415 TSETSE FLIES AND TRYPANOSOMIASIS. SOME QUESTIONS SUGGESTED BY THE LATER HISTORY OF THE SLEEPING SICKNESS EPIDEMIC IN UGANDA PROTECTORATE. BY H. LYNDHURST DUKE, M.D., D.T.M. & H. (CAMB.), Bacteriologist, Uganda Protectorate. CONTENTS. PAGE Parti. I. Historical 415 II. Assumptions on which Sir H. Hesketh Bell based his suppressive measures 417 III. Outcome of the measures 418 IV. Examination of the available statistics bearing on the epidemic ........ 418 V. The justification for the preventive measures . 421 VI. Early criticisms of the measures . 421 VII. Comparison between bovine and human trypanosomi- asis in Uganda 422 Part II. VIII. The tsetse fly as a transmitter of human trypanosomes 423 IX. Comparison between ft palpalis and 0. morsitans as vectors of mammalian trypanosomes . 424 X. Part played by each of the above two methods of trans- mission in the perpetuation of trypanosome strains ........ 425 Part III. XI. Conclusions to be reached regarding the trypanosomes present in man at the time of the epidemic from a consideration of the mortality statistics . 427 XII. General conclusions 428 PART I. I. HISTORICAL. THE actual commencement of the great wave of human trypanosomiasis, which claimed so many thousands of lives along the shores of Lake Victoria, is difficult to determine. The attention of Europeans was first attracted to the disease early in 1901, when eight cases of sleeping sickness were admitted to Mengo hospital by the Drs Cook,' who had been established in Uganda some five years, to whom the clinical picture was quite new. Enquiry among the chiefs of Buganda revealed the fact that sleeping sickness was known to the natives as mongota, and was more prevalent in the eastern portion of the Pro- Parasitology xi 27 416 Tsetse Flies and Trypanosomiasis tectorate than in Buganda itself. A large number of deaths had already occurred in Busoga Province and in Buvuma Island. The existence of this name, mongota, in the Luganda language is of itself strong evidence that an identical or similar disease existed previous to the recognition of sleeping sickness in 1901. There is no evidence that the word was coined to fit a previously unknown complaint. It is possible, however, that several more or less obscure diseases may have been confused in the general application of the name. From a general biological point of view it seems probable that some form of human trypanosomiasis had existed in the Victoria Nyanza fly zone previous to the epidemic. So far as is known, in no other part of Africa is fly and man in such intimate contact as in this region. The disease is endemic in the Gambia, in the Congo, in Nigeria and along the shores of Lake Tanganyika, in fact in all places where Glossina palpalis occurs in any degree of contact with human beings. Enquiries instituted in connection with the early days of the Uganda epidemic elicited the fact that the disease occurred within the Protectorate in various palpalis areas, along the Nile, around lakes Edward and George, and in the 'Mpologoma region. It was supposed to have spread to these localities from the great lake, or, in the case of the Nile area, from the Congo. There is however at any rate a possibility that the disease in these districts had existed for years and was only recognised in consequence of the careful search which resulted from the epidemic. On this explanation, also, regarding man merely as a mammal susceptible to trypanosomes, we should expect to find a certain degree of tolerance in the natives of such a thickly infested fly area as the northern shores and islands of Lake Victoria. The sudden increase in the number of cases of mongota, in some of which somnolence was perhaps not a marked feature, the terrible mortality and consequent disorganisation of food supplies were all unprecedented. Such a combination of circumstances was indeed "unknown to the natives," although typical sleeping sickness cases might be recognised as mongota. To return to the Uganda epidemic, however, it is known that from 1898 to 1900 there was a great deal of distress in Busoga and on Buvuma Island coincident with drought and failure of crops, and attended by a considerable mortality. Before July, 1901, there was no medical officer in Busoga, and very little was known of the dense and lawless populations of this Saza and the neighbouring Buvuma Islands. It may well be that cause and effect were confused in assigning this mortality to the famine which, in reality, both masked and accentuated the effects of the disease. H. L. DUKE 417 II. THE ASSUMPTIONS ON WHICH SIB H. HESKETH BELL BASED HIS SUPPBESSIVE MEASURES. In November, 1906, as a result of the investigations which were carried out by the various Commissions appointed for the purpose, H.M. Commissioner and Acting Governor Sir H. Hesketh Bell put forward a scheme for