Contra Costa County officials have urged residents to take precautions against West Nile virus after two sentinel chickens and three more dead birds recently tested positive for the virus.
So far this year, 11 groups of mosquitoes, 15 dead birds and the two sentinel chickens have tested positive for the virus in Contra Costa County.
The eastern part of the county has seen most of the West Nile virus activity thus far, but one of three dead birds found recently was in Concord, Contra Costa Mosquito & Vector Control District officials said.
"The first positive bird of the year was from Martinez. Now, with a bird from Concord, it's an important reminder that West Nile virus is not restricted to just one part of Contra Costa County," said district scientific program director Steve Schutz.
Two people in the county have been diagnosed with the virus so far this year, according to the state department of public health.
Since 2005, 70 people in Contra Costa County have been diagnosed with West Nile virus. In 2006, two people died from the disease.
Chickens are considered sentinels because when an infected mosquito bites a chicken, the bird can naturally resist the virus, developing antibodies that are detected in lab tests.
Both chickens recently found with the virus were from the Holland Tract in east Contra Costa County.
Some infected birds, especially crows and jays, are known to get sick and die from the disease.
When a mosquito bites an infected bird, the mosquito can become infected and transmit the virus to another bird or a person through a mosquito bite.
Residents are urged to take precautions to reduce the risk of mosquito bites. Virus transmission can continue until average overnight temperatures drop below 55 degrees for a week or longer.
Residents can reduce risk of the virus by dumping or draining standing water, since the insects develop from egg to adult in water. Repellents containing DEET, Picaridin, or oil of lemon eucalyptus are recommended.
Swimming pools should be chlorinated and filtered because just one neglected pool can produce up to 1 million mosquitoes and affect people several miles away, district officials said.
Residents are also advised to avoid the outdoors when mosquitoes are present, typically dawn and dusk.
Dead birds can be reported to the state hotline at 877-WNV-BIRD (968-2473) or online at http://westnile.ca.gov/report.php.