The EHV-1 Outbreak



EHV-1 is Equine herpesvirus 1, a virus that can cause serious disease in horses and other species. Two forms exist, one that causes abortion in mares and one that causes respiratory disease and neurologic disease. THE RECENT OUTBREAK IS OF THE RESPIRATORY AND NEUROLOGIC FORM. The virus is highly contagious and is spread by direct horse to horse contact, contaminated hands and equipment and for short periods through aerosolization in a stable environment/


Clinical signs begin with mild fever, 102 or greater. The fever may be accompanied by nasal discharge and coughing. If neurologic signs appear the horse will be uncoordinated, weak and have trouble standing. Dribbling urine or difficulty urinating and defecating may appear. Symptoms may progress to including brain dysfunction and coma. The incubation period is 2 to 8 days. Signs may worsen over a period of 7 days from the beginning of the first symptoms. If a horse shows any of these symptoms it should be isolated right away and tested for EHV-1. Any area that the horse has been in should be disinfected if possible. Be sure to wash and disinfect hands between handling horses. This also applies to equipment. Bleach water is effective.


A nasal swab and blood sample can be taken from horses exhibiting signs of the disease. These samples can be tested for the virus. The PCR test can differentiate between neuropathogenic virus and non-neuropathogenic virus. The test does not help predict clinical outcome.


Several vaccines are on the market for both EHV-1 and EHV-4. Label claims on all vaccine are for the respiratory and or abortive form of the disease NOT FOR THE NEUROLOGIC FORM. Duration of immunity with the vaccines is rather short lived. It is not recommended to booster vaccinate horses that have been potentially exposed. However at this time booster vaccination of horses that have not been exposed may be helpful. Remember that as with any vaccine 100% prevention of disease is rarely obtained. Usual results are a reduction in the percentage of population that will aquire the disease and reduction of the severity of symptoms. Currently booster vaccination with one of the following vaccines is recommended, Rhinomune, Calvenza, Pneumobort K, or Prodigy if the horse has not been vaccinated in the last 90 days.



Currently many equine events have been closed to try to eliminate spread of the virus. As of today 5/18/2011 the border between Oregon and California has not been closed to equine transport as some have heard. Effective immediately EHV-1 has become a reportable disease in Oregon. I hope this answers some of your questions and please feel free to email, or call me, 541-883-3874 with any further questions you may have. As well Chanda Engel and Willy Riggs of our extension office are staying abreast of the situation and are there to help.