- Email: [email protected]
Some observations on the incidence of malaria amongst the nilotic tribes
TRANSACTIONS OF THE ROYAL SOCIETY O1" TROPICAL MEDICINE AND HYGIENE.
Vol. XXV. No. 4.
January, 1932o
S O M E O B S E R V A T I O N S ON T H E I N C I D E N C E OF MA L A RIA AMONGST THE NILOTIC TRIBES.* BY
L. H. HENDERSON, M.D., B.Sc., D.T~M. & H.
Sudan Medical Service.
T he Nilotie tribes inhabit the Upper Nile Province of the Sudan, a flat, marshy plain approximating 15,000 square miles embracing the White Nile and its tributaries from parallel 6 ° N. to parallel 12 ° N. T h e y are divided into three tribes : Nuer, Dinka and Shilluk, all of whom have sprung from common ancestors. Anthropologically, all these tribes present very similar characteristics. T h e y are very tall, sparely built, and long limbed with somewhat dolicho-cephalic skulls and slight prognathism. T h e Nuers inhabit the most swampy part of the province--the Sudd region--and extend eastward to the Zeraf, Sobat, and Pibor rivers and westward to the Ghazel river. Th e Dinkas are divided into two sections : the southern, found on the west bank of the Nile between Bor and Shambe, and the northern, scattered along the east bank of the river between Kodok and Renk. T he Shilluks--the most compact and sedentary of the tribes--inhabit both banks of the river between Lake No and Kodok and extend still further north on the west bank only as far as Gelhak. All three tribes are very similar in their habits ; they are practically naked savages whose whole lives are bound up with the welfare of their cattle. In the rains they live in fairly permanent villages composed of circular mud huts thatched with grass. In the dry weather, however, the villages are usually left *The writer wishes to express his indebtedness to Major R. G. ARCHIBALD,C.M.G., D.S.O., Director of the Wellcome Tropical Research Laboratories for revising the MS., and to Dr. O. F. H. ATKEV,C.M.G., F.R.C.S., Director, Sudan Medical Service for permission to publish this paper. Thanks are also due to Mr. H. H. KINC, Wellcome Tropical Research Laboratories and to Dr. P. A. BUXTON, London School of Hygiene and Tropical Medicine, for the identification of the mosquitoes mentioned in this paper. F
9,89,
MALARIA AMONGST THE NILOTIC TRIBES.
to the very old and very young, the rest of the tribe moving into temporary shelters near the river where good grazing can be obtained. This applies mostly to Dinkas and Nuers, as the Shilluks, by building their villages on the actual river bank, are within easy reach of green fodder all the year round. The women cook inside the mud huts thereby keeping them comparatively free from mosquitoes. Unfortunately, however, these people are wont to sit about in sociable groups in the early evening, and in warm nights, they sleep outside without any protection. Thus they continually expose themselves to infection. Fever is looked upon as a normal part of a child's actual existence and treatment is rarely sought. Vital Statistics and Administration.--No accurate statistics are available. The tribes under review number approximately half a million, with the males and females approximating equal numbers. There is a preponderance of children over adults in the ratio of roughly 3 : 2. As most women marry and bear on an average, five to six children, it will be seen that the infantile mortality is exceedingly high. To appreciate the distribution of malaria a note on the administration of the province is necessary. Province Headquarters is at Malakal where there is a handful of British officials with some five or six hundred Arabs, Egyptians, etc., serving as government officials, servants, and merchants. District Commissioners with correspondingly smaller retinues of similar origin are dotted about the province. At other points there are Arab merchants who derive a precarious livelihood by bartering beads, bangles, etc., for native grain and hides. Malaria. The most prevalent diseases are malaria and yaws. The latter is decreasing rapidly under intensive treatment ; but the former presents problems of great difficulty. It is to the ravages of malaria that the high infantile mortality of approximately 50 per cent. is chiefly attributed. Distribution.--Malaria is endemic in the province throughout the whole year. The indigenous type among the Nilotics is benign tertian, with small loci of quartan in two or three isolated parts. At Malakal, government posts, and trading stations, generally malignant tertian is found. This type has obviously been introduced by the Arab from the north. It shows little inclination to spread widely beyond the immediate vicinity in which it first appears, and little tendency to die out when once introduced. Seasonal Incidence.--The rainy season in the province lasts from May to early October. At this time, and continuing till December, the incidence of malaria assumes pandemic proportions. In the dry season, or at least that part of it between January and April, the incidence drops considerably especially in the northern part of the province where the dryness and cold winds of this period keep the mosquito density very low.
