Our site is currently being updated and pages are changing regularly. We thank you for your patience during this transition and hope that you find our new site easy to use.

Equine herpesvirus overview

Equine herpesvirus associated with abortion or neurological signs in horses is a notifiable disease

Under Queensland legislation, if you suspect the presence of this disease in horses, you must report it to Biosecurity Queensland.

Call us 13 25 23 or
Emergency Disease Watch Hotline 1800 675 888



Equine herpesvirus


Equine herpesvirus (EHV) commonly causes mild respiratory disease and can cause abortion, stillbirths, deaths of newborn foals and neurological disease in adult horses. There are five strains of EHV. EHV1 is the most serious viral cause of abortion in horses though EHV4 can also rarely cause abortion.

EHV associated with abortion or neurological signs in horses is a notifiable disease under legislation and all suspect and confirmed cases in horses should be reported to Biosecurity Queensland.

Where the disease occurs

The disease occurs wherever horses are kept. Abortion and neurological signs are reported infrequently compared to respiratory signs. Neurological cases have been reported, particularly in the United Kingdom and the United States.

Only the respiratory form of the disease was recognised in Australia before 1977. Since that time single abortions and abortion storms due to EHV1 have occurred sporadically. Neurological disease associated with EHV1 infection is extremely rare in Australia.

The disease in animals

There are 5 strains of EHV (EHV1-5):

  • EHV1 is the most significant because it is widespread and causes abortion, stillbirths, septicaemia in newborn foals, respiratory and nervous signs.
  • EHV2 causes mild respiratory disease.
  • EHV3 causes ulcerative sores on the vulva and vagina of mares and penis of stallions, being spread during mating. Pain may prevent mating but recovery is usually complete within 2 weeks.
  • EHV4 usually causes upper respiratory tract disease. On rare occasions it may be associated with abortions in individual mares.
  • EHV5 causes mild respiratory disease.

Symptoms of both EHV1 and EHV4 include fever, depression, nasal discharge and a cough, lack of appetitie and possibly swelling of the lymph glands around the throat. Milder respiratory disease may involve only conjunctivitis and a cough with little impairment of respiratory function. The nasal discharge and cough can last up to 3 weeks. Secondary bacterial infection can result in pneumonia.

Abortion can occur between 2 and 12 weeks after infection. Infected foals may be normal at birth but become weak, very depressed and die in a few days with signs of respiratory disease.

Adult horses can be affected by the nervous form of the disease. Signs can vary from slight temporary ataxia to severe incoordination and recumbency, requiring euthanasia.

How the disease spreads

This disease is highly contagious and spreads easily in horse populations. The virus is found in nasal secretions or in the products of abortion. Horses contract the disease from inhaling infected droplets or eating contaminated material. The virus can survive 14-45 days outside the body depending on environmental conditions.


Paired blood samples should be collected to demonstrate rising antibody levels. When aborted foetuses are autopsied, sections of a range of organs should be collected, both preserved and either fresh chilled or in virus transport medium. (Include thymus and gut contents.)

Control of the disease in animals

A vaccine is available and is recommended for use on studs, in racing stables and for competitive horses. It will not guarantee complete protection but will greatly reduce the debilitating effects of viral respiratory disease and reduce the number of abortions in an outbreak. Isolation of introduced horses for at least 3 weeks, especially for pregnant mares is recommended. All pregnant mares should be kept isolated from weanlings and yearlings.

Can people get the disease