Equine Respiratory Herpesvirus

Equine respiratory herpesvirusWhat is Viral Rhinopneumonitis, or “Rhino”?

Equine herpesvirus type 1 (EHV-1) and type 4 (EHV-4) are highly contagious pathogens responsible for a variety of symptoms in horses including mild to moderate respiratory disease, fever, poor appetite, and depression.  More serious manifestations of disease include neurological symptoms and spontaneous abortion by pregnant mares (EHV-1).  The disease process caused by these infectious agents is more commonly called Viral Rhinopneumonitis, or “Rhino”; true equine rhinovirus, closely related to the human rhinovirus that causes the common cold, inflicts similar yet less progressive upper respiratory disease than EHV.

What are the symptoms of Rhino?

Horses contracting Rhino will usually develop a serous (transparent) or mucopurulent (milky) nasal discharge as the disease becomes established 2 to 10 days post exposure.  They will typically have an increased temperature ( > 102 F) and will sometimes develop a cough.  Lymph nodes beneath and at the back of the jaw will become enlarged, and interest in food will wane.  Infections with EHV may then become complicated with neurological manifestations or spontaneous abortion.  Foals are more likely than adults to develop serious pneumonia.

Pregnant mares infected with Rhino may abort late in pregnancy and show little or no obvious clinical symptoms prior.  Aborted foals rarely survive.  EHV-1 has been shown to be responsible for sweeping outbreaks of abortions in groups of mares on common grounds or stabled together.

Neurological symptoms (equine herpesvirus myeloencephalopathy), caused by EHV-1, may include mild to significant hind-limb ataxia, or incoordination, and may present alongside urinary incontinence, and/or fecal retention.  Horses affected by this manifestation of the disease may begin to sit on their haunches (dog sitting position) and may eventually become completely unable to stand.

Secondary respiratory bacterial infections are common with Rhino and may further complicate the disease, increasing recovery time or decreasing the overall prognosis.

How is Rhino spread?

Rhino is easily spread by direct contact with infected horses, inhaling aerosolized respiratory secretions, and by the use of contaminated equipment, feed, or water.  Immunity after exposure lasts only a few months at best; therefore, disinfection and quarantine procedures are critical to stop the disease from spreading throughout a group.  Under ideal conditions, the virus may survive in the environment without a host for up to 14 days.  The Equine Herpes Virus may lie dormant in an infected horse and cause illness only after a period of stress or coincidental disease.  This is called a latent infection.

How is Rhino treated?

There are currently no antiviral drugs known to specifically treat equine herpes type 1 and type 4 infections.  The treatment for Rhino is mainly supportive and is targeted at alleviating symptoms and reducing stress which may further compromise the animal’s immune system.  Broad-spectrum antibiotics with good respiratory system perfusion are often prescribed prophylactically and in the case of secondary infections.  Non-steroidal anti-inflammatory drugs (NSAIDs) are sometimes used to help reduce fever and respiratory tract swelling, and bronchodilators may help to relieve respiratory inflammation and breathing distress.

When horses refuse to eat and drink, they become susceptible to the systemic effects of dehydration.  An electrolyte-fluid replacement solution may be given orally; or for more advanced cases, it may be administered intravenously to reduce stress and improve the outcome.

The horse affected by EHV requires rest and recovery time, and should never be worked or ridden until a full recovery is seen.

Mares who abort usually require no specific treatment unless symptomatic or if injury has occurred during parturition.  Still-born foals should be packaged in heavy plastic, refrigerated (not frozen) if possible, and delivered to the veterinarian or diagnostic laboratory as soon as possible for examination and a confirmation of EHV.  Improper care and disposal of the fetus may result in the spread of the disease to other horses.  Consult a veterinarian about when the mare can again be bred safely.

If the horse is persistently recumbent and will not / is unable to rise, you should keep its bedding clean at all times of waste, and contact a veterinarian for guidance.

How can I prevent my horse from getting Rhino?

Vaccination for type 1 and type 4 EHV is available.  Unfortunately, it offers only short immunity (2 to 3 months) from the abortive form, 6 months for the respiratory form, and no protection from the neurological form of the disease.  Nevertheless, it is recommended for healthy horses in groups where an individual has acquired the disease or has been exposed to Rhino (especially horses <5 years old).  Consult your veterinarian about vaccinating pregnant mares.

Thorough sanitation procedures of stalls and equipment, and quarantine of EHV infected (or suspected) horses is the best method to prevent the spread of Viral Rhinopneumonitis.  Any food, water, bedding, etc exposed to an infected horse should be disposed of, and all contaminated surfaces should be cleaned with disinfectant and rinsed with clean water.  If you have any questions about Rhino, vaccination protocols, or suspect your horse may be at risk, you should contact your veterinarian as soon as possible.

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