The strain of equine herpes virus-1 (EHV-1) most commonly associated with neurological disease in horses has been present in New Zealand for at least two years, the Ministry for Primary Industries says.
The ministry, in its latest update on an outbreak at a Waikato stud farm, said a study conducted at Massey University found the D752 EHV-1 strain – the form most commonly associated with neurological disease – in samples taken from a thoroughbred at an abattoir in February 2012.
Genetic testing showed that the same horse also carried the N752 EHV-1 wild strain – the lower risk variant of the virus.
The findings suggested that the neuropathogenic D752 strain has been present in the New Zealand horse population for at least two years, the ministry said. It stressed that further testing of the samples from the study were still in progress.
The researchers, whose findings have yet to be published, had tested samples taken from 52 horses processed at the abattoir.
A ministry spokesperson said the stud in the Cambridge area where 15 horses were infected, resulting in seven of them being euthanised, remained under voluntary quarantine. There have been no further cases reported since mid-February.
The eight other horses were recovering, but one was subsequently euthanized for reasons unrelated to EHV-1.
Ministry staff remained in regular contact with the stud farm and the farm’s veterinarian. Staff were now working with the affected stud and the New Zealand Equine Health association on a plan for removing quarantine restrictions.