Tsetse fly ecology and risk of transmission of African trypanosomes related to a protected forest area at a military base in the city of Abidjan, Côte d'Ivoire

Abstract

African trypanosomoses, whose pathogens are transmitted by tsetse flies, are a threat to animal and human health. Tsetse flies observed at the military base of the French Forces in Côte d'Ivoire (FFCI base) were probably involved in the infection and death of military working dogs. Entomological and parasitological surveys were carried out during the rainy and dry seasons using "Vavoua" traps to identify tsetse fly species, their distribution, favorable biotopes and food sources, as well as the trypanosomes they harbor. A total of 1185 Glossina palpalis palpalis tsetse flies were caught, corresponding to a high average apparent density of 2.26 tsetse/trap/day. The results showed a heterogeneous distribution of tsetse at the FFCI base, linked to more or less favorable biotopes. No significant variation in tsetse densities was observed according to the season. The overall trypanosomes infection rate according to microscopic observation was 13.5%. Polymerase chain reaction (PCR) analyses confirmed the presence of Trypanosoma vivax and T. congolense forest type, responsible for African animal trypanosomosis. Our findings suggest that there is a risk of introduction and transmission of T. brucei gambiense, responsible for human African trypanosomiasis, on the study site. This risk of transmission of African trypanosomes concerns not only the FFCI base, but also inhabited peripheral areas. Our study confirmed the need for vector control adapted to the eco-epidemiological context of the FFCI base.

Keywords: Abidjan; Côte d’Ivoire; Ecology; Glossina palpalis palpalis; Trypanosoma; Vector control.

Figure 1

Study area (Source: Institut Pierre Richet, 2023, published with authorization).

Figure 2

Distribution of catch traps set in May 2019 (left) and January 2020 (right) (Source: Institut Pierre Richet, 2023, published with authorization).

Figure 3

Distribution of ADTs, infection rates and blood meals of tsetse flies in the FFCI base according to season (Source: Institut Pierre Richet, 2023, published with authorization).

Figure 4

Total number of tsetse flies caught (N) in the different areas of the FFCI base and the different seasons. 95% confidence interval $\mathrm{CI}=N\pm {\mathrm{t}}_{\alpha =0.05, \mathrm{\nu } =\mathrm{n}-1 }\times (s/\sqrt{n}$), where CI is the confidence interval; N is the sample mean; t is the critical value of the Student distribution corresponding to the confidence level chosen and the degrees of freedom associated with the sample; n − 1 is the degrees of freedom, where n is the sample size; s is the standard deviation of the sample; $\sqrt{n}$ is the square root of the sample size.