Disease factsheet: Equine Viral Arteritis - Identifying shedder stallions
When a seropositive stallion is identified, it is vital to establish whether he is shedding EAV in his semen. If so, he is a primary source of infection.
The stallion must be kept in strict isolation for at least a month. The following methods should be used to determine whether he is a shedder. These must be carried out under strict isolation and veterinary supervision.
Virus Detection
Two methods are available for detection of the virus in semen - the Virus Isolation (VI) test or the PCR test. In the UK, the VI test must be used by law under the EVA Order 1995.
For either test, collect a whole ejaculate of semen and send it immediately to a competent laboratory. Collect a second whole ejaculate at least 7 days later, and send it immediately to the same laboratory. Transport requirements (eg. cooling) should be arranged with the laboratory.
If the virus is detected in either of the semen samples, the stallion or teaser is a shedder and must be kept in isolation. He must not be used for mating or AI, or teasing, as long as he is still shedding, unless his use for these purposes is permitted under an official licence issued by the national competent authority.
In the event of negative results for both semen samples, experience has shown that it is advisable to confirm these results by test mating the stallion or teaser.
Test Mating
This must be done only in strict isolation. The stallion and mares must be kept away from all contact with other horses. Apply the following procedure:
- Identify at least 2 seronegative mares
- Take and store blood samples from each then isolate the mares. Speak to the testing laboratory about storage conditions
- Mate each mare twice a day with the stallion on 2 consecutive days
- Keep the mares in isolation
- After 28 days, take blood samples and send them, with the pre-isolation samples, to a competent laboratory for a virus neutralisation test
If the mares remain seronegative, the stallion is unlikely to be a shedder and can be released after a clinical examination.
If one or more mares becomes seropositive, the stallion is a shedder and must be kept in isolation. He must not be used for mating or AI as long as he is still shedding, unless his use for these purposes is permitted under an official licence issued by the national competent authority.
Seropositive mares must remain in isolation until they are no longer infectious.
Review of Recent History of Mares
Subject unvaccinated mares which have recently been mated to the stallion to veterinary clinical examination and blood testing. If they show clinical signs of EVA or have become seropositive after mating, the stallion may be a shedder.
This method is insufficient on its own to confirm shedding and should
be used with one or both of the other methods.
Stallions which are shedders must be kept in isolation until their future
is decided. Options include:
- euthanasia
- castration (followed by 6 weeks' isolation)
Page last modified:
August 28, 2008