Two people who were in close contact with a horse infected with Hendra virus in Mackay, North Queensland, will receive an antibody therapy on "compassionate" grounds, aimed at preventing them from developing the deadly disease.
One is deemed to be at high risk of contracting Hendra virus and the other is considered moderate-to-high risk, after exposure to the infected horse's respiratory secretions.
Mackay Hospital and Health Service said five people had been identified as having had contact with the infected horse, which had since been euthanised.
However, the ABC understands only two have had high enough exposure to be at risk of contracting the infection.
None of the contacts has been admitted to hospital, but the pair with the highest exposure to the horse will receive an antibody therapy developed in the United States that has been given to fewer than 100 people.
It has been administered on compassionate grounds in more than a dozen Queenslanders after exposure to infected animals.
A safety trial of the antibody therapy involving about 40 healthy human volunteers, published in 2020, found it was well tolerated.
Hendra virus was identified in 1994 in the northern Brisbane suburb of Hendra.
Seven confirmed cases of the disease have been diagnosed in humans, resulting in four deaths.
Dr Geoffrey Playford — the infectious diseases director at Brisbane's Princess Alexandra Hospital — treated three of the seven cases.
He said the Hendra virus antibody therapy was manufactured at the University of Queensland-based Australian Institute for Bioengineering and Nanotechnology and stored there for use in humans exposed to an infected horse.
"The manufacture of the product is done to pharmaceutical-level standards, so we know it's safe," he said.
Four people have died from Hendra virus
The latest Mackay case is the first identified in a horse in Queensland in five years.
Hendra is a bat-borne virus that can spread to horses, which can then pass the infection on to humans.
Rockhampton veterinarian Alister Rodgers was the first person in the world to receive the US-developed antibody therapy in a desperate, unsuccessful bid to save his life after he was diagnosed with Hendra virus in 2009.
The 55-year-old contracted the virus after looking after a sick horse on a property at Cawarral, near Rockhampton.
Dr Rodgers — who had worked in the industry for 30 years — became the fourth person to die from the disease.
Dr Playford said the antibody therapy was given too late and at too low a dose to be effective in Dr Rodgers' case.
Other Queenslanders given the therapy after exposure to horses infected with Hendra virus have not gone on to develop the disease.
"We don't know if we'd done nothing in those cases, what would have happened but, given the severity of consequences, we really do have to give it if someone has had significant exposure," Dr Playford said.
He said the therapy needed to be given after a person had contact with an infected horse but before they developed symptoms.
"That's when the product, from the animal models, appears effective at preventing that infection."
Scientists said the antibodies bind to the virus to prevent it from entering human cells.
Mackay horse not vaccinated against Hendra virus
Dr Playford said vaccinating horses was the best way to prevent Hendra disease.
The Mackay horse had not been vaccinated against the virus.
"Horses with symptoms need to be treated as if they have Hendra until proven otherwise and to minimise contact until they've been assessed by a vet," Dr Playford said.
Symptoms can be neurological — such as the horse becoming unsteady on its feet — or respiratory, including laboured breathing and a frothy, nasal discharge.
The vet called to the Mackay horse suspected Hendra virus and had worn personal protective equipment.
