Chickens Serve as Lookouts in the War on West Nile Virus

Half a dozen creamy white leghorn chickens gabble nervously in a cage under a giant willow tree at the edge of Corona Airport. After months of having needles stuck in their jugular veins, they thrash their wings in a futile attempt to escape a pair of approaching researchers.

So goes the decidedly low-tech front-line battle against the deadly, mosquito-borne West Nile virus, which continues to spread rapidly across the Western United States.

The chickens are prime targets for the virus-carrying mosquitoes and, if tested properly, can act as an early-warning system for the approach of the disease.

“This is the sentinel chicken flock,” says Heather Atamian, a Cal State San Bernardino student who helps “bleed” the chickens every two weeks, gathering samples for state laboratories. “It reminds me of ‘Chicken Run’.... But it’s better to have chickens than humans in cages getting bitten by mosquitoes, I guess.”

The shady spot in the marshes along the Santa Ana River is just one of 222 sites statewide where sentinel chickens stand guard, from the Salton Sea to the Central Valley.

Fed and watered well, the plump fowl are placed in wetlands, backyards and other spots likely to attract mosquitoes. In the Southwest, females of the culex tarsalis mosquito in particular are carriers, and they love to bite birds. The virus has moved west rapidly since its discovery in New York in 1999, and has been detected in 44 states.

The virus was first detected in California in August near the Salton Sea, where mosquitoes trapped alive with dry ice bait were found to be carrying the disease. Within weeks, sentinel chicken flocks in Imperial County and the Coachella Valley tested positive.

A dead crow found on the front lawn of an Arcadia home tested positive earlier this month, showing the disease’s inexorable spread west to heavily populated urban counties. State health officials urge people to call the dead-bird hotline at (877) WNV-BIRD ([877] 968-2473) promptly if they see a dead bird that has not died from obvious causes.

By Friday, 4,416 human cases had been reported, up 1,200 from the week before, according to the U.S. Centers for Disease Control and Prevention. While two-thirds of those cases were mild, there have been 84 deaths so far this year, mostly among the elderly and others with weakened immune systems.

California has been spared any locally contracted human cases of West Nile virus this year, and with cooler autumn weather now reaching other states, federal health officials say the state could escape human deaths from the virus this year. As temperatures drop, mosquitoes die off and birds head elsewhere.

Lal Mian, a Cal State San Bernardino entomologist specializing in mosquitoes, scans federal maps showing the spread of the virus every day. With decades of experience studying mosquitoes and diseases, he said there is no way Californians will escape in the long run.

“It’s a matter of time,” he said. The state’s 60 vector control districts are on emergency alert status. In addition to the sentinel chickens, wild birds are being snared and bled, giant metal mosquito traps swing from trees or lampposts, and trucks are quietly spraying suburban neighborhoods with pesticides in the predawn hours. Bacterial “briquettes” that destroy larval mosquitoes’ intestines are being placed in bodies of water.

Federal and California health officials say the pesticides have been tested and approved by the U.S. Environmental Protection Agency, and leave it up to local jurisdictions to decide whether to use them.

“California has one of the best surveillance programs and one of the best mosquito control programs in the nation,” said Roy Campbell, the medical epidemiologist who oversees national West Nile surveillance efforts for the U.S. Centers for Disease Control and Prevention. “The state is very well prepared to detect the virus early and respond to it before it becomes a major public health problem. And that includes the chickens, for sure.”

A perimeter line of sentinel chicken flocks was first set up in the Golden State in the 1930s, Campbell said, as an early-warning system for American cousins of the West Nile disease such as St. Louis encephalitis. The concept was developed by Dr. Bill Reeves, a longtime UC Berkeley entomologist who first determined that birds bitten by infectious mosquitoes could be transmitters. Ever since, California and Florida in particular have used sentinel chickens.

Since crows began dropping from the sky in New York City four years ago, a grim herald of the aggressive West Nile strain, several other states beset by the disease have added their own flocks. New York health officials have also caged and tested city pigeons.

“Chickens are actually ideal sentinel animals because ... they rapidly clear the infection, so they don’t get sick and die, and they can’t transmit it,” said Vicki Kramer, chief of the vector borne disease section at the California Department of Health Services.

There are limitations. Caged birds can be tested repeatedly, but they are only indicators of what is going on in a small area. In some states, humans became ill before the birds tested positive. It also takes at least two weeks to ship blood samples to UC Davis or state labs in Richmond for testing. By then, the rapidly spreading disease may have moved on.

Wild birds can also be used to detect the spread of the virus, if they can be caught.

In the industrial backyard of the Northwest Vector Control District in Corona, crews have erected a homemade wooden bird trap with a one-way opening on the top. Once birds fly in, they can’t escape.

On a recent Tuesday, lab technician Greg Williams reached inside and snared a fiercely twittering house finch. Rolling the inch-long bundle of agitated feathers on its back, he deftly “bled” it, poking a long needle into its tiny jugular before freeing the stunned bird.

Even as researchers in state-of-the art laboratories race to develop immunoglobulins and other potential cures for the aggressive virus, California’s old-fashioned monitoring system has proved its worth.

The virus has moved west rapidly since its discovery in New York. It hit Colorado hard this summer. Many scientists believe the virus is being carried by migrating birds. But some, like Campbell, note that birds’ migrations are north to south, and there have been no outbreaks in Central America.

Campbell thinks local trips by birds and bugs are spreading it incrementally, or that cross-country trucks carrying a few mosquitoes in cargo, or vacationers traveling by car, may have helped spread it.