L. H. HENDERSON.
288
Age lncidence.--In the early months of life children are protected, to a certain extent, by their mothers. Later, however, commencing even before the first year is completed, practically every child contracts malaria repeatedly. Weakly children rapidly die off and only the fittest survive. Thus it is rare to see any but fairly sturdy looking children over the age of about four years. Attacks recur frequently especially during the rains until about the tenth year. Thereafter they are less frequent until by the age of sixteen infection is rare. In adult life the incidence of benign tertian malaria is very low. In the female it is twice as common as in the male. It appears to occur most frequently in adults whose general health has previously been undermined by some debilitating pathological or physiological condition. Thus adult males affected by malaria are frequently found to be suffering from tertiary yaw manifestations while in the female the attack frequently follows repeated child bearing. In government and trading posts, however, where the native is exposed to malignant tertian malaria, he frequently contracts the disease. Yet he does not suffer from malaria to anything like the same extent as the visiting Arab infected with benign and malignant tertian. Splenic Index.--The splenic index may be taken as an indication of the malariousness of the province, for kala-azar, schistosomiasis, and other diseases causing splenic enlargement rarely occur. It corroborates, to a large extent, the age incidence of the disease, and the average index for the whole area is 50 per cent. for children, 0-05 per cent. for male adults, and 0.1 per cent. for female adults. The earliest age at which splenic enlargement occurs is ten to twelve months, and the age most productive of enlargement is about the fifth year ; its steady decline in incidence between the tenth and the sixteenth years approximately is very noticeable. The index fluctuates of necessity in different parts of the province. The children of the southern Dinkas have one of approximately 70 per cent., whereas in the adults it is practically nil. The Nuers have a splenic index in children of 25 per cent. only while the average in adults is 1 per cent. occurring almost exclusively in females. In the Shilluk country the index in children is 30 per cent. and that in adults 0.5 and 1.1 per cent. for males and females respectively. ]t is thus apparent that, as a general rule, the splenic index in adults varies inversely with that in childhood. This generalisation, however, was not confirmed in the northern Dinkas who have an average index in children of only 25 per cent.; in adults there was practically no splenic enlargement but the incidence of malaria was found to be relatively very high. From the above it may be said that, with benign tertian malaria, the higher the incidence of the disease in childhood, the lower the rate of infection in adult life. It has been observed that near government posts, though the incidence of carriers may be just as high as elsewhere, the splenic index in children is
284
MALARIA AMONGST THE NILOTIC TRIBES.
