West Nile Virus Returns To Contra Costa County

CONTRA COSTA COUNTY, CA — Two groups of mosquitoes in Contra Costa County have tested positive for West Nile Virus, the Contra Costa Mosquito and Vector Control District reported Friday.

The mosquitoes were collected from a trap in the town of Discovery Bay and are the first mosquitoes to test positive for WNV so far this year in Contra Costa County.

West Nile virus is transmitted by the bite of an infected mosquito. As mosquitoes may transmit WNV with a single bite, it is important for Contra Costa County residents to take precautions to reduce the risk of mosquito bites, particularly now, as the summer heat increases, according to the Contra Costa Mosquito & Vector Control District.

"This week's increasing temperatures can increase both mosquito production and West Nile virus risk because mosquitoes can develop from egg to adult more quickly in hot weather, and West Nile virus can grow more efficiently when temperatures are consistently warmer than 55 degrees," said Steve Schutz, scientific program manager with the Contra Costa Mosquito & Vector Control District. "With the increasing risk of West Nile virus, the District recommends Contra Costa County residents wear insect repellent and report mosquito activity to the District."

The District recommends using EPA-registered insect repellents with one of the following active ingredients:

• DEET
• Picaridin
• Repellent version of Oil of Lemon Eucalyptus
• IR3535

According to the Centers for Disease Control and Prevention, when used as directed, Environmental Protection Agency-registered insect repellents are proven safe and effective. The district reminded people to always follow the instructions on the label when using repellent.

Another way to reduce the risk of mosquitoes, the District said, is to dump out containers holding any amount of standing water and scrub the inside of the containers to remove mosquito eggs. Containers can include buckets, cans, toys, plant saucers, bird baths, rain barrels, and any other items that may hold water for an extended period of time.

It is important to dump out any amount of water because mosquitoes can develop from egg to biting adults in as little as a bottle cap full of water, the district said. To prevent mosquitoes indoors, residents should make sure window and door screens do not have any rips or tears, and that all screens fit properly.

Since 2005, 75 people in Contra Costa County have been diagnosed with West Nile virus. In 2006, two people in Contra Costa County died from the disease.

In California, West Nile virus is the most common and serious vector-borne disease in the state. Since 2003, there have been more than 7,500 human cases and over 300 deaths reported in California.

Heavy rains this past winter led to an increase in mosquito populations across the Golden State, posing a greater risk for mosquito-borne diseases, according to the California Department of Public Health.

Recently, malaria, a mosquito-borne disease, has been making headlines in other states. There are no reported cases of malaria in California to date, according to CDPH.

West Nile has been detected in mosquito samples or dead birds in 21 California counties and St. Louis encephalitis has been detected in five California counties, according to CDPH. No human cases of WNV have been reported thus far this year in California although as of July 14, one human case of St. Louis encephalitis has been reported in Kern County.

CDPH monitors avian — bird— deaths as a way of predicting when and where people may be at greater risk. The state continues to work closely with local agencies such as the Contra Costa Mosquito & Vector Control District to reinforce prevention tips and control mosquito populations and the diseases they spread.

Contra Costa County residents can report dead birds by phone at 877-WNV-BIRD (968-2473) or online.

County residents can request mosquito service for residential property by calling 925-685-9301 or online.