Equine Herpesvirus: Outbreak Management and Horse Welfare

Equine herpesvirus (EHV) causes respiratory disease, abortion storms, and neurological disease (EHM) in horses, with outbreak management protocols having significant welfare implications for affected and exposed populations.

Key Facts

EHV-1 and EHV-4 are the most clinically significant strains; EHV-1 can cause neurological disease (equine herpesvirus myeloencephalopathy) in addition to respiratory and reproductive disease
EHM outbreaks are associated with competition horses and have caused significant fatalities at major equestrian events globally
The neurotropic mutation in EHV-1 (D752 neuropathogenic variant) correlates with higher EHM risk but neurological disease can occur with non-neuropathogenic strains
Shedding occurs from respiratory secretions; close horse-to-horse contact, shared equipment, and contaminated environments facilitate spread
Quarantine of exposed horses for 28 days following EHM diagnosis is the standard outbreak control measure
Vaccination reduces respiratory disease severity and abortion rates but does not reliably prevent neurological disease
EHM horses may experience blindness, inability to urinate, and progressive hindlimb ataxia before recumbency
Welfare-based euthanasia decisions for recumbent EHM horses must balance recovery potential against duration of suffering

Welfare Considerations

EHV outbreak management creates welfare tensions at multiple levels. Quarantine of exposed but clinically well horses prevents disease spread but causes social disruption, restricted movement, and psychological stress. Affected horses with EHM face significant suffering from neurological deterioration; supportive care including anti-inflammatory treatment, antiviral therapy (ganciclovir), and nursing care for recumbent horses requires intensive resources and expertise. The decision about when to proceed to euthanasia in recumbent EHM horses is among the most difficult in equine practice — recovery is possible but prolonged recumbency causes secondary welfare problems from pressure sores, aspiration, and muscle damage. Competition event outbreak responses must prioritize horse welfare over event completion.

What You Can Do

Maintain current EHV vaccination schedules for all horses at risk of competition exposure
Follow biosecurity protocols at competitions including avoiding nose-to-nose contact between unfamiliar horses
Report suspected respiratory illness in horses that have recently attended competitions promptly to your veterinarian
Support event organizer policies that prioritize horse health monitoring and rapid outbreak response over event scheduling
Familiarize yourself with EHM clinical signs including hindlimb ataxia, tail weakness, and inability to urinate