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U.S. Braces for Another West Nile Season

Simple precautions can offer protection from mosquito-borne virus

FRIDAY, May 28, 2004 (HealthDayNews) -- Although West Nile virus season has barely begun in the United States, experts are already urging people to take precautionary measures.

"Transmission is starting to occur in bird populations, and that means we know that people are going to be at risk and it's time for people to start preparing for that," said Dr. Jennifer Brown, an epidemiologist with the division of vector borne infectious disease at the U.S. Centers for Disease Control and Prevention in Fort Collins, Colo. "It's time for people to start thinking about taking personal protective measures against mosquito bites."

So far this year, West Nile has been detected in birds and mosquitoes in 17 states, mostly in the eastern part of the country. The first human cases surfaced this week, one in New Mexico on Wednesday, and one that Arizona announced on Thursday.

The range and amount of activity is not unusual for this time of year, Brown added.

The same areas that were affected last year are likely to be affected this year, and possibly with more Western states involved.

"I think everybody in the field is sort of expecting that it will continue this westward movement and that in California there will be substantial activity," said Dawn Wesson, an associate professor of tropical medicine at Tulane School of Public Health and Tropical Medicine in New Orleans.

West Nile was first identified in the United States in 1999 in the New York City area.

Last year, West Nile infected humans in all but three of the 48 contiguous states. Washington and Oregon escaped unscathed (no birds, mosquitoes or humans were infected), while Maine had activity only in birds and mosquitoes.

In all of 2003, there were 264 deaths nationwide out of a total of 9,862 human cases reported.

The virus is spread by mosquitoes that pick it up when feeding on infected birds and animals. About one in 200 humans infected with the virus actually becomes seriously ill with encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord), while about 20 in 200 will experience less severe, flu-like symptoms.

There may actually be fewer reported cases this year, as the intensity of reporting seems to be declining with every new season.

"I think that's because people have become somewhat used to the fact that it's here and you can get it without dying or becoming severely ill," Wesson explained. "There are probably fewer people running to the doctor with a headache and fever."

The season for human infection stretches roughly from late spring to early fall, with peak infection rates occurring in late summer and early fall.

It's too early to know which geographical areas will be hardest hit this year, Brown said. Last year, it was the Rocky Mountain states, particularly Colorado and Wyoming. Those areas may get a slight reprieve this year as a result.

"The Rocky Mountain area will probably not be affected to the extent we saw last year," Wesson said. "Usually the year after an area is hit really hard, it's a little bit the next year."

It's also possible that events will take a completely unexpected turn. "We're still learning because this thing acts a little different every year," Wesson said. "This time of year you're still watching and waiting. It's there and you know you are going to see a lot of activity later in the season."

While watching, waiting and wondering, experts are recommending the same precautions as any other year. People over the age of 50 and those with compromised immune systems are the most vulnerable to serious illness and need to take extra care.

Officials advise getting rid of standing pools of water where mosquitoes might breed -- including toys and flower pots in your backyard as well as clogged gutters.

Wear insect repellant, preferably one containing DEET, when you go outside. Also wear long-sleeved shirts and long pants. Try to avoid going outside when mosquitoes are most hungry -- evenings and early mornings. And make sure screen doors and windows are in good repair.

More information

For more information on West Nile virus, how it's spread and how you can protect yourself, visit the U.S. Centers for Disease Control and Prevention.

SOURCES: Jennifer Brown, D.V.M., epidemiologist, division of vector borne infectious disease, U.S. Centers for Disease Control and Prevention (CDC), Fort Collins, Colo.; Dawn Wesson, Ph.D., associate professor, tropical medicine, Tulane School of Public Health and Tropical Medicine, New Orleans; CDC surveillance
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