West Nile virus arrives

The vast majority of people bitten by infected mosquitos won't experience anything beyond the typical bug bite, said San Mateo County Health Officer Dr. Scott Morrow.

Only about one in 150 people bitten by infected mosquitos suffer long-term neurological damage, he said. These people can suffer symptoms that may have long-lasting impacts on their sight and gait. Just a small fraction of these people will die as a result, he said.

About 250 people died from West Nile virus last year, Morrow said. To put things in perspective, about 30,000 people die from influenza every year.

"It's true that the flu is much worse," Morrow said. "This is just frightening because it's never been here before."

About 15 percent to 20 percent contract a flu-like illness called West Nile fever. Symptoms including fever, stiff neck and headaches last about a week and are not life threatening, Morrow said.

Those most susceptible are the elderly, very young and those with weaker immune systems, said Beverly Thames, public information officer for the county's Health Department.

Controlling mosquito breeding is key to keeping the spread of the disease in check, Morrow said.

To prepare for its arrival, officials created a Mosquito Abatement District several years ago. The idea is to control the spread of the disease by controlling the proliferation of mosquitos.

For several months now, catch basins, backyards and other breeding sites have been treated for mosquito control.

In San Bruno, officials have closely monitored places like the Mills Field area, said Robert Reichel, the city's representative to the district.

For several months, Reichel said the district has treated the water with dry pellets that "trick mosquitos into not breeding." Sentinel chickens have also been placed behind the Belle Air Elementary School; their blood is checked regularly for signs of the virus.

"It's the first line of defense," Reichel said.

The West Nile virus is passed primarily between birds by mosquitos. Humans, horses and other animals can become infected if bitten by an infected mosquito. Birds are highly susceptible to the virus. Reports of dead birds are an early indication the virus is circulating in the environment.

The first birds to test positive in California were identified in Southern California in 2003. Since then the number of infected birds and mosquitoes has swelled as the virus made its way north, according to the San Mateo County Health Department.

Yunmi Choi can be reached by e-mail at yunmi@smdailyjournal.com or by phone: (650) 344-5200 ext. 109. What do you think of this story? Send a letter to the editor: letters@smdailyjournal.com.