The clinical relevance of the recently discovered equine parvovirus hepatitis virus (EqPV-H), capable of causing serious liver disease in horses, is becoming increasingly apparent, according to the authors of a just-published review.
EqPV-H was first described in 2018 in a fatal case of Theiler’s disease, which followed the administration of a biological product of equine origin.
The virus has since been frequently identified in serum and liver tissue of horses affected by Theiler’s disease — an acute, severe hepatitis.
EqPV-H appears to be associated with subclinical to severe hepatitis in horses, and is a likely cause of Theiler’s disease, Anna Sophie Ramsauer, Marcha Badenhorst and Jessika-M. V. Cavalleri wrote in the Equine Veterinary Journal.
Theiler’s disease has also been termed serum hepatitis, acute hepatic necrosis, or serum-associated hepatitis. Although it is most frequently reported after the administration of equine-origin biological products, it can also occur among in-contact horses.
Transmission may be via contaminated equine-origin products such as equine serum, botulism or tetanus antitoxin, and mesenchymal stem cells, or by mouth. Other possible routes, such as biting insects, warrant further investigation, they said.
Since its discovery, a worldwide prevalence of EqPV-H antibodies and DNA has been reported in symptom-free horses, the trio, with the University of Veterinary Medicine Vienna, noted.
Surveillance studies in clinically healthy horse populations in the United States, China, Germany, and Austria have demonstrated DNA prevalence between 7.1% and 17%, and seroprevalence of between 15% and 34.7%.
EqPV-H-positive horses suffering from acute, severe hepatitis have reportedly developed clinical signs including jaundice, lethargy, lack of appetite, and neurological abnormalities, with increased liver-associated biochemistry parameters recorded.
The most common abnormalities seen in liver samples under the microscope are necrosis, collapse of the lobular architecture, and lymphocytic infiltration.
“Despite EqPV-H research still being in its infancy, the clinical relevance of this virus is becoming increasingly apparent,” the review team said.
“Based on strong evidence indicating that EqPV-H causes hepatitis in horses, veterinarians should consider this virus an important differential diagnosis in such cases.”
The virus should be considered and investigated even in cases of clinical and subclinical hepatitis with no history of biological product administration — cases have been reported in horses with no history of being given biological products.
“Awareness of the potentially fatal consequences and legal implications of administration of contaminated biological products is crucial for equine practitioners,” they said.
“In future, a better understanding of transmission routes of the virus will enable practitioners to advise owners on the implementation of appropriate preventative protocols.”
The authors noted that although infection studies have provided strong evidence of the association between EqPV-H infection and acute hepatitis in horses, other contributing factors cannot currently be excluded, such as co-infection with one of the other three viruses known to cause hepatitis in horses — two pegiviruses and a hepacivirus.
The authors noted: “Although the potential detrimental effect of EqPV-H infection — particularly persistent, subclinical infections — on athletic performance of horses remains to be thoroughly investigated, this does warrant consideration in equine athletes.”
Equine parvovirus hepatitis. Anna Sophie Ramsauer, Marcha Badenhorst, Jessika-M. V. Cavalleri. Equine Veterinary Journal, 8 June 2021, https://doi.org/10.1111/evj.13477