The reported cases have occurred on one property in a group of thoroughbred mares without recent history of travel. Horses have presented with central nervous system signs including ataxia and weakness or paralysis of limbs. In several cases, affected horses were found laterally recumbent without previous clinical signs. All affected horses have been within adjacent areas of the farm, with either nose-to-nose contact or shared contact with equipment or handlers. Horses on this farm were up-to-date on EHV-1 vaccines, and vaccination history did not prevent illness.
The owner of the farm has voluntarily quarantined the affected paddocks and put biosecurity measures in place.
Equine herpes virus 1 (EHV-1 ) is endemic in New Zealand; it probably arrived in the country with the first horses. Many foals become infected from their dams and infected foals may or may not show clinical signs of respiratory disease. Like the human cold sore virus, EHV-1 can enter a latent state in a previously infected animal and it can reactivate in later life, often at times of increased stress. The neurological form of EHV-1 has been known to occur in countries such as North America, Europe and Australia. This is the first time it has been confirmed in New Zealand.