Quantitative studies on the transmission of Onchocerca volvulus by Simulium damnosum s.l. in the Tukuyu Valley, South West Tanzania.

A survey of the Simulium breeding and the transmission of Onchocerca volvulus was carried out in and around the Tukuyu valley, S.W. Tanzania, S. damnosum s.l. was found breeding in the midstretches of the main rivers in the valley and their bigger tributaries, and also in the boundary river to Malawi and the most northerly of the three rivers draining the Livingstone Mts. to Lake Nyasa (L. Malawi). A total of 19,500 S. damnosum s.l. females was caught and 13,200 dissected. The annual biting rate varied between 2,000 and 23,800. 7.6% of all the flies were infected with O. volvulus and 1.5% carried infective larvae in the head capsule, on average 2.7 per fly. The transmission was mainly in the dry season and the annual transmission potential varied between 0 and 1,120. The entomological data showed many similarities to those from the Mahenge Mts., Tanzania, and correlation of places with comparable transmission potentials suggests a similarity in the relationship parasite-human host between the West African rain forest and the two Tanzanian foci.