FIVE people are being monitored after the first Hendra virus death in NSW this year.
Local Land Services district vet Ian Poe urged horse owners to vaccinate after a 31-year-old stockhorse died on Thursday night, near Murwillumbah.
Earlier that day, the horse was found in a dam and treated for very low body temperature.
Mr Poe said Hendra virus probably resulted in the horse ending up in the dam.
"Hendra virus can affect the nervous system in horses," Mr Poe said.
Mr Poe said he was awaiting test results for the five other horses at the property.
He said the property would remain in quarantine for several weeks.
Mr Poe said horse owners should avoid keeping their horses near flowering trees which attract bats, as they carry the virus.
"The best thing is vaccination, as it can help to prevent the disease in horses."
Hendra virus has caused four known fatalities in humans since 1994.