Artificial feeding of Simulium vectors of human and bovine onchoceriasis.

A technique for feeding simuliids artificially in a feeding-tube containing blood covered by a membrane has been developed with a view to studying the development of Onchocerca volvulus of man and O. gutturosa of cattle in their respective vectors. A number of different kinds of membranes were tested, but skin from 2-day-old chicks was found to be most satisfactory. S. ornatum, the vector of O. gutturosa in England, fed readily on human and ox blood. The trials were carried out in a constant-temperature room with artificial lighting supplied by 60- or 100-watt clear blue-glass lamps illuminating the feeding-tube with 20 lumens per ft(2). Ultraviolet illumination was not satisfactory but light filtered through coloured screens gave good results in the middle of the spectrum. The flies fed well up to a temperature of 21 degrees C (70 degrees F) and a relative humidity of 65%-75%. The over-all feeding rate was 24.5%.The work was extended to trials with the vectors of human onchocerciasis at Kumba in West Cameroon and Amani in Tanzania. Successful membrane-feeding was achieved with the anthropophilic strains of S. damnosum from West and East Africa and with S. woodi, the main vector of O. volvulus in the Amani region. S. vorax, which is a good laboratory host for O. volvulus also, fed readily. S. nyasalandicum could be induced, but not readily, to feed through membranes. Once again, skin from 2-day-old chicks was the best membrane and human or ox blood, defibrinated or heparinized, either fresh or deep-frozen, was accepted by the flies. Wild and laboratory-bred S. damnosum also fed on a chimpanzee in a dark-room with artificial illumination at Kumba.