954). Filariasis Research Unit Annual Report, for the years ending 1951, 1952 and 1953. HAWXmG, F. (1940). Ann. trop. ivied. Parasit., 34, 107. HOPKINS, C. A. (1952). 1bid., 46, 165. JACHOWSKr, L. A. & OTTO, G. F. (1952). Amer. J. trop. Med. Hyg., 1, 662. JORDAN, P. (1952). Trans. R. Soc. trop. Med. Hyg., 44, 207. (1953). E. Afr. reed. ft., 30, 361. - (1945a). 1bid., 31, 537. - (1954b). ft. trop. Med. Hyg., 57, 8. (1955). Ann. trop. Med. Parasit., 49, 42. , TRANT, H. & LAURIE, W. In press. LOWMAN, E. W. (1944). Nay. reed. Bull., Wash, 42, 341. MANSON-BAHR, P. E. C. (1951). S. Pacific Commission. Conference of Experts on Filariasis and Elephantiasis, Sept., 1951. (Mimeographed summary of proceedings) p. 8. McFADZEAN, J. A. (1954). Trans. R. Soc. trop. Med. Hyg., 48, 267. McGREGOR, J. A. & SMITH, A. (1952). Ibid., 46, 463. MCMAHON, J. P. (1940). Ibid., 34, 1. ME'~mRS, F. M. & KOUWENAAR,W. (1939). Geneesk. Tijdschr. Ned. Ind., 80, 2230. MICHAEL, P. (1944). Nay. reed. Bull. Wash., 42, 1059. MUIRHEAD-THoMSON,R. C. (1951). Brit. reed. ft., 1, 1114 - (1954). ft. trop. Med. Hyg., 57, 107. O'CONNOR, F. W. (1923). Res. Mem. Lond. Sch. trop. Med., No. 4. & HULSE, C. R. (1935). Puerto Rico ft. publ. Hlth. trop. Med., U, 167. POYNTON, J. O. & HODGKIN,E. P. (1938). Bull. In~,t. med. Res. F.M.S., No. 1 of 1938. RAO, S. S. (1936). Indian ft. reed. Res., 23, 871. SHARP, N. A. D. (1928). Trans. R. Soc. trop. Medl Hyg., 21, 371. SMITH, A. (1953). Personal communication. TANGANYrKA (1950, 1951 & 1952). Annual Report of the Medical Department for the years ending 1949, 1950 and 1951. -

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