Symons said the horse had died on June 28.
"Initial test results from samples taken from the horse were negative for Hendra virus.
"Samples were then sent to AAHL for further testing for a cause of death.
"AAHL conducted a series of further tests and found that the horse had antibodies to Hendra virus.
"This further testing showed the horse had extremely low levels of Hendra virus in its blood at the time it was sampled.
"This, together with the level of antibodies, suggests that the horse may have had a previous Hendra virus infection and had developed some antibodies."
Symons said there were no other horses on the property.
"There is no need to quarantine the property, but it has now been added to the list of current cases in Queensland taking the total to seven this year - nine horses have died.
"The number of horses currently being monitored on quarantined properties remains unchanged at 83," he said.
Queensland chief health officer Jeannette Young said six people had been identified as having had contact with the infected horse.
All had low to negligible risk of getting infected and all have had initial blood testing done.
Young said Queensland Health had also started to receive results back from the second round of testing of people at the Beaudesert properties - to date all have been negative.
"It should be noted that these people had very low risk of being infected with Hendra virus and this is a very pleasing result," she said.
"With all our knowledge to date, this puts these people in the clear but we are still recommending a third round of testing for these people.
She said Queensland Health would continue to monitor and assess all identified contacts.
Four horses have also died in New South Wales, taking the Hendra toll to 13 in little more than a month.