Seasonal variation in onchocerciasis transmission in the Santiago focus of Ecuador.

Man-biting rates and natural infection rates with filariae were determined for anthropophilic black flies in a preliminary survey during the wet and dry seasons at three localities, either hypoendemic or hyperendemic for onchocerciasis, in the Santiago onchocerciasis focus of Ecuador. Simulium exiguum was an efficient vector associated with hyperendemicity whereas S. quadrivittatum was thought only to sporadically transmit the parasite. Parasite transmission by these two species varied seasonally. Two other man-biting species, S. bipunctatum and S. escomeli, were discounted as vectors because of their largely zoophilic habit and rarity, respectively. The need is emphasised to investigate species distributions thoroughly before entomological surveys to obtain baseline data for vector control are investigated.