North Valley mosquito districts track West Nile virus as summer activity surges

MADERA COUNTY, Calif. (KFSN) -- As mosquito season peaks in the North Valley, mosquito control districts in Merced and Madera counties are monitoring activity and testing for West Nile virus, with officials reporting different trends in each county.

In Merced County, officials described the season as relatively mild so far. Fourteen mosquito samples have tested positive for West Nile virus, and no human cases have been reported.

"We've done heavy amounts of Larviciding this year. We've actually seen relatively low numbers of trap counts," said Adara Culpepper with the Merced County Mosquito Abatement District.

Culpepper said the district is performing better than it did last year.

"We're faring better than last season. This year we went ahead, we went out and we got to things very, very early," Culpepper said.

Mosquito control efforts include trapping, truck-mounted insecticide treatments, and aerial applications.

Crews are also monitoring mosquito populations during what officials say is the busiest time of year for mosquito activity.

In neighboring Madera County, officials said increased testing has led to higher numbers of West Nile-positive mosquito samples. More than 200 mosquito samples have tested positive, and one human case was reported last week.

"July, August, September is our peak season for mosquito activity," said Abraham Velazquez of Madera County Mosquito and Vector Control District.

Crews in Madera collect mosquitoes from traps and test them for diseases. Lab Manager Laura Muratore demonstrated the process of identifying and sorting mosquitoes.

"I'm separating not only by mosquito species but by sex because female mosquitoes are the only ones that bite," Muratore said.

"Taking a sample of those mosquito populations allows us to test for those diseases that mosquitoes can be spreading to people," she said.

Officials also prioritize testing water sources and inspecting potential mosquito breeding areas.

In Madera County, mosquito fish are used as part of control efforts to help reduce mosquito populations. The fish are available free to homeowners in the area.

"Think big water sources like ponds, green pools, unmaintained swimming pools, water troughs," Velazquez said, describing locations that can become mosquito hotspots.

Through July, the Merced Abatement District predicts a moderate risk of human infection from the West Nile virus. Officials said residents should take precautions because infection can occur from a single mosquito bite.

Experts recommend remembering the "three D's" for mosquito protection: use repellents containing DEET, take precautions during dawn and dusk when mosquitoes are most active, and drain standing water around homes and properties.

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