Equine Herpesvirus: Protecting Horses From a Serious Threat

Equine herpesvirus is a widespread pathogen causing respiratory disease, abortion, and potentially fatal neurological disease in horses requiring stringent biosecurity.

Key Facts

Equine herpesvirus type 1 causes respiratory disease, abortion storms, and equine herpesvirus myeloencephalopathy
EHV-4 primarily causes respiratory disease and occasional abortions but rarely causes neurological disease
Most adult horses carry latent EHV-1 infection that can reactivate under stress, making complete eradication impossible
Equine herpesvirus myeloencephalopathy causes rapid-onset ataxia, urinary incontinence, and sometimes complete hindlimb paralysis
The neurotropic strain of EHV-1 is associated with more severe neurological outbreaks, though any strain can cause EHM
Transmission occurs through direct contact, respiratory secretions, and aborted fetuses which shed virus heavily
Vaccination reduces respiratory and abortion risk but current vaccines do not reliably prevent neurological disease
Biosecurity during events and transport is critical to prevent spread; horses should not be mixed from different premises casually

Welfare Considerations

EHV disease causes significant suffering across multiple clinical presentations. Respiratory disease causes fever, nasal discharge, and fatigue in affected horses. Abortion is traumatic for mares who have carried their foal for months, and the physiological toll of late-term abortion is substantial. Neurological EHM is perhaps the most distressing presentation, causing horses to be unable to walk, stand, or urinate without assistance, with many requiring intensive hospitalization and some never recovering. Outbreaks can devastate competition yards and breeding operations, affecting many horses simultaneously. Prevention through vaccination, biosecurity awareness, and testing of new arrivals is essential for protecting horses from this widespread and serious pathogen.

What You Can Do

Vaccinate horses against EHV-1 and EHV-4 according to your veterinarian recommendations, especially broodmares
Implement quarantine protocols for all new horses arriving at your property for at least 21 days
Isolate any horse showing fever or respiratory signs from the general population immediately
Follow equine event organizers biosecurity requirements and report sick horses promptly
Learn the early neurological signs of EHM including hind leg weakness and tail head paralysis to enable rapid response