Updating of entomological and parasitological parameters in Hypoendemic HAT foci in San Pedro and Soubré (Côte d'Ivoire)

Context: Human African Trypanosomiasis was eliminated as a public health problem in Côte d'Ivoire in December 2020. To preserve the gains from vector control in Bonon and Sinfra, surveys were conducted in hypoendemic foci. This study aimed to assess disease risk in San Pedro and Soubré through entomological and parasitological data, to better understand transmission dynamics and guide post-elimination surveillance toward interruption of transmission by 2030.

Methods: Tsetse flies were trapped in San Pedro and Soubré using 116 Vavoua traps, then identified, dissected, and tested for trypanosomes by microscopy and PCR. Fly age and infection rates were assessed, and statistical analyses were performed to compare the apparent density per trap (ADT) and Glossina infection rates between the two study sites.

Results: Two tsetse species were identified: Glossina palpalis palpalis (predominant) and G. pallicera s.l. (rare). Tsetse density was higher in San Pedro (3.05/trap/day) than in Soubré (1.97/trap/day), likely due to wildlife. Molecular analysis detected Trypanosoma vivax (16 cases) and T. congolense forest-type (22 cases), the latter being predominant. No T. brucei s.l. was found. The high number of young (nulliparous) flies increases transmission risk due to early feeding. PCR was more sensitive than microscopy, confirming its usefulness in early detection.

Conclusion: This study highlights the predominance of G. p. palpalis and T. congolense forest-type. The absence of T. b. gambiense, despite historical relevance, is notable. The findings underscore the value of molecular tools in early surveillance and the need for vigilance in San Pedro. Investigation of animal reservoirs is recommended to identify potential parasite sources.