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Medical Index
First Posted: June 9, 2007
Mar 20, 2011

Equine Rhinopneumonitis Virus (EHV1)

Update: "As part of the Maryland Department of Agriculture's (MDA) ongoing work to expedite the identification and control of disease, the College Park Animal Health Diagnostic Laboratory is now able to perform polymerase chain reaction (PCR) testing for equine herpesvirus-1 (EHV-1), the causal agent of a common equine respiratory disease that's often called "rhino" (short for rhinopneumonitis). This test includes the capability to detect the neuropathic strain of the virus that causes neurologic herpes (equine herpes myeloencephalopathy), a form of EHV-1 that is often fatal."

UC Davis has had this availability. Equine Herpes Virus EHV-1

Equine rhinopneumonitis virus (EHV1 or equine abortion virus) is a highly infectious disease that usually affects the respiratory system. Occasionally, the virus may also cause neurological disease. Transmission likely occurs by inhaling infected droplets or ingesting material contaminated by nasal discharges or aborted fetuses. To date, there is no effective treatment for EHV1. Clinical symptoms include a fever of 101.5 or higher, or one or more degrees above the horse’s normal rectal temperature, difficulty urinating, depression, and stumbling or weakness in the hind limbs. Supportive therapy is often successful in treating these cases. In severe cases, horses will be unable to stand; these cases have a very poor prognosis.

EHV1 poses no known health threats to humans. The disease first appeared in the United States in 2001, and Virginia had its first case in 2002. Several types of vaccine are available and horse owners should work with their veterinarian to choose a vaccine and a vaccination schedule to protect their animals.

The following is an excellent article that will give lots of information about this EHV-1 Virus. It is a direct quote from the following web site: Country View Vets

"Frequently Asked Questions: Equine Herpes Virus-1

February 17, 2006

J. Liv Sandberg
UW Madison
Equine Extension Specialist Dr. Larry Bauman
UW-River Falls
Extension Veterinarian

What is Equine Herpes Virus-1 (EHV-1)?

Equine Herpes Virus-1 (EHV-1) is a contagious viral disease of horses that can cause respiratory disease, abortion and occasionally neurologic disease.

Is there another name for Equine Herpes Virus?

Rhinopneumonitis or 'rhino.' It is a herpes virus that is common among horses.

How is the EHV-1 disease spread?

Aerosol (airborne) and fomites (feed, clothing, boots, hands, etc.)

Can EHV-1 spread to humans?

No, but people can transport the virus on their clothes, boots, etc.

Can EHV-1 spread to other species of animals?


What are the clinical signs or symptoms seen with EHV-1?

Respiratory disease, abortion and occasionally neurologic disease (lack of coordination, inability to stand, etc.)

Are these clinical signs similar to any other equine diseases we have in our horse population?

Yes. Equine Influenza Virus may cause respiratory disease. Equine Viral Arteritis may cause abortions, and West Nile Virus may cause neurologic disease.

If my horse has some of the above clinical signs, will I be able to tell which disease he/she may have contracted? No

Is there a vaccine available to help prevent the spread of EHV-1?

Yes, but it doesn't directly protect against the neurological form of the disease cause by EHV-1.

My horse is up to date on its vaccinations, including EHV-1. Can my horse still be at risk of contracting the disease?

It's possible, but horses that have not been vaccinated are at a much higher risk.

Will EHV-1 affect all of my horses or are some of my horses at more of a risk of contracting the disease?

Young, old, weak, high exposure, immune challenged, and stressed horses are more likely to get sick.

How long will it take for my horse to show clinical signs of the disease after he/she has been exposed to the disease?

Horses can shed the EHV-1 from the onset of clinical signs until 1-2 weeks after the clinical signs are gone. A 21 day quarantine period following the disease is recommended.

How do you test for EHV-1?

A blood test is available. Test results will usually take 3-7 days to be completed.

I only have one horse. Do I have to be concerned about my horse contracting EHV-1?

Yes. While the virus is spread more readily from horse to horse via infected droplets in the air, on facility surfaces, fences, buckets and a common water source, etc., there is also the possibility of spreading the disease as a result of droplets being carried on clothes, boots, jackets, etc.

As a horse owner, what should I do to prevent the potential spread of the EHV-1?

Horse owners do not need to panic, but they should following appropriate bio-security measures such as those listed at the end of this article.

What about vaccinations?

There are vaccines available to protect horses against EHV-1. Since EHV-1 is a common virus in horses, it is recommended that all horses be vaccinated at least once a year. For horses congregating at shows and competitions, more frequent vaccinations may be recommended. Consult your local veterinarian to discuss the risk potential and vaccination recommendations for your horse.

What disinfectant(s) are best to use for cleaning my facilities?

Generic disinfectants such as bleach, chlorhexidine, quaternary ammonias and others are effective in killing the EHV-1 virus.

I have only a couple horses. Do I have top follow the preventative measures?


