Specially designated “sentinel chickens” allow health officials to track the emergence of infectious diseases like West Nile virus amongst human populations.
West Nile virus, like many diseases, spreads between species. For some animals, like birds, the virus often produces no symptoms – so it’s not a big deal for the bird. But when a mosquito bites an infected animal and then goes on to bite a human, West Nile fever and the resulting risks to that person’s life and limb inevitably follow.
It’s rare for West Nile virus to move from human to human. (In terms of viral load, we’re a dead end.) That progression – bird to mosquito to human – is the dangerous one. So some public health officials have devised a clever way to follow the spread of the disease: sentinel chickens.
Essentially, the chickens are our early warning system. Small flocks of young chickens are housed in strategic coops spread around the area to be monitored. At regular intervals health workers test those chickens for viral antibodies. If antibodies for West Nile virus show up in the sentinel chickens, that means the virus is probably present in the wild bird population. People in the area are at risk.
When a sentinel chicken throws up a warning like this, local health authorities can deploy extra defences like mosquito eradication programmes. Sentinel chickens monitor the spread of West Nile virus in the United States and West Nile-like viruses in Australia; in both places, they have proven invaluable in tracking the emergence of the virus before it gets out of control.
[Thanks to Debra L.]
The Generalist Academy 
