An elderly woman died Thursday in central Contra Costa County from West Nile virus, a mosquito-borne disease transmitted to humans and animals through mosquito bites.
Mosquitoes become infected when they feed on infected birds or squirrels.
“The death is unfortunate,” said Wendel Brunner, director of public health for Contra Costa County.
There have been three known cases this year in Contra Costa County. To date there have been two deaths in California and 96 human cases reported. The state’s first death this year was reported earlier this month in Butte County.
There have been no human cases detected in Alameda County, though 10 birds were found with the virus, nine of them in the warmer Tri-Valley area of Livermore, Pleasanton and Dublin. The mosquito carrying the virus has also been detected in the city of Alameda.
Two years ago, the virus was detected in a dead American Crow in Berkeley, but Berkeley has had no signs of the virus since that time, said Linda Rudolph, Berkeley’s public health officer.
In Contra Costa 24 sentinel chickens in three flocks located in Martinez, Holland Tract, and Oakley tested positive for the virus. In response, the county sprayed adult mosquitoes from the air last week from Martinez to Pittsburg along the waterfront. Spraying was done by helicopter using pyrenone 25-5, applied at a rate of 0.75 ounces per acre, according to a press statement issued by the Contra Costa Mosquito and Vector Control District.
“Spraying is less risky than the virus,” Brunner said.
To date, spraying has not been necessary in Alameda County, said John Rusmisel, director of the Alameda County Mosquito Abatement District. He said the district is able to control the mosquito population by killing or disabling the mosquito larvae in catch basins.
Aerial spraying in Alameda County would be a last resort, Rusmisel said. If they had to spray, the mosquito district would also use pyrenone 25-5, which Rusmisel said is less toxic to non-targeted organisms than pyrethreum, which is sometimes used,
The Mosquito Abatement Board, with one representative from each city, “decided if we do use aerial fogging, we will have a community meeting first,” he said, noting this delays the process, but gives people the information they need and allows them to make plans to leave the area for the day if they choose.
Over the 12 years he’s managed the district, Rusmisel said he’s used less than five gallons of the substance. “One county used over 100 gallons in a three-week period,” he said, declining to name the county.
The elderly and those with impaired immune systems are at the highest risk of West Nile Virus. “80 percent of those infected don’t have any symptoms at all,” Brunner said.
People experiencing severe headache, high fever, stiff neck, confusion, tremors, convulsions or muscle weakness should contact their health care provider right away, Susan Farley, public health nurse for Contra Costa County said in a press statement. She said coma and paralysis are other possible symptoms. Symptoms generally appear three to 15 days from a bite of an infected mosquito.
There are a number of things people can do to reduce the mosquito population and lessen the risk of being bitten:
• Get mosquito-larvae eating fish for ponds (Rusmisel noted there are a lot of backyard fish ponds in Berkeley);
• Report dead birds or squirrels: 1-877-WNV-BIRD; www.westnile. ca.gov;
• Drain standing water that can support mosquito breeding;
• Avoid spending time outside when mosquitoes are most active, especially at dawn and the first two hours after sunset;
• Apply insect repellent.