often comparatively low and the incidence of malaria in adults, even excluding cases of malignant tertian, correspondingly relatively high. At these posts, natives are under a certain amount of supervision and children with fever are frequently taken to the dispensary for quinine. Unfortunately, the natives do not understand the necessity for a complete course of treatment and attendances cease with the subsidence of the fever. This point will be referred to again under " Immunity." Blood Examination.--Considerable difficulties are experienced in the taking and examination of films in the field. Working in an atmosphere impregnated with dust and flies, it is practically impossible to keep slides clean. Overrapid drying of thin films in the tropical sun causes crenation of the red blood corpuscles. Stain quickly dries up and precipitates in the film. The number of parasites found in the peripheral blood is always very small. Slides taken from children about the fourth or fifth year with splenic enlargement are more productive of parasites than specimens from adults actually suffering from the disease. Rings and gametocytes are the forms most frequently observed. Sporulating forms are rarely seen. Mosquito Density.--Culicine species--more prolific and hardier than the average anopheline--are present in the province throughout the whole year. Anophelines, on the other hand, conform more generally in their habits to seasonal variation, increasing considerably during the rains and decreasing in the dry weather. Anophelesfunestus is probably the most active carrier in the whole area. In the north and central parts of the province, it is active only during the rains, but in the south, it persists all the year round. The female of this species impregnated at the breeding ground immediately seeks human habitation and remains there till ready for oviposition. In darkened rooms it bites freely all day but, in the open, it has been observed to bite only for an hour or so after sunset, and for a corresponding time before sunrise. A. gambia appears in all parts of the province just after the commencement of the rains but rapidly disappears in the dry weather even in places where ideal breeding grounds persist. This mosquito is found most commonly near native villages. A. pharoensis is found chiefly in the central parts of the province. In habits it is very similar to A. gambia, and like it, practically disappears during the dry weather. These three are probably the chief carriers of malaria in the province, but the following have also been found in small numbers in various parts of the province near human habitations: A. squamosus, A. maurtianus, and A. rhodesiensis. A. nili and A. wellcomei are the chief anophelines found in areas remote from villages. In hunting and fishing round Lake No the latter gives one no peace, biting voraciously during all the hours of daylight.
L. H. HENDERSON.
285
Immunity.--It may be assumed from the foregoing that amongst these primitive people repeated attacks of benign tertian malaria in childhood are productive of a definitely high degree of immunity to the disease in those surviving to adult life. This immunity begins to be apparent early in the second decade and is fully established by the time puberty is reached, and appears to persist throughout life. The protection afforded is specific; if exposure to quartan or malignant tertian occurs infection may result. A similar state of immunity seems to be acquired following repeated exposure in childhood to quartan malaria, but with malignant tertian, immunity of this nature was not apparent. Whether in this type of infection immunity fails to occur, or whether the high incidence of infections occurring in all Arabs visiting the province is due to exposure to different strains of the parasite, has not been determined owing to insufficient available evidence. Immunity to the disease causes some change in the peripheral blood stream which is detrimental to the growth of the parasite firstly in the asexual cycle then later in all its forms. To be effective this immunity requires to be supported by a high degree of physical resistance to disease generally. Thus it may fail in the presence of any condition adversely affecting the general health ; further it may be retarded or possibly inhibited altogether by the exhibition of irregular doses of quinine. Prophylaxis.--In such an extensive marshy area peopled by primitive tribes lacking in intelligence, it is difficult to adopt any but the most crude prophylactic measures. Propaganda is attempted but the natives are very incredulous and unwilling to attribute disease to anything but jok (bad luck). Chiefs and the more enlightened natives are encouraged to use mosquito nets ; they fail, however, to realise the importance of similar protection for their children. Breeding places, unless in close proximity to the larger government stations, cannot be dealt with, but attempts are being made to improve the general conditions under which these natives live, and though these may scarcely aspire to the term " bonification," it is hoped that the general improvement will be reflected in a reduced infantile mortality. Haphazard distribution of quinine may result in amelioration of malarial symptoms but is ineffectual in producing cures. SUMMARY AND CONCLUSIONS.
(1) The incidence of malaria amongst the Nilotic tribes inhabiting the upper reaches of the Nile is described. (2) Benign tertian malaria is endemic and becomes pandemic during the rains; scanty foci of quartan malaria occur and malignant tertian has been introduced but shows no tendency to spread. (3) The splenic index is high in children and low in adults ; considerable fluctuations occur in different parts of the province.
~6
MALARIA AMONGST THE NILOTIC TRIBES.
(4) Children become infected with benign tertian in their first year, and recurrent attacks lead to a high mortality during the initial years of life. (5) Infections with benign tertian decrease as adolescence approaches, and rarely implicates the adult of whom the female is twice as susceptible as the male. (6) Malignant tertian malaria is comparatively frequently contracted by adults, and the immunity observed in the case of benign tertian and of quartan malaria does not appear to develop. (7) The probable carriers in the province are A. funestus, A. gambiae and
A. pharoensis. (8) Prophylaxis is extremely difficult owing to topographical conditions and the ignorance of the tribes.
Vol. XXV. No. 4.