dealing with the disease. He assumed that, unless something drastic was done to check the spread of the epidemic, the whole population of the fly area would die of sleeping sickness. He based his measures mainly upon the following assumptions: (1) "That there are no authenticated instances of the transmission of the disease from sick persons to healthy, in districts where the tsetse fly is not found" (l). (2) "That the presence of even a single diseased person in a locality infested by tsetse flies may entail the infection of the whole community" (i). (3) That "the disease, so far, appears to be incurable"(i). (4) That "the tsetse fly was the indispensable link in the chain of in- fection, and that only by the elimination of that link could the spread of the disease be checked" (2). (5) That an enormous percentage of the population of the fly zone was already infected with the disease and that on certain islands the entire popu- lation had disappeared (3). (6) That" the decrease in the number of deaths in the kingdom of Buganda since 1903 is not believed to have been due to any diminution in the virulence of the disease, but simply to the reduction of possible victims in the infected areas" (4). The order of arrangement of the above six assumptions has no reference to Sir H. Hesketh Bell's reports, nor to order of precedence. He aimed at extermination of the disease as the extermination of the fly appeared to be unobtainable. His measures entailed the removal inland of the whole surviving populations of a two mile zone of the mainland shore line and of the islands, away from all possible contact with the fly. At the same time those actually suffering from the disease were to be segregated in various camps throughout Buganda and Busoga, also outside the fly zone. The segregation of the sick was commenced in December, 1906(5). By the end of 1907 the mainland population had been removed inland, and, from the German border on the west to the Ripon Falls on the east, the coastal zone to a depth of two miles had been cleared of inhabitants. During 1908 similar measures were completed in Busoga and in 1909 the islanders were removed from Buvuma and the Sesse group. It was hoped that after the disappearance of the disease, which was expected to follow these measures, the surviving populations would be able to return to their old homes. 27—2 418 Tsetse Flies and Trypandsomiasis These measures were enforced only within the limits of Uganda Protec- torate. Different policies prevailed in the neighbouring fly areas of German East Africa and British East Africa. The Germans combined deforestation measures with a limited depopulation scheme applied to certain particularly "dangerous" localities. In British East Africa the natives were left in contact with the fly, an attempt to encourage voluntary segregation and isolation from the fly proving abortive. III. OUTCOME OF THE MEASURES. As a result of these measures the most sanguine hopes were realised as regards the stamping out of the disease in the fly zone of Uganda Protectorate. In British East Africa, along the shores of the Kavirondo Gulf, the epi- demic apparently worked itself out after causing a very heavy mortality. The disease in this area now appears to be endemic and the population is reported to be again increasing. As regards German East Africa the authorities there described the measures pursued as "completely successful," yet they admit that isolated cases of fresh infection occurred from time to time. IV. EXAMINATION OF THE AVAILABLE STATISTICS BEARING ON THE EPIDEMIC. The figures quoted here are derived from official returns from the P.M.O.'s office and the Secretariat at Entebbe. In endeavouring to arrive at a true conception of the percentage of deaths to the total population exposed to the fly, data from the islands afford much more definite and reliable information than do figures from the mainland. Except on the big island of Buvuma, nowhere on the islands could the natives get more than 2J miles from the shore, and there was constant canoe traffic between the various islands and with the mainland, to say nothing of wholesale fishing. On the mainland, however, a large proportion of the population lived well outside the fly zone. Some might never see a tsetse fly and others only very occasionally be exposed to fly bite. The total number of deaths returned as by sleeping sickness in the kingdom or province of Buganda, including the Sesse and Buvuma Islands, from 1900 to the end of August, 1915, is as follows: 1900 8,430 1908 1,783 1901 10,384 1909 925 1902 24,035 1910 547 1903 12,891 1911 253 1904 11,251 1912 82 1905 8,003 1913 57 1906 5,304 1914 24 1907 3,407 1915 2l 1 Since 1915 the deaths by sleeping sickness in Buganda Kingdom or Province have been very few—exact returns are not available at time of writing.