Equine Viral Arteritis: Welfare and Biosecurity Guide

Key Facts

• EVA is caused by equine arteritis virus (EAV), spread by respiratory secretions and semen
• Most infected horses show mild or no signs, but mares can abort 10-33 days after infection
• Stallions can become persistent shedders, excreting virus in semen for months to years
• Vaccination of stallions before first exposure prevents persistent viral shedding
• International horse trade regulations require testing and sometimes vaccination before movement

Welfare Considerations

EVA creates welfare impacts primarily through abortion in infected pregnant mares and the regulatory burden imposed on horses that test positive. Late-term abortions are painful and exhausting for mares and represent significant reproductive losses. Stallions that become persistent shedders face movement restrictions and breeding bans that are stressful through repeated testing and isolation. Prevention through vaccination of colts before sexual maturity is highly effective at preventing persistent shedding. Breeding and event management requiring isolation of positive or exposed horses causes short-term welfare stress through separation from herd companions.

What You Can Do

• Vaccinate colts before sexual maturity to prevent persistent EAV shedding — it cannot be reversed once established
• Test stallions for EAV serostatus before first use at stud
• Isolate mares bred to seropositive stallions for 28 days post-breeding to prevent herd transmission
• Follow import and export testing requirements diligently to prevent international spread
• Consult your vet about vaccination status for mares before attending competitions with high horse density