Equine hepatitis viruses can affect liver health in horses. | Adobe StockEquine hepatitis viruses are a group of viruses that can affect the liver health of horses. While some infections may go unnoticed, others can lead to significant health concerns. The two viruses currently identified as liver-specific pathogens are Equine Hepacivirus (EqHV) and Equine Parvovirus-Hepatitis (EqPV-H).What Are EqHV and EqPV-H?Horses can contract these viruses through contaminated biologics, such as plasma or stem cells, as well as through natural horizontal transmission, for example the parvovirus can pass through nose-on-nose contact. Natural transmission routes still have to be explained further.EqHV is a virus that primarily causes chronic hepatitis in horses. Most horses infected with EqHV clear the virus within 20 weeks without showing any clinical signs. However, about 20% of cases may develop chronic hepatitis, which can persist for more than six months. This chronic condition may present as subclinical or with signs of liver disease, such as jaundice, lethargy or poor appetite.EqPV-H, on the other hand, is associated with acute hepatitis, a more sudden form of liver inflammation that can frequently present with severe clinical signs. This virus has been linked to Theilers Disease, a condition that can cause rapid liver failure in horses.EqHV is ubiquitous and between 20 to 40% of horses have circulating antibodies against the virus without signs of liver disease, and only a small number of horses develop clinical disease. This suggests that exposure to the virus is frequent but in most cases the horses immune system can successfully combat the virus without causing visible signs of disease. Similarly, approximately one-third of horses have been exposed to EqPV-H. While these infections often go unnoticed and do not cause clinical signs, a small percentage of cases can result in severe, potentially life-threatening liver disease, sometimes manifesting in several horses simultaneously as an outbreak.How Are These Viruses Diagnosed?Diagnosing these viruses involves a combination of blood testing and liver biopsies. For EqHV, veterinarians may use serial biochemistry and PCR tests to monitor viral load and liver enzyme activity. Chronic cases are confirmed when viremia (presence of the virus in the blood) and hepatitis persist for more than six months. For EqPV-H, liver biopsies are commonly used to confirm the diagnosis.Managing Infected HorsesManaging horses infected with EqHV or EqPV-H requires supportive care and careful attention to biosecurity.For EqPV-H, infected horses should be isolated for four to eight weeks after the onset of hepatitis. Horses that test positive for the virus can be housed together, but they must be kept separate from yet uninfected horses until the viral load decreases sufficiently to make transmission unlikely. Regular screening of all horses in the herd is recommended to identify new infections early. Typically, horses infected with EqHV do not require isolation due to the widespread distribution of the virus among non-clinically infected horses. However, monitoring the horses health and liver function is essential. With both viruses, severely ill horses may need to be referred to a veterinary care facility for specialized treatment. Routine monitoring of serum biochemistry and signs of disease progression are important.Prevention Tips for Horse OwnersWhile no specific antiviral treatments or vaccines are currently available for these viruses, prevention efforts emphasize the importance of quality control in equine biologic products. It is crucial to use biologics that have been tested and confirmed as free from these viruses to minimize the risk of transmission.Research and Future DirectionsResearch on equine hepatitis viruses is moving forward quickly to better understand how these viruses cause disease and explore potential treatment options. Another important research focus is investigating how environmental factors and potential reservoirs/carriers might spread these viruses. Although small amounts of viral genetic material have been found in stable flies (Stomoxys calcitrans), it is still unclear if this represents an infectious dose of virus or if stable flies can actually transmit the disease. Clarifying these transmission pathways could lead to improved prevention strategies.For prevention, early pilot studies on new vaccines for EqHV are already in progress, paving the way for more effective ways to protect horses in the future.Take-Home MessageEquine hepatitis viruses can pose a serious risk to a horses health, but with proper management and preventive measures, the impact can be minimized. Awareness of these viruses, their modes of transmission and the importance of early diagnosis can help horse owners take proactive steps to protect their animals. If you suspect your horse may be affected, consult your veterinarian promptly for diagnosis and guidance.Editors note: This is an excerpt from Equine Disease Quarterly, Vol. 34, Issue 3, funded by underwriters at Lloyds, London, brokers, and their Kentucky agents. It was written by Jessika-M. Cavalleri, Dr.med.vet., Dipl. ECEIM, head of the Clinicical Department for Small Animals and Horses at the University of Veterinary Medicine Vienna, in Austria.

