01342 823011 - 24hr emergency service 7days a week 365 days a year

Equine Herpes Virus

There are 2 main Equine Herpes Viruses: EHV-1 and EHV-4. Both of these viruses are endemic in the horse population and the majority of horses in this country have been exposed to these viruses. The most common disease caused by both of these viruses is a mild upper respiratory tract infection. However very rarely EHV can cause two much more serious conditions: Both EHV-1 and EHV-4 can cause abortion and EHV-1 can cause Equine Herpes Virus Myeloencephalopathy.

The important facts regarding Equine Herpes Virus are:

  • The vast majority of horses only experience the mild respiratory infections that usually go unnoticed by the owner! In very rare cases, the disease progresses into a neurological form. These horses are usually stressed, are very young or very old, and might have compromised immune systems.
  • Obviously abortion only affects in-foal mares.
  • When horses first contract EHV they experience fever, lethargy, clear nasal discharge, watery eyes and, occasionally, a cough. Because the virus does not stimulate a strong immune response, they might come down with EHV many times during their life, but each time they do, they experience milder symptoms.
  • There is some evidence that optimum athletic ability may be compromised if a horse becomes infected with the Equine Herpes Virus.
  • As many as 80% of horses become latently infected (the virus becomes inactive in the lymph nodes) and serve as reservoirs for the disease. When the latently infected horse is stressed by transport, competition, intense training, etc., it might start shedding the virus without showing clinical signs, making containment of the virus very difficult.
  • The incubation period of EHV (time from exposure to becoming ill) is one to two days, with clinical signs of fever, depression, nasal discharge and loss of appetite. If the neurologic form of the disease occurs, it usually does so within eight to 12 days and the horse develops clinical signs of weakness, lethargy, urine dribbling, decreased tail tone and the inability to stand.


A vaccine is available protecting against both EHV-1 and EHV-4.

To protect against respiratory infection an initial course of 2 vaccinations are given with a 3-4 week interval between doses. A booster is then required every 6 months.

To protect against abortion vaccinations are given during the 5th, 7th and 9th months of pregnancy.

We recommend that you talk to us before deciding on vaccinations as the decision must be made on a case by case basis.


  • All horses should be isolated for 21 days on arrival at any new premises.
    • If travelling to a competition or a new yard it is sensible to disinfect the stable before putting your horse in it. The best disinfectant on the market is Virkon.
    • Avoid nose-to-nose contact with other horses, and do not share water buckets, grooming items etc.
    • Avoid touching other horses and letting other people touch your horse.
    • Check your horse’s temperature each morning, as most respiratory infections, especially EHM, are preceded by an elevated body temperature (38.3 degrees centigrade or more).
  • If one of your horses becomes sick, isolate it immediately and contact us.

DISCLAIMER: This advice is intended for use by registered clients of Priors Farm only. The advice offered is general advice only. Priors Farm clients who wish to discuss the individual circumstances of their horse should contact the office. To speak to a vet please phone between 8.30 – 10.00 am on weekday mornings.