Acurrent rise in the incidence of Neurotropic equine herpesvirus-1 (nEHV-1) following a cutting event at the beginning of May in Ogden, Utah has sparked the interest and concern of the horse industry and has raised several questions.
Equine herpesvirus-1 is a common virus in horses and many horses are exposed to EHV-1 at a young age. Although many horses carry the virus latently throughout their life without showing signs of illness, the virus can be reactivated.
The expression of illness following recrudescence (reactivation) is influenced by the strain of virus, the horse affected, and environmental factors. It is exacerbated by stressors. The virus generally manifests as rhinopneumonitis, a respiratory disease found in young horses. It can also cause abortions in broodmares. The neurological form known as equine herpesvirus myeloencephalothy (nEHV- 1) is the third manifestation. The virus damages blood vessels that supply the brain and spinal cord which causes loss of neurological function.
Initially the disease is characterized by fever with temperatures greater than 38.5 C, lack of appetite, and depression. Generally signs of upper respiratory disease
such as serous nasal discharge and coughing will be evident. Although the neurological signs that follow in a few days or weeks can be quite variable, hind limb weakness and inco-ordination, urinary incontinence, and poor tail tone are typical. Some horses may be mildly affected, merely stumbling, while others are severely affected and unable to rise or urinate.
The equine herpesvirus-1 is not that unusual nor is its spread, however the number of horses that are developing the neurologic disease is unusual which has captured media attention. Horses that contract nEHV-1 can have a mortality rate up to 40 per cent. Those that become recumbent and are unable to rise are often euthanized due to the complications with a downer horse.
NOSE TO NOSE
The natural spread of the EHV-1 virus is primarily via horse-to-horse contact, when affected animals sneeze or cough and come into contact with nasal secretions. Although EHV-1 is highly contagious among horses, it is not transmissible to humans. The virus can hitch a ride from horse to horse on inanimate surfaces, and caretakers whom may unknowingly act as transmitters. Presently no vaccine has a claim for protection against this neurological disease.
Understanding the virus and how it works is key to prevention. The Alberta Veterinary Medical Association website: www.avma. ab.ca/resources/documents/EquineBiosecurityPrinciples andBestPracticesGuide. pdf is a comprehensive resource for all horse owners outlining biosecurity strategies. Biosecurity measures are particularly relevant when horses are travelling distances, commingling, and enduring greater stress. It is advisable that any horse showing signs of respiratory and neurological disease be examined by a veterinarian. The diagnosis of nEHV-1 is confirmed through testing of nasal secretions and blood samples.
Tracking of reported cases has been ongoing in Alberta, B.C. and Saskatchewan with currently less than 20 cases being found in these provinces and only one fatality.
Carol Shwetz is a veterinarian specializing in equine practice at Westlock, Alberta.