By Evelyn Nieves
The Associated Press

SAN FRANCICSO — Two plagues in California, fires and foreclosures, may be increasing the risk of another: West Nile virus.

Northern California wildfires have sullied the air in the Sacramento area so badly that officials there have held off aerial spraying of insecticide to combat the spread of the virus, which is transmitted to humans and animals by infected mosquitoes.

At the same time, water standing in backyard pools at abandoned, foreclosed properties has created a breeding ground for mosquitoes, raising the risk of West Nile infection.

The state has confirmed three human cases of West Nile in California so far this year - two in Stanislaus County, in the Central Valley south of Sacramento, and one in Tulare County, farther south in the valley.

The Sacramento-Yolo County Mosquito and Vector Control District held off spraying of mosquito insecticide last week because of concerns that airborne particulate matter from wildfire would bind with the insecticide, making it ineffective against the pests. The agency planned to start spraying on Wednesday.

The rate of infected mosquitoes in the Sacramento area is "pretty high - more than 10 in 1,000," making West Nile a significant concern, said David Brown, president of the Mosquito and Vector Control Association of California and manager of the Sacramento-Yolo agency.

But while a delay in spraying may have increased the risk of infection, Brown added, "One thing that may have been in our favor with all the smoke last week is that people stayed indoors."

To combat mosquitoes in standing water, officials in Sacramento and other parts of the state are turning to a tiny fish, the Gambusia affinis, which feeds on mosquito larvae.

Workers deliver the fish free to any homeowner who requests them, and the technicians plant the fish in pools if cities or real estate agents report abandoned homes, district spokeswoman Luz Maria Rodriguez said.

Statewide data on the number of foreclosed homes with pools aren't available, but in the Sacramento-Yolo district, workers have planted the fish at about 2,000 homes so far this year - compared with about 500 at the same time last year, Rodriguez said.

The Greater Los Angeles County Vector Control District also reported nearly double the number of service requests for the fish in May over the same period in 2007.

But in San Diego County, the fish is late to breed and in short supply. Officials there can't expect to fill their demand until late July or early August.

West Nile, which is widespread in Africa and the Mideast, arrived in the United States in 1999.

In 80 percent of the cases, people infected with West Nile have no symptoms. But about 20 percent of those infected experience mild symptoms such as headache, fever and nausea. In less than 1 percent of cases, West Nile virus can lead to paralysis, even death.