Improved identification of Nannomonas infections in tsetse flies from The Gambia

Trypanosomes from 36 midgut infections were isolated in procyclic culture from Glossina morsitans submorsitans and G. palpalis gambiensis in The Gambia. Twenty-eight stocks (78%) were identified using DNA probes specific for: (a) Trypanosoma (Nannomonas) congolense savannah type, (b) T. (N.) congolense riverine-forest type, (c) T. (N.) simiae and (d) Trypanozoon, T. simiae and savannah type T. congolense were found only in G.m. submorsitans while the riverine-forest type T. congolense was restricted to populations of G.p. gambiensis from two isolated areas of relict forest: one Trypanozoon stock was isolated from G.m. submorsitans. T. congolense accounted for only 17% of all Nannomonas infections, as identified by dissection, in G.m. submorsitans. This re-emphasises the importance of differentiating infections below the subgeneric level when estimating challenge to domestic animals. T. simiae could not be distinguished from T. congolense by the arrangement of trypanosomes in the fly proboscis. The 8 stocks which were not identified by DNA probes were separated into two groups on the basis of hybridization with total DNA probes and the cycle of development in experimental tsetse. One group of four isolates, all from G.m. submorsitans, was a new kind of Nannomonas which appeared to be common and widespread in The Gambia. The second group, which was found only in G.p. gambiensis, had a stercorarian cycle of development, maturing in the hindgut, and was morphologically similar to insect forms of the crocodile parasite T. grayi.