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.