On Sept. 23, a 6-year-old Percheron gelding in Highland County, Ohio, tested positive for West Nile virus (WNV). The unvaccinated gelding developed clinical signs on Sept. 14, including severe ataxia and weakness. He is now recovering.EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. TheEDCCis an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.WNV 101West Nile virusis transmitted to horses via bites from infected mosquitoes. Not all infected horses show clinical signs, but those that do can exhibit:Flulike signs, where the horse seems mildly anorexic and depressed;Fine and coarse muscle and skin fasciculation (involuntary twitching);Hyperesthesia (hypersensitivity to touch and sound);Changes in mentation (mental activity), when horses look like theyre daydreaming or just not with it;Occasional drowsiness;Propulsive walking (driving or pushing forward, often without control); andSpinal signs, including asymmetrical weakness; andAsymmetrical or symmetrical ataxia.West Nile virus has no cure. However, some horses can recover with supportive care. Equine mortality rates can reach 30-40%.Studies have shown thatvaccines can be effective WNV prevention tools. Horses vaccinated in past years need an annual booster shot, but veterinarians might recommend two boosters annuallyone in the spring and another in the fallin areas with prolonged mosquito seasons. In contrast, previously unvaccinated horses require a two-shot vaccination series in a three- to six-week period. It takes several weeks for horses to develop protection against the disease following complete vaccination or booster administration.In addition to vaccinations, owners should work to reduce mosquito population and breeding areas and limit horses mosquito exposure by:Removing stagnant water sources;Dumping, cleaning, and refilling water buckets and troughs regularly;Keeping animals inside during insect feeding times (typically early in the morning and evening); andApplying mosquito repellents approved for equine use.

For the 2025 breeding season so far, HSI has received 4870 applications and issued 2065 completed applications.4849 pedigree applications have had their foal kit sent to the applicant, with the remainder issued imminently.It is important to note that, to date, 1469 foal kits have not been yet returned from breeders to HSI for pedigree applications, which is 30 per cent of all applications.Of the 3380 applications who have returned their foal kits to HSI, 2065 have been completed and the passport issued and 361 are currently undergoing quality control checks, while the remaining 954 applications DNA samples are currently with the laboratory for analysis.Of the 2426 passport applications, where the DNA samples have been returned to HSI from the laboratory, 2065 are complete.The post Updated figures of passport applications processed on Horse Source September 26th, 2025 appeared first on .

On Sept. 25, a vaccinated Tennessee Walking Horse gelding in Henry County, Indiana, tested positive for West Nile virus (WNV). The horse developed clinical signs on Sept. 14, including minor ataxia in the front limbs, moderate ataxia in the hind limbs, and inappetence. He is still alive.EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. TheEDCCis an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.WNV 101West Nile virusis transmitted to horses via bites from infected mosquitoes. Not all infected horses show clinical signs, but those that do can exhibit:Flulike signs, where the horse seems mildly anorexic and depressed;Fine and coarse muscle and skin fasciculation (involuntary twitching);Hyperesthesia (hypersensitivity to touch and sound);Changes in mentation (mental activity), when horses look like theyre daydreaming or just not with it;Occasional drowsiness;Propulsive walking (driving or pushing forward, often without control); andSpinal signs, including asymmetrical weakness; andAsymmetrical or symmetrical ataxia.West Nile virus has no cure. However, some horses can recover with supportive care. Equine mortality rates can reach 30-40%.Studies have shown thatvaccines can be effective WNV prevention tools. Horses vaccinated in past years need an annual booster shot, but veterinarians might recommend two boosters annuallyone in the spring and another in the fallin areas with prolonged mosquito seasons. In contrast, previously unvaccinated horses require a two-shot vaccination series in a three- to six-week period. It takes several weeks for horses to develop protection against the disease following complete vaccination or booster administration.In addition to vaccinations, owners should work to reduce mosquito population and breeding areas and limit horses mosquito exposure by:Removing stagnant water sources;Dumping, cleaning, and refilling water buckets and troughs regularly;Keeping animals inside during insect feeding times (typically early in the morning and evening); andApplying mosquito repellents approved for equine use.