Up to eight people may have been exposed to the potentially deadly Hendra virus, authorities in Queensland believe.
It follows confirmation that a horse at Kerry, near Beaudesert, died this week
from the virus, which is carried by native fruit bats.
The risk of horses catching the infection rises during the bat breeding season, and there have been seven known instances where people have caught the virus from infected horses.
Of the seven people, four have died. The last two victims were equine veterinarians.
Authorities have put the level of exposure in the current case at low to moderate, and no-one was showing any symptoms of the infection.
They are being monitored and have undergone blood tests for the virus. Further tests will follow in three and six weeks.
Two properties have been placed in quarantine. One is at Kerry, where the horse had been agisted and first fell ill. The other is south at Biddaddaba, where the horse had been returned home to its owner.
In all, about 25 horses at the agistment property and five at the horse's home are being monitored.
Evidence suggests people have to be exposed to bodily fluids from a sick horse to catch the infection.
The Hendra virus was first isolated in 1994 following an outbreak in the Brisbane suburb of Hendra.
It is unclear at this stage whether any of those potentially exposed have been offered an experimental anti-viral drug which may reduce the chance of falling sick for those with significant exposure to the virus.
Horses that contract the virus are euthanised.
This latest cause is the 15th known incident of Hendra virus.
Little more than a month ago, Queensland Health announced $A180,000 in funding to continue the local production of an antibody for the Hendra virus in humans.
Queensland's Chief Health Officer, Dr Jeannette Young, said the cash would help ensure the continued development of the vital treatment.
Young said the drug therapy would help improve the survival rate of people exposed to Hendra virus.
Stocks of the antibody are now available to use to reduce the progression of the disease in people exposed to the virus.
The Queensland Horse Council stressed the need for horse owners to be aware that the Hendra virus can occur wherever there are flying foxes (native fruit bats) and horses.