Every Sunday evening Bec Parker, helped by her two-year-old son Tommy, takes a pinprick of blood from each of the 15 chickens in their regional New South Wales yard.
Using blotting paper to collect the tiny samples from under the birds’ wings, they work their way through the flock without drama. After three years of the ritual, Parker is well practised.
“The chickens’ welfare is the most important thing to us, so we’ve worked out a way to do it very quickly and easily,” says the mental health social worker. “My son hugs them. We call him the little chicken whisperer.”
Her family’s suburban block in Wagga Wagga is home to one of the state’s 13 inland flocks of sentinel chickens, a battalion of birds on the frontline protecting public health.
The chickens, hosted in urban and semi-urban settings, are part of NSW Health’s defences against mosquito-borne diseases including the potentially deadly Japanese encephalitis and Murray Valley encephalitis, as well as Kunjin and Ross River viruses.
Parker’s home is close to a lake and wetlands: prime mosquito territory. Samples from her Sunday evening blood collection during the wet and warm season are dried and then express-posted to the medical entomology laboratory at Westmead hospital in Sydney, where they are analysed. The chickens’ samples serve as an early warning system, triggering a raft of public health responses if one is found to carry an arbovirus that affects humans.
By the end of the peak mosquito season (which typically runs from November to April in Victoria and NSW), NSW had recorded five cases of Japanese encephalitis. Two cases, contracted in the Murrumbidgee region, were fatal.
There have been four deaths from Japanese encephalitis in NSW since the outbreak was detected in 2022, according to NSW Health.
As with humans, mosquitoes are attracted to chickens’ exhalations of CO2 – but unlike humans, chickens are continuously exposed to the insects. Despite being bitten up to 1,000 times a night, the viruses don’t harm the birds.
Before this year’s human cases emerged, the virus was detected in a sentinel flock overseen by Tony Burns, NSW Health’s senior environmental health officer in the Murrumbidgee and Southern NSW regions.
“We’re able to use that early information to provide … information to the general public,” Burns says.
“Cover up, spray up, use your mosquito repellent, screen up your home. People take that message – we hope.”
Along with the chicken samples, mosquitoes are trapped over the course of one night a week and sent to the lab for testing. Even if a virus is detected in the mosquitoes, the result does not indicate if there is enough virus to cause transmission. Chickens solve that problem, according to the arbovirus emerging diseases unit’s Assoc Prof Linda Hueston.
“We estimate chickens are bitten by mozzies up to 1,000 times a night, and every time a mosquito bites it injects saliva, and the virus is in that saliva,” Hueston has said previously.
“So, it’s a numbers game. With 15 chickens in each flock, the chances of finding the virus increase. As the number of positive birds in the flock increase, so does the risk of virus spillover to humans.”
NSW’s sentinel chickens date back to the 1970s. In 1974, an outbreak of Murray Valley encephalitis swept across parts of the country. Parker first heard about the program on the radio and contacted NSW Health to register her interest.
“I just thought it was fascinating, I didn’t realise chickens could be used as a first line of defence,” she says.
Going beyond NSW Health’s strict specifications for the chickens’ cages, Parker and her husband have converted a carport to create a “very large” enclosure with fox-proof mesh, shade, nesting boxes, water stations and an automated misting system to keep the birds cool.
“We want them to have a lovely time in our back yard,” she says.
Victoria also started a sentinel chicken program in 1974 which continued until 2021, when its flocks were retired. A spokesperson for VicHealth said the surveillance system had been superseded by advances in technology that allowed mosquitoes to be directly and more rapidly tested.
In 2021, the Victorian government said: “This new molecular testing method enables mosquito samples to be screened directly and has been used in Victoria since 2019 to screen mosquitoes for Ross River virus and Barmah Forest virus.” The laboratory results are available “within days”.
But given the prevalence of Japanese encephalitis since 2022, chickens continue to do a “very important” job that is potentially saving people’s lives in NSW, Burns insists.
“[NSW Health’s medical entomologists] still believe it is a very worthwhile, low-cost method that provides the right information in a timely way.”
Parker is onboard for as long as she can help, she says. The hens also play a role in her family’s permaculture routine, eating food scraps and providing nutrients for their veggie patch, while surplus eggs are shared with the children’s school teachers, who have now learned about the program.
“I just love knowing that we have the first line of defence at the moment. Being part of the greater good for the health of the community – it feels pretty good,” Parker says.
“Every time Tony calls asking do we want to do the next season of chickens, we tell him we’d love to stay in the program for as long as it is running.”
