Retrospective investigation of equine parvovirus-hepatitis in Italy.

Overview

• This study investigated the presence and spread of equine parvovirus-hepatitis (EqPV-H), a virus causing liver disease in horses, across Italy.
• It provided evidence of natural horizontal transmission of the virus among horses and characterized its genetic diversity within the Italian equine population.

Background and Purpose

• Equine parvovirus-hepatitis (EqPV-H) has recently been identified as the cause of Theiler’s disease, a significant acute hepatitis and liver failure condition in horses.
• Previous knowledge mainly focused on iatrogenic transmission routes (through medical procedures like blood transfusions), while natural horizontal transmission (horse-to-horse) was not well understood.
• The study aimed to conduct a comprehensive epidemiological investigation and molecular characterization of EqPV-H within equine populations in Italy.

Methodology

• The study tested 1320 archival serum samples from horses in northern and southern Italy for EqPV-H DNA using quantitative PCR (qPCR).
• A subgroup of 13 horses from a stable in southern Italy was longitudinally monitored to observe infection dynamics over time.
• Partial VP1 gene and complete viral genome sequencing were performed on selected strains for phylogenetic analysis.

Key Findings

• The overall prevalence of EqPV-H among tested horses was 9.6% (126 out of 1320 samples were positive).
• Infection rates were higher in southern Italy compared to the north.
• Co-infection with equine hepacivirus (EqHV) was found in 18.3% (23/126) of EqPV-H positive horses, indicating possible interaction or shared transmission routes between these viruses.
• In the longitudinal study, 8 out of 13 horses (61.5%) tested positive for EqPV-H, with some horses becoming infected after entering the stable, indicating horizontal transmission via contact with infected horses.
• Phylogenetic analysis showed that two Italian EqPV-H strains (ITA/2021/1040 and ITA/2023/27) grouped into distinct evolutionary clades, clustering with Austrian and Chinese strains, respectively. This genetic diversity suggests multiple introductions or diverse sources of infection within Italy.

Interpretations and Implications

• The presence and prevalence of EqPV-H across Italy confirm the virus as an actively circulating equine pathogen in the country.
• Evidence supports the hypothesis that EqPV-H can be transmitted naturally among horses, not just via medical or iatrogenic means.
• Higher prevalence in southern Italy could suggest regional factors influencing virus spread, such as differences in horse management or population density.
• Co-infections with EqHV may impact disease severity or transmission dynamics and warrant further research.
• Phylogenetic diversity indicates the virus is not monophyletic in Italy, pointing to complex epidemiological patterns that include multiple strain introductions.

Limitations

• Use of archival convenience samples may limit representativeness and generalizability of prevalence estimates.
• The longitudinal cohort size was small (13 horses), limiting the robustness of conclusions about transmission dynamics over time.

Conclusions

• This study adds valuable epidemiological and molecular data on EqPV-H from Italy for the first time.
• Results indicate EqPV-H is endemic in Italian horses and likely transmitted horizontally during normal contact, with multiple genetically distinct strains circulating.
• Further large-scale and prospective studies are needed to better define transmission routes, clinical impact, and control measures for EqPV-H infection in horses.