Last year, mosquito abatement districts contended with floodwater in their ongoing battle against West Nile virus.
This year, it's foreclosures and the sluggish resale housing market.
For-sale signs, especially if standing for weeks or months in front of empty houses, are red flags for vector control personnel looking for pockets of mosquitoes in residential areas.
As the weather warms up, it heightens the risk that infected mosquitoes will spread the virus to people.
"We are calling a lot of Realtors to get access to these properties," said Lloyd Douglass, general manager of East Side Mosquito Abatement District, which includes most of the northern half of Stanislaus County, including Modesto.
"If they are being foreclosed on or sold, there is no one there to take care of them."
District officials said that real estate brokers are cooperating with their requests to provide access to the back yards and contact the owners.
The Turlock Mosquito Abatement District treated for mosquito larvae at a couple of residential properties in Denair on Thursday.
Although there is no sign this year of the virus in Stanislaus County and no reports of people infected in the state, the abatement districts began efforts this month to control a virus that has killed here.
In 2005, Stanislaus County had 92 confirmed cases — the second-highest among the state's 58 counties — including one death. San Joaquin County had 36 people infected that year, including one fatality, and Merced County had 28 cases.
Last year was mild by comparison, but officials are not taking any chances.
With foreclosures on the rise and home sales at their lowest levels in a decade, the abatement districts in Stanislaus County are focused on unoccupied homes.
Even if owners drained their swimming pools before moving out, many pools will not completely drain, officials said. And, they added, pools collect rainwater. Mosquitoes also can breed in flower pots, buckets and tires left behind.
The mosquito abatement districts said neighbors have reported some of the green pools; other problems were discovered by surveillance personnel making their rounds.
The Turlock district also is going to homes identified as backyard breeders in previous years.
"We have found quite a few, and it is still early in the year," said Jerry Davis, manager of the Turlock district, which includes the south part of the county and areas west of the San Joaquin River.
The districts said they are working with people who have moved and are having trouble selling their homes. Abatement personnel will treat mosquitoinfested pools and can leave fish in the water to eat hatching larvae.
Because of the public health threat, officials are urging absent owners to continue maintaining their homes.
Dr. John Walker, health officer for Stanislaus County, said he is regarding the West Nile outlook for 2007 with cautious optimism.
Even though early spring flooding in 2006 created breeding areas for mosquitoes, there was a big decline in the number of West Nile cases last year. Another encouraging marker was that fewer than 10 horses were infected in 2006 compared with 46 the previous year, Walker said.
Officials cited several reasons for the lower caseload, including mosquito abatement efforts, people taking precautions and owners vaccinating their horses. In addition, birds, other animals and people build up immunity to the virus.
As of Thursday, the state's West Nile Virus Web site had reported six dead birds, one horse and two sentinel chickens infected in California, most in Southern California. A sentinel animal is one that's monitored for signs of illness.
The state is asking people to report dead birds and squirrels.
Davis said West Nile watchers should understand it's tree squirrels that carry the virus, not ground squirrels, which are far more common in the valley.
Tree squirrels live in area parks, have bushy tails, and people should be concerned if they find carcasses, officials said.