Equine Herpes Virus type 1 (EHV-1) Myeloencephalopathy

There has been a report made of a neurological condition called Equine Herpes Virus type 1 (EHV-1) Myeloencephalopathy on a single New Zealand stud farm.

Although there are increasing numbers of outbreaks of this disease being reported from other countries around the world, this is the first confirmed report of the neurological presentation of Equine Herpes Virus infection in New Zealand.

EHV-1 is a common virus in New Zealand, many horses are infected as foals and the virus can become latent with reactivation of virus possible in later life (It behaves in a similar way to the human Herpes Virus that causes cold sores or the Feline Herpes virus that causes cat flu). Infected horses may show no clinical signs of disease, or the disease can present as respiratory disease of varying severity, abortion, neonatal death and the rarer neurological form.

The Ministry for Primary Industries is advising horse owners to be vigilant for signs of disease and to contact their veterinarian if they are concerned.

Symptoms and severity of the neurological form of EHV-1 infection vary between horses, but fever usually precedes the neurological signs. A neurologically affected horse is likely to show some or all of the following:

  • Ataxia (uncoordination)
  • Urine incontinence
  • Loss of tail tone
  • Hind limb weakness
  • Recumbency

To decrease the risk of disease transmission, suspect cases should be quarantined. If the diagnosis is confirmed, the quarantine should remain in place until 21 days after the resolution of clinical signs.

  • Stringent biosecurity measures are key to preventing spread of infection, these are not limited to but include:
  • Stop movement of horses on to and off premises where there are affected horses.
  • Do not bring pregnant mares onto premises where active EHV-1 is circulating.
  • Those working with affected horses should not work with healthy horses.
  • Washing hands between handling different horses.
  • Use dedicated clothing and footwear when working with an affected horse.
  • Change out of clothes before leaving isolation area and handling other horses.
  • Use disinfectant to sanitize footwear.
  • Do not share equipment among horses.
  • Disinfect and destroy contaminated bedding.
  • Clean and disinfect premises, equipment and vehicles used for horse transport.

Treatment of cases is focussed on providing supportive care to affected animals. The prognosis is poor for recumbent animals. The welfare of any recumbent horse must be considered when developing a treatment plan.

Vaccination is only protective against the respiratory and abortigenic forms of EHV-1 infections; it is not protective against the neurological form.

For an easy to read brochure with more information please go to: