Equine Hepacivirus in Horses: Chronic Viral Hepatitis and What It Means

Equine hepacivirus, often shortened to EqHV, is a virus that infects horses and targets the liver. It is closely related to hepatitis C virus in people, which is one reason researchers are paying close attention to it. Current equine guidance from the American Association of Equine Practitioners notes that EqHV is common in the U.S. horse population, and many infected horses clear the virus within about 20 weeks without developing obvious illness.

That said, EqHV is not always harmless. Some horses develop persistent infection, meaning the virus stays in the bloodstream for months to years. In those horses, ongoing liver inflammation can lead to chronic hepatitis, fibrosis, and in some cases liver failure. Cornell researchers and AAEP guidance both describe EqHV as a virus with the potential to cause severe chronic liver disease, even though many infections stay subclinical.

For pet parents, the tricky part is that a horse can look fairly normal while liver damage is building. Some horses are diagnosed only after routine bloodwork shows elevated liver enzymes. Others are not recognized until they develop signs of liver dysfunction. Because the course can vary so much, your vet usually focuses on confirming whether EqHV is present, checking how well the liver is still functioning, and monitoring for progression over time.

EqHV is caused by infection with a hepacivirus that circulates widely in horse populations. AAEP guidance states that the virus has been identified in equine plasma products, so one recognized route of exposure is through equine-origin biologic products such as plasma or certain blood-derived therapies. Because of that, your vet may ask about any recent plasma, serum, stem cell, or other biologic treatments.

EqHV also appears to spread horizontally between horses outside of biologic product use. The exact route is still being worked out, but AAEP guidance says non-biologic transmission seems to occur mainly from spring through fall and that an insect vector is suspected. Horses do not need direct nose-to-nose contact to become infected.

Age may matter too. Current guidance suggests horses infected as adults seem to be at low risk for persistent infection, while infection in foals may carry a higher risk of long-term viral persistence. Researchers are still studying why some horses clear the virus and others go on to chronic hepatitis.

Importantly, EqHV is not known to pose a risk to people or other animal species based on current AAEP guidance. Still, because transmission is not fully understood, your vet may recommend practical biosecurity steps if EqHV is suspected in a barn or breeding setting.

Diagnosis usually starts with a careful history and bloodwork. Your vet will often run a CBC and serum chemistry panel to look for elevated liver enzymes, then add tests such as bile acids, ammonia, or clotting times if liver dysfunction is a concern. Merck Veterinary Manual notes that enzyme changes can show liver injury, but they do not always tell how much functional liver tissue remains.

To confirm EqHV infection, your vet may recommend a PCR test on blood to look for viral RNA. This helps show whether the virus is currently present in the bloodstream. Because many horses can carry the virus without severe illness, PCR results are interpreted alongside clinical signs and liver values rather than in isolation.

If bloodwork suggests significant or ongoing liver disease, your vet may add ultrasound and sometimes a liver biopsy. Merck states that percutaneous liver biopsy is the definitive way to diagnose hepatic disease and assess cause and severity, and ultrasound guidance helps reduce complications. In suspected chronic EqHV hepatitis, biopsy can help show whether there is active inflammation, fibrosis, or more advanced damage.

Typical U.S. cost ranges in 2025-2026 are about $250-$500 for an exam and baseline bloodwork, $150-$300 for bile acids or added liver function testing, $150-$300 for EqHV PCR, $300-$700 for abdominal ultrasound, and $800-$1,800+ for liver biopsy with pathology. Actual costs vary by region, farm-call needs, and whether emergency care is involved.

There is no vaccine for EqHV at this time. AAEP guidance also notes that, because the virus is so common, preventing lifetime exposure may be difficult. That means prevention is less about one perfect step and more about risk reduction.

One practical step is to talk with your vet before using equine-origin biologic products such as plasma, serum, or certain regenerative products. AAEP recommends using autogenous biologics when appropriate, or products that have been tested and confirmed free of the virus. This matters because EqHV has been identified in equine plasma products, and current USDA regulation does not routinely test equine biologics for EqHV.

Because horizontal spread is still being studied and an insect vector is suspected, good barn management still makes sense. Work with your vet on needle hygiene, avoiding unnecessary blood exposure between horses, insect control, and careful handling of any horse with suspected liver disease. AAEP does not currently recommend routine isolation of infected horses, but if separation is chosen, guidance suggests keeping them at least 200 yards from susceptible horses.

Foals may deserve extra caution. Preliminary evidence suggests horses infected as foals could be at higher risk for persistent infection, so your vet may recommend focusing biosecurity efforts around mares, foals, and any procedures involving blood products. If one horse on the property is diagnosed, ask your vet whether screening stablemates or reviewing recent biologic use is worthwhile.