A third horse in Australia has died from the hendra virus, and five people are now in hospital in Brisbane after coming into contact with infected horses.

Vet Dr Alister Rodgers is in a critical condition in the Princess Alexandra Hospital in Brisbane after treating a horse with hendra at a stud in Cawarral, Rockhampton.

Three stud workers and stud owner John Brady are also being monitored in hospital.

Two horses were put down after testing positive for the virus on 8 and 10 August.

Yesterday a third horse — a two-year-old filly called Winnie — was put down because of the virus.

Authorites suspect that a fourth horse died of the virus on 28 July, but its body was destroyed before it could be confirmed.

The future of the stud is now doubt.

It is state policy to put down any horse that tests positive for the virus as hendra poses a risk to humans.

“Horses can have the virus in their system and recover, but there is an ongoing risk of the virus remaining dormant and reappearing in the future and this presents a potential threat to human and horse health,” said a vet from Biosecurity Queensland.

Signs of hendra virus in horses may include frothy nasal discharge, a temperature higher than 40°C, and neurological changes including abnormal muscle twitching, weakness and loss of balance.

The disease can spread from horses to humans, but so far there have been no signs of human-human transmission.

Last year Ben Cunneen, a vet from Brisbane, died of the virus. He was the first human to die of hendra in 10 years.