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Oklahoma State University
Center for Veterinary Health Sciences

Healthy Animals - Healthy People

Equine Herpesvirus

Equine Herpesvirus (EHV) is a highly contagious virus that can spread quickly from horse to horse directly through nasal secretions or by sharing items such as buckets, tack, stalls or trailers. EHV can cause abortion, neurologic disease, respiratory illness and death. horse and foal

EHV-1 and EHV-4 are the two forms of greatest concern in performance horses. Both can cause respiratory disease, but EHV-1 can also cause abortions or a neurologic syndrome. Horses may be infected with EHV, yet appear clinically normal (so-called “latent” infections).  However, when the horse is stressed, such as during performance conditions, the virus can reactivate and be shed. Owners are encouraged to work with their veterinarians to maintain a current vaccination programs which should include EHV-1 and EHV-4.

Infection with EHV-1 may cause fever in excess of 102°F, nasal discharge, incoordination, hind limb weakness, urine dribbling and a flaccid tail. Contact your veterinarian immediately to collect samples for diagnostic testing by Polymerase Chain Reaction (PCR).

Preferred samples for EHV-1 PCR include:

  1. EDTA whole blood (5 mL minimum)
  2. Nasal swabs in red-topped blood tube with 1 ml saline
    Note:  Plastic (non-wooden) shaft and synthetic (e.g. Dacron) swabs are recommended. Collection is performed by swabbing nasal mucosa 6-18” into the external nares.

OADDL can assist with diagnostic testing for pathogens that mimic EHV-1 including: Equine Protozoal Myeloencephalitis (EPM), West Nile Virus (WNV), Eastern Equine Encephalitis (EEE), Equine Influenza and Rabies. See our website for a complete list of testing options.

In terms of public safety, the virus is not harmful to humans but people can transport it on their clothing or skin and subsequently infect healthy horses.