Equine Herpes Virus-1: What You Should Know

Jacob Werner, VMD
Assistant Professor of Veterinary Medicine and Dairy and Animal Science
Attending Veterinarian for Agricultural Animals and Wildlife
Animal Resource Program
The Pennsylvania State University

A recent outbreak of equine Herpes Virus 1 (EHV-1) in Southwest Pennsylvania has prompted many questions and concerns from horse owners. The farm has been quarantined to prevent the spread of the virus.  While there is no immediate threat outside that farm, horse owners should be vigilant and practice high levels of biosecurity.  Commonly known as Rhinopneumonitis or “Rhino,”  Equine Herpes Virus (EHV) has many different types and is best known by horse owners to cause respiratory disease and abortions.  It is important to know that EHV can cause other disease states in horses.  EHV-1 found in Southwest Pennsylvania was the cause of a neurologic form of the disease.

Horses infected with EHV-1 that causes neurologic disease occurs due to inflammation and damage to the spinal cord resulting in variable clinical signs depending on the severity of damage.  Often, horses will have a sudden onset of symptoms such as a wobbly stance, uncoordinated gate, and changes in tail movement.  Some horses will lose the ability to urinate appropriately and can become urinary incontinent.  Other signs of neurologic disease can occur and can be further identified by a veterinarian.  Since not every horse will have the same signs, a veterinarian should be consulted as early as symptoms appear.

EHV is transmitted through the respiratory secretions of infected horses or through aerosolized virus particles found in afterbirth fluids.  Direct nose-to-nose contact and sharing of feed or water troughs among horses is the primary transmission of the virus.  However, aerosolized particles can travel up to 35 feet and can cause infection.  Likewise people working around infected horses can carry the virus on their hands and clothes and can be vectors of transmission.

Because this is a viral disease, antibiotics are not useful in treatment of infected animals.  Supportive care and time are the best treatment.  It is important to contact a veterinarian at the first sign of abnormal neurologic behavior in order to properly diagnose and start supportive therapy.  Moreover, infected horses should be kept from travelling or coming in contact with other horses to prevent the spread of the virus.

Vaccines exist for EHV-1 and are effective at preventing the respiratory and reproductive diseases caused by this virus.  These vaccines , however, do not appear to be protective against the neurologic form of disease.  During an outbreak of EHV-1 causing neurologic disease, the use of vaccines is questionable.  Vaccination may reduce other forms of EHV-1 disease and reduce the presence of the virus leading to a reduction in the chances of developing the neurologic form; however, there is some evidence the vaccination may sensitize the horse’s immune system to allow the neurologic form to occur.

The use of the vaccine during an outbreak should only be used in discussions with a veterinarian.  Many vaccines can be purchased over-the counter, and it is important to discuss their use in depth with a veterinarian prior to their use as each individual case is different and may require different strategies for the health of the animal.


Smith, B.P. Large Animal Internal Medicine. 3rd ed. Mosby, Inc. St. Louis, MO. (2002) 885-886.