Abortion storm of Yili Horses is Associated with Equus Caballus Papillomavirus 2 Variant Infection

Background: Nine different species of Equus caballus papillomavirus (EcPV) and three bovine papillomavirus (BPV) have been reported to infect horses, however, there are so far no describing such infections in China. In January 2021, an abortion storm occurred in Yili horses, as a result of which 50 out of 93 aborted fetus samples were found to be negative for equid herpesvirus (EHV) and equine arteritis virus (EAV).Results: In our pioneer study with Chinese horses, we first found EcPV-2 in the nasal swabs (4/230, 1.7%) of Yili horses, and semen (3/18, 16.7%) of the Thoroughbred horses. This indicated that EcPV can be indeed hosted by horses in China, and that EcPV-2 might be transmitted though breeding. Further detection of EcPVs in the lung tissues of aborted fetus in Yili horses, which were originally negative for equid herpesviruses, established that EcPV-2 was positive in 19 of 50 samples, thereby indicating that EcPV-2 might be a new pathogen causing of abortions. Thereafter, the sequence analyses for L1 genes sequences of 26 China’s EcPV-2 were performed which indicated that EcPV-2, that primarily infected the horses in China, shared 98.3%-99.9% nt identity with the already published sequences for EcPV-2. These observations indicated that EcPV-2 identified in the current study were highly similar variants of the previously identified strains of EcPV-2. Phylogenetic analysis based on L1 genes in GenBank showed that EcPV-2, found in the Chinese horses, was closely related to and clustered together with an already known EcPV-2a lineage. Conclusion: Our study provides the first evidence related to EcPV-2 infection in the Chinese horses, which can serve as a causative agent for Yili horse abortions, and thus can possibly lay the foundation for a systematic and detailed epidemiological study of this infection in the Chinese horses.