Penetration of mid-gut cells of Glossina morsitans morsitans by Trypanosoma brucei rhodesiense

Abstract

UNTIL recently, the developmental cycle of African sleeping sickness trypanosomes in tsetse flies (Glossina spp.) was thought to follow exclusively the pattern described by Robertson¹. She suggested that trypanosomes ingested by a fly taking an infected blood meal multiplied in the gut and eventually invaded the salivary glands directly without leaving the confines of the alimentary tract. Inside the salivary glands the trypanosomes could develop into metacyclic forms capable of initiating fresh infections in mammals. In 1972, Mshelbwala² described stages of Trypanosoma brucei he had found in the haemolymph of three species of tsetse fly, and suggested that a more direct route from the gut to the salivary glands existed. According to his hypothesis, the trypanosomes from the gut of the fly penetrated the gut wall and entered the haemocoel; they then migrated to the salivary glands directly through the haemocoel, penetrating the glands and so completing the cycle of development in the fly. At this time there was no direct evidence that salivarian trypanosomes could penetrate the gut wall of their insect vector. In this communication we present electron microscopic evidence that T. b. rhodesiense penetrates the mid-gut cells of G. morsitans morsitans.