Equine Viral Arteritis

Equine viral arteritis (EVA) is caused by an RNA togavirus and produces clinical signs of respiratory disease, vasculitis, and abortion. Transmission is via respiratory and venereal routes. Subclinical infections predominate; however, occasional outbreaks are reported and can result in substantial economic loss.  The incubation period is 2–14 days with clinical signs of disease persisting for 2–9 days. Clinical signs of EVA infection in adult horses include:

• fever, anorexia, depression

• serous nasal discharge, cough

• conjunctivitis, lacrimation

• edema (palpebral, scrotal, periorbital)

• urticaria

• abortion (2–10 months gestation), transient subfertility in stallions

Neonatal foals infected with EVA develop a severe interstitial pneumonia and mortality is high. Diagnosis of EVA can be achieved through viral isolation, RT-PCR, or serology depending on fluid or tissue sample provided. For nasopharyngeal swabs or washes, RT-PCR is frequently used to detect viral nucleic acids or antigens. Treatment consists of supportive care and NSAIDs for fever and inflammation. A carrier state occurs in ~10–70% of stallions after natural infection and is primarily responsible for persistence of the virus in the horse population via infectious seminal fluids. Vaccination (modified-live virus) is targeted toward prevention of venereal spread of EVA in breeding animals as opposed to prevention of respiratory disease. See also the Equine Viral Arteritis chapter.