AAEP shares guidelines for Equine Viral Hepatitis

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The American Association of Equine Practitioners (AAEP) recently published its Equine Viral Hepatitis Guidelines to provide equine veterinarians comprehensive information and instructions concerning clinical signs, diagnostics, risk factors, transmission, and other considerations for 2 viral causes of liver damage in equine patients: Equine parvovirus-hepatitis (EqPV-H) and equine hepacivirus (EqHV).

“Both viruses can be present [horse is PCR positive] and not actively causing disease. Serial testing and early testing can help veterinarians interpret whether either virus is likely to be the cause of hepatitis,” said guidelines author Joy Tomlinson, DVM, PhD, DACVIM, assistant professor of large animal medicine at the University of Pennsylvania School of Veterinary Medicine, in an organizational release.¹

“If you diagnose a horse with hepatitis, I recommend either submitting the serum PCR right away or saving serum from the first visit in your freezer,” she added. “If you decide to pursue viral testing later, having that sample to compare to will be very helpful.”

According to the release, the guideline documents incorporate updates to guidance that was originally published for EqPV-H in 2021 as well as new and corresponding guidance for EqHV, which has been recently recognized as a cause of chronic hepatitis.¹ The Equine Viral Hepatitis Guidelines were approved and reviewed by the AAEP Infectious Disease Committee and board of directors.

Equine patients infected with EqPV-H are asymptomatic, but a small percentage will develop clinical hepatitis, and will demonstrate one or more of the following²:

• Lethargy
• Anorexia
• Jaundice
• Photosensitization
• Neurologic signs (altered behavior, head pressing, staggering, blindness)
• Elevated liver enzyme activities on bloodwork, especially AST, SDH, GLDH
• Elevated blood ammonia and bile acid concentrations
• Discolored urine
• Colic
• Recumbency
• Death (usually within 72 hours for severe cases)

The AAEP also noted that EqPV-H does not cause a fever in patients. Equine patients infected with EqPV-H typically remain asymptomatic carriers for years. Silent carriers have low levels of virus in their blood and pose little to no risk of natural transmission to other horses.²

EqHV transmission has been linked to biologic products, particularly equine plasma products. Horses with acute EqHV infection typically do not show clinical signs of liver disease and clear the virus within 20 weeks. For horses with chronic EqHV infection, the infection will last longer than 6 months with a small percentage developing hepatitis over months to years. Clinical signs may include one of more of the following²:

• Lethargy
• Anorexia
• Weight loss
• Elevated liver enzyme activities on bloodwork, especially GGT
• Elevated blood ammonia and bile acid concentrations
• Jaundice
• Photosensitization
• Neurologic signs (altered behavior, head pressing, staggering, blindness)
• Discolored urine
• Colic
• Recumbency
• Death

Like EqPV-H, EqHV does not cause fever in patients.

EqHV infects 40% of horses in the United States, versus 15% of EqPV-H, most clear the infection within 20 weeks and present with no clinical signs of liver or illness. Out of the horses infected with EqHV, 20% will develop persistent infection lasting longer than 6 months. The horses that are affected can also have subclinical infection or show signs of liver disease of varying severity. Treatment for clinically affected horses focuses on supportive care and managing liver dysfunction.

References

1. AAEP Publishes Equine Viral Hepatitis Guidelines. News release American Association of Equine Practitioners. February 3, 2025. Accessed February 24, 2025. https://aaep.org/post/aaep-publishes-equine-viral-hepatitis-guidelines/
2. American Association of Equine Practitioners. AAEP Infectious Disease Guidelines: Equine Viral Hepatitis. Accessed February 24, 2025. https://aaep.org/wp-content/uploads/2021/03/Equine-Viral-Hepatitis-Guidelines-Final.pdf