We propose to investigate the cellular tropism and transmission routes of Equine Parvovirus-Hepatitis (EqPV-H), which was recently discovered by our team and is the suspected cause of Theiler’s disease, a devastating, highly fatal liver disease. This work is especially relevant to the racing industry in 3 aspects. First, Theiler’s Disease frequently affects broodmares, associated with frequent use of tetanus antitoxin post-foaling or outbreaks that are not associated with biologic product administration. Second, we have recently identified 3 cases of Theiler’s Disease due to allogenic stem cell treatment, which is commonly used to treat orthopedic injuries in racehorses. Third, EqPV-H has been associated with the high gamma-glutamyltransferase (GGT) syndrome that can be seen in poorly performing racehorses.

EqPV-H belongs to the Parvoviridae, which are a family of small viruses that preferentially infect rapidly dividing cells. Since normal liver tissue contains very few dividing cells, it is of critical importance to identify which cell types EqPV-H targets to develop suitable in vitro tools that allow for studies on viral replication and kinetics. Moreover, it is highly important to identify potential modes of transmission to gain better insights into the pathogenesis of EqPV-H in vivo.

Our specific objectives are, therefore, to (i) characterize the tissues and cells infected by the virus, (ii) advance molecular virology studies of EqPV-H in vitro, and (iii) provide additional evidence that EqPV-H can be transmitted by allogenic stem cell treatment in vivo, with the common end goal to formulate methods of prevention and treatment.

To this end, we will use a combination of PCR, immunohistochemistry, and a highly sensitive in situ hybridization (ISH) technique on banked tissue samples from Theiler’s Disease cases and experimental EqPV-H infected horses to fully define tissue and cellular tropism of EqPV-H (Aim 1). We will further characterize cellular susceptibility by inoculating various equine cells in culture with EqPV-H-positive serum and determining which cell types can sustain EqPV-H replication (Aim 2). Additionally, we will confirm the clinical suspicion that allogenic stem cells could be an emerging route of transmission by inoculating EqPV-H naïve horses with allogenic EqPV-H positive bone marrow-derived stem cells and determining whether these animals become infected (development of viremia and/or signs of liver-disease).

This work will provide the foundation for further investigations of viral kinetics, transmission requirements and pathogenesis. Future work is expected to describe the full scope of equine diseases that can be attributed to EqPV-H, risk factors for fulminant hepatitis, vaccine development, and treatment modalities. Our long-term goal is to significantly improve safety of equine biologic product administration, to prevent outbreaks of Theiler’s Disease on breeding farms, and to reduce morbidity in horses that are infected.