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EL MONTE, Calif. — The chickens are used to the needles.

They don’t fuss when vector ecologist Tanya Posey pulls opens the door of a coop in a community garden here, firmly grasps a Leghorn, and pulls a blood sample out of its wing vein. She’s so good, she can bleed a chicken in about 30 seconds.


That’s helpful, because she has a lot of chickens to test.

More than six dozen sentinel chickens, living in coops dotted around Los Angeles, make up one of the first lines of defense in this sprawling county’s fight against West Nile virus. The disease has been a background threat for years here, but cases have spiked this fall to worrisome levels. Six deaths have been reported by Los Angeles County this year — including three just last week.

And the cases are alarmingly severe: Of 98 reported infections here this year, 79 have led to serious neurological side effects, and 87 have required hospitalization. Because it’s still peak mosquito season, more deaths are expected.

So local public health officials this week launched an all-out attack. They’re sending teams of green-shirted vector control agents door to door to tell residents to wear bug spray, install window screens, and dump the stagnant water where the insects breed. They’re plastering the county with posters that read “It’s Not Just a Bite” and “No Es Solo Un Piquete.” They’ve even created a rap video featuring a fetid swimming pool, a giant dancing mosquito, and teams of uniformed agents rapping, “You’ve got to dump the water out, drain the water flow, tip the water out, toss the water slow.”


“You’ve got to dump the water out, drain the water flow, tip the water out, toss the water slow.”

On a national level, a duo from Johns Hopkins and the Bill & Melinda Gates Foundation last week petitioned for a new mosquito emoji, arguing that it could lend some buzz to public health efforts.

West Nile virus causes no symptoms in 8 of 10 infected people, according to the Centers for Disease Control and Prevention. But some, particularly the very young and very old, can get fevers, fatigue, and flu-like symptoms. (Dr. Lyle Petersen, the director of the CDC’s division of vector-borne diseases, experienced that misery himself back in 2003, when he was infected with West Nile virus after going out to pick up his mail without insect repellent.)

The virus has caused more than 2,000 deaths in the U.S. since it first appeared in New York in 1999. States hit hardest in recent years include California, Arizona, Texas, Colorado, Oklahoma, Nebraska, and South Dakota. This year, 22 states have already reported 49 deaths and 658 of the most severe cases, known as “neuroinvasive,” which can involve meningitis, encephalitis, and paralysis.

But at least here in Southern California, residents don’t seem to be concerned.

“You can’t imagine how much outreach we’re doing, but it’s really hard to get people to pay attention,” said Kelly Middleton, who directs community affairs for the Greater Los Angeles County Vector Control District.

Some experts blame complacency, because West Nile is old news. Others blame the months of media coverage over the past year on Zika, another mosquito-borne virus that can cause grave birth defects when it infects pregnant women. Though there’s no evidence Zika is being transmitted by mosquitoes in Southern California, residents nonetheless seem focused on that — instead of the far more prevalent threat of West Nile.

“Certainly we all care about infants and birth defects, so Zika gets a lot of attention,” said Dr. Benjamin Schwartz, deputy chief of the county’s program for acute communicable disease control. “But West Nile causes more deaths than Zika does — and it causes them every year.”

West nile chickens
Harold Morales, with the l takes a sentinel chicken from a coop for a blood sample.

Flocks of chickens generate vital data

To control West Nile virus, first you have to know where it’s lurking. It’s a monumental task for the district, which covers a territory of more than 1,340 square miles — roughly the size of Rhode Island.

The district has some 180 mosquito traps. Checking them all involves grueling drives five days a week by two field assistants.

But simply detecting virus inside mosquitoes doesn’t confirm that the insects are infectious. Finding infected birds does. The district collects and tests dead birds — crows and blue jays — when residents alert them, but such reports can be spotty.

So the district relies on its sentinel chickens, checking their blood for West Nile virus antibodies every two weeks.

On a recent day, Posey and her teammate Harold Morales checked a group of 10 white Leghorns — the iconic white chickens with bright red combs. (An attempt to use Rhode Island Reds failed miserably; the birds couldn’t handle the Southern California heat.) Seven of the chickens had already tested positive for West Nile, so Morales bled the three that hadn’t, dropping a few milliliters of blood onto filter papers he would later send to a state testing lab.

“It’s just like going to the doctor and getting a blood sample,” said Susanne Kluh, who heads disease surveillance for the district. “Some get feisty, but it’s pretty easy on the chickens.”

Wild birds don’t seem to mind the needles, either. Many that have been trapped for surveillance, banded, and released return repeatedly to the traps — where they can be tested again to see if they have immunity. “They give their blood and get free food,” Middleton said. “The same birds come back week after week.”

“It’s just like going to the doctor and getting a blood sample. Some get feisty, but it’s pretty easy on the chickens.”

Susanne Kluh, head of disease surveillance for the Los Angeles Vector Control District

Unlike sparrows, finches, jays, and crows — which can die from West Nile and also transmit it to new mosquitoes — chickens don’t get sick or spread the virus. Indeed, the sentinel Longhorns are healthy enough that local gardeners gather their eggs and use their manure for fertilizer. Once testing season ends in late fall, the birds are given away — for pets or meat. “They’re good eating,” said Kluh.

And they’re good data generators, helping Kluh and colleagues generate a precise map of where the virus is active. The district can then target outreach and abatement efforts.

Human cases are too slow to be useful for surveillance, she said, because people often don’t go to the doctor right away and doctors don’t always report cases. (Indeed, the number of actual West Nile deaths is likely higher than stated because of underreporting, public health officials say.)

West nile chickens
Vector ecologist Tanya Posey takes a blood sample.
West nile chickens
Blood samples from the chickens are categorized.

An army of invading mosquitoes

Los Angeles County public health officials credit the vector control district with keeping the outbreak from being far worse. But for Kluh and her team, every West Nile death is difficult.

“It’s hard,” Kluh said. “We take it really personally.”

This month, 84-year-old Julia Shepherd, an active grandmother from a Los Angeles suburb, died of West Nile after becoming paralyzed and disoriented.

The case is exactly the type public health officials fear, one that robs healthy older adults — those most likely to be outdoors — of either their lives or their independence. Some half of older adults who have been infected with neurological symptoms have still not recovered their ability to function independently after a year, Schwartz said.

West nile chickens
A notice on a coop that holds sentinel chickens.

While they’re focussed on West Nile, which is transmitted by Culex mosquitoes, Kluh and her team do still monitor the spread of Aedes aegypti, which can transmit Zika. She’s also tracking Aedes albopictus, the Asian tiger mosquito that’s a carrier of dengue and chikungunya. And she’s got her eye on the newly arrived Aussie Mozzie mosquito — Aedes notoscriptus — that transmits yet other viruses.

“I guess I’ve got job security,” she joked.

Kluh sees a silver lining in the invasion of these aggressive new species. Unlike California’s resident Culex mosquitoes, the newcomers bite humans more than birds, bite all day long, and tend to raise welts that are itchier and more noticeable. Because of this, many people here are finally starting to complain about mosquitoes — and that’s music to Kluh’s ears.

“Because it’s so unpleasant,” she said, “people might finally start protecting themselves from getting bitten.”

  • In the South as a generalist I saw a handful of cases in the early 2000’s. I’ve seen next to none until this year when I treated one of the worst neurology-invasive cases I’ve seen.
    The first report I read of West Nile was in Scientific American, must have been 1999. I distinctly remember discussion of sentinel chickens in that article as well.

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