Queensland Health yesterday confirmed the second case among a total of 50 people who either worked at the practice or may have had contact with the horses.
Brisbane medical officer Dr Brad McCall said both people are under close medical observation in a Brisbane hospital.
Both acquired the infection through close contact with the horses in the late stage of their illness or at autopsy.
"It is important to understand that the Hendra virus is rare in horses and in humans. In any outbreaks of this disease there has been no evidence of person-to-person transmission of the Hendra virus," Dr McCall said.
"There is no risk to the wider community."
Queensland Health says those who have been tested have been provided with information about the virus and advised on personal health and hygiene precautions.
Next week all close contacts will undertake a second round of blood testing.
A total of three horses at the clinic contracted the disease. One died from it and another was euthanized. A third recovered.
An unrelated case in northern Queensland has also been reported.
The Hendra virus, first isolated in 1994, is carried by native fruit bats. The risk to horses appears greatest during the bats' breeding season.