Australian health officials urged tourists who visited a popular adventure ranch west of the Great Barrier Reef at the weekend to come forward after a horse died from from the killer Hendra virus.
Passed from fruit bats (flying foxes) to horses and highly fatal to humans, Hendra claimed the life of a horse at the Blazing Saddles adventure farm on Monday, west of the Reef gateway city Cairns.
At least six people were known to have had contact with the sick animal and Queensland health officials said they were working to determine how many others could have been exposed at the popular tourist site.
"I would like to reassure any tourists or visitors to the property over the weekend that transmission of the virus requires close contact with body fluids of the sick horse," said Queensland health chief Jeannette Young.
"Queensland Health staff will continue to undertake contact tracing work to ensure all people potentially exposed to the sick horse have been identified.
Anyone who had visited the ranch since last Thursday and had concerns were urged to call the public health hotline, she said.
"Queensland Health stands ready to provide any assistance, counselling, information, testing or treatment that may be required," added Young.
At least 48 people have been exposed to Hendra in the past month in an outbreak which has spread from Cairns to within 500 kilometres (300 miles) of Sydney, worrying the city's thoroughbred race trainers.
No humans have yet been infected.
Hendra has killed four of the seven people who have contracted it since it was first identified 1994, but Young stressed that infections were rare.
"While there is an increase in the number of infections this year, I would stress that this is still a rare disease and these are discrete incidents," she said.
Named after the Brisbane suburb in which it was discovered, Hendra is thought to be unique to Australia and is spread from infected bats via half-chewed fruit or water and food contaminated by their urine and droppings.