Hendra virus usually causes serious lung damage, with massive fluid build-up. While neurological signs from the virus are known to occur, it was the main symptom in the four horses that have so far tested positive for the disease. Two have died.
Their primary symptoms were a lack of muscular co-ordination (ataxia), head tilt, facial nerve paralysis, as well as increased temperatures and purple mucous membranes.
The horses were located at a veterinary practice, which may remain under quarantine for up to two weeks. About 35 horses remain at the practice.
Queensland's chief veterinary officer, Dr Ron Glanville, was advised on Monday of unusual neurological cases in horses at the practice.
A total of four horses were reported as being affected over a three-week period from late June.
Equine herpes virus was at first suspected as the cause involved and the veterinarian reporting the cases sought advice on the matter.
Biosecurity Queensland veterinarians secured all available samples, including post mortem ones, and they were tested for both equine herpes and Hendra.
The next day, Tuesday, results indicated three of the horses had been affected by Hendra. A fourth has since been confirmed in further testing.
The case believed to be the first was in a long-term resident of the hospital. It had deteriorated quickly after initially displaying ataxia and then rapidly progressing to being unable to be handled. The horse died on or about June 26.
Biosecurity officials have determined there are no known colonies in the area of fruit bat, which are known reservoirs for the virus. Outbreaks have been linked to the birthing season of the bats.
Meanwhile, the Australian Veterinary Association (AVA) has applauded the actions of the veterinary hospital at the centre of an outbreak.
"The clinic has been following all appropriate precautions from the outset and even placed itself into voluntary quarantine after they notified the Department of Primary Industries that they suspected an unusual disease outbreak," said Dr James Gilkerson, president of Equine Veterinarians Australia, a special interest group of the AVA.
"Four horses have since tested positive to the virus and the clinic has now initiated comprehensive and systematic disinfection procedures to ensure containment.
"This is not like the situation with equine influenza virus which had a greater capacity to spread between horses. The Hendra virus is not so contagious.
"Outbreaks of Hendra virus disease in horses are very uncommon, but the horse-owning public and the veterinary profession need to be vigilant.
"Symptoms are neurological rather than respiratory and affect the horse's balance and gait.
"While the disease is of concern because of its ability to be transmitted to humans, it is not highly contagious. The public health risk is generally limited to those who have exposure to the horse's body fluids," Dr Gilkerson said.
"The detection of the Hendra virus highlights the need for stringent biosecurity procedures when handling animals with illnesses, and AVA applauds the swift action of the vets involved in this outbreak."