Yellow fever outbreak investigation in Mgbakwu, Awka North Local Government Area (LGA), Anambra State, Southeast Nigeria - Entomological perspective.

Abstract

Background:Nigeria has reported cases of Yellow fever (YF) since 2017.Cases have been confirmed in at least 18 states, including the capital, Abuja. The disease is mostly transmitted by mosquitoes of the Aedes genus. We determined the risk of transmission of YF in Dunokofia, Awka-North and Awka-South Local Government Areas.Method:We conducted a baseline study to establish presence of the vectors and risk of the disease transmission in one community each of the three LGAs (Dunokofia, AwkaNorth and Awka-South) of Anambra State. We used major mosquito sampling methods – ovitrapping, larval survey, human landing catch and light trapping – to ascertain the biting and breeding behavior of the vector. We collected samples day and night. We identified adult collections right in the field using standard identification keys, while immature stages were reared to adults for proper identification. Results:A total of 1,014 mosquitoes were collected in the study. Of these,72 (7.1%) were YF non-related vectors while Aedes species (Ae. aegypti, Ae. albopictus, Ae. circumluteolus and Ae. simpsoni complex) accounted for 942 (92.9%). Aedes albopictus, 478 (50.7%) and Aedes aegypti, 461 (49%) were predominant across all locations surveyed. The House Index ranged from 60-80% while the Breteau Index ranged from 75-131, across all sites. No Aedes mosquito was collected indoors.Conclusion:The high larval indices, abundance and diversity of the vectors across the study locations make them high-risk areas for transmission of the disease. This is underscored by the YF outbreak in Awka-North LGA and the large number of primates in the study area. There was Immediate reactive mass vaccination in the affected State. Residual treatment of discarded containers, as well as massive community sensitization and mobilization on larval source reduction, to reduce vector density in the study area were recommended and initiated.