Detection of Equus Caballus Papillomavirus Type-2 in Asymptomatic Italian Horses

Equine Papillomavirus 2 (EcPV2) is responsible for squamous cell carcinomas (eSCCs) of external genitalia of both male and female horses. However, few studies report the EcPV2 prevalence among healthy horses. Currently, the lack of these data does not permit identifying at-risk populations and, thus, developing screening protocols aimed at the early detection of the infection, as for humans. The aim of our study was to estimate the genoprevalence of EcPV2 in clinically healthy horses in Italy and to evaluate their innate immune response. For this purpose, penile and vulvar swabs of 234 healthy horses were collected through sampling with sterile cytobrushes. Nucleic acids were isolated and EcPV2-L1 presence (DNA) and gene expression (RNA) were checked by RT-qPCR. Our results showed EcPV2-L1 DNA presence in 30.3% of the samples and L1 expression in 48% of the positive samples. No statistically significant differences were found in genoprevalence in relation to sex, age, and origin, while, concerning breeds, the Thoroughbred had the highest risk of infection. Concerning specifically the mares, 40.2% of them resulted in being positive for EcPV2; our findings show a major positivity in pluriparous (p = 0.0111) and mares subjected to natural reproduction (p = 0.0037). Moreover, samples expressing L1 showed an increased expression of IL1B (p = 0.0139) and IL12p40 (p = 0.0133) and a decreased expression of RANKL (p = 0.0229) and TGFB (p = 0.0177). This finding suggests the presence of an effective immune response, which could explain the low incidence of SCCs in positive horses, despite a high EcPV2 genoprevalence (30%).