A 25-year-old unvaccinated mare has been euthanised on a property near Scone after contracting Hendra virus.
According to Local Land Services, the horse developed neurological signs of the virus on Friday June 7, three days after being confined to a yard.
It's owners then called the animal diseases hotline. It was euthanased by the owners after becoming unresponsive.
It's understood a District Veterinarian from Hunter Local Land Services visited the property on Sunday June 9 to collect samples for Hendra Virus testing.
The Hendra virus infection was then confirmed by NSW Department of Primary Industries on Wednesday June 12.
It's the first confirmed case of Hendra virus in the Hunter Valley, with most cases in NSW having been on the north coast.
A case in Kempsey in 2013 was the most southern case prior to the current case.
Hunter Local Land Services says no other horses on the property are showing any signs of ill health. Their health status will be monitored daily.
Officers from NSW health are undertaking risk assessments of people who have had varying degrees of contact with the affected horse to determine their risk.
Tracing of horse movements in the previous 16 days will be undertaken and a Biosecurity Direction is in place to control the movement of animals and people on and off the property.
Hendra virus infection is notifiable in NSW under the NSW Biosecurity Act.
In NSW to date there have been 22 horse deaths as a result of Hendra virus on 20 properties since the first NSW case in 2006.
There have been no human deaths from Hendra virus in NSW.
Vaccination of horses is the most effective way to help manage Hendra virus disease.