Lack of evidence for arthropod or vertical transmission of Hepacivirus bovis in a persistently infected dairy herd

Abstract Hepacivirus bovis (BovHepV) has been detected globally since its initial description in 2015, but its transmission routes remain largely unknown. Arthropod-borne or vertical transmission is a common route for several livestock viruses, including Rift Valley fever virus and bluetongue virus. Moreover, many members of the genus Orthoflavivirus (family Flaviviridae ) are transmitted by hematophagous arthropods, raising the possibility that hepaciviruses such as BovHepV, which also belongs to the Flaviviridae family, could share similar transmission routes. In this study, we examined possible transmission routes of BovHepV, including the involvement of mosquitoes, hematophagous flies, biting midges, and mites. Arthropods were collected on a dairy farm with documented circulation of BovHepV genotypes 1 and 2 and were subsequently tested for the presence of BovHepV RNA by quantitative real-time PCR. Furthermore, multiple bovine sample types were examined for the presence of BovHepV RNA. To assess local spread, serum samples from cattle on a neighboring farm within flight range of stable flies and mosquitoes were analyzed. Potential vertical transmission was evaluated by testing serum samples from 20 calves and 20 young heifers. None of the analyzed samples tested positive for BovHepV RNA. However, BovHepV was detected in blood samples collected for bovine herpesvirus 1 (BoHV-1) surveillance one month after the arthropod collection periods in both 2022 and 2023, confirming ongoing virus circulation on the farm. Under the conditions investigated, no evidence was found to support transmission via arthropods or vertical transmission. However, rare transmission events or low-prevalence vector involvement cannot be excluded and warrant further investigation.