Why ‘sentinel chickens’ are a first line of defence against mosquito-borne disease

Like most chicken owners, Luke Bailey checks on his hens every day, collecting their eggs and feeding them vegetable scraps.  

But his chickens play an important role in defending the South Australia against mosquito-borne disease. 

Mr Bailey is a regional mosquito surveillance and control officer for SA Health and his flock in Mannum makes up one of ten troops of chickens scattered along the Murray River and around the state’s regions.

From November to April, the chickens have their blood tested monthly to check for antibodies from viruses like Japanese encephalitis.

“With the chickens being outside all the time, they’re constantly being bitten by mosquitoes,” he said.

“If they’re bitten by a mosquito that carries a virus, the chicken will develop antibodies.

“Because the chickens suffer no symptoms from the virus, they’re basically our first line of defence.” 

If the blood tests reveal antibodies for mosquito-borne disease, SA Health can issue public health warnings advising people to protect themselves from bites. 

‘Just eating and having fun’

Mr Bailey said the chickens were not too bothered by the testing process and although they had an important role, most of the time they lived a normal life.

“They’re just eating and having fun,” he said.

“They’re very well looked after by SA Health, who provide the coops, food and watering devices.

“The families just make sure that they’re fed, so they have a very good life.”

A personal connection

Helping to protect people is especially important to Mr Bailey, who contracted Ross River virus around 15 years ago. 

“I was starting to feel fatigued, really sore in the hips and my ankles and I went to donate blood,” he said.

“They suggested based on my symptoms that I should get a proper blood test and it came back as having Ross River [virus].

“I was out of action for about four weeks, but I’m one of the lucky ones because some people can have long-term effects from that virus.” 

Mr Bailey said his flock of sentinel chickens also helped awareness about mosquito-borne disease.

“It becomes a talking point, when you’re out in the community, a lot of people aren’t aware that this program even exists,” he said. 

“It’s really good that we’ve got them and can share that knowledge with everyone.”

Spanning the Murray River

Upstream, Rebecca Burton is the environmental health officer for the Renmark Paringa Council, where she helps tackles the problem through mosquito trapping.

Mosquito traps use a small light and dry ice, which produces carbon dioxide, to attract bugs, while a fan pushes them into a net below.

“We are not aiming to trap all of the mosquitoes in the area, or kill them,” she said.

“We are just taking a sample to see what species are around, the number, and if there’s any viruses present in the mosquitoes.”

Less than a year after the region experienced a major flooding event, Ms Burton said there had actually been a decrease in mosquito numbers.

“This is mostly due to the change in climatic conditions — it’s a lot drier this year than it has been in the last couple of years,” she said. 

Importance of management

Craig Williams, a professor at the University of South Australia with a research focus on mosquito-borne diseases, said despite low mosquito numbers, it was important for management techniques like sentinel chickens and trapping to be ongoing. 

“You have to maintain your surveillance of mosquito borne diseases [and] control mosquito populations, because if something pops up, you need to be able to respond and having those management systems in place enables you to do that,” he said.

“There are some estimates that during an outbreak … it could be one in one thousand mosquitoes carrying the virus.

“That sounds like a really small number … but there are millions of mosquitoes out there. 

“You can be bitten by a lot of mosquitoes and not get a virus, but you don’t know which one is going to be carrying the virus, so it’s good to just not get bitten.”