Trypanosoma brucei rhodesiense: enhancement of infection rates in the tsetse fly, Glossina morsitans, by feeding artificial bloodmeal mixtures.

Low mature salivary gland (SG) infection rates (6%) in less than 24-hour-old flies fed on blood containing bloodform trypanosomes can be significantly enhanced by feeding flies an artificial mixture containing procyclic forms in a red cell: culture medium mixture (procyclic mixture, SG rate = 21.0%). However, enhancement is not solely a function of the use of procyclic forms since blood forms fed to flies in the same red cell: culture medium mixture produce SG rates (15.4%) intermediate to those of blood forms in blood and procyclic mixtures. Use of these artificial mixtures produces a similar result in 24- to 48-hour-old flies and also tends to equalize their infection rates with those found in less than 24-hour-old flies. The possible relationships between the different infection rates observed and digestive proteinases in the tsetse fly are discussed.

African sleeping sickness: new evidence that mature tsetse flies (Glossina morsitans) can become potent vectors.

Starved mature male tsetse flies (21 to 25 days old) are capable of developing salivary gland (SG) infections of Trypanosoma brucei rhodesiense at rates nearly comparable to teneral males less than 24 hours old when given an infective meal containing parasites, horse red cells and culture medium. Although the over-all SG infection rate for mature males starved for three, four or five days before infection was about half that for teneral males less than 48 hours old (8.0% v. 15.6%), males starved for four days developed infection rates (12.3%) that were comparable to those of teneral flies less than 24 hours old (11.8%). It is suggested that the acquisition of infection by mature flies should be considered when evaluating factors contributing either to maintenance of endemic infections or perhaps even epidemic infections of human sleeping sickness.

Some phenomena associated with the development of Trypanosoma brucei rhodesiense infections in the tsetse fly, Glossina morsitans.

Immature salivary gland (SG) infections averaging 10(3) parasites per fly can apparently develop into mature gland infections averaging 10(5) parasites per fly in as little as 4 days. Frequently flies which extrude parasites in their saliva prove to have no parasites in the SG, but often show trypanosomes in the esophagus, cibarial pump, and proboscis. In some instances, SG infections have cleared, resulting in a loss of infectivity. Results of studying numbers of parasites regurgitated upon feeding or probing have shown that number to be highly variable and not necessarily related either to previous feeding status or the total number of parasites in the glands. Cloning of metacyclics in mice has been achieved, indicating that the minimum effective dose is one parasite. To date, no infections in mice have resulted from inoculation of extraglandular parasites. Histological and dissection studies support both the classical route and an alternate route of infection development in flies. No SG-infected flies have been found which did not also have proventricular and anterior and posterior midgut (AMG and PMG) infections. Although the AMG is where the heaviest MG infections occur, the PMG seems to support the last survivors in a moribund MG infection. No parasites have been found in the hindgut.