Disease factsheet: Equine Viral Arteritis - Preventing infection - Recommendations
Imported horses (including returning 'shuttle' stallions) and imported semen
Growth in the practice of importing stallions for mating, or importing their semen for AI, increases the risk of spread of EVA infection. Strict precautions are therefore needed.
- Where it is intended to import horses, semen or embryos, veterinary or other specialist advice should be taken on the incidence of EVA in the exporting country. As a general guide, the importer should take the following precautions if the horse is imported from a country where EVA is known or suspected to occur.
- As a condition of the purchase agreement, ensure that the horse is tested for EVA before leaving the country of origin. The samples should be sent to a competent laboratory, which does not need to be in the country of origin.
- Place the horse in isolation immediately on arrival and keep it there for at least 21 days. Your veterinary surgeon should take blood samples on the horse's arrival in this country and at least 14 days later and send them to a competent laboratory for examination for antibodies to EAV. When the results are available, consult your veterinary surgeon about the next steps.
- When importing semen for use in AI, the status of the donor stallion at the time when the semen was collected must be established. If the stallion was seropositive, the semen should not be used unless it can be proved that he was not a shedder. See also sub-section F below.
- When importing embryos, establish the status of both the stallion and mare at the time of conception. For mares, seronegative status, or seropositive status with stable or declining EAV antibody levels, is required. For stallions, seronegative status, or seropositive status with proof that they are not shedders, is required.
Domestic Stallions and Teasers
After 1st January in any year, all unvaccinated stallions and teasers should be serologically tested. Your veterinary surgeon should take samples and send them to a competent laboratory. Do not use stallions or teasers for mating, teasing or collecting semen until the results are available.
If the stallion or teaser is seronegative, mating, teasing, collection and insemination of semen may begin.
If the stallion or teaser is seropositive, notify the DVM of Defra immediately. The stallion/teaser may be a shedder and must be isolated while steps are taken to determine whether or not he is shedding virus in his semen - for information on testing methods, see the section titled "Identifying shedder stallions" towards the end of this Code of Practice. He must not be used for mating, AI or teasing during this time.
If he proves to be a shedder, he or his semen must not be moved and he must remain in isolation until his future is decided. Previously released semen should be traced and recipients notified.
Vaccinated stallions and teasers may be seropositive or seronegative, depending on when the last course of vaccine was given and on whether the horse might have become infected since the effect of the vaccine wore off. These horses should be blood tested after 1st January. Do not use them for mating, teasing or for collecting semen until the results are available.
If the stallion or teaser is seronegative, mating, teasing, collection and insemination of semen may begin.
If he is seropositive, his history in the past 12 months - including dates of EVA vaccinations, results of pre-vaccination blood testing and contacts with other horses since the last vaccination - should be reviewed. If there is any possibility that his seropositive status is the result of infection rather than vaccination, the DVM of Defra should be notified immediately, and the stallion or teaser should be isolated and further tested to determine whether he is shedding virus in his semen - see "Identifying shedder stallions" below for test methods. He must not be used for mating, AI or teasing during this time.
Domestic Mares
The risk associated with any mare can vary. Decisions regarding the testing of mares visiting stallions should therefore be made at local level, in consultation with the veterinary surgeon, according to the circumstances of individual studfarms and the mare's history and contacts with other horses in the past year.
In any breeding season, the safest way to avoid risk is to blood test all mares within 4 weeks before mating. Your veterinary surgeon should take the samples and send them to a competent laboratory. Do not mate the mare until the results are available.
If a mare is seronegative, mating may begin. If she is positive, she must be isolated - preferably off the stallion stud. Repeat blood samples should be taken by your veterinary surgeon at intervals of at least 2 weeks and sent to the same laboratory that tested the first samples. When it is proven from the results that the mare is no longer infectious - as indicated by stable or declining antibody levels - then she is safe to mate. In any other situation, consult your veterinary surgeon. If any result is positive unexpectedly, the mare's in-contacts should be isolated and screened for EAV. Any foster mares on the premises should also be tested.
The circumstances in which EVA in mares is notifiable by law are set out in Section 7 above.
Foaling - Seropositive Mares
Any pregnant seropositive mares should be foaled in isolation unless the vaccination or infection which caused seropositivity occurred before the pregnancy. If in any doubt, consult the veterinary surgeon.
Abortion and Newborn Foal Death
If there is any possibility that EVA caused an abortion or newborn foal death, the foetus/carcase together with blood from the mare and appropriate samples from her placenta and her clinical history must be sent immediately to a competent laboratory for specific examination.
Artificial Insemination
Stallion studs must record the dates of collection of semen and its movement to other premises.
To prevent infection, mares must not be inseminated with semen from infected stallions. The EVA virus survives in chilled and frozen semen and is not affected by the antibodies added to semen. Donor stallions must therefore be checked.
- Mare owners planning to inseminate their mare with semen from a domestic
or imported stallion must ensure that the stallion/semen tests at A
or B above have been carried out, and negative results obtained, before
accepting any semen.
- Mare owners planning to use chilled semen from an overseas stallion must check that the semen is accompanied by papers certifying that a blood sample was taken from the stallion and tested with a negative result shortly before the semen was collected. If the imported semen is frozen, it must be accompanied by papers certifying that the stallion or semen have been tested negative after the semen collection was made in the country of origin. Any test should have been carried out in a competent laboratory, which does not need to be in the country of origin.
Additionally, it should be tested on arrival in this country. Provided
all straws from the semen collection were taken from the same stallion
at the same time, it is only necessary to test one straw. If that straw
does not contain the EAV, it can be taken that the other straws are free
from infection.
For practical reasons, it is not possible to test imported chilled semen
on arrival in this country.
Under EU legislation, it is not permitted to import semen from shedding stallions.
Sport Horses
It is thought that there is a particular risk of EVA transmission associated with the international movement of sport horse stallions and/or their semen. Precautions are therefore needed when these are used for mating or semen collection and insemination. Where these stallions are imported from any member state of the European Union (EU), they are not required to undergo any official EVA testing. Their EVA status must therefore be established privately before mating or semen collection or insemination. Official EVA testing requirements for stallions imported from non-EU countries are laid down in EU Rules. However, additional private testing may be carried out as a further precaution.
If a stallion is normally resident in this country, testing should be repeated each time he returns from international competition.
Mares and stallions in this category may readily acquire EVA through the respiratory route.
Page last modified:
August 28, 2008