Progress Toward an Equine Hepacivirus Vaccine

Researchers tested a vaccine model that could help them develop effective protection against equine hepacivirus.
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Shetland Pony Grazing
The study involved Shetland ponies receiving an equine hepacivirus E2 recombinant protein vaccine before being infected with equine hepacivirus. | Photo: iStock

Equine hepacivirus (EqHV) is common liver virus that can cause fatal chronic hepatitis in horses. The virus causes disease that mimics that caused by the closely related hepatitis C virus (HCV) in humans.

Because it’s unclear to what extent equine hepacivirus causes disease in horses, and some horses do not show obvious clinical signs, owners are often unaware their horses are infected until the liver has already been severely damaged, explained Janet Daly, BSc (Hons), PhD, of the School of Veterinary Medicine and Science at the University of Nottingham, in the U.K. Daly was part of a research team working on a hepacivirus vaccine study led by Marcha Badenhorst, BSc, BVSc, MSc, PhD, of the Clinical Unit of Equine Internal Medicine at the University of Veterinary Medicine, in Vienna, Austria.

In her research Badenhorst noted that multiple factors have impeded the development of a hepatitis C vaccine for horses. Among them are divergent virus strains, difficulty establishing a culture system, and limited experimental vaccine models.

“The main challenge is that it is not easy, virtually impossible, to culture viruses that replicate in liver cells, such as EqHV and hepatitis C, in the laboratory,” Daly said. “This means we cannot develop traditional inactivated virus vaccines against them.”

The study included six healthy Shetland ponies ages 8 to 12. Half were mares, half were geldings. Before the study began, researchers confirmed on a serum analysis that none had equine hepacivirus.

Next, four ponies received an equine hepacivirus E2 recombinant protein vaccine with an adjuvant (an ingredient used to modulate or amplify the immune response). One month later they received a booster. Two ponies, serving as controls, received only adjuvant injections.

The researchers then infected all the study ponies with equine hepacivirus. Over 26 weeks they collected blood samples and liver biopsies and observed how the vaccine changed their responses to the virus.

“Although vaccination did not result in complete protective immunity against experimental EqHV inoculation, most vaccinated ponies cleared the serum EqHV RNA earlier than the control ponies,” the study authors wrote. “Most vaccinated ponies appeared to recover from the EqHV-associated liver insult earlier than the control ponies. The equine model shows promise as a surrogate model for future hepacivirus vaccine research.”

This was a small study, and further research is needed to understand what constitutes a protective immune response to the virus, so scientists know what to aim for when developing a vaccine, Daly explained.

“The type of vaccine (recombinant protein) used in this study is very safe and does not require the virus to be cultured but is known to be relatively weak at stimulating an immune response, so it would be worth exploring other vaccine strategies,” she added.

An Equine Model for Vaccination against a Hepacivirus: Insights into Host Responses to E2 Recombinant Protein Vaccination and Subsequent Equine Hepacivirus Inoculation first appeared in Viruses in 2022.

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Written by:

Katie Navarra has worked as a freelance writer since 2001. A lifelong horse lover, she owns and enjoys competing a dun Quarter Horse mare.

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