Mosquito-Based Detection of Endogenous Jaagsiekte Sheep Retrovirus 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 report the first identification of Jaagsiekte Sheep Retrovirus (JSRV)-related sequences in blood-fed mosquitoes collected in Senegal. JSRV, a betaretrovirus responsible for ovine pulmonary adenocarcinoma, is typically found in sheep, but its genetic trace in mosquitoes offers a novel perspective on host-vector contact and surveillance. 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: A diverse array of viruses across mosquito species, including both arboviruses and non-arthropod-borne viruses. A JSRV-related sequence was detected in a single blood-fed mosquito pool collected in Barkedji (2019). The RT-qPCR assay confirmed JSRV presence, validating the sequencing results. Phylogenetic analysis revealed strong similarity to known endogenous JSRV (enJSRV) sequences integrated in the sheep genome, indicating that the detected material likely originated from host DNA ingested during blood feeding. Discussion: This study presents the first report of endogenous retroviral sequences detected in mosquitoes, alongside the identification of actively circulating viruses, highlighting the broader potential of mosquitoes as environmental sentinels. While mosquitoes are not biological vectors for JSRV, 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.