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Equine Herpesvirus-1 Update

Do you ever wonder what the “Rhino” is in your horse’s “Flu/Rhino” shot? Chances are if your horse shows, travels or lives at a boarding farm, your veterinarian has recommended vaccinating your horse with this vaccine. The “Flu/Rhino” vaccine protects against two common equine respiratory diseases, Equine Herpesviruses (EHV-1 and 4) and Equine Influenza. Recent reports of Equine Herpesvirus-1 in Virginia make it a great time to review our understanding of this disease and the role of the Flu/Rhino vaccine.

The “Rhino” is short for rhinopneumonitis and is a commonly used shorthand for the two most common equine herpesviruses, EHV-1 and 4. The term rhinopneumonitis describes the typical symptoms of this disease which are inflammation (-itis) of the nose (rhino-) and lungs (-pneumo) that causes fever, nasal discharge, and coughing. The other common manifestation of these viruses targets the reproductive tract of pregnant mares, leading to abortion. Importantly, the respiratory strain of EHV-1 can also cause a neurologic syndrome, Equine Herpesvirus Myeloencephalopathy (EHVM), and unlike the respiratory and reproductive forms of the virus, EHVM is NOT prevented by vaccination. Given the recent EHVM cases in Virginia, we will focus on that particularly aspect of the disease in this article.

Initially, EHVM can appear very similar to the respiratory form of the disease, with the development of mild respiratory signs and a fever. However, within the span of a week neurologic signs develop. The most common signs include incoordination, weakness, lethargy and difficulty standing, urinating or defecating. If your horse develops any of these signs in conjunction with a fever and respiratory illness, isolate him from other horses on the property and call your veterinarian right away. Equine Herpesvirus-1 causes a serious illness, with potentially lasting neurologic deficits and a 30% mortality rate. Nasal swabs and a blood test are used to diagnose EHV-1. Unfortunately, like most viral infections, there is no cure for EHV-1. Instead treatment consists of anti-inflammatories (bute or Banamine) and supportive care.

Because there is no vaccine effective in preventing Equine Herpsesvirus Myeloencephalopathy, the veterinary and equine communities consider prevention of transmission of the disease of the utmost importance. Most horses in the world are exposed to the virus at a young age (< 2 years), as it is prevalent in the environment. They may have had no symptoms or only mild symptoms, but continue to harbor the virus for the rest of their life. During periods of stress, such as travel, strenuous exercise, or illness, the virus can reassert itself and either be shed in nasal secretions, exposing other horses, or cause disease in that individual. A few cases develop in this way, without exposure to an ill horse, as is suspected in the recent cases in Virginia. More typically, EHV-1 is typically spread by direct contact with nasal secretions of infected horses or with people or objects that have been contaminated with infectious materials.

Thus the mainstay of preventing the spread of EHVM is by adhering to good biosecurity protocols both at home and on the road. At home, assign each horse their own equipment, from buckets and brushes, to tack and blankets. Quarantine all horses newly arriving or returning to the farm for an appropriate length of time. When travelling, limit contact between your horse and other horses and people. Vaccination does appear to decrease the amount of virus shed by infected horses, however, so vaccination of unexposed horses can play a role in managing outbreaks. Take this opportunity to review some excellent resources to make sure your farm is doing all it can to prevent the next Equine Herpesvirus-1 Outbreak!

Helpful Resources:

As always, feel free to call our office at (540) 854-7171 to discuss vaccinating your horse against EHV-1, 4 and Equine Influenza or with any questions or concerns!

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