Equine Herpes Virus

Herpes Virus in Horses

The herpes virus is a large family of viruses. Most mammalian species are susceptible to at least one type of herpes virus. Fortunately, this virus is very species-specific, meaning that humans do not catch equine herpes virus, and vise versa. There are five known subtypes in horses, but Equine Herpes Virus-1 (EHV-1) and EHV-4 are the two severest forms of the virus. EHV-3 is another type of major herpes virus, although it is normally associated with coital exanthema, a venereal disease that can be transmitted to horses.

The different classifications of equine herpes virus affect different systems; one affects the reproductive and neurological systems, whereas another causes respiratory issues. The virus type will also determine the symptoms the horse displays.


The incubation period for the virus depends on the subtype affecting the horse, but it is generally 4 to 10 days, after which the following symptoms may be seen:

  • Fever
  • Nasal discharge
  • Enlarged lymph nodes
  • Decreased fitness performance
  • Weakness in hind legs
  • Strange gait
  • Anorexia
  • Lethargy

 Neurological issues may occur, such as paralysis or uncoordinated body movements (ataxia), even seizures, the inability to stand up, and death. This is usually in cases of EHV-1. EHV-1 can also cause abortions in pregnant mares.


Equine herpes virus is highly contagious and spreads from horse to horse rapidly through inhalation of respiratory secretions, as well as direct contact. If strict quarantine is not followed, it can be carried on a person from one horse to another. Equine herpes virus is everywhere in the U.S. and there tend to be severe outbreaks in a portion of the horse population about every year, usually affiliated with stables or shows that have a high volume of horses traveling through.


A veterinarian can make a presumptive diagnosis of the equine herpes virus by the clinical signs the horse is presenting, especially if more than one horse at a barn has the same clinical signs. Viral isolation can be done on nasal swabs from suspect horses.

lymph nodes

Small structures that filter out the lymph and store lymphocytes


a condition in which an animal must be controlled in some manner in order to prevent a disease from spreading


The process of turning an egg into a bird


The term used to describe the movement of an animal


The name for the species of horses, donkeys, mules


A medical condition in which an animal is unable to control the movements of their muscles; may result in collapse or stumbling.

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