New observations on cyclical development of Trypanosoma vivax in Glossina.

It is widely held that cyclical development of Trypanosoma vivax in Glossina is confined to the proboscis. This view has been re-examined in a series of experiments. Teneral G. morsitans centralis were fed on a goat infected with T. vivax IL 1392 and dissected 1-2 h after feeding. The infection rates in the labrum and hypopharynx were 40% and 0%, in contrast to 82% and 58%, respectively, observed in a control group dissected on day 25. This suggested that in a significant number of tsetse, cyclical development of T. vivax was initiated at sites other than the proboscis. Subsequent experiments revealed the presence of trypomastigotes, pre-epimastigotes and epimastigotes in the cibarium/oesophageal region of tsetse dissected 1-48 h after an infected feed. To investigate this further, tsetse proboscides were excised at intervals beginning 1 h after an infected feed, and transferred to in vitro culture conditions. Parasite multiplication and full cyclical development were only observed in proboscides excised 4 h or later after the infected bloodmeal. Thus, it would appear that at least in a number of tsetse, T. vivax cyclical development initially occurs in the cibarium/oesophageal region from where parasites migrate to the food canal of the proboscis and development is completed to infective metatrypanosomes in the hypopharynx.