Petaluma mosquitoes test positive for West Nile virus

West Nile virus has been detected in mosquitoes in Sonoma County for the first time this year, and the disease has infected two people in Butte County, public health officials said this week. The announcements come amid rising reports of the disease around the state.

Nevada County health officials also confirmed to a local news agency that they are investigating a human death as a suspected West Nile case, though the results of ongoing tests will not be known for several days.

The infected mosquitoes from Sonoma County were taken from a trap in Petaluma, near the city’s Ellis Creek Water Recycling Facility on Cypress Drive, off of South McDowell Boulevard, the Marin/Sonoma Mosquito & Vector Control District announced.

The site is also near walking trails that lead to and from Shollenberger Park and have been posted with information about the discovery of virus-positive mosquitoes in the area, district spokeswoman Nizza Sequeira said.

District personnel fogged the area Wednesday night to cut down adult mosquito populations in the area and were continuing to trap and monitor insects to control the number and disrupt the transmission cycle, she said.

But the findings mean the virus is here and potentially transmittable to humans, Sequeira said.

“It is imperative that residents take the threat of (West Nile Virus) seriously and protect themselves against mosquito bites,” she said.

Health officials say it’s likely that the reduced availability of water because of the drought has forced birds to congregate in greater concentrations, aiding transmission of the virus between birds and mosquitoes around the state this year. Mosquitoes breed in standing water.

Two people in Butte County who donated blood that tested positive for the neurological virus were reported as the first human cases in California this year, the Butte County Public Health Administration said.

The two individuals, who are unrelated, were symptom-free, but their blood tested positive for the virus during routine screening, the agency said in a news release Thursday.

The results follow a statement made just last week by California State Health Officer Dr. Karen Smith, who declared it “only a matter of time before we see the first case” of human infection, given the recent rise in virus activity.

California had 801 human cases in 2014, including 31 deaths.

This year, to date, evidence of West Nile virus has been found in 31 California counties - about a third more than last year at this time, Smith said.

At least 348 mosquitoes have tested positive for the virus this year, as have 185 dead birds and three sentinel chickens used as part of the state’s virus surveillance system.

In Sonoma County, two infected birds were found in Windsor last May.

Only about 20 percent of the people who become infected with West Nile virus develop symptoms, which include fever, headache, body ache, nausea, rashes, swollen lymph nodes and vomiting.

About one in 150 people infected with the virus develops serious illness, which may result in neurological damage or even death.

Officials urge people to take precautions against breeding mosquitoes and being bitten, including using repellents containing DEET or other recommended agents; wearing sleeves and long pants at dusk and dawn, when mosquitoes are most likely to bite; using tight-fitting window screens in good repair; eliminating all sources of standing water; and using mosquito fish, where appropriate, to keep down insect populations in ponds and other water features.

The Marin/Sonoma Mosquito & Vector Control District can help. In Sonoma County, residents also are urged to report mosquito problems to the district at 285-2200 or online at www.msmosquito.com.

You can reach Staff Writer Mary Callahan at 521-5249 or mary.?callahan@pressdemocrat.com. On Twitter?@MaryCallahanB.