[Entomological investigation during the chikungunya epidemic in Chad in 2020].

Objectives: The aim of this study was to identify chikungunya vectors and study their bioecology in order to contribute to the response to the 2020 epidemic in the cities of Abéché and Biltine in eastern Chad.

Materials and methods: Immature stages of Aedes mosquitoes were collected and epidemic risk indices (Container index, House index and Breteau index) were calculated and compared using the Chi-square test. The collected larvae and nymphs were reared, and the resulting adults were morphologically identified using a dichotomous key. Residual endophilic fauna was sampled by morning insecticide spraying in chambers. Only female mosquitoes were collected.

Results: A total of 2,039 mosquito specimens belonging to three genera were collected: 470 (23%) were identified as Aedes aegypti, 731 Anopheles spp (36%), and 838 Culex spp (41%). Flowerpots were the most common breeding sites (69%), followed by jars/water barrels (17%) and abandoned tires or containers (14%). The risk indices were all well above the epidemic thresholds defined by the WHO. Between the two cities, only the house index showed a significant difference (p=0.004): it was higher in Abéché than in Biltine.

Conclusion: The study identified A. aegypti as a likely vector of chikungunya in both cities. It is important to understand its biting and resting behavior, as well as its sensitivity to different classes of insecticides, in order to organize effective vector control.