|Equine Herpes Virus (EHV) also known as Equine Rhinopneumonitis is a highly infectious and contagious disease of horses. There are currently 9 known EHVís and of these EHV-1, EHV-3, and EHV-4 are the most problematic. EHV-3 causes a venereal disease called coital exanthema and is only a reproductive threat. EHV-1 and EHV-4 cause upper respiratory disease, abortions and/or neonatal death, and neurological disease. There has been an increase in Equine Herpes Myloencephalopathy (EHM) which is the neurological form in recent years. Most horses over 2 years of age have been exposed to the virus, many while nursing, but like other herpes viruses it can lay latent in the body only to come out during times of stress such as weaning, strenuous exercise, or events and travel.
The virus is spread by both direct and indirect contact. Direct contact is via coughing horses or nasal secretions or contact with fetal tissues or fluids. Indirect contact is via common tack, water troughs, feeders, feed, people, etc. EHV-3 of course is spread via breeding or contaminated breeding equipment. Clinical signs from EHV-1 and EHV-4 include fever, lethargy, nasal discharge, and cough for respiratory disease; abortions and/or neonatal disease; and head tilt, loss of tail tone, stumbling, hind limb or all limb weakness, and down and unable to rise for the neurologic form. Some may have mild or no signs. Treatment consists of supportive care and most horses with uncomplicated infections will recover fully. The neurologic form carries a much worse prognosis.
Recently 2 horses in Deschutes County have tested positive for the neurological form. Both had attended shows in Eugene, both developed EHM and both had to be euthanized. They had attended different shows at the same venue but not at the same time. Both ranches are under quarantine for a minimum of 28 days.
Prevention starts with good biosecurity. Isolate new horses and horses returning from shows for 30 days if possible. Do not share tack, equipment, use common water troughs, etc. Limit human contact with other horses or at least wash hands, change clothes, etc. Vaccines are effective at preventing or lessening the severity of respiratory disease and preventing abortions. As the disease can be latent in a mare and then come out and cause abortions including abortion storms even if mares are isolated, it is recommended to vaccinate all pregnant mares at 5, 7, and 9 months of gestation. Unfortunately, none of the vaccines are labeled as effective against the neurologic form (EHM). Vaccines are still our best tool; they prevent or lessen disease and decrease viral shedding which may in turn prevent exposure, thus having some indirect effect on preventing the neurologic form. Contact Lakeview Animal Hospital if you have questions.