We provide evidence from isoenzyme analysis, hybridization with repetitive DNA probes, behavioural studies and morphometrics that 4 trypanosome isolates from Glossina morsitans submorsitans in The Gambia constitute a new species now named Trypanosoma (Nannomonas) godfreyi. The bloodstream trypomastigotes of T. (N.) godfreyi are relatively small with a mean length of 13·7 μm (range: 9·1–21·8 μm) and a mean width of 1·65 μm (range: 0·65–2·69 μm). There is no free flagellum and the marginal kinetoplast is subterminal to a rounded posterior end; the undulating membrane is usually conspicuous. As with other Nannomonas, T. godfreyi developed in the midgut and proboscis of Glossina and infections matured in 21–28 days in laboratory G. m. morsitans. In The Gambia the normal vertebrate host appears to be the warthog, Phacochoerus aethiopicus, although elsewhere other wild and domestic suids may also be implicated in the life-cycle. T. godfreyi was identified unequivocally using a 380 bp DNA probe specific for a major genomic repeat sequence; its isoenzyme profile distinguished it clearly from T. simiae and three strain groups of T. congolense: savannah, riverine-forest and kilifi.

African trypanosomes of the subgenera Nannomonas and Pycnomonas have been recorded from both wild and domestic suids. However, complete descriptions of some of these trypanosomes with regard to host range, pathogenicity, transmission and distribution are still lacking. Neither the recently described Trypanosoma (Nannomonas) godfreyi nor Trypanosoma (Nannomonas) congolense Tsavo have been isolated from mammalian hosts, while Trypanosoma (Pycnomonas) suis remains the rarest of the Salivarian trypanosomes. The only isolate presumed to be of the latter species is maintained at the Kenya Trypanosomiasis Research Institute, Nairobi. We present here the results of characterization of this isolate by morphology, tsetse transmission, the use of species-specific DNA probes and DNA sequence analysis. Morphology in stained blood smears revealed a small trypanosome with a free flagellum. Experimental transmission through Glossina morsitans morsitans showed a developmental cycle typical of subgenus Nannomonas. A positive identification was obtained with species-specific PCR primers for T. congolense Tsavo; moreover, the sequence of the SSU rRNA gene was almost identical to that of T. congolense Tsavo on database. In phylogenetic analysis of the SSU rRNA genes of Salivarian trypanosomes, T. congolense Tsavo grouped with T. simiae rather than T. congolense, suggesting that the name T. simiae Tsavo is more appropriate.

Trypanosoma congolense and T. simiae have been the two recognized species within the subgenus Nannomonas. T. congolense is pathogenic to cattle and the small ruminants but not to pigs, while T. simiae causesdisease only in plgs. The two species are difficult to distinguish from each other because both share the same developmental cycle in the tsetse and are broadly similar morphologically. However, their isoenzyme and DNA characteristics are quite different. Even more confusing is the fact that T. congolense itself is composed of a number of “strains”, or types; historically the different types of T. congolense were often considered as separate species by different workers.

Now isoenzyme and DNA charaterizatlon show that T. congolense is composed of at least three different types, which are probably equivalent to subspecies. Furthermore, evidence for another species within the subgenus Nannomonas has come recently from isolates from tsetse midguts in The Gambia.

Specific DNA probes have now been produced for the different kinds of Nannomonas. With these, it is now possible to identify the different infections from midgut dissections of wild tsetse. This should now facilitate an elaboratestudy to determine the distribution and prevalence of the different types across Africa, their association with the different species of tsetse, and the significance of each in the causation of disease in domestic livestock. The information gained will also help clarify the taxonomic status of each type within the subgenus.