Despite near-record rainfall and a lot of standing water, West Nile virus has yet to crop up this spring in several Southern California counties, including Riverside and San Diego. Public health officials from this area say they are cautiously optimistic that Riverside County will see a milder outbreak of the mosquito-borne disease this year than in 2004, when 116 people were infected and two died.

While officials stopped short of making predictions, let alone promises, they said there are reasons to believe the 2005 season may be milder.

No humans or horses across California had become infected as of Friday, and not a single dead bird or sentinel chicken —— key barometers of West Nile activity —— had tested positive for the virus in Riverside County, state and county statistics show.

Meanwhile, animals have had time to build up immunity against the disease since its arrival in late 2003. After last year's outbreak decimated bird populations, there are fewer crows around. Because concentrations of the virus buildup in crows, they tend to act like a reservoir for the virus and accelerate its spread. As well, vector control workers are on the prowl, hunting for signs of mosquito breeding and pouncing on larvae wherever they find them.

"It's early in the season, but by this time last year we already had West Nile activity," said Barbara Cole, director of disease control for the Riverside County Department of Public Health. "We're hopeful that this will be a quieter year, but I just cannot predict that at this time."

The downturn in activity has occurred despite a winter and spring of near-record rainfall, which left behind many more pools than last year's storms did and fueled fear early on that 2005 could see a severe outbreak.

Fears put on hold

"Certainly, we have had a lot of precipitation this year," said Vicki Kramer, chief of the state Department of Health Services' Vector-Borne Disease Section, from her Sacramento office. "But temperatures have been cooler and that may have a dampening effect on West Nile virus transmission."

Kramer said mosquitoes are most prolific at breeding in hot weather. Spring so far in Southern California has been mild overall, despite warmer-than-normal temperatures during the weekend. That may be partly why the virus has not been found in any animal in Riverside and San Diego counties this year, and has been discovered in just one chicken in San Bernardino County, state officials said.

"We're not picking up anything in our sentinel chicken flocks or the birds that we have trapped so far," said Steve Van Stockum, deputy director of environmental health for Riverside County.

That could change in a hurry, Kramer warned.

"It is good that we haven't detected West Nile virus in some of those (Southern California) regions, but that doesn't mean that we won't detect it soon," she said.

Barry Hess, an environmental health specialist for Riverside County, said, "It is still relatively early. We have a large amount of standing water."

With all that water, mosquitoes could produce a bumper crop of babies this year and send an army out into the field, launching a fresh West Nile virus assault. Consequently, Hess and Jeff Lythgoe, an environmental health technician, have been regularly inspecting ponds across the county and treating them with chemicals to kill mosquito larvae upon finding signs of babies.

On a recent morning, the duo was out inspecting the cattail-ringed pond along Monroe Avenue, across the street from Calvary Chapel Murrieta.

"Keep in mind, mosquitoes not only transmit disease, they are a pest," Hess said. "People don't like them buzzing around their heads."

Back yard problems

Van Stockum said county vector-control workers also are regularly checking chickens at ranches in the Temecula-Murrieta area, Woodcrest and near Lake Perris for the presence of West Nile. Also, they are testing birds found dead on the county's bustling city streets and quiet back-country lanes.

Whether this season winds up being milder than the last one, Riverside County residents will have to adapt to life with the virus lurking nearby.

"We believe that West Nile is here to stay," said Christine Pearson, a spokeswoman for the national Centers for Disease Control and Prevention in Atlanta. "Once it enters a state, it stays there. It doesn't disappear. And the best thing people can do is to go ahead and protect themselves."

Public health officials say it is easy to protect oneself from being bitten by the spindly, blood-sucking insect that transports West Nile. They say residents can empty fountains and bird feeders, replace damaged window and door screens, stay inside around dawn or dusk when mosquitoes are active, wear long pants and sleeves outside and spray insect repellent on exposed skin.

"A lot of the problem is people's own back yards —— their ornamental ponds," Lythgoe said.

Besides protecting oneself, Cole said animal lovers should consult with veterinarians and come up with a plan for vaccinating their horses. According to the state Department of Health Services, Riverside logged the most equine infections, 102, of any county in California last year. Half of the infected horses died.

Statewide, 540 horses were infected. Health officials say horses are particularly vulnerable to the virus.

When it comes to humans, about 80 percent of those who are infected do not experience symptoms, officials say. Most of the rest develop only mild symptoms, such as headache and fever.

3rd most cases in 2004

On the positive side, once people are exposed they tend to build up immunity and, like the measles, tend to get infected with West Nile only once, Cole said.

"If you've already been infected, it is very unlikely that you would get it again," she said.

However, that first infection is fatal for some.

Some —— mostly the elderly, very young or people with compromised immune systems —— contract a life-threatening disease. Infection is most dangerous when it develops into encephalitis, inflammation of the brain; meningitis, inflammation of the tissue surrounding the brain and the spinal cord; or myelitis, inflammation of the spinal cord.

In 2004, California recorded a total of 830 human cases of infection, state statistics show.

Riverside County had the third most in the state, 116, trailing only Los Angeles, with 331, and San Bernardino, at 197. Officials reported 64 cases in Orange County and two in San Diego County.

Infection killed 27 people statewide, including 14 in Los Angeles County, five in San Bernardino County, four in Orange County, two in Riverside County, and one each in Kern and Tehama counties.

"We anticipate that West Nile virus activity will be greater in 2005 in the northern and central regions of the state, but for Southern California, it's a little more difficult to predict," Kramer said,

West Nile was first detected in this country in 1999 in New York. In the half dozen years since, it has spread to nearly every state.

Contact staff writer Dave Downey at (951) 676-4315, Ext. 2616, or ddowney@californian.com.