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Equine Herpesvirus 

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Equine herpesvirus (EHV), also known as equine rhinopneumonitis, is a family of

highly contagious viruses found in horses worldwide. Of the nine known

herpesviruses, EHV-1, EHV-3, and EHV-4 pose the highest disease risk to U.S. horses.

They do not pose a risk to people.
EHV-1 primarily causes upper respiratory disease and abortions/stillbirths in horses.

In some cases, it causes a neurological disease called equine herpes

myeloencephalopathy (EHM) that can be fatal. EHV-3 causes a venereal disease

called coital exanthema. EHV-4 primarily causes respiratory disease in foals and

abortion in mares but can also produce cases of EHM. EHV-infected horses that don't

develop EHM generally recover with no side effects.

What To Look For

Clinical signs of EHV may not be specific, and some horses may not show any signs

of illness. In clinically affected horses, look for:

Fever

Difficulty urinating

Nasal discharge and cough

Depression

Head tilt

Loss of tail tone

Stumbling or weakness in the hind limbs that progresses to all limbs

Down and unable to rise

Abortion in pregnant mares

How To Prevent This Disease

EHV-1 and EHV-4 are spread via nose-to-nose contact; contaminated equipment

(water and feed buckets, tack and grooming supplies, and shoes); and respiratory

secretions within stalls and stables. Aborted fetuses and afterbirth can also contain

these viruses. EHV-3 is spread through breeding or contaminated equipment used

for breeding. To prevent the disease:

Vaccinate your horses. Vaccines are available to prevent the forms of EHV

that cause respiratory illness and abortion. These vaccines reduce the severity

of symptoms and viral shedding. They also reduce the risk of abortions. These

vaccines are strongly recommended, especially in breeding operations. None of

the vaccines are effective against the neurologic form of the disease (EHM).
Isolate new or returning horses. Isolate new horses and horses returning to

the farm after an event for at least 21 days. Monitor them for signs of disease.

Keep pregnant mares with foals at their side in small groups away from new or

returning horses.

Always practice good hygiene and biosecurity. Regularly clean and

disinfect all water/feed buckets, mucking equipment, tack, and any other

equipment. Do not share or borrow tack or equipment at shows, events, or

boarding facilities.

How It Is Treated

In most cases, treatment consists of supportive care, which may include intravenous

fluids and anti-inflammatory medicines to reduce fever. In more severe neurologic

cases, treatment may include hospitalization with more intensive veterinary care.

Report Signs of Animal Disease

Producers or owners who suspect an animal disease should contact their

veterinarian to evaluate the animal or herd. Find an accredited veterinarian.

Animal health professionals (veterinarians; diagnostic laboratories; public health,

zoo, or wildlife personnel; and others) report diagnosed or suspected cases of

nationally listed reportable animal diseases to APHIS District Offices and to the State

animal health official as applicable under State reporting regulations. 

Controlling Equine Herpesvirus

Guidelines for State Animal Health Officials

The Equine Herpesvirus Myeloencephalopathy (EHM) Incident Guidelines for State

Animal Health Officials (815.11 KB) provide science- and field experience-based

disease control recommendations to consider during an EHM incident.

Recommended Sources for More Information

Equine Herpesvirus Resources (American Association of Equine Practitioners)
Equine Rhinopneumontis (Infection With Equid Herpesvirus-1 and -4) (World

Organisation for Animal Health)