Susceptibility of tsetse (Glossina species) to trypanosome infection in relation to midgut trypsin, trypsin-like enzymes and other molecules

Abstract

Post-feeding midgut trypsin levels and abilities of midgut homogenates to transform parasites were compared in Glossina morsitans morsitans, G. longipennis and G. fuscipes fuscipes. Peak midgut enzyme levels in the different species occurred between 48 and 72 h post-feeding. Glossina m. morsitans had the lowest peak in enzyme activity whereas G. f. fuscipes the highest. These differences were highly significant (P < 0.05, F = 0.02, n = 28). Midgut enzyme levels in the three Glossina species were, however, similar upto 24 h post-feeding (P > 0.05). The abilities of midgut homogenates of G. m. morsitans, G. longipennis and G. f. fuscipes to agglutinate Trypanosoma brucei brucei, were investigated. Glossina f. fuscipes and G. longipennis midguts had twice as much lectin as G. m. morsitans, basedon their ability to agglutinate T. brucei. However, there was no significant difference in the levels of enzyme inhibition in the midguts of these Glossina species by T. b. brucei and T. congolense. Rates of infection with T. b. brucei and T. congolense in the different Glossina species were studied. Mature T. b. brucei infection rates in G. longipennis were less (P < 0.05, F = 0.38, n = 12) than those infection rates were higher in G. m. morsitans (P < 0.05, F = 0.28, n = 16) than those in G. longipennis and G. f. fuscipes. There were no significant differences between the species with regards to midgut infections with either T. b. brucei or T. congolense. The effect of age of flies on their susceptibility to trypanosome infection was studied in G. m. morsitans, G. longipennis and G. f. fuscipes. There were no differences between the teneral and non-teneral flies in the ability of their midguts to transform T. b. brucei and T. congolense (P > 0.05). However, the midguts of non-teneral flies showed greater lysis of T. b. brucei than their respective tenerals. Glossina f. fuscipes midgut contents had the greatest lytic effects on T. congolense among the non-teneral flies. In addition, there were no significant differences with respect to rates of infection in either teneral or non-teneral flies. The midgut trypsin profiles in teneral and non-teneral starved (120 h) flies did not differ within species. Two different G. pallidipes populations were assessed for midgut trypsin levels and their ability to transform parasites. There were no statistical differences, in enzyme profiles and trypanosome transformation rates, between Lambwe Valley and Nguruman populations of G. pallidipes. My study has shown that higher post-bloodmeal trypsin and lectin activities exist in the midguts of G. longipennis and G. f. fuscipes compared to those of G. m. morsitans. This gives a concomittantly greater lysis and agglutination titres in the two species, affording them lower susceptibility to trypanosome infection than in G. m. morsitans. Similarities in trypanosome transformation and midgut infection rates in the different Glossina species may be attributed to similarities in their trypsin and lectin levels during the first 24 hours post-feeding. Any differences in trypanosome infection rates between the Lambwe Valley and Nguruman G. pallidipes probably result from other factors, such as sources of bloodmeals.