Peninsula guarding against West Nile

Guardian chickens, mineral oil and animal testing are all being used this summer to prevent an increase in mosquitoes in San Mateo County, after South Bay cities experienced a surge in possible carriers of the West Nile virus.

Parts of San Jose, Los Gatos and Campbell are experiencing an increase in mosquitoes that carry the virus. Dead animals are often indicators of West Nile, signs that virus season could be severe in August and September.

County officials have been working vigilantly to make sure an increase in such indicators is not experienced locally.

Throughout the Peninsula, extensive spraying of a refined mineral oil called Golden Bear is done yearly to prevent the growth of mosquitoes in the county’s lagoons, creeks and ponds. The oil suffocates larvae and weighs down adults, preventing them from leaving the water.

“We do fogging when necessary, but right now, we’re doing a lot of treatment at the larval and immature stages,” said San Mateo County Mosquito Abatement District spokeswoman Lauren Marcus.

In June and July, 47 dead animals were reported to the county, but only one tested positive for the virus — a dead squirrel found July 9.

There were 278 reported cases of West Nile virus among California residents last year, mostly in Southern California, according to the abatement district. Seven people died; no human cases were reported in San Mateo County.

Local residents have been working hard to prevent mosquitoes from finding a place to spawn.

“In our growing areas of the plant nursery at Redwood High School we strictly ensure that the drainage saucers dry out every four days,” said Barbara Patterson, who lives near San Carlos’ Cordilleras Creek.

In addition to testing dead animals, the county sets mosquito traps in areas known popular with the pests and even employs a flock of ten sentinel chickens to act as early indicators of possible diseases.

The chickens — kept in an undisclosed location — are tested periodically for diseases including West Nile, Western equine encephalitis and St. Louis encephalitis. The birds do not die from the diseases, but their immune reactions can be tested for the presence of the diseases.

As a result of the South Bay increase, Santa Clara County fogged for mosquitoes last week. Two more fogging runs are scheduled for tonight.

“It’s starting to worry us a bit — our numbers of dead birds are over double what they were last year at this time,” said Santa Clara County Vector Control District spokeswoman Kriss Costa.

By the numbers

» 80 percent of those infected with West Nile virus develop no symptoms.

» 20 percent of those infected develop fevers, aches and nausea.

» One in 150 people infected will develop severe illness, including high fever, headache, neck stiffness, stupor, disorientation and paralysis.

» Infected people typically develop symptoms within three to 14 days.

– Source: Centers for Disease Control and Prevention

jgoldman@examiner.com

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