Detection of Flaviviruses in Mosquitoes from a Livestock Farm in Ibadan, Nigeria

Background Flaviviruses represent a diverse genus within the Flaviviridae family, comprising over 70 enveloped, single-stranded positive-sense RNA viruses that pose significant global health threats. Yellow fever virus (YFV) remains a significant public health concern in Nigeria, with suboptimal vaccination coverage and persistent transmission risk. Understanding local flavivirus circulation in mosquito vectors is crucial for disease surveillance and prevention strategies. Methods Adult female mosquitoes were collected from the University of Ibadan’s dairy and teaching farms between June and August 2022 using stationary human-bait catches and miniature light traps. Mosquitoes were morphologically identified, pooled by species and collection site, and screened for flaviviruses using hemi-nested reverse-transcription PCR targeting the NS5 gene. Positive samples were sequenced and phylogenetic analysis carried out. Results A total of 600 mosquitoes, representing six species from three genera were collected, with Aedes aegypti predominating (60.67%). Of 22 mosquito pools tested, three were positive for flaviviruses. Yellow fever virus was detected in one pool of 37 A. aegypti specimens, while insect-specific flaviviruses were identified in two other pools of the same mosquito. Phylogenetic analysis showed that the YFV isolate clustered with recent Nigerian strains (2018–2020), indicating local circulation. Conclusions This study confirms ongoing flavivirus circulation in mosquito populations, underscoring potential transmission risk to humans despite low infection rates. The detection of YFV in A. aegypti and co-circulating insect-specific flaviviruses warrants sustained monitoring to mitigate zoonotic and arboviral threats.