LAUSR

BACKGROUND Equine parvovirus-hepatitis (EqPV-H) has been proposed as the etiologic cause of Theiler's disease, also known as serum hepatitis. EqPV-H-associated Theiler's disease has not been previously reported in Europe. OBJECTIVES To determine whether EqPV-H infection was associated with a 2018-2019 outbreak of Theiler's disease in four horses on a stud farm. STUDY DESIGN Descriptive case series. METHODS The medical records of four horses from the same farm diagnosed with fatal Theiler's disease were examined retrospectively. Information collected included a clinical history, physical examination findings, tetanus antitoxin exposure, serum biochemistry, and necropsy reports. Liver tissue from all four horses were tested for EqPV-H using PCR and in situ hybridisation (ISH) assays. RESULTS Three of the horses had a history of recent (7-11 weeks) tetanus antitoxin administration. Liver tissue from all four horses tested positive for EqPV-H with PCR. In situ hybridisation revealed a widespread distribution of viral nucleic acid in hepatocytes in one case, and a more sporadic distribution in the remaining three cases. MAIN LIMITATIONS Case controls were not available from the farm in question given the retrospective nature of analysis. CONCLUSIONS This case series documents the first reported EqPV-H-associated Theiler's disease in Europe and the first use of ISH to visualise the viral nucleic acid in liver tissues of horses with Theiler's disease.