Twelve horses residing in a pasture in the Kooralbyn area of Queensland, Australia, are dead, but the cause of death remains unknown, according to an Oct. 7 press release from Biosecurity Queensland. Of the 12, seven horses died and five were euthanized.

The press release indicated that although authorities initially suspected hendra virus as the cause of death when investigating the scene yesterday (Oct. 6), tests have confirmed that none of the deceased horses were infected by the virus.

Queensland Chief Veterinary Officer Rick Symons, BVSc, MBA, PhD, said Biosecurity Queensland would perform postmortems on the horses to try and determine what made them fatally sick so rapidly.

"We don’t expect to have the complete postmortem results until next week," he said. "There were a total of 25 horses on the property. Three of the surviving horses are showing signs of the illness and are being monitored