The first reported outbreak of equine herpesvirus myeloencephalopathy in New Zealand.

The study revolves around an outbreak of equine herpesvirus myeloencephalopathy that first appeared in New Zealand in 2014. On a stud farm, 15 mares showed neurological symptoms with tests revealing that 80% tested positive to a potent form of the herpesvirus that can cause severe neural damage. The outbreak had significant impacts, resulting in multiple euthanasia and abortions, demonstrating the severity and implications of herpesvirus myeloencephalopathy in equine populations in New Zealand.

Research Background and Scope

• The outbreak began on 9th January 2014 when a mare from a stud farm in Waikato, New Zealand presented signs of urinary incontinence without any fever.
• Over the next 33 days, 15 mares became clinically affected with neurological signs, with all but one having a foal at foot. The most common signs were hind limb paresis (partial loss of movement) and ataxia (lack of muscle control).

Scientific Findings and Results

• A highly potent form of equine herpesvirus (EHV) type 1 was detected in various tissues collected post mortem from two mares.
• The DNA sequencing data from the polymerase gene of the virus showed a nucleotide transition at position 2254. This particular mutation encodes amino acid D752, which is highly linked with the neuropathogenic genotype of EHV-1.
• Out of the 15 mares affected, 12 were confirmed positive for EHV-1 through PCR (Polymerase Chain Reaction) testing.
• Furthermore, results from virus neutralisation tests, ELISA on paired serum samples, whole blood and nasal swabs confirmed that 95% of the horses from four paddocks were likely exposed or infected with EHV-1.
• Following the outbreak, two mares aborted – one at nine months and another at 10 months. The cause of the abortion was confirmed as EHV-1, the same genotype involved in the outbreak.

Conclusions and Recommendations

• The outbreak demonstrates the massive impact that equine herpesvirus myeloencephalopathy can have on equine populations in New Zealand.
• Early diagnosis and biosecurity measures not only helped reduce the outbreak’s effect on the farm, but also prevented the virus from spreading to other horse enterprises.
• These findings highlight the need for stringent monitoring, effective biosecurity measures and regular testing in the equine industry to prevent and address such outbreaks promptly.