Is EVA Under Your Radar? Be EVA-Savvy when Selecting a Stallion By Gigha Steinman
Odds are you’ve never heard of either “EVA” or “EAV.” In a world prone to abbreviate practically everything, it’s easy to get lost in the alphabet soup of acronyms that runs the gamut from EIA (Equine Infectious Anemia, the disease for which the Coggins test checks) to EHV (the rhino pneumonitis virus).
E
VA (Equine Viral Arteritis) is a contagious disease caused by EAV (Equine Arteritis Virus), which
is spread via respiratory secretions or infected semen when breeding.
The
most common symptoms are fever, flu-like symptoms and swelling of the lower legs, but most cases have no symptoms at all, hence its potential danger. If you’re not a horse breeder, you may have little or no
need to understand either one. But if you are, it is very important to understand this virus, particularly if you are considering breeding to an EVA-positive carrier stallion or if your mare is kept in a herd with other mares who are being bred to EVA-positive carrier stallions. This is because EVA can cause pregnant mares to abort their foals. It can also cause death in young foals and can cause stallions to become permanent carriers of the disease. The mortality is rare in adult horses and most horses will make a full recovery. EVA was first identified in 1953 after an outbreak on
a Standardbred breeding farm in Ohio. The disease then gained global prominence after an epidemic in Kentucky in 1984, which affected 41 Thoroughbred breeding farms and threatened the Thoroughbred breeding industry. The disease is now recognized worldwide—only Japan and Iceland are believed to be free of it. Some countries have strict regula- tions and/or bans on EVA-positive horses or infected semen entering those countries, in an attempt to control the disease and its effects. Mares, geldings and sexually immature colts who contract
EVA will usually develop a strong immunity and cannot be carriers of the virus (except during the initial acute stage of infection) although they will test either seropositive (i.e. showing a high level of antibodies) or positive for it. Only stallions can become EVA carriers because it is
testosterone dependent. EAV is then transmitted during breeding via infected semen. Not all seropositive stallions
will become “carriers” of EVA: The Gluck Equine Research Center in Kentucky estimates 44 percent of EVA seroposi- tive stallions are carriers of the disease. EVA can be spread through live cover (if the stallion is an EVA carrier) and also through artificial insemination with infected fresh or frozen semen. There is no process in the collection, cooling and/or freezing of semen that will eliminate EVA.
Concern for Breeders EVA is a concern to breeders because it can cause abor- tion in pregnant mares. The abortion can occur when an EVA-infected mare (i.e. one who’s just been bred with EVA- infected semen or one who’s been recently vaccinated for EVA) is exposed to pregnant mares who have no immunity to the disease (because they’ve never been previously exposed nor vaccinated). Those pregnant mares can then become infected with EAV, causing them to abort their foals. The Merck Veterinary Manual estimates the abortion rate at 10 to 60 percent, and the USDA Animal and Plant Health Inspec- tion Service (APHIS) estimates abortion rates as high as 70 percent. For this reason, breeders must exercise extreme caution when breeding to an EVA-positive carrier stallion if there is a chance they could be exposing additional pregnant mares to the disease. An EAV-infected mare can also spread the disease to non-pregnant mares, geldings, and stallions during the acute stages of infection.
Is He EVA-Positive? It is recommended that stallions be tested annually and/or vaccinated for EVA. Some breed registries, like the KWPN- NA (Dutch Warmblood), SWANA (Swedish Warmblood) and the Belgian Warmblood Breeding Association list the EVA status of their approved stallions on their websites. Others, like the American Hanoverian Society, caution breeders that they “make no claim as to the fertility or freedom from disease of any stallions listed.” Most registries, however, seem to make no mention at all of EVA or of the EVA status of
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