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Ominous Start for West Nile Season

West Nile Virus 2007: Fastest Start Yet for Mosquito-Borne Illness
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Because so many infections have no symptoms, the CDC's official case count is a huge underestimate. But nearly every case of West Nileencephalitis or meningitis (affecting the brain or lining around the brain) is reported -- so by multiplying the number of these cases by 150, it's possible to get a rough estimate of the true number of infections.

So far this year, there have been 42 cases of neuroinvasive West Nile infection. That suggests there have already been about 6,300 total infections with West Nile. By the end of worst year, 2003, there were 2,866 reports of neuroinvasive disease, suggesting there were nearly 430,000 infections.

Whether this year will be as bad as that depends largely on the weather. Birds carry West Nile virus, and mosquitoes get the bug after feeding on birds. The virus then has to grow inside the mosquito to levels infectious to humans. This happens most efficiently in hot weather.

If August and September are relatively cool, the bug might not be a big problem. But that's just speculation. The U.S. history of West Nile virus is too short for scientists to make accurate predictions.

One prediction can be made for sure: You will have a much lower risk of West Nile infection if you avoid mosquito bites.

"From the early numbers, it looks like we have a pretty busy West Nile season going," Zielinski-Gutierrez says. "Get out that repellent. The take-home message at this point for the American public is, 'Whoa -- there seems to be a lot of West Nile out there. When I go out there I'd better do something to keep from getting mosquito bites.'"

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