Planning ahead to protect your farm against Equine Viral Arteritis
Last year, the equine industry was shocked by the report of an Equine Viral Arteritis (EVA) outbreak. The outbreak was initiated in June 2006 in a Quarter Horse farm in New Mexico. Soon, other cases followed in Utah, Oklahoma, Texas and Kansas. Due to the devastating economic losses that EVA can cause, it is important that you learn how to protect your farm, your stallions and your foal crop during this coming breeding season.
What is EVA?
Equine Viral Arteritis is caused by the Equine Arteritis Virus (EAV). It is a contagious, primarily respiratory viral disease that affects horses and other equids of any age. Although typically not life-threatening to healthy adult horses, it is of special concern because it can result in abortion in pregnant mares, illness and death in young foals, and establishment of the carrier state in stallions.
What are the signs of EVA?
Most infected horses show no signs of disease and are asymptomatically infected. However, even though signs are not present, they can still spread the virus. In cases where illness develops, affected animals can show fever, swelling of legs, scrotum, sheath, mammary glands and other dependent parts of the body, loss of appetite, depression, watery to mucoid nasal discharge, conjunctivitis, skin rash, pneumonia, pneumonia with enteritis, and abortions.
How is EVA transmitted?
EVA can be transmitted through respiratory and venereal routes. Acutely infected horses shed the virus through their respiratory tracts. Other horses can become infected after direct contact with exhaled secretions. This is the main way EVA is spread in racetracks, shows and sales, but also in breeding farms. However, venereal transmission plays a major role in dissemination of the disease in breeding farms. EVA can be spread during teasing, mating or insemination through contact with semen or reproductive tract secretions of acutely infected stallions and mares. In addition, chronically infected carrier stallions also shed the virus in their semen. The virus is resistant to cooling or freezing and transmission can occur after insemination with infected fresh, cooled or frozen semen. Mechanical spread can also occur through tack or equipment shared by horses and hands and clothes of personnel. Finally, unborn foals can become infected by transmission of the virus across the placenta.
How does EVA affect my breeding operation?
EVA possesses a major threat to immunologically na´ve mares and stallions. The virus is generally first introduced into a farm by a mare that has recently been bred or inseminated with infected semen, or by an asymptomatic animal that has acquired the infection via respiratory route in a show or sale. If these animals are housed together with pregnant mares that have no antibodies to EAV, pregnant mares may abort after clinical or asymptomatic infection. Abortion rates can be as high as 70% and an entire foal crop can be lost.
Infection of a breeding stallion can result in temporary subfertility for up to 8 weeks. After acute infection, stallion fertility recovers but the stallion can remain chronically infected. Duration of virus persistence varies from several months to years. During the carrier state, the stallion harbors the virus in the accessory sex glands and shed virus constantly in his semen. Venereal transmission rates can be as high as 100%. Although some carrier stallions can spontaneously eliminate the virus, carrier stallions remain as the main reservoir of EAV in a breeding farm.
Direct economic losses to the
breeding operation result from abortions, disease or death of foals,
decreased commercial value of carrier stallions and their semen,
reduced demand to breed to carrier stallions, denied export markets
to carrier stallions and their semen, reduced export markets for
horses positive for serum antibodies against the virus.
How can I protect my farm against EVA?
Specific guidelines to control the EAV have been published in a document called “Equine Viral Arteritis-Uniform Methods and Rules”. The following is a summary of the guidelines proposed (Fig.1 and 2):
In areas or breeds with a high prevalence of EVA, vaccinate all colts under
270 days of age.
To date, there is only one vaccine available in the market (ARVAC«, Fort Dodge Animal Health). ARVAC is a modified-live virus vaccine. It is safe and effective and protection afforded by vaccination is considered to last several years. Immunization against EVA effectively reduces shedding of the virus by mares inseminated with infected semen, and prevents development of the carrier state in stallions.