Equine Herpesvirus (EHV)

Equine herpesviruses are DNA viruses that are found in most horses all over the world. Almost all horses have been infected with the viruses and have most of the times no serious side effects. It is currently unknown what causes some infected horses to develop the serious neurological forms associated with EHV1 that may be fatal.

EHV is a common DNA virus that occurs in horse populations worldwide. The two most common species are EHV-1, which causes abortion, respiratory disease and neurologic disease; and EHV-4, which usually causes respiratory disease only but can occasionally cause abortion and rarely neurological disease.

**EHV stands for equine herpes virus.  This is a family of viruses which are named by numbers such as EHV 1, 2, 3, 4 and 5.  There are more viruses in this family, but EHV 1, 3, and 4 pose the most serious health risks for domestic horses.**

* EHV-1: Can cause four manifestations of disease in horses, including neurological form, respiratory disease, abortion and neonatal death.
* EHV-3: Causes a venereal disease called coital exanthema that affects the external genitalia but has not been shown to affect fertility.
* EHV-4: Causes a nonfatal upper respiratory tract disease in foals and is uncommonly associated with abortion and rarely with neurological disease.

**How does EHV spread?**

EHV-1 is contagious and spread by direct horse-to-horse contact via the respiratory tract through nasal secretions. It is important to know that this virus can also be spread indirectly through contact with physical objects that are contaminated with the virus.

**What are some of the signs of EHV?**

After infection, the incubation period may be as short as 24 hours, is typically 4-6 days, but can be longer. EHV-1 typically causes a biphasic (two-phase) fever peaking on day 1 or 2 and again on day 6 or 7. With respiratory infections there is often serous or mucoid nasal and ocular discharge, but not a lot of coughing. There may be some persistent enlargement of submandibular lymph nodes (lymph nodes under the jaw). With the neurologic form, there are typically minimal respiratory signs, fever (rectal temperature greater than 101.5 degrees F) being the only warning sign. Neurologic disease appears suddenly and is usually rapidly progressing, reaching its peak intensity within 24 to 48 hours from onset of initial neurologic signs. It is also pertinent to mention that horses may develop EHM even without any preceding fever and/or respiratory signs. Clinical signs of the neurologic disease may include:

* Incoordination
* Hind limb weakness
* Loss of tail tone
* Lethargy
* Urine dribbling
* Head tilt
* Leaning against a fence or wall to maintain balance
* Inability to rise

**If your horse develops fever, respiratory signs or neurological signs, immediately notify your veterinarian and do not move the horse or horses in the immediate area. Alert those who have horses in the adjacent area to cease all movement of horses in and out of the facility until a diagnosis is confirmed by testing and a targeted plan for the control of spread of disease is developed in consultation with your veterinarian.**

For horses that may have been exposed to the infectious agents and therefore at risk for disease, there are some steps to take to minimize the risk of spread of the disease in their home facility. Even if these horses are returning home from events at which no disease was reported, and even if these horses appear healthy, precautions are needed as these horses could bring it home and spread it at their home farm – this is the classic way this disease spreads:

* These horses should be isolated from any other horses when they return to their home facility. Isolation requires housing them away from other horses (i.e. the horse should be stabled in a barn, turn out shed, paddock or another area where there is no contact with other horses), using different dedicated equipment to feed, clean and work with them than is used with any other horses, and rigorous hygiene procedures for horse handlers (hand hygiene, wearing separate clothes when contacting the horses, etc.). Please discuss this with your veterinarian.
* We strongly advise owners to call their veterinarians to discuss how long to keep the horses isolated at home, but even if they don't develop fevers this should be at least 21 days.
* These horses should have their temperature taken twice a day and recorded, as elevation in body temperature is typically the first and most common sign of infection. Horses with elevated temperatures (101.5 degrees F or greater) should have nasal swabs and blood drawn  by your veterinarian.
* If a horse develops a fever and is found to be shedding EHV-1 then the level of risk to other horses on the premises increases significantly. Affected farms should work closely with their veterinarian to develop a targeted management plan for that situation, if it develops.