Studies in filariasis in East Africa: 1. Filariasis on the Island of Pate, Kenya

Abstract

1. 1) Filariasis was studied in the village of Faza on Pate Island which lies 5 miles east of the northern part of the Kenya coast. The incidence of W. bancrofti in night bloods was 32 per cent. and in day bloods 4 per cent.; the average number of microfilariae per 20 c.mm. was 9.4 and 0.16. The highest parasite rates and densities were in the 16 to 20 age-group. 2. 2) A fortnight after mass treatment with diethylcarbamazine the W. bancrofti rate fell to 25 per cent. and the microfilarial density to 1.5. Eight months later the infection rate was 16 per cent. and the microfilarial density 1.1. 3. 3) Seven filarial species were found in animals. Monkeys ( Cercopithecus aethiops) were infected with D. corynodes ; dogs, cats, and genets ( Genetta tigrina) with W. patei and D. repens. Dogs were also infected with D. immitis and a Dipetalonema. Donkeys and cows were infected with Setaria sp. 4. 4) The commonest mosquitoes in houses were Ae. pembaensis, C. p. fatigans, and Ae. aegypti. Anopheles were almost absent from Faza ; only three A. gambiae were caught. 5. 5) Precipitin tests indicated that Ae. pembaensis feeds on monkeys, dogs, cats, cattle, goats and donkeys as well as man. C. p. fatigans and Ae. aegypti, though predominantly anthropophilic, also feed on animals. A number of C. p. fatigans contained avian blood. 6. 6) Over 15,000 mosquitoes were dissected at Faza. The filarial infection rate for Ae. pembaensis was 3 per cent. to 4 per cent. ; infective larvae were present in 2 per cent. to 3 per cent. Only 2 per cent. of Ae. aegypti were infected. After the diethylcarbamazine campaign the C. p. fatigans rate fell from 25 per cent. to 6.6 per cent ; the infection rates of the other mosquitoes were unaffected. 7. 7) In feeding experiments, only W. bancrofti and D. immitis developed well in C. p. fatigans. Ae. pembaensis proved a good experimental host of W. patei, D. repens, D. immitis, D. corynodes and the donkey Setaria. 8. 8) It was found possible to distinguish most of the infective larvae in mosquitoes, and these were studied in 187 mosquitoes found infected in nature. C. p. fatigans contained only W. bancrofti, and Ae. pembaensis only animal filariae.