Summary
Preliminary studies on various factors influencing the transmission of onchocerciasis were made in December 1975 on the river Toototobi in northern Amazonas. Microfilariae of O. volvulus were more abundant in the trunk than in the limbs of two Yanomama indian volunteers. Three anthrophilic species of Simuliidae were captured and have been temporarily nemaed as Simulium sp.A., sp.B., sp.C. until a definitive identification is made. Only the former species was abundant biting mainly in the early afternoon. The finding of sausage larva in a naturally infected fly and the successful experimental infection of wild flies with microfilariae of O. volvulus, which subsequently developed to the late sausage stage, suggest that Simulium sp.A is a probable vector of onchocerciasis in the area.