Dotted around a handful of backyards and on farms in regional New South Wales are special flocks of chickens that play a key role in helping NSW Health Pathology protect the community from serious diseases.

They are known as ‘sen­tinel chick­ens’ and since the 1970s they have been used to give us an ear­ly warn­ing about the pres­ence of poten­tial­ly dead­ly virus­es such as Mur­ray Val­ley encephali­tis virus, Kun­jin virus and Japan­ese encephali­tis virus, which are spread via mosquitoes.

So how does the sur­veil­lance pro­gram work?

Dur­ing the wet and warmer months of the year blood sam­ples are tak­en from the chick­ens once a week and sent to NSW Health Pathology’s Insti­tute of Clin­i­cal Pathol­o­gy and Med­ical Research (ICPMR) labs at West­mead for testing.

The head of the Arbovirus Emerg­ing Dis­eases Unit, Prin­ci­pal Sci­en­tist Asso­ciate Pro­fes­sor Lin­da Hue­ston, explains why chick­ens are used and what her team is look­ing for when the blood sam­ples arrive.

“Most of the virus­es of inter­est – Mur­ray Val­ley encephali­tis virus, Kun­jin virus, and now Japan­ese encephali­tis virus (JEV) – are cir­cu­lat­ing in wild bird pop­u­la­tions,” she said.

“But chick­ens are much eas­i­er to catch and to test than wild birds.”

“In the 1990’s I devel­oped a series of high­ly spe­cif­ic defined epi­tope block­ing ELISA tests for Mur­ray Val­ley encephali­tis virus, Kun­jin virus and for JEV. These tests are not just high­ly spe­cif­ic they can be used to detect anti­body in any species. This allows us to com­pare results between animals.”

Health author­i­ties are also test­ing mos­qui­to pop­u­la­tions for the same virus­es, but A/Prof Hue­ston insists the infor­ma­tion from test­ing the chick­ens is vital.
“Mos­qui­toes are trapped one night a week and test­ed, but that doesn’t give you an idea of how much virus is there, or if there is enough virus to cause trans­mis­sion, which is where the chick­ens come in” she said.

“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.”

“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.”

A/Prof Hue­ston said expe­ri­ence shows that a pos­i­tive test in a chick­en gives health author­i­ties about two weeks’ notice before the virus spreads to the human pop­u­la­tion, enough time to imple­ment pub­lic health mea­sures in the area.

The virus­es don’t harm the birds and all sen­tinel chick­en flocks are sub­ject to ani­mal ethics com­mit­tee approvals, as well as reg­u­lar checks by vet­eri­nar­i­ans to ensure they’re prop­er­ly housed and well cared for.

“They have to be in peak con­di­tion to be the best sen­tinels for the pro­gram, so it’s in everyone’s best inter­est to make sure the birds are healthy and hap­py,” A/Prof Hue­ston said.

Want to see more? One of our flocks in Grif­fith in the Rive­ri­na was vis­it­ed in Jan­u­ary 2023 by British YouTu­ber Tom Scott who made this awe­some video.

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