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What it Does: The most common of five types of equine herpesvirus, EHV-1 typically causes the respiratory infection known as rhinopneumonitis. It can also infect the placental walls of pregnant mares, causing abortion. In rare cases, it attacks the central nervous system, producing signs ranging from incoordination to paralysis, sometimes with fatal consequences. This neurologic form is technically known as equine herpesvirus myeloencephalitis and is often referred to as “neuro” EHV-1.
How it Spreads:
Highly contagious, EHV-1 is passed through the nasal secretions of an infected and clinically ill horse. The virus can spread through aerosolized secretions from infected coughing horses, by direct nose-to-nose contact or via shared water buckets, tack or even the clothes and hands of human caretakers.
A horse can also be a latent carrier of EHV-1, meaning that the virus is in his system and he may shed it, but he is not ill nor is he likely to infect other horses. Stress, such as competition or travel, may cause the virus to reactivate, but this has not been scientifically documented.
Signs of Infection:
The incubation period of EHV-1 is two to seven days. The initial signs of the neurologic form are nonspecific, but a horse may develop a fever in excess of 102 degrees Fahrenheit, and the normally pale pink mucous membranes that line his body passages may turn red.
One to seven days after a fever appears, the horse may experience:
- weakness, particularly in the hind limbs
- gait abnormalities
- difficulty defecating and/or urinating
- trouble rising or standing.
In extreme cases, the horse may slip into a coma-like state.
Treatment: Supportive care, including nursing, anti-inflammatory drugs and DMSO, is the only treatment. Researchers are investigating the efficacy of antiviral drugs to treat cases in their very early stages.
Prevention: Vaccines against EHV-1 are available but none are labeled for protection against the neurologic form of the disease. By far the best way to protect your horse from EHV-1 is to limit his contact with horses who may have the disease or whose health status is unknown to you.
- Keep your horses from coming in direct contact with unfamiliar animals. Don’t even allow them to rub noses. Don’t share tack, grooming tools or water buckets. Don’t put one horse into an uncleaned stall that recently housed another, particularly at public events like shows.
- After handling one horse, wash your hands or use a hand disinfectant before moving on to another, particularly if you aren’t familiar with the individual’s health status.
- Abide by all quarantines, which typically remain in place for three weeks after the last case is diagnosed. Some sites are quarantined as a precaution when a case of neurologic EHV-1 is suspected. If it’s not confirmed, the quarantine may be lifted immediately. It is safe to return to a site that is no longer quarantined.
This fact sheet originally appeared in the April 2007 issue of EQUUS magazine.