For 40 years, theyve held the front line in Floridas fight against mosquito-borne diseases. And it turns out that the chickens standing sentinel in cities, marshes, woodlands and residential backyards are clucking good at their job.
Last year, chickens in 268 coops in over a third of Floridas counties provided scientists weekly blood samples that revealed whether the birds had been bitten by mosquitoes carrying West Nile virus or the Eastern equine encephalitis or St. Louis encephalitis viruses.
If a chickens blood tests positive for antibodies to one of those viruses, authorities know that the pathogen is circulating. And if enough birds have the antibodies, state officials can ratchet up mosquito-killing measures such as pesticide spraying to help halt disease spread.
The sentinel chicken surveillance programs are “a really good way of monitoring” for certain virus activity, says Thomas Unnasch, a biologist who studies vector-borne diseases at the University of South Florida in Tampa. The birds “are sampling literally hundreds or thousands of mosquitoes every day,” he says. (The chickens cant keep tabs on dengue or Zika; the mosquitoes carrying those viruses prefer to bite people rather than birds.)
In 2018, 833 chickens tested positive for West Nile virus antibodies in Florida, but only 39 people did, according to data from the states health department. For Eastern equine encephalitis virus, 154 chickens tested positive in 2018, compared with only three people.
Chickens that test positive for the viruses being surveyed dont transmit them, and people dont either. Both are considered “dead-end hosts,” meaning that the viral concentration in the blood doesnt get high enough to infect another mosquito after it bites. Infected cardinals, robins and other backyard birds are the animal reservoirs that help keep the three viruses spreading in the area.
Sentinel chickens, by detecting where and when disease-carrying mosquitoes are buzzing, are also providing valuable data on how a virus can spread. Data from 2005 to 2016 revealed that Eastern equine encephalitis virus is active year-round in the Florida panhandle, making the area a source from which the virus moves elsewhere in the state and along the eastern United States, Unnasch and his colleagues report online March 11 in the American Journal of Tropical Medicine and Hygiene.
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