May 08, 2018

Chickens: An Unlikely Ally in Disease Detection

Sentinel chicken programs are a longstanding One Health initiative to detect the presence of infected mosquitoes before viruses can spread to humans.
By Amanda Carrozza
Sentinel ChickensNot all heroes wear capes. In fact, some don’t even wear pants. In spite of advancing technologies that can print 3-dimensional replicas of bone structures or create full-functioning prosthetics for pets, a seemingly primitive method for detecting some of the world’s most widespread diseases reigns supreme in counties across the country: sentinel chickens.

How Sentinel Programs Work
Although each vector control program using chickens has its own nuances, the basic detection methods are the same. Designated chicken coops are placed in areas believed to be endemic to infected mosquitos. There, the chickens are fed and cared for and go about living “normal” chicken lives while waiting to be bit. On a regular basis, blood is drawn from the chickens and tested for viruses known to be carried by mosquitoes, most notably West Nile virus (WNV). When chickens test positive for WNV, it is a clear indication that there are carrier mosquitoes in the area.

In 2017, the Centers for Disease Control and Prevention received reports of WNV infections in 47 states and the District of Columbia, and 2002 cases were reported in people. Unlike humans, however, chickens don’t get sick from the diseases they contract from mosquitoes.

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“Without the sentinel program, it would be a total guess as to the level of virus activity happening,” said Glen-Paul Edson, assistant operations manager for mosquito control in Pinellas County, Florida. “We would be effectively flying blind until human cases started popping up.”

Sentinel Programs in Action
Florida’s statewide sentinel chicken program began in 1978, which prompted some counties in the state to start their own targeted programs in subsequent years as a means to detect mosquito-borne illnesses before they spread to residents. The Pinellas County program commenced in 1981. Similar approaches to virus detection are currently in place in various states around the country, including Long Beach, California; Washoe County, Nevada; and Mobile, Alabama.

In Mobile, the health department’s vector services division has monitored sentinel chickens for almost 30 years. Each year, 100 chicks are inducted into the program and raised until they’re mature enough to be placed in one of the 13 coops set up around the county or held in a reserve coop until they’re needed. On a weekly basis, vector control inspectors draw blood samples from the wings of two hens at each location. The samples are then sent to a lab in Tampa, Florida, and the results are made available that Friday. If a sample returns positive, the county’s health department increases spraying and conducts door-to-door surveys in the immediate area.
 
Chicken Coop in Pinellas
A chicken coop used in the Pinellas program.
In 2017, 5 sentinel chickens tested positive for WNV and 4 others tested positive for eastern equine encephalitis (EEE). “There are no health benefits to being bitten by a mosquito,” Bernard H. Eichold II, MD, PhD, FACS, health officer for Mobile County, said in a news release to residents. “Don’t let your guard down. EEE has a human mortality rate of 50 to 75 percent, while [that of] West Nile Virus is between 3 and 15 percent. EEE is a very serious mosquito-borne illness.” The Mobile program generally begins in late spring and continues into December.

Pinellas runs its program all year. Some districts feel that the risk of mosquito-borne viruses is seasonal enough that chickens can be removed in the winter, said Edson, “but we have shown positive transmissions during this time of year and therefore prefer to be constantly monitoring the virus situation in our county.” 

In Pinellas, 8 permanent coops—each with 7 chickens—are located strategically throughout the county. “The locations were chosen based on breeding sites of the correct species of mosquitos and of known bird roosting habitats,” Edson explained. “We secure blood samples every Monday and receive results from the state lab every Friday.”

Protocol for Positive Poultry
West Nile MosquitoIf a chicken tests positive, it is swapped with a chicken from a reserve coop located at the county’s district office because, as Edson explained, once a chicken tests positive for the antibodies it will always test positive.
 
Upon receiving a positive test result, mosquito control jumps into action to protect area residents as early as the following morning. “We also send technicians out to the area to try and locate any breeding of mosquito larvae,” he added. “They will then either treat using backpacks or pump-up sprayers, or call in for aerial larvicide treatment with one of our Bell 47 helicopters that help treat larger areas the technicians cannot effectively treat by hand.” 

In 2017, the county received 27 positive WNV results from its sentinel chickens, but no infections for EEE, St. Louis encephalitis, or Highlands J virus were detected. No chickens have yet tested positive for any of the viruses in 2018.

The programs in both Mobile and Pinellas rehome chickens that have tested positive or fulfilled their sentinel duties for the year. “We have donated these chickens to youth farms and shelters who use the great egg production to help feed those in need, Edson explained. Chickens are also donated to citizens who would like to raise them. 


video courtesy of Mobile County Health Department

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