EHV 1 Guide: Horse Herpes Causes, Symptoms, Recovery

EHV 1 is one type of equine herpes virus that is common in horses around the world. This potentially serious disease comes in three forms that may cause respiratory disease, abortions, and neurologic disease. Most horse owners are familiar with EHV 1 due to several outbreaks that have led to quarantines. Unfortunately, the equine herpes virus is very contagious and may be spread horse-to-horse. It can also remain dormant for some time.


What Is EHV 1?

Equine herpesvirus 1 is a common virus in horses. Most horses are exposed to this virus early in life and have a lifelong latent infection with no side effects. EHV 1 is one of five types of equine herpesviruses. Along with EHV 5, it’s known for having the greatest risk of serious disease in horses.

The initial signs of an active EHV 1 infection are often nonspecific. Many horses develop a fever of at least 102 degrees, which may be the only observable symptom. Respiratory symptoms, which are most common in young horses, may come in the form of a cough, nasal discharge, and a red mucous membrane. The most serious form of the infection causes neurological disease. Horses with this complication become weak, uncoordinated, and have difficulty standing and walking. Many also have trouble defecating and urinating. Abortion is another common side effect of infection that may affect pregnant mares.

Equine communities should understand signs of the virus as it typically becomes active when a horse is stressed or ill. Once active, the virus can spread to other horses. There have been numerous outbreaks of EHV 1 in the United States in recent years. The disease first rose to worldwide prominence in 2011 after an outbreak involving the National Cutting Horse Association Western National Championships in Utah. This 2-month outbreak led to 90 confirmed cases in 10 states and the deaths of 13 horses.

What Causes EHV 1?

Most horses are exposed to EHV 1 when they are young and carry the dormant disease. This contagious disease can be spread through horse-to-horse contact of nasal secretions and indirectly by touching contaminated objects, including human hands or contaminated water or feed buckets. The virus is also known to be airborne and may survive up to 7 days on objects. Once exposed, horses become latent carriers but the virus can be reactivated when the horse is stressed, ill, or treated with high doses of corticosteroids.

Treatment Options Available for EHV 1

Treatment will always follow a proper diagnosis of equine herpesvirus based on clinical signs and virus isolation. A veterinarian may perform nasal swabs and collect blood samples to confirm a diagnosis.

There is no specific treatment available for EHV 1 and treatment options are limited with no guarantees. Veterinarian treatment is necessary to diagnose the condition and administer treatments. There are several treatments a veterinarian may administer to reduce symptoms and improve the chance that the horse will recover.

The most commonly recommended treatment approach is the use of IV fluids and anti-inflammatory drugs to reduce inflammation, pain, and fever. These may be combined with supportive care such as round-the-clock nursing and slings. A veterinarian will also monitor the horse throughout the treatment. The most important side effect to monitor is difficulty urinating, as the disease can potentially cause the bladder to rupture. Bladder catheterization may be necessary to help the bladder drain safely.

Some antiviral drugs like famciclovir and penciclovir have been used to treat EHV 1, but the use of these drugs in equids has not been studied sufficiently.

Horses with mild cases of the disease typically recover fully after a few weeks to a few months. Horses who develop neurologic disease have more variable recovery rates that depend on the severity of the symptoms. Horses who are recumbent have a poor prognosis.

Prevention of Horse Herpes

There are vaccines that may control EHV 1 but not prevent it. Vaccine use is also controversial. The inactivated vaccine is designed to protect against respiratory disease but the performance is variable and it will not work for all horses. A modified live vaccine can be used for healthy horses at least 3 months old. These vaccinations must be given in 6-month intervals, but different horses will need to be vaccinated at different times. Infection and clinical disease will still occur in horses that have been vaccinated.

Aside from vaccination, there are other steps that can prevent the spread of EHV 1. Horses that have been exposed to the virus should not come into contact with horses that are unexposed during travel or movement. Horses with active signs of disease should be isolated or quarantined for at least 21 days.

Because EHV 1 can be spread through contaminated items and contact with humans and horses, disinfection is essential. Individuals handling sick horses should take care to disinfect footwear and use gloves to reduce spreading the virus. Barns, buildings, and feeding receptacles should be routinely cleaned and disinfected. If an outbreak occurs, it’s important to reduce stress on horses as this can cause a latent infection to activate.


Many horses that develop an EHV 1 infection recover and live their lives normally, but the disease should still be taken seriously. Equine herpesvirus can spread easily from horse-to-horse without careful prevention and potentially lead to abortions, neurologic disease, and respiratory disease. Horse communities should take care to understand how to recognize symptoms of the disease to seek prompt medical treatment for infected horses.


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