Are stable flies (Diptera: Stomoxyinae) vectors of Trypanosoma vivax in the Central African Republic?

The epidemiology of Trypanosoma vivax infections was studied at a riverside site in the Ouro-Djafoun livestock area situated in the Central African Republic during the period between July 1991 and July 1992. This paper examines the possibility that stable flies (Diptera: Stomoxyinae) were also vectors of this trypanosome species in a non-cyclic way. Previous studies have revealed that the usual cyclic transmission by the tsetse fly Glossina fuscipes fuscipes was probably not the only transmission route. At the study site, at least five species or subspecies of stable flies were encountered: Stomoxys nigra nigra (approximately 60% of the sample), S taeniata, S sitiens, S omega omega and Haematobia spp. The hypothesis that stable flies could be good vectors of T vivax in this country is supported by three main observations: i) stable flies were very abundant at the cattle resting site; ii) an estimation of the 'contact index' between the cattle and stable flies demonstrated close interactions between cattle and stable flies at this site, particularly during the rainy season, and iii) there was a good correlation (P < 0.05) between the apparent stable fly densities at the resting site and the frequency of T vivax in the cattle. The relevance of this phenomenon in terms of epidemiology and combatting T vivax-caused nagana is discussed.