A veterinary clinic in Brisbane's south has been closed down after two horses died there of the virus. The owner of the clinic said a man who tested positive for Hendra was part of a team of vets and nurses directly involved with infected horses.
He was one of more than 20 staff employed at the bayside practice where three horses were infected with the virus last week.
One horse died, another was put down and a third is recovering after the outbreak.
Brisbane Southside Population Health Unit medical officer Dr Brad McCall said the person who tested positive for the virus was admitted to hospital on Monday for observation and assessment, but was allowed to return home yesterday afternoon.
"The person was in good spirits and not exhibiting apparent symptoms," Dr McCall said.
"The risk of human to human spread of this virus is very minimal. However, the person has been advised to stay home for a week and will undergo further tests."
Redlands Veterinary Clinic owner David Lovell said initial blood tests showed the man was okay, but he had developed symptoms over the weekend.
Queensland Health confirmed a second and final round of tests of up to 50 people, including clinic staff and others associated with the infected horses, will take place next Tuesday.
Before Monday's confirmed human infection, just four people had contracted the Hendra virus from very sick or dead horses since 1994 - two of those people died.
While difficult to transmit, the virus can kill horses within a day, but Dr McCall said the impact of the virus on humans is still unknown.
"Our experience is limited, and certainly while people have been known to die from the disease, others have been known to survive and have good health," Dr McCall said
"It's by no means a predictable outcome."
Symptoms in humans include and influenza-like illness, which can progress to pneumonia, or encephalitis - inflammation of the brain - type symptoms such as headache, high fever and drowsiness, which can progress to convulsions or coma.
Horses develop an acute respiratory syndrome, quickly leading to death in most cases.
Biosecurity Queensland chief veterinary officer Dr Ron Glanville confirmed another horse, at Cannonvale in north Queensland, died as a result of the virus on the weekend, but he stressed there was no cause for alarm.
"The horse at Cannonvale has no connection to the vet practice in Brisbane, and all scientific evidence at the moment points to the timing being a coincidence," Dr Glanville said.
A statement released by the Department of Primary Industries and Fisheries said the death of the horse at Cannonvale over the weekend represented just the 11th known case of Hendra virus in Queensland since it was first seen in 1994.
"There are more than half a million horses in Queensland and although Hendra cases are still rare, some cases are expected periodically," Dr Glanville said.
Dr Glanville said the property where the horse died would be placed under quarantine while investigations continued.
The rare virus had never been seen before it killed Queensland horse trainer Vic Rail and 14 horses in September 1994.
Hendra virus is rare in horses and even rarer in humans. There is no evidence of human to human spread of Hendra virus either.
Fruit bats are the natural hosts for the virus.
Human infections have occurred from handling infected horses (both ill horses and dead horses at post mortem examination), so great care should be taken in regard to personal protective measures.
In particular, contact with blood and other body fluids (especially respiratory and nasal secretions, saliva, and urine) and tissues should be avoided.
People owning or working with horses are at risk from this disease Contamination should be avoided but if it occurs there should be vigorous washing of the contaminated skin with soap and water.
Any cuts or abrasions that become exposed or contaminated should be washed with soap and water and then be treated with either iodine-based antiseptic or ethyl alcohol, experts advise.
In the past, cases of Hendra virus in horses have occurred at sites in eastern Queensland and northern New South Wales. While it is extremely difficult for people to become infected, staff from Queensland Health are contacting those involved with the sick horses to advise on personal health and hygiene issues associated with the disease.