SAN DIEGO —— With the rainy season ending and temperatures warming up, county environmental health officials are preparing to begin a third straight year of fighting to keep West Nile virus at bay —— and hoping to be as successful as the first two years.

Last year, while neighboring counties reported hundreds of human cases of the mosquito-driven, sometimes fatal disease, San Diego County had just two —— the county's first two.

County officials said last week that they expect the 2005 West Nile fight to be tougher.

The region's wettest winter in years could make it harder to control mosquito populations.

But officials said there are signs that the disease could be held in check in San Diego County despite its rapid spread across the country.

County pest-control trappers haven't yet seen a spike in mosquito populations, said Jack Miller, county environmental health division chief.

And statistics suggest the numbers of human cases in other parts of the country have decreased sharply as governments have mustered a fight to control its spread, he said.

For example, the total number of human cases in the United States dropped from 9,862 in 2003 to 2,470 in 2004. Cases in Colorado dropped from 2,947 to just 276 over the same period; from 1,039 to 51 in South Dakota; and from 720 to 158 in Texas.

A UC San Diego infectious-disease doctor predicted San Diego County would not see a huge spike in human West Nile virus cases because the local mosquito population doesn't seem to be as frenzied as in other parts of the country.

"Mosquitoes in San Diego seem to be less desperate and more oriented to feeding on other animals (rather than people)," said Joseph Vinetz, an associate professor in UCSD's school of medicine in the division of infectious diseases. "I don't think there are going to be huge numbers of sick."

Wildfire

West Nile virus —— which is mainly a bird disease but can be spread to humans, horses and other animals by mosquitos that feed on infected animals and then on people —— has spread like wildfire across the United States since it was discovered in the country in 1999.

Public health officials said about 20 percent of the people who are bitten by infected mosquitos suffer mild flulike symptoms. Fewer than 1 percent get seriously ill, they said, but the virus can cause brain inflammation in rare cases.

In 2002, while West Nile virus numbers were shrinking in many other parts of the country that it hit first as it traveled west, California's human cases spiked.

In 2003, California reported just three human cases of West Nile virus and no deaths.

Last year, that number swelled to 830 human cases and 27 deaths, according to state health records.

But San Diego County, with only two human cases reported, remained an island of immunity compared with surrounding counties.

Nearby Orange County reported 64 cases; Riverside County, 116; San Bernardino County, 197; and Los Angeles County, 331.

Aerial attack

Environmental health director Gary Erbeck told county supervisors at a recent meeting that his workers believe their decision to use helicopters to drop tons of granular larvicide to kill off baby mosquitoes kept West Nile virus at bay.

Erbeck said San Diego was the only county in the state that did the aerial drops, a series over the spring and summer months in 25 waterways that were close to where people lived but that could not be reached by vector-control teams on foot.

The North County waterways included the San Luis Rey River, Agua Hedionda Lagoon, the Rancho Bernardo lakes near Black Mountain Road, and San Elijo Lagoon.

Expensive fight

However, Erbeck said, two years of conducting the expensive helicopter drops and marshaling extra efforts to prevent the spread of West Nile virus had exhausted the county's funding for vector control, which involves managing insects and vermin that carry diseases.

He said by the end of the fiscal year in June, the vector-control division will have a $1.3 million deficit.

Because of that, county supervisors voted to conduct a mailed-ballot election in May or June to ask home- and property owners throughout the county to pay $8.55 per home more a year, and roughly $2 more per apartment a year, for pest control.

Currently, home and property owners pay the county $2.28 to $3 a year to fund regional pest control efforts to contain bugs, rodents and animals that can spread diseases such as West Nile virus, hantavirus dengue fever and bubonic plague.

Miller, meanwhile, said that there is little evidence that mosquito populations are rising and that the county does not plan to restart the larvicide drops immediately.

He said the decision to hold off on the drops had nothing to do with dwindling cash for the project, adding that the county didn't start aerial drops last year until May.

"We're going to continue with the aerial application this year," Miller said. "They were really effective. When it starts warming up and we get a couple of weeks of warmer weather, we expect to see breeding increase."

Still watching

Until that happens, Miller said, county officials plan to continue tracking breeding areas and respond to calls from county residents who report mosquitoes.

He said county officials this week will again urge people to protect themselves by draining pools of standing water, wearing insect-repellent with the chemical DEET, and reporting dead birds they find to the county.

UCSD's Vinetz advised taking precautions but said he didn't think San Diego County would ever see huge numbers of people contracting West Nile virus.

He said the county's generally milder, drier weather is not nearly as conducive to mosquito breeding as other parts of the country, or state.

Smaller populations, he said, mean fewer disease transmissions.

"I moved to Galveston, (Texas), in July of 1998," he said. "And in August we broke a long drought and had a lot of rain. Within six to seven days the entire outer walls of our house —— which were white —— were brown with mosquitos.

"I've seen mosquitoes (in San Diego County) but nothing like the sheer numbers you'll find in the Southern United States or cold places like Colorado where there are short feeding seasons," he said.

For more information about West Nile virus and how to protect yourself from it, people can visit the county's "Fight the Bite" Web site at sdfightthebite.com or call the county's toll-free telephone number at (888) 551-4636.

Contact staff writer Gig Conaughton at (760) 739-6696 or gconaughton@nctimes.com.