Doctors are assessing four people who were exposed to a horse with Hendra virus at Beenleigh, south of Brisbane.
The horse was put down on the weekend and a property was quarantined.
Biosecurity Queensland officers returned to the property this morning to continue testing two horses that had been in contact with the infected animal.
Queensland Health officials have interviewed people known to have been exposed to the sick horse.
The department’s public health physician, Dr Mandy Seel, says two vets and a horse owner have been deemed low risk, but another owner is being monitored more closely.
“We’re still having ongoing conversations with her and investigating more thoroughly exactly how much exposure she had, what type of exposure she may have had to this sick horse,” she said.
Queensland Health says it will continue to monitor the four people for the next three weeks.