Prevalence and pathology of equine parvovirus-hepatitis in racehorses from New York racetracks

Abstract

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.

Naturally acquired equine parvovirus-hepatitis is associated with a wide range of hepatic lesions in horses

“…3,6,10,24,33,34,32,37,40 Previous reports that included histopathology of EqPV-H-positive horses described lobular hepatitis with lymphocytic infiltrates, satellitosis, hepatocellular degeneration and necrosis, and portal infiltrates. 3,6,8,10,24,32 In our present study, the most common histologic features in EqPV-H-positive cases were individual hepatocyte death, lobular infiltrates, portal infiltrates, and ductular reaction. With the exception of ductular reaction, these features have been described previously in cases of mild to moderate hepatitis in experimentally infected horses.…”

“…Previous studies have described the histologic features of either experimental or naturally occurring EqPV-H infections with subclinical disease. 8,32 To assess whether other lesions could be associated with EqPV-H infection in horses with clinical liver disease, we assessed each case for 15 individual histologic features (Table 1, Supplemental Table S1). To facilitate a consistent categorization, independent histologic examination was performed on archived FFPE blocks of liver tissues by a board-certified veterinary anatomic pathologist (M.C.J.).…”

“…However, we observed histopathological evidence of hepatitis associated with EqPV-H infection in a large cohort of racehorses at New York State racetracks with features that mimicked those described in experimental infections. 8 Therefore, we hypothesized that EqPV-H could still be an important cause of clinical hepatitis. In addition to EqPV-H, equine hepacivirus (EqHV), the closest relative to hepatitis C virus (HCV) in humans, is also known to cause acute hepatitis and suspected to cause chronic hepatitis in horses.…”