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In order to identify pathogenic trypanosomes responsible for African trypanosomiasis, and to better understand tsetse-trypanosome relationships, surveys were undertaken in three sites located in different eco-climatic areas in Côte d'Ivoire during the dry and rainy seasons. Tsetse flies were caught during five consecutive days using biconical traps, dissected and microscopically examined looking for trypanosome infection. Samples from infected flies were tested by PCR using specific primers for Trypanosoma brucei s.l., T. congolense savannah type, T. congolense forest type and T. vivax. Of 1941 tsetse flies caught including four species, i.e. Glossina palpalis palpalis, G. p. gambiensis, G. tachinoides and G. medicorum, 513 (26%) were dissected and 60 (12%) were found positive by microscopy. Up to 41% of the infections were due to T. congolense savannah type, 30% to T. vivax, 20% to T. congolense forest type and 9% due to T. brucei s.l. All four trypanosome species and subgroups were identified from G. tachinoides and G. p. palpalis, while only two were isolated from G. p. gambiensis (T. brucei s.l., T. congolense savannah type) and G. medicorum (T. congolense forest, savannah types). Mixed infections were found in 25% of cases and all involved T. congolense savannah type with another trypanosome species. The simultaneous occurrence of T. brucei s.l., and tsetse from the palpalis group may suggest that human trypanosomiasis can still be a constraint in these localities, while high rates of T. congolense and T. vivax in the area suggest a potential risk of animal trypanosomiasis in livestock along the Comoé River., (© V. Djohan et al., published by EDP Sciences, 2015.)

Glossina palpalis gambiensis and G. tachinoides are the main vectors of human and animal trypanosomoses in West Africa. In some parts of their distribution area, they co-exist in sympatry, but little is known about their interactions. This study aimed to explore their respective flight height and daily activity when co-existing or alone. Attractive targets were used, made of a black/blue/black cloth covered with adhesive film, so that all tsetse that landed were caught. The study was conducted in two areas in South Burkina Faso: Kartasso, upstream the Mouhoun river, where G. p. gambiensis is the only tsetse occurring; and Folonzo, on the Comoé river, where both species occur. Out of more than 3,800 tsetses caught in total, in Folonzo, G. tachinoides occurred at higher densities than G. p. gambiensis (84 vs 16% of the total densities). The mean height of capture was 55 cm for G. tachinoides, and 65 cm for G. p. gambiensis. As a comparison, in Kartasso where G. p. gambiensis is alone, the mean height of capture was 46 cm, these differences being statistically significant. In average, females were caught higher in altitude than males, and the two species showed a similar activity profile in the day. These results are discussed in the light of differences in the nature of the forest gallery, or possible interspecies competition behaviour in relation with their limited energy metabolism and flight capacities, or also with species differences in landing behavior, linked to host feeding detection. These observations have consequences on control tools releasing attractive odours, which may have contrasted efficacy depending of the flight height of the species.

Entomological and phyto-sociological surveys were undertaken in Folonzo, southern Burkina Faso, along the Comoé river. The purpose of this survey was to compare densities and diversity of tsetse species in a protected versus a non protected area, by the mean of transects going from the river bank to the savannah. A detailed phytological description was made in all the trapping sites. The entomological data were also compared to what was obtained in 1980 in the same trapping sites. The phytogeographical study showed great vegetation homogeneity between transects, particularly in the forest gallery, while savannah showed more heterogeneity. Four tsetse species were caught in the area, with 74% G. tachinoides, 20% G. m. submorsitans, 4% G. p. gambiensis and 2% G. medicorum. There was a significant difference in tsetse densities between the protected and the non-protected area, with in average, four times more tsetse in the protected one. This difference was particularly high for G. m. submorsitans with a ratio of 1/9. This decrease was attributed to the reduction in wildlife density in the non protected area, and can be applied to the situation of the whole country where this tsetse species is of decreasing importance. It is one of the consequences of the increase in human densities, this latter causing much less visible changes in phytological species composition. From the comparison between old (1980) and new data collected on the river bank, we see a general trend of decrease in density, which affects less G. palpalis gambiensis.