Authorities confident outbreak of neurological EHV-1 is contained

The EHV-1 virus
The EHV-1 virus.

New Zealand authorities remain confident an outbreak of the neurological form Equine Herpes Virus-1 (EHV-1) on a Waikato stud farm is contained.

The Ministry for Primary Industries (MPI) has been monitoring horses that left the property before the outbreak was confirmed.

“Any horses that have come from this farm, including yearlings, are healthy,” the ministry reported.

In total, 14 horses on the property have been affected by the disease, seven of which were euthanised.

The ministry said the neuropathogenic strain of EHV‐1 had been detected in samples from one affected horse. However, the non‐neuropathogenic strain had also been detected from one other affected horse on the same property.

Transmission of EHV.
Transmission of EHV.

“This demonstrates the complex association between EHV‐1 variants and clinical disease,” it said.

All horses that are sick are located in one area of the stud farm, which is under quarantine.

“The area with affected horses is separated from the yearling operations,” the ministry said.

“All routine work, including vet work and farriery has been suspended on this area of the farm. Quarantine measures will not be lifted on this farm until it is certain that no horses on the property are clinically affected or actively shedding virus.”

Laboratory results from a sample of yearlings from the stud farm have come back as negative on nasal swabs and blood.

“This adds confidence to the yearling operation not having been exposed up to the date of sampling, and provides assurances of the efficacy of the farm biosecurity practices to date.

“The attending veterinarian and MPI are confident that active infection related to the current outbreak of EHV‐1 in the Waikato appears to be contained.

“This outbreak is localised to a single property that does not pose a risk to other farms in the area.

“Veterinarians and horse owners should be reminded that, despite the rare presentation of the neurological form of EHV‐1, it should be expected to occur sporadically in New Zealand, as it has done in other countries around the world.”

The cases were in a group of thoroughbred mares without recent history of travel. The victims presented with central nervous system signs, including poor co-ordination and weakness, or paralysis of limbs.

In several cases, affected horses were found down 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. Current vaccinations are not known to be effective against the neurological form.

The owner of the farm had voluntarily quarantined the affected paddocks and put biosecurity measures in place:

  • No routine procedures involving handling of the animals have been conducted on the stud farm.
  • There are five paddocks on the stud farm and no‐one has entered these paddocks since January 20.
  • The farm has provided disinfection footbaths and overboots.
  • Personnel handling the sick animals are showering afterwards.

The ministry released a question-and-answer sheet on the virus on Tuesday, in which it explained the nature of transmission of the virus – via a respiratory route due to direct contact with an infected horse, or via shared equipment or the hands and clothes of people handling horses. The virus can spread by air, but probably over distances of less than 50 metres.

The virus can survive for up to 30 days in the environment, but is susceptible to all common disinfectants.

It said EHV-1 was endemic in New Zealand and probably arrived in the country with the first horses.

The ministry said it was unclear if the neurological form of EHV‐1 in these cases was caused by a different strain of virus to the respiratory and abortion forms.

“There are genetic variants of EHV‐1 that have been linked to outbreaks of neurological disease in the USA and these have been named ‘neuropathogenic strains’.

“However, this situation is far from clear, and it is apparent that not all outbreaks of neurological disease are caused by these ‘neuropathogenic’ variants. All strains of EHV‐1 should be regarded as potentially able to cause neurological disease.”

The ministry said it was impractical to declare the disease notifiable.

“EHV‐1 is widely distributed throughout the horse population in New Zealand and many animals carry latent virus.

“Horses that recover from clinical disease may remain carriers for life. There is no effective treatment, and vaccination does not appear to confer protection against the neurological strain.

“The ante‐mortem detection of the neuropathogenic strain is difficult and results are not 100 percent
reliable, making it impractical to declare this disease notifiable.”

The full Q&A can be read here.

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