Chickens immune to West Nile virus, but as carriers they serve as valuable sentinels

By TIM TESCONI
THE PRESS DEMOCRAT

Chickens stationed in Sonoma and Marin counties are poised to sound the alarm when the West Nile virus, which is expected to arrive on the North Coast in a few months, makes its appearance.

"It's not a matter of 'if' but 'when' the West Nile virus gets here. The way it looks now it could arrive by early next year," said Piper Kimball, assistant vector ecologist with the Marin-Sonoma Mosquito and Vector Control District in Cotati.

The virus is carried by migrating birds and poses a threat to people, horses and other animals.

This week, Kimball was making her twice-monthly rounds to "bleed" the district's sentinel chickens to determine whether they've been bitten by mosquitoes infected with the virus.

Sentinel chicken flocks have been used in Sonoma and Marin counties for 15 years, part of a statewide disease warning system. Across the state, there are 200 such flocks monitored by health officials.

The West Nile virus -- commonly found in Africa, West Asia and the Mideast -- has been creeping across the United States since 1999, when it was identified in New York City. In August, a Los Angeles woman tested positive for the virus, the first locally contracted case in the West.

The virus is spread by migrating birds and the mosquitoes that prick them for warm blood. The mosquitoes transmit the virus to other hosts.

There are more than 20 mosquito species in Sonoma and Marin counties, making mosquitoes a year-round problem. Although the mosquito population reaches its height between April and October, some mosquito species hatch in fall and winter.

Most people infected with West Nile virus have no symptoms of illness. Only about one in four people will come down with a mild illness, suffering flu-like symptoms such as fever, headache and body aches.

But for the elderly and people with compromised immune systems, West Nile virus can be severe, causing encephalitis, a potentially fatal brain inflammation. So far, 176 people in the United States have died from West Nile and 3,231 people have tested positive.

Kimball is among those on the front line in the battle against the virus. Part of her job is drawing blood from the chickens, small flocks of laying hens strategically placed to monitor for West Nile and other viruses, including St. Louis and Western equine encephalitis.

Chickens are immune to West Nile, which makes them valuable sentinels, Kimball said.

When chickens are bitten by mosquitoes infected with West Nile, their bodies produce antibodies to fight off the virus. If the chickens' blood tests positive for certain antibodies, it means mosquitoes are transmitting the West Nile virus.

Kimball uses a lancet to prick the chickens' combs to draw the blood.

"Chickens are a great surveillance because they are outside 24/7, getting bitten by mosquitoes," Kimball said while drawing blood from a feisty red hen.

Kimball takes a blood sample to test for the West Nile virus and other diseases from a chicken in the Healdsburg sentinel flock.

State health officials are enlisting help from the public in spotting another tell-tale sign of West Nile virus: dead birds.

Crows, jays and ravens die from the virus within two weeks of infection. Once the virus arrives, dead birds will appear in parks and neighborhoods.

Kimball said residents who find dead crows or other birds are asked to call a toll-free number, 877-WNV-BIRD, to report it. The bodies of birds that have been dead for less than a day will be tested for the virus, supplementing the testing of the sentinel chickens and the mosquito population.

The district provides 10 hens, cage, coop and feed for people such as Bob Platt of Healdsburg who take care of the chickens. Platt's property is an ideal location, along the Russian River and in a wooded area where there are plenty of mosquitoes.

Although there is no vaccine for humans, there is a West Nile vaccine for horses, which costs about $60 the first year and then $30 annually for booster shots.

While some veterinarians believe it's too early to start vaccinating horses for the virus, Dr. John Kaufman, a leading equine veterinarian in Sonoma County, has advised his clients for the past year to vaccinate their horses. He said many horses he treats are valuable show animals that travel out of state, but he's recommending the vaccination to even backyard horses.

You can reach Staff Writer Tim Tesconi at 521-5289 or ttesconi@pressdemocrat.com.