Retrospective investigation of equine parvovirus-hepatitis in Italy.

Equine parvovirus-hepatitis (EqPV-H) has recently been identified as the etiological agent of Theiler's disease, a major cause of acute hepatitis and liver failure in horses. While iatrogenic transmission of EqPV-H is well-documented, the natural horizontal transmission of the virus remains poorly understood. This study provides the first comprehensive epidemiological investigation and molecular characterization of EqPV-H in equine populations across Italy. A total of 1320 archival serum samples from northern and southern Italy were screened for the presence of EqPV-H DNA by qPCR. The overall prevalence was 9.6% (126/1320), with a higher infection rate observed in horses from southern Italy. Moreover, 18.3% (23/126) of EqPV-H-positive horses were co-infected with equine hepacivirus (EqHV). Longitudinal monitoring of a small cohort (Collection A, n = 13) from a stable in southern Italy revealed that 8/13 (61.5%) of the animals tested positive for EqPV-H, with several horses acquiring the infection post-entry, suggesting horizontal transmission of the virus via contact with viremic resident horses. Partial VP1 and complete genome sequencing, followed by phylogenetic analysis, were also conducted. Phylogenetic analysis of the genome sequences of two Italian strains, ITA/2021/1040 and ITA/2023/27, showed that they clustered into distinct clades, segregating independently alongside Austrian and Chinese strains, respectively. While these findings establish EqPV-H as a circulating pathogen in the Italian equine population, study limitations include the reliance on archival convenience samples and the small size of the longitudinally monitored cohort. Overall, these results demonstrate active circulation and support the hypothesis of natural horizontal transmission of the virus.