Equine herpesviruses are very common in horses. While they most commonly cause mild respiratory signs, sometimes they can cause neurologic disease (herpesvirus encephalitis). Clinical signs of herpesvirus encephalitis include:
- Fever (> 101°F [38.6°C])
- Incoordination of the hind (and occasionally fore) limbs
- Leaning against a wall or other surface, ataxia (wobbly gait)
- Abnormal urination/urine dribbling
- Recumbency (inability to rise)
- Abnormal mentation, seizures, or cranial nerve deficits
The highest risk of disease spread is via direct contact with an infected horse, although airborne exposure (via coughing or snorting) can also occur. The virus can live in the environment for several weeks, so it can be spread by contaminated footwear or clothing, shared equipment or tack, or surfaces such as stalls and wash racks. Onset of clinical signs after exposure may be as little as 24 hours but is usually 4-6 days or longer.
Virus is typically shed for 7-10 days after the resolution of clinical signs but can be longer. Neurological deficits may persist even after the horse has recovered from the disease. Equine herpesvirus cannot be spread to humans or most other species.
Testing to confirm herpesvirus is done with a nasal swab +/- blood. Test results are generally reported within 48 hours after sample submission.
Please contact your veterinarian if your horse develops a fever, respiratory signs, or any of the neurologic signs described above. Affected horses should be quarantined from the general population for 28 days after resolution of fever. Horses that have been in contact with affected horses may also need to be quarantined for 14-28 days, depending on the nature of the contact, results of testing, and recommendations by the state veterinarian.
For more information, see the American Association of Equine Practitioners (AAEP) Infectious Disease Guidelines for Equine Herpesvirus: https://aaep.org/wp-content/uploads/2024/02/EHV1-4-guidelines-2021.pdf
