Nineteen horses in the Kooralbyn area of Queensland, Australia, have now died or been euthanized as the result of an unknown ailment, according to an Oct. 9 press release from Biosecurity Queensland.

Last Thursday (Oct. 6), officials responded to calls of seven horses dead in a pasture. A veterinarian later euthanized another five, bringing the initial death toll to 12. An Oct. 7 Biosecurity Queensland press release indicated that although authorities initially suspected hendra virus as the cause of death, tests confirmed none of the deceased horses were infected by the virus.

Over the weekend, seven of the surviving horses either died or were euthanized after developing signs of illness; the clinical signs the animals exhibited were not reported.

"The six surviving horses were moved to another property on Friday evening and are under the care of a private veterinarian," the press release noted. "Biosecurity Queensland officers are on site conducting further checks of the paddock where the horses became sick. "On Friday we began the process of performing postmortems on the deceased horses," the release continued. "We expect to have the complete postmortem results sometime this week