Year one results of an ongoing investigation into vector-borne transmission of Cache Valley virus and bluetongue virus in northwest Arkansas

In recent years, pregnant sheep at a livestock operation in northwest Arkansas have experienced embryo loss, abortion, and fetal abnormalities. Evidence suggests sheep are being infected with Cache Valley virus (CVV) and bluetongue virus (BTV), which are transmitted by mosquitoes and Culicoides biting midges, respectively. To investigate putative insect vector species and their seasonality in sheep pastures at the affected farm, CDC-CO2 Traps and CDC Gravid Traps were deployed at three unique sites in or near sheep pastures every two weeks from May-October 2024. Samples were identified to species and screened for CVV and BTV using RT-qPCR. A total of 1248 Culicoides and 2407 mosquitoes were collected across 12 trapping events. Nine species of Culicoides were collected, and the majority (94.6%) were identified as C. stellifer, a putative vector of BTV. Seven genera of mosquitoes were observed in collections, with the most abundant being Culex (69.6%), Aedes (20.0%), and Psorophora (7.6%). Numerous putative CVV vector species were collected near sheep pastures including Aedes vexans, Anopheles punctipennis, Culex tarsalis, Coquillettidia perturbans, and Culiseta inornata. Culicoides activity peaked between September-October, and mosquito activity was consistent throughout the survey period. No Culicoides tested positive for BTV, and no mosquitoes tested positive for CVV. Despite not detecting viral nucleic acid in any insect samples, serological evidence and continued poor reproductive outcomes in ewes suggest these viruses continue to infect sheep at this site. Collections are ongoing at this site in 2025 and will inform management strategies of arboviral vectors in this sheep production system.