Mosquito-based detection of retroviruses and arboviruses in Senegal: expanding the scope of xenosurveillance.

Background: Mosquitoes are well-known vectors for arthropod-borne viruses, yet their role as passive carriers of non-arthropod-borne viruses remains underexplored. Xenosurveillance, a method that utilizes blood-feeding arthropods to sample host and pathogen genetic material, has emerged as a valuable tool in viral ecology. In this study, we investigated the viral landscape of blood-fed mosquitoes from Senegal and report the first detection of Jaagsiekte Sheep Retrovirus (JSRV)-related and Enzootic Nasal Tumor Virus 2 (ENTV-2)-related sequences, alongside endemic arboviruses. Our study aimed to investigate whether mosquitoes can serve as sentinels for detecting both pathogens and host-derived markers in complex ecosystems.

Methods: Mosquitoes were collected between 2016 and 2019 from three ecologically significant regions in Senegal (Louga, Barkedji, and Kedougou). Blood-fed mosquitoes were pooled and subjected to RNA extraction and metagenomic sequencing using Illumina NextSeq550. Sequencing data were analyzed with CZ-ID and BLAST for viral identification. RT-qPCR assays were designed to validate the presence of JSRV-related sequences, targeting conserved regions of the envelope gene and 3' untranslated region. Phylogenetic analysis was conducted using MAFFT and IQ-TREE to compare the detected sequence with global exogenous and endogenous JSRV references.

Results: Sequencing revealed a broad viral diversity across mosquito species, including insect-specific viruses, arboviruses (West Nile, Sindbis, Bagaza, Usutu, Barkedji), and two retroviral sequences. A JSRV-related sequence was confirmed in a pool from Barkedji (2019) and clustered phylogenetically with endogenous JSRV. A nearly complete ENTV-2 genome, closely related to pathogenic Chinese strains, was recovered from the same pool. Other viruses grouped within established African lineages, supporting persistent regional circulation.

Discussion: This study presents the first report of retroviral sequences detected in mosquitoes, alongside the identification of actively circulating arboviruses and insect-specific viruses, highlighting the broader potential of mosquitoes as environmental sentinels. While mosquitoes are not biological vectors for retroviruses, their ability to capture both host-derived retroviral material and pathogenic viral genomes through bloodmeals reinforces the value of xenosurveillance for monitoring livestock-vector-environment interactions. These findings contribute to broader efforts in integrated disease surveillance and underscore the utility of combining metagenomics with molecular diagnostics to detect diverse viral signals in high-risk ecological settings.