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U.S. West Nile Cases Near 5,000

New record set while CDC reports small malaria outbreak

THURSDAY, Sept. 25, 2003 (HealthDayNews) -- The number of cases of West Nile virus set an annual record this week, the U.S. government reports, and is rapidly approaching the 5,000 mark.

As of Thursday, 4,952 human cases of West Nile had been reported with a total of 95 fatalities, says Llelwyn Grant, a spokesman for the Centers for Disease Control and Prevention (CDC) in Atlanta. Those cases came from 40 states.

Last year, which also established a record, saw 4,156 cases of West Nile. However, so far this year the virus has been less lethal; in 2002, it claimed 284 lives. West Nile was first identified in the United States in 1999 in New York, and has rapidly moved westward.

Thankfully, though, the country seems to be approaching the end of the season. According to Grant, the third week of August marked the high point last year. Although cases were still being reported into November (which meant mosquitoes were still biting in October), they were clearly tapering down by the end of September.

"We try not to make projections, but it seems that the pattern we're witnessing this year is similar to last year," Grant says. Last year, 55 percent of cases occurred between mid-August and the end of September.

The naked truth is that as the weather gets nippy, mosquitoes stop nipping.

In Montana, temperatures are dipping down the high 20s and mid 30s at night. To Patricia Denke, the state entomologist, that is a cause for rejoicing.

"Right now, we're sitting at the end of our mosquito season," she says. "We're on the end of the curve. We'll probably be detecting new human cases for at least another month but as for mosquito transmission, we're probably done."

One hard frost, the kind that kills plants and forces you to scrape the car windshield clear, is usually enough to rid an area of mosquitoes, as long as the temperature stays consistently low, Denke says.

If the temperatures rise above 55 degrees during the day, as they are now in Big Sky country, adult females will come out and "act as if nothing happened," Denke says. However, at this point the critters are more inclined to look for nectar or sugar sources rather than blood meals.

Even the thousands of mosquitoes that are still being collected in certain locations in Montana are not such a cause for concern, Denke says, because they're not usually the mosquitoes that act as disease vectors. "We're not worried," she adds.

But West Nile is not the only mosquito-borne threat to plague these shores. This week, the CDC publication Morbidity and Mortality Weekly Report details an outbreak of malaria in Florida's Palm Beach County. Unlike most cases of malaria identified in the United States, these were acquired on American soil (or air space).

Since 1992, 11 outbreaks involving 20 cases of malaria probably acquired locally have been reported to the CDC.

The current outbreak involved seven people who fell ill in July and August.

All the victims were men and all reported spending time outdoors either for work or pleasure. One, a 45-year-old man, said he slept in a homeless camp in a wooded area near a canal.

Each of the men lived within 10 miles of Palm Beach International Airport and two attended the same July 4th party.

None of the individuals had a previous history of malaria, recent blood transfusion, organ transplantation, or IV drug use. Six had never traveled to regions where malaria is endemic, although one man did immigrate from Bogota, Colombia. Although parts of Colombia have malaria, Bogota, the capital, does not.

Officials in Florida tested mosquitoes for malaria but found no evidence of the disease.

The outbreak, the first reported involving extended transmission in the United States since 1986, is obviously a cause for concern.

And nothing is driving mosquitoes to extinction -- in fact, quite the opposite seems to be happening. They are excellent reproducers. So for now, use insect repellant with DEET and wear long sleeves.

More information

The CDC has information on West Nile virus and on malaria.

SOURCES: Patricia Denke, Ph.D., state entomologist, Department of Agriculture, State of Montana, Helena; Llelwyn Grant, spokesman, Centers for Disease Control and Prevention, Atlanta; Sept. 26, 2003, Morbidity and Mortality Weekly Report
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