Printed in our March/April 2015 issue. Written by Dr. Emily McNally with Rappahannock Equine Clinic

In February of this year, there was a confirmed case of the neurologic form of equine herpesvirus (EHV-1) in Albemarle County, Virginia. The horse was located at a boarding facility that had to be placed under quarantine. Luckily, the horse recovered, but not all horses are so fortunate. What is equine herpesvirus and what can you do to help prevent your horse from contracting this potentially devastating disease?

EHV cellsThere are nine strains of equine herpesvirus (EHV), three of which can cause serious problems in the horse. EHV-3 causes a venereal disease affecting the external genitalia and EHV-4 is most commonly associated with a nonfatal respiratory disease in foals. Uniquely, EHV-1 can target three separate organ systems (respiratory, reproductive, and central nervous systems), giving rise to outbreaks of respiratory disease, abortion, neonatal death or paralytic neurologic disorder. The neurologic form of the disease is rare and is called equine herpesvirus myeloencephalopathy (EHM).

The virus is shed through the respiratory tract and the most common way the virus spreads in a population is by direct horse-to-horse contact. However, it can also be spread indirectly through tack, grooming equipment, feed and water buckets and people’s hands.

On average, clinical signs are initially seen within 4–7 days of infection. The first clinical sign is usually an elevation in temperature, and horses may or may not also have respiratory signs such as a cough and nasal discharge. Most horses recover uneventfully from these signs. If neurologic signs develop, they are usually seen 8–12 days after the primary infection involving the fever. The horse affected with EHM will become uncoordinated, more commonly in the hind limbs, and have difficulty walking and standing. Tail tone is often decreased and the urinary bladder can become paralyzed, leading to urinary incontinence. Less commonly, there may also be evidence of lesions in the brain, such as depression, lethargy and facial weakness. Complications are usually a result of trauma associated with weakness and inability to rise.

A blood sample and nasal swab are used to test for the virus and make a definitive diagnosis. Cerebrospinal fluid can also be collected and analyzed to look for evidence of infection by EHV-1.

Treatment relies heavily on supportive care such as the rolling of animals and use of supportive slings for horses who are recumbent (unable to rise). Other treatments may include IV fluids and anti-inflammatory drugs. Antibiotics have no effect on the virus itself but may be used to treat secondary bacterial infections. Isolation of affected horses is crucial to preventing an outbreak. Many horses can recover completely but the time to recovery can vary from a few days to more than a year, depending on the severity of the neurologic signs. Prognosis is poor if horses become recumbent.

If your horse develops a fever with respiratory and neurologic signs, immediately notify our office and do not move your horse or any other horses in the immediate area until diagnosis is confirmed with testing. Only by working together can we prevent a debilitating outbreak. Please call our office with any questions or concerns you may have at 540.854.7171.