Equine viral arteritis

It is caused by the equine arteritis virus (EAV). The virus occurs worldwide in thoroughbred and non-thoroughbred populations. It does not affect humans.

Equine viral arteritis is a notifiable disease if suspected in:

• stallions (male horses)
• mares (female horses) that have mated or been inseminated within 14 days

If you suspect the disease, you must report it immediately. Call the Animal and Plant Health Agency (APHA) Wales on 0300 303 8268.

Failure to do so is an offence.

You should also isolate the horse(s) concerned and stop all breeding activities.

Clinical signs can vary widely, with some infected horses showing no signs at all. 

Clinical signs may include:

• fever
• lethargy
• depression
• swelling of the lower legs, around the eyes, or of the scrotum or mammary glands 
• conjunctivitis (“pink eye”)
• nasal discharge (runny nose)
• abortion (loss of pregnancy in mares)

In rare cases, the disease can cause severe illness or death in young foals. 

EVA can spread between horses:

• directly during mating
• directly or indirectly during teasing
• via artificial insemination 
• contact with aborted foetuses or birth materials
• contact with contaminated equipment
• via respiratory spread (for example via droplets from infected animals) 

Stallions can:

• carry the virus for extended periods without showing clinical signs 
• spread the virus through mating
• spread the virus if their semen is used for artificial insemination

Mares can spread the virus:

• to their foals, during pregnancy or through milk
• to a stallion through mating
• to other horses via respiratory spread

Vaccination is key to prevention and control, particularly for stallions and teasers. You should ensure animals are free from EVA infection before breeding activities begin.

You can help prevent the disease by: 

• vaccinating stallions against the disease - talk to your vet for advice
• testing all stallions, teasers and mares before breeding
• practise good biosecurity on your premises, especially if you’re involved in breeding
• following guidance on isolation and testing for EVA when importing horses

You can find more guidance on prevention and control of EVA is available in the Horserace Betting Levy Board (HBLB) Code of Practice.

HBLB International Codes of Practice | Equine Viral Arteritis - EVA

Biosecurity guidance is also available on the BEVA website.

If the disease is confirmed the outbreak will be controlled in line with the contingency plan for exotic notifiable diseases.

Equine viral arteritis is controlled under the Equine Viral Arteritis Order 1995 (on legislation.gov.uk).