January, 1932o
S O M E O B S E R V A T I O N S ON T H E I N C I D E N C E OF MA L A RIA AMONGST THE NILOTIC TRIBES.* BY
L. H. HENDERSON, M.D., B.Sc., D.T~M. & H.
Sudan Medical Service.
T he Nilotie tribes inhabit the Upper Nile Province of the Sudan, a flat, marshy plain approximating 15,000 square miles embracing the White Nile and its tributaries from parallel 6 ° N. to parallel 12 ° N. T h e y are divided into three tribes : Nuer, Dinka and Shilluk, all of whom have sprung from common ancestors. Anthropologically, all these tribes present very similar characteristics. T h e y are very tall, sparely built, and long limbed with somewhat dolicho-cephalic skulls and slight prognathism. T h e Nuers inhabit the most swampy part of the province--the Sudd region--and extend eastward to the Zeraf, Sobat, and Pibor rivers and westward to the Ghazel river. Th e Dinkas are divided into two sections : the southern, found on the west bank of the Nile between Bor and Shambe, and the northern, scattered along the east bank of the river between Kodok and Renk. T he Shilluks--the most compact and sedentary of the tribes--inhabit both banks of the river between Lake No and Kodok and extend still further north on the west bank only as far as Gelhak. All three tribes are very similar in their habits ; they are practically naked savages whose whole lives are bound up with the welfare of their cattle. In the rains they live in fairly permanent villages composed of circular mud huts thatched with grass. In the dry weather, however, the villages are usually left *The writer wishes to express his indebtedness to Major R. G. ARCHIBALD,C.M.G., D.S.O., Director of the Wellcome Tropical Research Laboratories for revising the MS., and to Dr. O. F. H. ATKEV,C.M.G., F.R.C.S., Director, Sudan Medical Service for permission to publish this paper. Thanks are also due to Mr. H. H. KINC, Wellcome Tropical Research Laboratories and to Dr. P. A. BUXTON, London School of Hygiene and Tropical Medicine, for the identification of the mosquitoes mentioned in this paper. F
9,89,
MALARIA AMONGST THE NILOTIC TRIBES.
to the very old and very young, the rest of the tribe moving into temporary shelters near the river where good grazing can be obtained. This applies mostly to Dinkas and Nuers, as the Shilluks, by building their villages on the actual river bank, are within easy reach of green fodder all the year round. The women cook inside the mud huts thereby keeping them comparatively free from mosquitoes. Unfortunately, however, these people are wont to sit about in sociable groups in the early evening, and in warm nights, they sleep outside without any protection. Thus they continually expose themselves to infection. Fever is looked upon as a normal part of a child's actual existence and treatment is rarely sought. Vital Statistics and Administration.--No accurate statistics are available. The tribes under review number approximately half a million, with the males and females approximating equal numbers. There is a preponderance of children over adults in the ratio of roughly 3 : 2. As most women marry and bear on an average, five to six children, it will be seen that the infantile mortality is exceedingly high. To appreciate the distribution of malaria a note on the administration of the province is necessary. Province Headquarters is at Malakal where there is a handful of British officials with some five or six hundred Arabs, Egyptians, etc., serving as government officials, servants, and merchants. District Commissioners with correspondingly smaller retinues of similar origin are dotted about the province. At other points there are Arab merchants who derive a precarious livelihood by bartering beads, bangles, etc., for native grain and hides. Malaria. The most prevalent diseases are malaria and yaws. The latter is decreasing rapidly under intensive treatment ; but the former presents problems of great difficulty. It is to the ravages of malaria that the high infantile mortality of approximately 50 per cent. is chiefly attributed. Distribution.--Malaria is endemic in the province throughout the whole year. The indigenous type among the Nilotics is benign tertian, with small loci of quartan in two or three isolated parts. At Malakal, government posts, and trading stations, generally malignant tertian is found. This type has obviously been introduced by the Arab from the north. It shows little inclination to spread widely beyond the immediate vicinity in which it first appears, and little tendency to die out when once introduced. Seasonal Incidence.--The rainy season in the province lasts from May to early October. At this time, and continuing till December, the incidence of malaria assumes pandemic proportions. In the dry season, or at least that part of it between January and April, the incidence drops considerably especially in the northern part of the province where the dryness and cold winds of this period keep the mosquito density very low.
