The year's first case of West Nile in the county was confirmed Friday in a dead crow found near Moss Beach, launching what experts say could be the most severe season for the virus so far locally.
After an unusually warm winter and drenching spring, the mild temperatures have allowed many mosquitoes, typically active only during the summer months, to survive the winter and begin breeding early. At the same time, the salt marsh mosquitoes normally active in winter are also thriving, county Vector Ecologist Chindi Peavey said.
“We've had lots of rain and we’re expecting the standing water to remain later into the summer, so we’ll be doing stepped up surveillance and treatment,” Peavey said.
The disease, with symptoms similar to flu, is most commonly transmitted to humans through mosquito bites after the insect feeds on an infected bird, officials said.
“I do expect to see at least one human case of West Nile virus originate in San Mateo County this year, but nothing on the order of Sacramento County last year,” which led the state with 177 human cases, said Dean Peterson, director of environmental health for the county. The one human case of the virus reported in the county in 2005 was brought in from outside, Peterson said.
Because of the threat of West Nile, mosquito abatement techs plan to begin treating storm water basins May 1, three weeks earlier than last year. Already in 2006, abatement techs have sprayed the marshes near Bair Island twice by helicopter and a third spraying may be required, said James Counts, operations supervisor for the county Mosquito Abatement District. Helicopter spraying was done just once last year, Counts said.
The mosquito problem is already so severe that techs will take the unusual step of spraying Foster City with a truck-mounted fogger on Wednesday night from midnight to 5 a.m., officials said. While foggingFoster City isn’t unheard of, such treatment is usually used as a last resort and shows that the mosquitoes have already outgrown the waterborne stages, Peavey said.</p>
Aside from increased breeding along the Bay, standing water near homes is an issue because of the amount of rain in recent weeks. “We've been discovering about three times as many houses that have mosquitoes breeding underneath them this year,” Peavey said.
With 15 full-time staff and eight to 10 summer employees, abatement district techs will have to pull out all the stops to cover the county’s 450 square miles from Año Nuevo to Daly City, working weekends if necessary, Counts said. “Our biggest mission is to be preventative and [treat the mosquitoes] at the aquatic stage rather than wait until they are adults,” Counts said. Doing so lets his techs treat 10 to 30 times as many mosquitoes compared to those that grow into adults and can fly as far as 20 miles, he said.