What every equestrian should know about Equine Herpesvirus (EHV)

What is Equine Herpesvirus (EHV)?

Equine Herpesvirus (EHV) is a viral infection. The disease has no major side effects but has been a major threat to horses in the United States and all over the world. Unfortunately, most equestrians are ignorant of the highly contagious disease which causes different types of neurological illnesses that are considered fatal—in most cases.

Equine Herpesvirus is categorized as EHV 1, 3 and 4 depending on the family of viruses. There are other forms of the virus—about nine of them—but these three are considered the most fatal for domesticated horses.

What are the causes and symptoms of EHV?

Researchers have been unable to identify what causes development of this deadly neurological sicknesses in horses. However, horses infected with EHV 1 have symptoms such as rhinopneumonitis (the respiratory tract infection which equine experts described as highly dangerous to foals).

EHV 1 has been identified as the main cause of abortion among pregnant mares, neonatal death, respiratory diseases, and neurological form.

EHV 3 causes coital exanthema (a venereal disease which affects the genitals). Findings show that this family of EHV does not affect horses’ fertility despite its impact on the reproductive organs.

EHV 4 is known to cause mild upper respiratory tract infections which has been attributed to miscarriage in horses although it rarely causes neurological ailments.

Generally, EHV is considered a DNA virus affecting more horses around the world in their large numbers. EHV 1 and EHV 4 are the most common. All three families of the deadly virus, nonetheless, present major health risks for yearlings and weaned foals during winter and autumn. Moreover, EHV goes undetected and is easily transmitted to young horses without early signs of infection.

What’s the relationship between EHV and Equine Herpesvirus Myeloecephalopathy (EHM)?

EHV is associated with equine herpesvirus myeloecephalopathy (EHM), the neurological disease-causing virus which damages blood cells in the brain and tissues in the spinal cord thereby incapacitating horses—and, eventually, leading to death.

EHM is also attributed to most cases of blood clot and inflammation of blood vessels among horses. The viral disease may affect individual horses or groups, if there has been a case of multiple exposure to the disease.

Animals infected by EHV or EHM should be euthanized to control spread and treated immediately to reduce chances of a virus outbreak. The Georgia Department of Agriculture in 2016 confirmed that EHM is highly contagious, with possible symptoms such as coughing, sneezing, fever, ocular discharge, hind limb weakness, neurologic and respiratory ailments, urine dribbling, inability to rise or maintain balance, and abortion which may occur between 2 weeks after conception and several months from the time of infection.

How does EHV spread among horses?

The virus is directly passed from one horse to another through mucus from their noses. It is also important to know that the animals can contact the disease by touching physical objects (such as tack and equipment) that have been polluted. Other possible factors that may increase spread of the virus are through:

  • humans, when they touch horses with infected hands, clothing or wipe rags
  • (ii) vehicles, when the animals are transported in germ-prone trailers
  • (iii) and use of dirty grooming equipment or
  • (iv) contaminated feed and waterer.

More importantly, EHV is airborne and may have invisible traces in the shed. Researchers have been unable to find what distance the virus can spread, including the atmospheric conditions that increases risk of contracting the disease.

What’s the survival rate of EHV on a horse’s body?

Findings show that—under normal circumstances—EHV can survive about 7 days. However, the virus can remain alive for up to one month under a conducive atmospheric condition. This highlights the importance of cleanliness.

You should always wash and sanitize their grooming equipment, shed, and water buckets following a proper disinfection process that ensures that your hands do not spread the deadly pathogens.


There are medications for treating EHV but the vaccines are only effective in reducing viral mutations. Current drugs for EHV 1 have not been proven to offer protection against neurologic form of the ailment. However, experts in the field advise regular use of biosecurity practices as the best measure against viral outbreak, adding that “the best cure is prevention.” Early vaccinations increase a horse’s immunity to the diseases.

Although EHV is deadly to horses, the contagious virus does not affect humans. But you have a responsibility to contact veterinarians as soon as the EHV symptoms are noticed.