RESUMO
BACKGROUND: Theiler's disease, a.k.a. equine serum hepatitis, is a devastating, highly fatal disease of horses. Equine parvovirus-hepatitis (EqPV-H) has been identified as the likely cause of this disease. While the incidence of Theiler's disease is low, the prevalence of EqPV-H DNA in horses is high, with up to 37% in some regions, suggesting that subclinical or persistent infection is common. METHODS: To determine the prevalence and pathogenicity of EqPV-H infection at New York racetracks, DNA was extracted from archived formalin-fixed, paraffin-embedded liver tissues from racehorses submitted for necropsy to the Animal Health Diagnostic Center as part of the New York State Gaming Commission-Cornell University postmortem examination program. A total of 191 liver samples from horses between 2 and 13 years old were evaluated. Extracted DNA was tested for EqPV-H using PCR and gel electrophoresis. PCR-positive samples were further assessed for tissue morphology using histology and detection of viral nucleic acid using in situ hybridization. RESULTS: Forty-two samples were PCR positive (22%). Of those, 31 samples had positive viral nucleic acid hybridization in hepatocytes with 11 samples showing positive hybridization in necrotic hepatocytes associated with inflammatory cells, indicating active hepatitis. Both individual hepatocyte necrosis and hepatitis were positively associated with EqPV-H detection (p < 0.0001 and p = 0.0005, respectively). CONCLUSION: These findings indicate that presence of EqPV-H in the liver and parvoviral-associated hepatitis are prevalent in racehorses from New York racetracks, thus warranting additional studies examining potential associations between EqPV-H infection and racehorse performance.