West Nile Cases Fall From ’04

Despite the heavy winter rains and an expected increase in the mosquito population, confirmed human cases of West Nile virus remain few and far between -- but health officials aren’t ready to relax yet.

West Nile hit hard last year, particularly in Southern California. A total of 28 people died statewide, and there were 830 recorded infections, according to state health officials.

Some experts are predicting a milder season locally this year because many people may now be immune to the disease. Northern and Central California, which were affected by the disease only late last season, may see more cases this time around, experts said.

West Nile is transmitted through the bite of mosquitoes to humans and other animals. The mosquitoes become infected after feeding on infected birds.

The vast majority of people infected do not get sick; those who do generally have symptoms similar to flu. In extreme cases, meningitis and encephalitis occur, sometimes resulting in death.

According to data released Tuesday by the California Department of Health Services, there are 14 reported human cases of the virus statewide, compared to 24 cases in mid-July last year. On July 22 of last year, the state reported its first death blamed on West Nile. No deaths have been reported in 2005.

Throughout the state, local agencies have become more vigilant about mosquito control, aided by a $12-million grant to help combat the virus.

“The bottom line is we’re seeing fewer [human] cases this year than last year,” said Vicki Kramer, chief of the Vector-Borne Disease Section of the California Department of Health Services. “It’s still too early to say how ’05 is going to compare to ’04 because it is now just starting to get hot.”

Warmer weather is crucial to the virus’ transmission because hotter temperatures increase mosquito activity. A cooler-than-average spring and early summer may have delayed the onset of the season this year, experts said. August is traditionally the month when the threat of human infection is highest, officials said.

The wet winter also remains a factor in transmission because it contributed to more pools of standing water, providing a prime breeding ground for mosquitoes, said Greg Lanzaro, director of the University of California mosquito research program.

Ted Toppin, a spokesman for the Mosquito and Vector Control Assn. of California in Sacramento agreed: “There’s a whole lot of water on the ground.”

Toppin said Central and Northern California, where many people will be exposed to the disease for the first time, could be harder hit by the disease while Southern California, the epicenter last year, may see fewer cases. He said the experience around the country has been that many people in heavily affected areas develop immunity because they were bitten by an infected mosquito.

In Merced County, the first human case of West Nile was confirmed Thursday. Last year, the county didn’t report its first human case until Aug. 17. In addition, this week’s case was clearly contracted locally; last year’s only case probably was contracted outside the county, said Richard Rios, public information officer and epidemiologist with the Merced County Department of Public Health.

“We’re seeing what we have been bracing for the past couple of years,” Rios said. “We are anticipating that this year we will get a number of human cases of West Nile virus.”

On Tuesday, the California Department of Health Services reported 15 cases in horses, 456 cases in birds and five cases in sentinel chickens, which are placed in areas at risk for West Nile to monitor the disease. A reported spike in infected sentinel chickens in Riverside County, where 21 chickens were reported to have the disease, was not included in the report because the state had not confirmed the cases.

As of July 15 last year, there were 26 reported cases in horses, 1,073 cases in birds and 166 cases in sentinel chickens.

There is no cure for West Nile virus. Because it can develop into a serious health problem, officials continue to urge prevention, including using insect repellent containing DEET and wearing long-sleeved shirts and pants while outside at dusk and dawn, when mosquitoes are most active.

Officials also recommend emptying pools of stagnant water to help stop mosquitoes from breeding.

“Thus far the news is good, but we need to remain vigilant,” said Jonathan Fielding, public health director for Los Angeles County.

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West Nile is back

California’s West Nile virus season is off to a slower start this year, but August is the month in which humans are most likely to be infected.

*--* Reported cases* 2004 2005 Humans 24 14 Horses 26 15 Birds 1,073 456 Sentinel chickens 166 5 Counties affected 21 39

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*As of July 15, 2004, and July 19, 2005.

Note: Sentinel chickens are placed in areas affected by West Nile and then tested to monitor the disease. 2005 figures above do not include 21 unconfirmed sentinel chicken cases in Riverside County.

Source: California Department of Health Services