Equine Viral Arteritis

By Rebecca Bott,

SDSU Extension Equine Specialist

Introduction

Equine viral arteritis (EVA) is a viral infection of horses caused by the equine arteritis virus. EVA leads to respiratory illness, inflammation, bleeding, and abortion in pregnant mares, creating significant economic losses to the equine industry. The disease is caused by an enveloped RNA virus, which infects equine species. The virus is environmentally sensitive, meaning that it is generally not able to persist outside of the horse, though it can persist longer in a cold environment.

Transmission

EVA is spread by: aerosolized respiratory droplets, sexual intercourse, artificial insemination with infected sperm, or by people and equipment that can transfer virus from infected to non-infected horses. Rare cases of transmission by contact with feces or urine have been reported but not substantiated, likely due to the environmental sensitivity of the virus.

This viral pathogen can cause rapid illness or can persist for a long period of time. Horses of all types and some other equine species can be infected by EVA and show signs of this disease. While mortality in younger equids can be an issue, most adult horses will recover completely, though stallions may become asymptomatic carriers, shedding the virus in semen for months post-recovery. In addition, a horse that does not show any signs of infection can shed the EVA virus in the latent period prior to showing symptoms.

Implications of EVA infection

EVA is present in horse populations around the world and is a common cause of economic loss in the equine breeding industry. Due to this, many international restrictions have been placed on the transport of semen from horses that test positive to EVA. While vaccination is available, careful documentation of seronegativity (no EVA-specific antibodies) prior to it is important, as they will test seropositive for EVA post-vaccination despite being free of the disease. Mares infected with EVA while pregnant have a greater likelihood of spontaneous abortion, and foals born to an infected mare that can still spread the virus, are at risk for contracting the disease.

Clinical Signs

Signs of EVA can vary greatly, and in some instances, there are no clinical signs. In other cases, symptoms can range from depression, decreased appetite, and leukopenia (low white blood cell count) to swelling, severe respiratory distress, and abortion (Del Piero, 2000). Natural outbreaks of the disease are characterized by abortion in pregnant mares, severe respiratory disease in newborn foals, and persistent infection in stallions. Abortion in mares usually occurs between 3 and 10 months of gestation and is not preceded by any other clinical signs. Abortion rates in outbreaks can range from 10-50% and the mare can be infected by either natural or artificial insemination. The variation in signs between horses is attributed to age, physical condition, environment, and viral dose. The incubation time for the EVA virus is 3-14 days. Since the virus can be transmitted in many ways including respiratory, venereal, in utero, and through contaminated tack or equipment, early detection and control are very important.

Diagnosis, Treatment, and Prevention

EVA is a manageable disease with many control and prevention strategies. Diagnosis is based on laboratory tests since the clinical signs of EVA overlap with many other equine diseases, including equine herpesvirus and African Horse Sickness. Diagnosis can be based on virus isolation or identification of viral particles through lab testing. If a horse is diagnosed as having EVA it is important to eliminate both direct and indirect contact with susceptible horses. Most horses will clear the infection on their own within 2-3 weeks however, in severe cases, a veterinarian can provide treatment.