‘Sentinel chickens’ form a front line of defense against West Nile
“Hi, girlfriend,” Susanne Kluh said as she lifted a white leghorn chicken officially numbered “1406” out of her shaded coop.
The chicken, one of eight kept in a semi-secret location in Long Beach’s nearly 400-acre El Dorado Park, squirmed as Kluh examined a spot under her wing. The bird wanted back in her coop, where she had been clucking about and sipping water from a pipe suspended overhead.
But she had a job as a lookout for a silent and invisible foe.
In an era of costly high-tech medicine and sophisticated contagion control, 1406 and dozens of other “sentinel chickens” form a simple and efficient front line of defense against West Nile disease, a mosquito-borne illness that can cause flu-like symptoms and, in rare instances, death.
Through regular blood testing of the birds, disease hunters can predict when and where people are at risk of catching the virus.
“They give us a warning,” said Kluh, who heads disease surveillance for the Greater Los Angeles County Vector Control District, which maintains seven groups of sentinel chickens across the county.
In late July, Kluh’s team found that 1406 and four others in her coop had antibodies for the West Nile virus in their systems — evidence they’d been bitten by infected mosquitoes. Within two weeks, the city of Long Beach and L.A. County health officials reported their first human West Nile cases of the year.
“The chickens are the stars of the show,” said Levy Sun, a spokesman for the vector control district. “We really can’t do our job effectively without them.”
Over the years, California public health agencies have relied on sentinel chickens to track bird-hosted, mosquito-borne illnesses such as Western equine encephalomyelitis and St. Louis encephalitis. Los Angeles vector control groups began testing chickens for West Nile antibodies in 2003, the year after the virus made its first appearance in California.
Scientists also monitor West Nile’s spread by tallying infections in wild birds and mosquitoes. In California this year as of Friday, 1,410 dead birds in 33 counties and 2,040 mosquito samples in 29 counties — from Humboldt in the north to San Diego in the south — had tested positive for the virus, the California Department of Public Health has reported.
Adding sentinel chickens to the mix provides more precise information about where human infections might occur, Kluh said.
“When we have chickens positive, we know that the mosquitoes can actually transmit the disease,” she said. “We know there’s a close correlation with human cases.”
Chickens make perfect sentinels because they don’t get sick from West Nile virus, Kluh said, and never develop high enough levels of the virus in their blood to give the disease back to mosquitoes, which in turn might fly off and bite people or horses.
The chickens also give disease control workers a better idea of where infected mosquitoes are nesting. Because wild birds and people circulate freely, it is hard to know where they were when they were bitten. But sentinel chickens are infection-free when they arrive at their coop and remain in place. If they test positive for West Nile, vector control workers know to examine the nearby area for mosquito breeding locations.
So far, the chickens in El Dorado Park are the only ones monitored by Kluh’s team that have tested positive for West Nile antibodies. But according to the Department of Public Health, various vector control agencies in Los Angeles County have reported more than 20 sentinel chicken positives this year.
Thus far in 2014, there have been 57 human cases of West Nile disease confirmed in California. Four patients, in Sacramento, Shasta and Stanislaus counties, have died from the illness.
August is generally too early to know how widespread human infections will be in a given year, said Dr. James Watt, chief of the division of communicable disease for the state public health agency.
About 80% of people infected with the virus have no symptoms, he said. Close to 20% get a mild, flu-like illness. Very few experience the severe neurological symptoms that can require hospitalization.
Watt urged Californians to practice “the three Ds” of prevention: Use DEET or another effective insect repellent to ward away mosquitoes; be especially careful at dawn and dusk, when mosquitoes are active; and drain standing water to keep the insects from breeding.
In the meantime, Kluh and her colleagues are keeping a close eye on their coops.
They may soon retire and replace the current El Dorado flock. Once chickens have West Nile antibodies, they can’t be used for detection anymore.
The chickens — which Kluh said pose no threat of transferring the West Nile virus to people — are passed along to new owners, with some adopted as pets.