I have an active and full barn of horses that frequently travel through out the state and out of state. What preventative measures should I be practicing to minimize the risk of spreading EHV-1?

See the recommendations for isolation and bio-security measures listed at the end of this article. Prior to traveling with your horses, check on the current health status of horses at your final destination.

My farrier is scheduled to come and work on my horses' feet? Should I still have him/her come or cancel the visit?

Have them come unless there is a high level of disease in surrounding barns. Practice the appropriate bio-security measures, regardless of area farm status. If the work is not needed immediately and there is a high level of disease in the area, rescheduling to a later date may be the wisest decision.

If I have new horses coming to barn, what should I do before they arrive and after they arrive? Your horses should be up to date with their EHV-1 vaccinations. Quarantine/separate the new arrivals for 3 weeks.

We like to trailer to another barn and ride. Can we still do this?

While your barn may not be under quarantine, the potential to spread the disease is minimized if horses are not exposed to additional sources of contamination. It is important to still enjoy spending time with your horse. However, by taking the initiative to keep unnecessary travel to a minimum, the potential for spreading EHV-1 will be reduced.

How long should we not travel from barn to barn during an EHV-1 outbreak?

No definitive answer can be given as the length of time is dependent on the success of minimizing the EHV-1 outbreak.


Immediately isolate any sick horses in the barn. Isolate any new horses or horses returning from another location or show for at least 7 days. If horses were exposed to sick horses while away, take further precautions and isolate horses for at least 21 days.

As the EHV-1 virus can be spread on clothing, all human traffic (clients taking lessons, borders, visitors, trainers, blacksmiths, veterinarians) should be vigilant about disinfecting boots before entering and leaving a different barn, wearing clothing (ex: jeans, jacket) that have not been worn in another horse barn, and washing hands before handling the horses. At the entrance of the barn, provide a tub of disinfectant and instructions for all to use. Bleach water (1 part bleach to 10 parts water) may be used and should be changed daily. Phenolic based disinfectants will be less effective if a lot of feces and other organic material collects in the tub, so clean out and replace the disinfectant solution regularly.

Do not rotate horses from stall to stall. Don't share feed tubs or water buckets among the horses. Inserting a water hose previously submerged in a bucket of a sick horse can potentially spread a virus.

Disinfect any areas of the barn that may have been exposed to a sick horse or a horse that is of question, including disposal of all bedding and hay/feed. The above disinfectants can be used. If the stall is needed, allow disinfectant to dry before placing a horse in the same location.

Always work with the sick horses(s) last in your chore routine and exit the barn without completing any other tasks.

When possible, separate horses into small groups to minimize the number of horses that may be exposed if you do have an infected horse."

More information can be obtained Equine Herpes Virus 1 (EHV-1)

New Information on Equine Vaccines


Neurologic EHV-1

"The final neurologic disease discussed by Reed is that of equine herpesvirus-1 (EHV-1), which can cause respiratory disease (rhinopneumonitis), abortion, severe neonatal disease, and it uncommonly takes a neurologic form that is acute and progressive. EHV-4 also can cause neurologic disease.

EHV-1 can be a mutated or nonmutated strain that induces symmetric ataxia with ascending (starting at the rear and moving forward) paralysis beginning with urinary incontinence, poor tail and anal tone, and incoordination in the rear limbs. The virus attacks the blood vascular supply of nerves. An affected horse might also show facial nerve signs, head tilt, and nystagmus (involuntary, rapid eye movement), as well as dementia and other cerebral signs.

The 2003 EHV-1 neurologic outbreak in Ohio demonstrated the rampant communicability of this disease. Of 137 horses in a barn, 117 had fever, and 46 of those showed neurologic signs, 14 of which died. Fever, cough, and nasal discharge preceded ataxia or recumbency by about five days. All horses had been previously immunized with rhinopneumonitis vaccines, which afforded no protection. Reed said the virus multiplies rapidly once the horse is exposed, thus increasing its contagion level.

The EHV-1 mutated strain also magnified the degree of virulence for longer. In 132 Thoroughbred broodmares, George Allen, PhD, found that while 46% harbored the wild-type strain, 8% harbored the mutant EHV-1 strain in their submandibular lymph nodes; the mutant strain comprised 18% of the total latent viral reservoir (the horses that weren't showing signs of illness). This high proportion of neurologic herpesvirus necessitates implementing measures to control its spread.

Veterinarians have learned from neurologic EHV-1 outbreaks that they must enforce diligent biosecurity measures in suspected outbreaks to limit the numbers of horses exposed. Horses older than 15 years of age and especially older than 20 seemed to be at the highest risk of infection; these are horses with less competent cell--ediated immunity. Stress plays a huge role in onset of clinical signs.

Reed believes that future goals for managing neurologic disease in horses should be to decrease mortality and improve outcomes. This would be best achieved by developing improved diagnostic tools to facilitate early diagnosis and treatment along with providing the ability to identify unknown disorders."

AAEP 2008 Milne Lecture: Neurology is Not a Euphemism for Necropsy

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