EHV (Equine Herpes Virus)

Equine Herpes virus 1 and 4 are common in the horse population. They most commonly cause mild respiratory disease, abortion and ocular disease. Neurologic disease (also called Equine Herpes Myeloencephalopathy  or EHM) is not common.

EHV-1 is spread by direct contact from horse to horse through nasal discharge or as aerosol droplets. It can also be spread indirectly by horses coming into contact with contaminated clothes, barns or stables. Humans can spread the virus by contaminated hands and clothing.  Strict biosecurity rules should be applied to reduce the risk of infection in at-risk premises. These include changing clothes or wearing overalls when handling a new horse, using boot covers/foot dips in and out of the stable, washing hands between horses, mucking out the isolation horse last and taking rectal temperature twice daily. It is important to remember that most disinfectants only work on a surface which has first been cleaned.

Signs of EHV-1 infection may include any of the following:

  • Rectal temperature above 38.5°C
  • Nasal discharge, ocular discharge, cough
  • Leg-filling
  • Dullness, lethargy, abnormal behaviour
  • Incoordination or abnormal posture, urine dribbling Late abortions in pregnant mares (usually 7 months)
  • If any of these clinical signs occur, please contact your vet for advice: laboratory testing can be done on nasal swabs and/or blood testing depending on the case. If a case of EHV is confirmed then horses which have potentially come in to contact with that animal may need to be isolated and monitored, usually over a 2 week period, to ensure they are free of the disease. Horses which have not had any contact with clinical cases or at-risk animals are not subject to any movement restrictions, but increased biosecurity measures and vigilance is advised during an outbreak.

    A vaccine is available with inactivated EHV type 1 and type 4, which has been shown to reduce the incidence of respiratory disease and viral shedding, as well as reducing abortions due to EHV-1. There is no indication that the vaccine would help prevent the neurological form of EHV-1 in individual horses. This means that vaccination could be useful for maintaining herd immunity and reducing spread of the virus, but not necessarily protect individuals against disease. Current research suggests that zinc supplementation helps to prevent the development of EHM in horses. It is advisable to add to your horse’s feed daily to help reduce the risk of severe disease.

    This document was prepared based on the contributor’s knowledge and current experience of the EHV outbreak and will be reviewed as necessary.