News

Spring Is in the Air—So Is Threat of West Nile

By Deb Kollars -- Bee Staff Writer
Published 2:15 am PST Tuesday, February 7, 2006
Story appeared on Page A1 of The Bee

David Brown (Sacramento Bee Photo) The mosquito control district manager calls the unusually warm weather a 'wake-up call" to begin taking precautions.

The warm sunny spell that has settled over Sacramento has people stepping into their gardens, raising their windows and enjoying long walks, faces tipped toward the sun.

We are not the only ones coming to life after winter.

The unseasonably warm temperatures also are awakening mosquitoes. And the Sacramento-Yolo Mosquito and Vector Control District wants people to begin taking precautions.

Although no West Nile virus activity has been detected this year, it is inevitable the disease will make another appearance as it did last summer and fall in birds, horses and human beings.

The disease is spread by infected mosquitoes. The more steps people take to prevent mosquitoes from breeding or biting them, the more it will help reduce the spread of the disease, said David Brown, general manager of the mosquito control district.

"We have no virus activity to date this year, but this is still a wake-up call for people," he said.

In particular, Brown is urging people to drain standing water on their property to reduce breeding grounds for mosquitoes. They should make sure door and window screens are in good condition to keep mosquitoes out. And they should wear long sleeves and use repellent to protect themselves from bites when outside.

Sacramento can expect plenty of sunshine and high temperatures in the mid-to upper-60s this week, which is notably warmer than the typical high of about 59 for early February, said Jim Mathews, a National Weather Service forecaster.

The warmth, along with longer periods of daylight each day, serve as an alarm clock for mosquitoes that have survived the winter, said Greg Lanzaro, director of the mosquito research program at the University of California, Davis.

During the peak of summer, mosquitoes live about two months. Those alive at the end of summer will go into semihibernation, or "diapause." When temperatures drop, they park themselves in garages, outbuildings, hollow logs or tree holes and go into a state of torpor, not eating or drinking or buzzing or biting.

"They just sort of sit quietly," Lanzaro said. The more rain and dampness during this time, the better for mosquito survival. If the weather dries out, they are so small they can dehydrate and die.

If a wintering mosquito is infected with West Nile, the virus also will survive. Come spring, the infected mosquito will be "loaded and ready to go," Lanzaro added.

For the past two years, California led the nation in human infections of West Nile. Last year, Sacramento County, with 175 human cases, was known as the leading hot spot for the disease.

The virus affects different people differently. Among those infected, four out of five don't have symptoms. The virus makes about 20 percent sick, usually with flulike ailments. Just one in 150 experiences the most serious consequences such as paralysis, brain inflammation or meningitis that can bring death.

Last summer, as the number of West Nile cases rose in birds, horses and people, the mosquito agency aerially sprayed pesticide over 110,000 acres of urban Sacramento County. The spraying triggered widespread panic and anger among people who feared breathing the spray, which officials said was safe in the dosages used. District and state studies later found the spraying effective in reducing mosquito numbers and the spread of the disease.

This year, district officials will continue to track infection rates for West Nile.

Birds, a favorite target of mosquitoes, play a critical role in the spread of the disease. When bitten by infected mosquitoes, birds can become "reservoirs" for the virus, passing it along to uninfected mosquitoes that bite them. Mosquitoes, in turn, infect people and other animals.

Some bird species are more vulnerable than others. The corvid family - which includes crows, jays and magpies - is particularly susceptible.

Because crows monitored in Yolo County died at a lower rate than scientists had expected last year, now there are concerns that Yolo County might not have seen the worst and could be in for a year of greater West Nile infections, while Sacramento County may have seen its peak.

On Monday, Brown said it is not possible to predict where a hot spot may turn up. Typically the disease shows a spike in cases one year, then a marked reduction as the disease moves elsewhere. This year, rather than Yolo County, the disease may spread to Northern California, Oregon or Washington, Brown said.

He cautioned that even though the virus migrates, exposed communities continue to be at risk. "West Nile is here to stay," Brown said.

Which is why, he said, people should not let up in the battle against mosquitoes.

About the writer:

• The Bee's Deb Kollars can be reached at (916) 321-1090 or dkollars@sacbee.com.