Experiments on the mechanical transmission of West African strains of Trypanosoma brucei and T. gambiense by Glossina and other biting flies

Four strains of T. brucei have been successfully transmitted by the direct method, using G. tachinoides as mechanical vector. Direct transmissions of T. brucei by G. tachinoides have only been carried out where the interval between the break in the infecting feed and the resumption of the flies' meal on a clean animal does not exceed ten minutes. Successful transmission has been effected by as few as four infecting bites. Direct transmissions of T. brucei by the agency of G. tachinoides have only proved successful where the average number of trypanosomes in the peripheral blood of the infected animal exceeds one in five microscopic fields. Some difference appears to exist in the direct transmissibility of the three strains of T. brucei used. Negative results have been obtained in each of fifteen direct transmission experiments in which attempts were made to transmit six strains of T. gambiense by the agency of G. tachinoides. T. brucei has been successfully transmitted by S. calcitrans by the direct method. Experiments in which attempts have been made to employ A. costalis, A. funestus, Aëdes vittatus, and Lyperosia (sp.?) as mechanical vectors of T. brucei have failed to effect transmissions. Dissection and examination of the proboscis of G. tachinoides at intervals after an infecting meal, reveals the fact that motile trypanosomes may survive in the proboscis for as long as three hours; and that the maximum number of trypanosomes contained in the proboscis immediately after an infecting meal is often very considerably in excess of 600 when trypanosomes are abundant in the peripheral blood of the infected animal. A brief account is given of the behaviour of trypanosomes taken up during an infected blood meal in the proboscis and gut of Stomoxys, A. costalis, A. funestus and Lyperosia. In none of these flies do the trypanosomes survive in the proboscis as long, or in such large number, as in G. tachinoides.