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Equine Herpes Virus

May 8, 2018

Cases of Equine Herpesvirus (EHV) have been identified across the United States. It is imperative that horse owners recognize the clinical signs of EHV, understand how it was transmitted, and especially how to prevent the disease.

EHV is a virus that appears in horse populations around the nation. Two strains of the virus, EHV-1 and EHV-4, account for the majority of EHV infections. EHV is easily spread among horses through close contact. The disease generally manifests itself through three syndromes (signs) including respiratory infection (“rhinopneumonitis”), abortion, and neurological disease.

Clinical Signs

  • Respiratory infection. Signs may be mild or unapparent in horses that have been vaccinated. It is often seen in younger horses such as weanlings and its symptoms are fever, nasal discharge, cough, and swelling of lymph nodes. This syndrome is caused by EHV-4, and is commonly followed by a secondary bacterial infection.
  • Abortion. Infection with EHV-1 is associated with late term abortion (7-11 months of gestation). In rare occasions exposed mares may give birth to a live foal. However, the foals are often weak have secondary bacterial infections and usually only live a few days.
  • Neurological disease. This syndrome is caused by EHV-1. Symptoms include incoordination, lameness, loss of tail and bladder function and paralysis depending on which part of the nervous system is affected.


  • Diagnosis can be difficult and time sensitive. If you suspect EHV it is important to enlist the help of your veterinarian. Generally nasal swabs or blood samples may be collected to test for the virus.

Treatment and Outcome

  • In most cases treatment of is supportive, meaning you treat symptoms as they arise. Unfortunately the disease can progress to the point where euthanasia is the only option.


  • Vaccinations for both EHV-1 and EHV-4 are available; however, they do not prevent the neurological signs associated with EHV. Initial vaccination of foals begins at 3-4 months of age with a booster 4-8 weeks later. Subsequent boosters are recommended every 3-6 months to maintain an adequate level of protection. Your local veterinarian should be able to help you determine which EHV vaccines to select and how often to vaccinate based on the specific risk factors for your horse. Horses that are frequently traveling and coming into contact with other horses should likely receive boosters every 90 days. Pregnant mares should be vaccinated with an EHV vaccine that is labeled for prevention of equine abortion at 3, 5, 7, and 9 months of gestation.
  • Additional management practices can help limit the risk of EHV on your property. When you have a new horse arrive adhere to a strict 3-4 week isolation period. If during this time no signs of illness arise in the new horse it may be introduced to your herd. Try to only attend events where health certification and vaccination requirements are enforced. Finally, cleanliness and disinfection of trailers, water buckets and other equipment will help prevent the spread of EHV and other communicable diseases.

Source: Russ Daly, iGrow