Relationships between protease activity, host blood and infection rates in Glossina morsitans sspp. infected with Trypanosoma congolense, T. brucei and T. simiae.

Midgut protease activity in Glossina morsitans centralis and G.m. morsitans, at 48 h post bloodmeal averaged 1.8IU of trypsin-like activity. These two tsetse subspecies differ in their susceptibility to trypanosome infection. Except for low levels in flies fed on waterbuck blood (0.7 IU), activity did not differ in flies fed a variety of host bloods (goat, pig, cow, buffalo, eland) and trypanosome species (Trypanosoma congolense, T. brucei, T. simiae). Protease activity was also not correlated with infection rates, despite large differences in infection rates among experiments. Nevertheless, addition of 0.06 M D(+)-glucosamine to parasitaemic blood resulted in a three-fold reduction in protease activity, coincident with a large increase in infection rate. This effect did not occur when parasites or D(+)-glucosamine were added alone to the bloodmeal, suggesting that the effect was due to metabolism of D(+)-glucosamine by parasites.

Some observations on factors associated with the development of Trypanosoma brucei brucei infections in Glossina morsitans morsitans.

The susceptibility of Glossina morsitans morsitans to Trypanosoma brucei brucei infection was shown to be age-dependent during the first 12 h: the youngest age group (1-8 h after emergence) being more susceptible than the older ones. The susceptibility was enhanced by cooling the young flies to a temperature of 0-5 degrees C for 30 min. Male flies were found to be more susceptible than females. The number of trypanosomes ingested did not influence the subsequent salivary-gland infection rates observed in G.m. morsitans; however, there was a relationship between the number ingested and subsequent T.b. brucei midgut infections in the flies.