Equine Viral Arteritis

Resources:

Understanding Equine Viral Arteritis
American Association of Equine Practitioners

The Rationale For Greater National Control of this Disease
Dr. Peter J. Timoney, Gluck Equine Research Center

Guidelines for Breeding to an EAV Shedding Stallion Contact: American Horse Council

EVA Video
Available from USDA at no charge from 
Dr. Timothy R. Cordes
Senior Staff Veterinarian, Equine Diseases, USDA, APHIS, VS

Contacts:
United States Department of Agriculture:
Dr. Timothy R. Cordes
Senior Staff Veterinarian, Equine Diseases, USDA, APHIS, VS

Equine Arteritis Virus  (EAV) is a viral infection of horses that can affect both the respiratory and reproductive systems. The virus is the cause of the disease called Equine Viral Arteritis (EVA). The virus is present in horse populations in many countries throughout the world and as high as 80% of adult horses of some European breeds and a similar percentage of adult Standardbreds in the US are seropositive for antibodies to the virus. 

The most common routes of infection are via the respiratory tract and venereally, by stallions that shed the virus in their semen. One can safely breed a mare to a stallion that sheds by adopting a few simple precautions. See Guidelines for Breeding to a EAV Shedding Stallion.

Clinical response of horses exposed to EAV can range from an absence of symptoms to a disease of variable severity. The vast majority of infected horses do not show symptoms of disease.

The acute phase of the infection occurs 3 - 14 days after exposure to the virus for the first time. Horses may have fever, depression, loss of appetite, discharges from nostrils and eyes, filling of the legs and other dependent parts of the body. 

Unvaccinated or previous uninfected mares may abort or deliver weak foals which invariably die within a few days to weeks. Abortion rates can range from less than 10 percent to as high as 50 to 70% in susceptible mares. 

Mature stallions may become persistently infected and shed the virus in their semen for many years, transmitting the infection to susceptible mares through live breeding, fresh cooled or frozen semen.  (Persistent infection is not established in mares or geldings.) This carrier state can occur in as high as 30 to 60% if stallions naturally infected with EAV and these infected stallions play a major role in the transmission and perpetuation of the virus. Vaccination of sexually immature colts and seronegative stallions can prevent the establishment of the carrier state.