Another horse on the Waikato stud farm affected by an outbreak of Equine Herpes Virus-1 has fallen ill, but its symptoms are reported to be mild.
That brings the number of cases to 15 on the farm. The death toll remains at seven.
The Ministry for Primary Industries said the latest case, reported on Wednesday, was in a mare in the same paddock where previous cases occurred. No new cases have been diagnosed in the two days since then.
It described the clinical signs as very mild, with the mare showing only urinary incontinence.
“This is not unexpected and more cases are possible,” it said.
The stud farm remained under voluntary quarantine and ministry staff were in daily contact with the owners and the farm’s veterinarian.
No other properties have been affected.
The ministry’s Animal Health Laboratory in Wallaceville is undertaking whole-genome sequencing of EHV-1 viruses from affected horses.
The neurological strain of EHV-1 has been detected in DNA sequencing analysis of samples from one affected horse at the stud farm in Cambridge – the first time it has been reported in New Zealand.
However, the non-neurological strain of EHV-1 has also been detected from one other affected horse on the same property.
The ministry said this showed the complex association between genetic variants of EHV-1 and clinical disease.
It said further DNA sequencing analysis and epidemiological investigations were required to fully understand this finding.
“It is apparent that not all outbreaks of neurological disease in horses are caused by neuropathogenic variants. All strains of EHV-1 should be regarded as potentially able to cause neurological disease.”
It said, based on information available to date, it was not unexpected to find multiple strains of EHV-1 circulating within the New Zealand horse population.
It said the animal health laboratory was forming collaborative efforts with The Maxwell H. Gluck Equine Research Centre at the University of Kentucky. The centre is designated by the World Organisation for Animal Health (OIE) as a global reference centre for three significant equine viral diseases, including EHV-1.