The Herald Sun newspaper reports that a vet involved in putting down the horse last week was accidentally injured by a used needle. She was admitted to hospital for testing to determine whether she had been exposed to the virus, the paper reported.
The fatal injection was the sad end of the road for Tamworth, a $A200,000 racehorse whose owner, Warren Small, had fought unsuccessfully to save.
National biosecurity rules require horses that survive Hendra infection to be put down as a safety measure.
The disease, which is carried by native fruit bats called flying foxes, is able to jump from horses to humans and two staff of the Brisbane clinic at the centre of the outbreak remain hospitalised with the infection.
It is understood that final tests have been conducted on the Redlands clinic staff and all returned negative results for the dangerous disease.
In all, five horses at the clinic lost their lives through the outbreak, either through succumbing to the disease or having been euthanised after positive blood tests.
Meanwhile, Queensland's chief veterinary officer Dr Ron Glanville has issued an updated report on the outbreak.
Dr Glanville said the symptoms shown by affected horses included depression, poor appetite, fever, darkened mucous membranes, reduced gut sounds, colic, ataxia, regular lying down, trembling, head tilting, circling, loss of vision, aggression, and rapid deterioration.
Most died or were euthanized after one day, two at most.
"Examination of clinic records identified three horses, which had died or were euthanized in the weeks preceding the first confirmed case and fitted the clinical case definition of sudden onset, fever, rapid deterioration over 24/48hrs, and neurological and/or respiratory system involvement," he said.
The first horse was reported to have had multiple neurological symptoms on admission, the second was reported to have had mild respiratory disease, and the third was reported as depressed on admission and collapsed the following afternoon.
The latter two horses had pre-existing medical conditions.
"Efforts were made to ascertain the Hendra virus infection status of these horses," Dr Glanville said.
"Samples available from an external diagnostic laboratory were limited to blood smears for each horse (other samples had been discarded). All were negative by PCR assay, but this result is not regarded as conclusive by the testing laboratory because of the sub-optimal sample.
"Investigations on the property of origin of all three horses found no evidence of infection in any in-contact horse. On the basis of these investigations, the three horses are regarded as improbable cases."
Investigations point to a horse who was a long-term resident at the clinic as being the primary case.
"In the fortnight prior to its illness (the horse) was housed in yards overhung by trees.
"Flying foxes, the recognised natural host of Hendra virus, are regularly observed in trees in the area.
"It is hypothesised that (the) horse was exposed to infectious body fluids from a flying fox, plausibly via contamination of feed, water or yard rails, and became infected.
"The timeline suggests that horse #1 was likely the source of infection for horses #2-4."
Studies are continuing into the behaviour of Hendra virus, including an investigation into how it jumps from bats to horses.