Herpes Virus in Horses
The herpes virus is a large family of viruses. Most mammalian species are susceptible to at least one type of herpes virus. Fortunately, this virus is very species-specific, meaning that humans do not catch equine herpes virus, and vise versa. There are five known subtypes in horses, but Equine Herpes Virus-1 (EHV-1) and EHV-4 are the two severest forms of the virus. EHV-3 is another type of major herpes virus, although it is normally associated with coital exanthema, a venereal disease that can be transmitted to horses.
The different classifications of equine herpes virus affect different systems; one affects the reproductive and neurological systems, whereas another causes respiratory issues. The virus type will also determine the symptoms the horse displays.
The incubation period for the virus depends on the subtype affecting the horse, but it is generally 4 to 10 days, after which the following symptoms may be seen:
- Nasal discharge
- Enlarged lymph nodes
- Decreased fitness performance
- Weakness in hind legs
- Strange gait
Neurological issues may occur, such as paralysis or uncoordinated body movements (ataxia), even seizures, the inability to stand up, and death. This is usually in cases of EHV-1. EHV-1 can also cause abortions in pregnant mares.
Equine herpes virus is highly contagious and spreads from horse to horse rapidly through inhalation of respiratory secretions, as well as direct contact. If strict quarantine is not followed, it can be carried on a person from one horse to another. Equine herpes virus is everywhere in the U.S. and there tend to be severe outbreaks in a portion of the horse population about every year, usually affiliated with stables or shows that have a high volume of horses traveling through.
A veterinarian can make a presumptive diagnosis of the equine herpes virus by the clinical signs the horse is presenting, especially if more than one horse at a barn has the same clinical signs. Viral isolation can be done on nasal swabs from suspect horses.
Since the infective agent is a virus, there is no cure. Only supportive care will help with the recovery of the horse. Herpes viruses have the ability to remain dormant in the horse's body and re-emerge at any time (especially when the horse is stressed). In this way, the disease can easily be spread. When an outbreak occurs, strict and prompt issuance of quarantine procedures will help contain the disease.
However there are medications, such as antibiotics, that can help with the secondary infections that can occur while the horse’s immune system is trying to fight off the viral infection. Anti-inflammatory drugs may be administered to help keep the horse comfortable and encourage the horse to remain eating and drinking.
Living and Management
It is imperative that a horse infected with the equine herpes virus be isolated from other horses to prevent the spread of the disease.
There are vaccines that can give horses immunity against the herpes virus. These vaccines must be administered on a regular basis, usually every year, or sometimes every six months if the horse is at high risk for contracting the disease. There is even a vaccine that can guard against abortions in pregnant mares, a common symptom in certain subtypes of the virus. Consult your veterinarian to learn more about these vaccines and to see if it is of use for your horse.