The equine herpes virus has two strains: EHV1, which can cause respiratory problems, abortion in pregnant mares and, in rare cases, neurological problems leading to paralysis; and EHV4, which most commonly causes respiratory problems and occasionally abortion in pregnant mares.

Early signs of equine herpes include:

  • Increased temperature
  • Coughing
  • Nasal discharge
  • Lack of interested in food

A horse showing these signs should be isolated and a vet called. To prevent the spread of the disease, all horses who have come in contact with the infected horse should remain on the yard until the vet has confirmed diagnosis.

Under Horserace Betting Levy Board rules a yard with an outbreak must remain closed (no equine movement in or out) for 28 days from the date the last case was identified.

A horse can carry the equine herpes virus without showing any signs and it is believed that most older horses have been exposed to it at some point. A blood test is available to see if a horse has recently been exposed to the virus, although the test cannot tell the difference between the antibodies caused by the virus and those caused by vaccination.

Equine herpes virus vaccinations: pros and cons

There are vaccines currently available that work against both strains of EHV, including a combined vaccine, which also acts against equine flu. However, although the vaccines are effective against the respiratory effects of the virus, they are not registered for use against the paralytic form.

The Animal Health Trust advises that only healthy horses be vaccinated, and that horses should not be vaccinated during an on-going outbreak of EHV. This is to reduce the chance of a horse, which is currently incubating the virus, receiving the vaccine.

Vivienne Irwin of the Animal Health Trust says: “Although the vaccine is very safe to use, if you have a horse currently incubating the virus, it may lead to the animal suffering a more severe case of the disease.

“It is standard practice that vaccinations should only be carried out on healthy horses. A horse showing any signs of respiratory disease should be thoroughly checked out by a vet.”

The AHT also says that the vaccine can safely be given to a horse who has previously come in contact with the virus, as long as the animal is not showing clinical signs or incubating the virus at the time. However, it does warn that the vaccine won’t be as effective when given to a carrier as it would be if given to a horse which hasn’t come in contact with the virus.

“We encourage owners to begin the routine vaccination of their horses from an early age to prevent the spread of the infection,” says Vivienne. “The current vaccines are very safe and we do recommend them, but if owners have any concerns they should contact their regular vet, who has knowledge of their particular circumstances.”

First published: 19 Jan 2004