Wet weather isn't necessarily harbinger of bad West Nile year

Saturday, June 28, 2003

ATLANTA -- With record-setting rainfall along the East Coast, it's already a "hopping, popping mosquito season," the experts say. But that may not mean a bigger outbreak of West Nile virus.

"Over the past 70 years of mosquito-borne viruses, people have tried to correlate outbreaks with vague associations with the weather," said Dr. Anthony Marfin, a medical epidemiologist with the Centers for Disease Control and Prevention. "The logic does not always translate."

The virus has thrived even in drought-stricken states. Last year, Louisiana was already one of the hardest-hit states when two large storms dumped even more rain on the swampy region in October. The increase in water didn't cause more West Nile cases, health officials there said.

"It's not the number of mosquitoes, it's the age of the mosquitoes," Dr. Raoult Ratard, state epidemiologist for the Louisiana Department of Health and Hospitals. "It takes an old mosquito to transmit the disease. It has to feed on a bird, the virus has to multiply."

The virus is passed to humans or horses from mosquitoes that first have fed on an infected bird, the virus' host reservoir.

Virus activity is usually slow in the spring, then, as more mature mosquitoes are available to spread the virus from infected birds, it picks up in August. Culex mosquitoes, believed to be the main carrier of West Nile virus, may live up to 50 days.

This spring was one of the wettest ever in Virginia and the Carolinas, with above average rainfall from New York to Florida. Although some states have seen early evidence of infected birds, it remains to be seen if there will be more cases of the virus.

The disease is not spread by all mosquitoes, said Laurel Garrison, epidemiologist for the Georgia Division of Public Health. The Culex breeds in small containers near homes, not in puddles of water formed by recent rain.

However, recent heavy rains have created plenty of potential breeding spots, filling small vessels that people don't normally consider to be mosquito habitats.

Last year's West Nile outbreak was the largest in history, with 4,100 cases and 284 deaths. Most people who get the virus never even have fever or other symptoms, but for some -- people over 50 are most at risk -- the virus turns into dangerous encephalitis or meningitis.

This year, virus activity has been found earlier than last year, with birds and other animals testing positive in 27 states. But no human cases have shown up.

Experts are warning that the virus -- which can be fatal -- may complete its coast-to-coast march this summer. Only nine of the continental states have escaped it so far.

Meanwhile, states are working hard on prevention, examining bird feeders, abandoned tires and any other standing water traps where mosquitoes could breed.

In suburban Atlanta, Tom Campbell, environmental health manager for the Cobb County Center for Environmental Health set up mosquito traps on the leafy floor of a wooded lot. Last year the county had 119 infected birds but no human cases.

"We expected to have a bunch of mosquitoes this year from all the rain, but we haven't seen a real high increase in numbers yet," he said.

The story is different in North Carolina.

"We've had a lot of rain in North Carolina and had a lot of mosquito complaints," said Nolan Newton of the North Carolina Department of Environment and Natural Resources. "It's just a hopping, popping mosquito season."

"What's really important is what happens in terms of the virus and mosquitoes and birds over the next four to five weeks," said the CDC's Marfin. "Which is why we always come back to ... prevention."

The CDC says people should make sure they wear protective clothing and use insect repellent to keep mosquitoes at bay. They also should empty any containers of standing water.

People should start taking steps now to protect themselves from mosquitoes, Marfin said, "before the peak of the activity comes along in mid-August."


On the Net:

CDC info: www.cdc.gov/ncidod/dvbid/westnile/index....

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