West Nile virus worries high with heavy rain and snowfall

Cool temperatures in Alameda County have helped shield the area from the West Nile virus. However, public health officials are worried that the lull won’t last with warm weather on the way.

Rising temperatures combined with this year’s heavy snowfall and a rainy winter create ideal breeding grounds for mosquitoes and the West Nile virus they transmit to humans and animals.

“We expect to see more cases if the predictions are right,” said John Rusmisel, district manager of the Alameda County Mosquito Abatement District. He said mosquitoes already are more plentiful this year.

Last month’s discovery of a dead crow in Sunnyvale increased concerns, although the bird could have contracted the virus elsewhere, Rusmisel said.

In any case, Alameda County plans to continue its aggressive campaign that has helped prevent the spread of West Nile virus. It also will encourage residents to take precautions.

Clearing stagnant water is key to controlling mosquito larvae before they become adults. Alameda County uses inspectors on foot as well as airplanes to spot foreclosed homes where water in pools attracts thirsty birds and mosquitoes. Mosquitoes contract the disease when they feed on infected birds.

The county uses bacteria that occurs naturally in soil to kill the larvae in the water and to treat sewer catch-basins to prevent breeding.

Alameda County has never had to spray insecticides and would only use them in extreme cases, Rusmisel said. “A healthy environment keeps things in check.”

Abatement efforts and a cool summer made 2010 one of the mildest seasons since the first case of West Nile virus was recorded in Alameda County in 2003. No human cases of the virus were found in 2010, according to the Alameda County Public Health Department. Only one bird tested positive; no squirrels or mosquito pools tested positive.

Outbreaks tend to be more severe in areas where warm temperatures combine with water, such as hot spots like the Springtown area of Livermore and county fairgrounds in Pleasanton, Rusmisel said.

The risk increases for other areas from July 4 until the end of October.

The virus will be worse some years than others, he said, but “it’s here to stay.”