L. H. HENDERSON.
288
Age lncidence.--In the early months of life children are protected, to a certain extent, by their mothers. Later, however, commencing even before the first year is completed, practically every child contracts malaria repeatedly. Weakly children rapidly die off and only the fittest survive. Thus it is rare to see any but fairly sturdy looking children over the age of about four years. Attacks recur frequently especially during the rains until about the tenth year. Thereafter they are less frequent until by the age of sixteen infection is rare. In adult life the incidence of benign tertian malaria is very low. In the female it is twice as common as in the male. It appears to occur most frequently in adults whose general health has previously been undermined by some debilitating pathological or physiological condition. Thus adult males affected by malaria are frequently found to be suffering from tertiary yaw manifestations while in the female the attack frequently follows repeated child bearing. In government and trading posts, however, where the native is exposed to malignant tertian malaria, he frequently contracts the disease. Yet he does not suffer from malaria to anything like the same extent as the visiting Arab infected with benign and malignant tertian. Splenic Index.--The splenic index may be taken as an indication of the malariousness of the province, for kala-azar, schistosomiasis, and other diseases causing splenic enlargement rarely occur. It corroborates, to a large extent, the age incidence of the disease, and the average index for the whole area is 50 per cent. for children, 0-05 per cent. for male adults, and 0.1 per cent. for female adults. The earliest age at which splenic enlargement occurs is ten to twelve months, and the age most productive of enlargement is about the fifth year ; its steady decline in incidence between the tenth and the sixteenth years approximately is very noticeable. The index fluctuates of necessity in different parts of the province. The children of the southern Dinkas have one of approximately 70 per cent., whereas in the adults it is practically nil. The Nuers have a splenic index in children of 25 per cent. only while the average in adults is 1 per cent. occurring almost exclusively in females. In the Shilluk country the index in children is 30 per cent. and that in adults 0.5 and 1.1 per cent. for males and females respectively. ]t is thus apparent that, as a general rule, the splenic index in adults varies inversely with that in childhood. This generalisation, however, was not confirmed in the northern Dinkas who have an average index in children of only 25 per cent.; in adults there was practically no splenic enlargement but the incidence of malaria was found to be relatively very high. From the above it may be said that, with benign tertian malaria, the higher the incidence of the disease in childhood, the lower the rate of infection in adult life. It has been observed that near government posts, though the incidence of carriers may be just as high as elsewhere, the splenic index in children is
284
MALARIA AMONGST THE NILOTIC TRIBES.
