News

Sep 16, 2023

Contra Costa Sees Increase In West Nile Virus Activity

CONTRA COSTA COUNTY, CA — The Contra Costa Mosquito and Vector Control District on Friday reported its third dead bird of the year and its third group of trapped mosquitoes that tested positive for

CONTRA COSTA COUNTY, CA — The Contra Costa Mosquito and Vector Control District on Friday reported its third dead bird of the year and its third group of trapped mosquitoes that tested positive for WNV.

The bird was a California scrub jay collected from Oakley, while the mosquitoes were trapped in Brentwood. Last month, two groups of trapped mosquitoes from Discovery Bay and two dead birds; one from Brentwood and the other from Martinez, tested positive for WNV in Contra Costa County.

WNV can be transmitted to birds, other animals and people through a single mosquito bite. With WNV activity on the rise within Contra Costa County, the District recommends county residents take steps to avoid mosquito bites and reduce the risk of WNV (see below).

"Statistically, this is the time of year when we typically see the highest risk of human cases, so it is very important for Contra Costa County residents who plan to be outside when mosquitoes are present, to wear an EPA-registered insect repellent that includes one of the four most effective active ingredients: DEET, Picaridin, IR3535, or the repellent version of Oil of Lemon Eucalyptus. And always follow the instructions on the label when using insect repellent," said Steve Schutz, scientific program manager for the Contra Costa Mosquito and Vector Control District.

West Nile Virus In The Bay Area

On Friday, Napa County confirmed its first sign of West Nile Virus activity this year. A mosquito specimen sample collected July 19 in Calistoga tested positive for the virus.

No human cases of WNV have been reported in Napa County, Contra Costa County or the Bay Area thus far in 2023. However, all Bay Area counties have reported positive mosquito samples.

In response to the increase in WNV activity in Contra Costa County, district employees will conduct surveillance and control as needed in the areas where the dead bird and mosquitoes were found.

Current West Nile Virus Activity In California

Thus far this year in California, eight human cases from five counties have tested positive for the virus — six of which were reported this week. Of the eight cases, one was in San Joaquin County, one was in Merced County, two were in Tulare County, one was in Kern County and two were in San Bernardino County.

Two horses from two California counties and 27 sentinel chickens from four counties have tested positive for WNV this year.

As of Friday, 181 dead birds from 20 counties have tested positive for the virus across California, while there have been 1,582 positive mosquito samples reported from 27 counties, according to Westnile.ca.gov. At this time last year, there were 965 positive mosquito samples reported in the Golden State.

West Nile Virus In Contra Costa

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

With WNV activity on the rise within Contra Costa County, the district recommends county residents take steps to avoid mosquito bites and reduce the risk of WNV.

Most people —about four of five — infected with the West Nile virus will not develop any symptoms. About one in five will develop mild flu-like symptoms, including fever, headache, body aches, nausea, vomiting, and swollen lymph glands. However, about one in every 150 people infected with WNV will develop severe neurological disease. In rare cases, WNV infection can be fatal.

Anyone can be infected with WNV but those at greater risk of developing severe illness include people 60 or older, people who have received organ transplants, and people with certain medical conditions such as cancer, diabetes, hypertension, and kidney disease.