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Time Again for West Nile Virus

Too Soon to Know How Deadly Virus Will Be, Experts Say
By
WebMD Health News
Reviewed by Louise Chang, MD

July 7, 2006 -- Experts say it is too soon to know just how deadly this year's West Nile season will be, but they worry that people are no longer as concerned about protecting themselves from the mosquito-borne virus as they should be.

Bird fluBird flu may have replaced West Nile in the headlines, but the CDC's top vector-borne disease expert tells WebMD that West Nile is a much greater imminent threat.

"A couple of years ago everyone was asking about West Nile," says Lyle Petersen, MD, MPH. "Now it is bird fluflu. I can tell you with absolute certainty that your bigger fear this summer is West Nile."

More Than 1 Million Infections

That is because, so far, at least, bird flu is only a threat to humans who have had direct contact with infected birds. West Nile virusWest Nile virus is also found in birds, but it is spread to humans by mosquitoes that bite the infected birds and then bite them.

Between Jan. 1 to Dec. 31 of last year, 3,000 cases of West Nile virus were reported in the United States, according to the CDC. Roughly 1,200 people with West Nile had meningitismeningitis (inflammation of the lining around the brain and spinal cord) or encephalitisencephalitis (inflammation of the brain), and 119 people died.

More than a million Americans have been infected since the virus was first reported here in the late 1990s, but only a small percentage of those who are infected develop symptoms.

The elderly are most at risk for serious illness and death, but deaths have also occurred among the very young and middle-aged and younger adults.

Petersen says it may never be possible to predict the severity of West Nile outbreaks from year to year before the peak mosquito-bite months of July, August, and September.

As of late June, two cases of West Nile virus had been reported in Texas this year, with one case each having been reported in Mississippi and Colorado.

"Historically, we have very few cases at the beginning of July and quite a few by the end of July," he says. "I think we will have a better idea of how things are shaping up by the end of the month."

Katrina Worries

Fears that major West Nile outbreaks would occur in Louisiana and Mississippi late last summer following the devastation of Hurricane Katrina were not borne out.

Petersen says it appears that the hurricane had little direct impact on West Nile transmissions in the area last year. Torrential rains and flooding may have even reduced transmissions by diluting the stagnant waters that mosquitoes favor for breeding, he adds.

The mosquito that most often carries the West Nile virusWest Nile virus typically breeds in small, stagnant, mucky pools of water that are nutrient rich.

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