often comparatively low and the incidence of malaria in adults, even excluding cases of malignant tertian, correspondingly relatively high. At these posts, natives are under a certain amount of supervision and children with fever are frequently taken to the dispensary for quinine. Unfortunately, the natives do not understand the necessity for a complete course of treatment and attendances cease with the subsidence of the fever. This point will be referred to again under " Immunity." Blood Examination.--Considerable difficulties are experienced in the taking and examination of films in the field. Working in an atmosphere impregnated with dust and flies, it is practically impossible to keep slides clean. Overrapid drying of thin films in the tropical sun causes crenation of the red blood corpuscles. Stain quickly dries up and precipitates in the film. The number of parasites found in the peripheral blood is always very small. Slides taken from children about the fourth or fifth year with splenic enlargement are more productive of parasites than specimens from adults actually suffering from the disease. Rings and gametocytes are the forms most frequently observed. Sporulating forms are rarely seen. Mosquito Density.--Culicine species--more prolific and hardier than the average anopheline--are present in the province throughout the whole year. Anophelines, on the other hand, conform more generally in their habits to seasonal variation, increasing considerably during the rains and decreasing in the dry weather. Anophelesfunestus is probably the most active carrier in the whole area. In the north and central parts of the province, it is active only during the rains, but in the south, it persists all the year round. The female of this species impregnated at the breeding ground immediately seeks human habitation and remains there till ready for oviposition. In darkened rooms it bites freely all day but, in the open, it has been observed to bite only for an hour or so after sunset, and for a corresponding time before sunrise. A. gambia appears in all parts of the province just after the commencement of the rains but rapidly disappears in the dry weather even in places where ideal breeding grounds persist. This mosquito is found most commonly near native villages. A. pharoensis is found chiefly in the central parts of the province. In habits it is very similar to A. gambia, and like it, practically disappears during the dry weather. These three are probably the chief carriers of malaria in the province, but the following have also been found in small numbers in various parts of the province near human habitations: A. squamosus, A. maurtianus, and A. rhodesiensis. A. nili and A. wellcomei are the chief anophelines found in areas remote from villages. In hunting and fishing round Lake No the latter gives one no peace, biting voraciously during all the hours of daylight.
L. H. HENDERSON.
285
Immunity.--It may be assumed from the foregoing that amongst these primitive people repeated attacks of benign tertian malaria in childhood are productive of a definitely high degree of immunity to the disease in those surviving to adult life. This immunity begins to be apparent early in the second decade and is fully established by the time puberty is reached, and appears to persist throughout life. The protection afforded is specific; if exposure to quartan or malignant tertian occurs infection may result. A similar state of immunity seems to be acquired following repeated exposure in childhood to quartan malaria, but with malignant tertian, immunity of this nature was not apparent. Whether in this type of infection immunity fails to occur, or whether the high incidence of infections occurring in all Arabs visiting the province is due to exposure to different strains of the parasite, has not been determined owing to insufficient available evidence. Immunity to the disease causes some change in the peripheral blood stream which is detrimental to the growth of the parasite firstly in the asexual cycle then later in all its forms. To be effective this immunity requires to be supported by a high degree of physical resistance to disease generally. Thus it may fail in the presence of any condition adversely affecting the general health ; further it may be retarded or possibly inhibited altogether by the exhibition of irregular doses of quinine. Prophylaxis.--In such an extensive marshy area peopled by primitive tribes lacking in intelligence, it is difficult to adopt any but the most crude prophylactic measures. Propaganda is attempted but the natives are very incredulous and unwilling to attribute disease to anything but jok (bad luck). Chiefs and the more enlightened natives are encouraged to use mosquito nets ; they fail, however, to realise the importance of similar protection for their children. Breeding places, unless in close proximity to the larger government stations, cannot be dealt with, but attempts are being made to improve the general conditions under which these natives live, and though these may scarcely aspire to the term " bonification," it is hoped that the general improvement will be reflected in a reduced infantile mortality. Haphazard distribution of quinine may result in amelioration of malarial symptoms but is ineffectual in producing cures. SUMMARY AND CONCLUSIONS.
(1) The incidence of malaria amongst the Nilotic tribes inhabiting the upper reaches of the Nile is described. (2) Benign tertian malaria is endemic and becomes pandemic during the rains; scanty foci of quartan malaria occur and malignant tertian has been introduced but shows no tendency to spread. (3) The splenic index is high in children and low in adults ; considerable fluctuations occur in different parts of the province.
~6
MALARIA AMONGST THE NILOTIC TRIBES.
(4) Children become infected with benign tertian in their first year, and recurrent attacks lead to a high mortality during the initial years of life. (5) Infections with benign tertian decrease as adolescence approaches, and rarely implicates the adult of whom the female is twice as susceptible as the male. (6) Malignant tertian malaria is comparatively frequently contracted by adults, and the immunity observed in the case of benign tertian and of quartan malaria does not appear to develop. (7) The probable carriers in the province are A. funestus, A. gambiae and
A. pharoensis. (8) Prophylaxis is extremely difficult owing to topographical conditions and the ignorance of the tribes.