West Nile virus flies past the county

BURLINGAME — Dire predictions that this was the summer the first locally contracted human cases of West Nile virus would occur in the county failed to materialize thanks in large part to stepped-up pesticide treatments, officials said Monday.

Summer hires by the county Mosquito Abatement District, normally brought on in June or July, instead hit the streets in March and April spraying storm water basins, where many of the most dangerous West Nile-carrying mosquitoes breed, according to Robert Gay, district manager.

“Knowing it was going to be a really bad year, we started earlier,” Gay said. Vector control experts began warning that this year could bring the county’s first human cases of West Nile after exceptionally heavy spring rains. The rains grounded helicopters used to drop pesticide on Bair Island — essentially 2,600-acres of mosquito breeding grounds — and created pools of standing water in backyards and creeks all over the county.

Because larval treatments on Bair Island were delayed, mosquitoes there got a head start forcing officers to fog parts of the county along the Bay in May, an unusual step, said Chindi Peavey, county vector ecologist. The fogging, combined with early storm water basin treatments, drastically reduced mosquito larva by summer, Peavey said.

In addition, about $225,000 from the state has helped the county fight West Nile in the last two years, officials said. The district used the funds to buy three pesticide spray trucks and additional pesticide for treating larval mosquitoes, Gay said. Extensive trapping, used to triangulate mosquito breeding grounds, also allowed abatement officers to better focus their treatment, Peavey said.

No human cases of West Nile virus were diagnosed in San Mateo County this year, although seven dead birds were found to carry the disease. In neighboring Santa Clara County 220 dead birds were collected with West Nile and five human diagnoses were reported, state Department of Health data shows.

While this year’s peak mosquito season is behind us, the virus continues to be a threat and residents should report dead birds and drain any standing water from near their house, county health officials said. “Just because no cases were diagnosed [this season] doesn’t mean nobody contracted West Nile virus,” said Dr. Catherine Sallenave, assistant county health officer.

ecarpenter@examiner.com

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