September 13, 2005
Tuesday

Clouds of mosquitoes are rising from the stagnant waters left by Hurricane Katrina, plaguing recovery workers and posing a disease threat.

"The mosquito numbers have taken off and are building," said Janet McAllister, an entomologist with the U.S. Centers for Disease Control and Prevention. We're talking biblical proportions. Clouds of mosquitoes."

McAllister is one of six CDC mosquito experts in Louisiana and Mississippi. She is working with state health officials to revive mosquito-control programs disrupted by the storm.

Two Air Force planes are spraying insecticide around New Orleans, McAllister said.

The main mosquito-borne disease of concern is West Nile virus. Sixty-two cases of West Nile illness have been reported in Louisiana and Mississippi this year.

Some eastern equine encephalitis cases also were observed in animals before the storm hit.

Mosquito numbers started exploding about three days ago, McAllister said. One Louisiana mosquito-control district reported that the number of trapped mosquitoes has increased 800 percent over pre-Katrina levels, she said.

Many of the newly hatched mosquitoes are "floodwater" species that don't normally pose a serious disease threat. Mosquitoes that usually live in tree canopies have been forced to the ground by storm damage, and populations of salt-marsh mosquitoes are booming.

"They're very aggressive biters, and they can get to such numbers that the power linemen can't work - even with repellent on," McAllister said. "They can't function because there are so many mosquitoes."

Dr. Lyle Petersen, director of the CDC lab at Fort Collins, Colo., said it's unclear how the number of human West Nile cases will be affected.

"We've never had a hurricane hit when there was a lot of West Nile virus activity happening at the time, so we're not quite sure what's going to happen," Petersen said. "We're kind of in uncharted territory."

Areas hit hardest by Katrina might see little increase in the number of West Nile cases. In those places, West Nile-infected mosquitoes were either killed or blown away by the storm. And many of the wild birds that serve as a reservoir for the virus are gone as well.

"It's outside the hardest-hit areas that we would expect the West Nile that's in the area to continue," said McAllister, who grew up in New Orleans.

Mosquito populations are exploding on the Gulf Coast at a time when the risk of human exposure to the bloodsuckers is very high.

Rescue-and-recovery teams spend all day outside, and some of them camp in tents at night. Some displaced residents are living outside. In storm-damaged houses that remain habitable, lack of air conditioning due to ongoing power outages has forced occupants outside to escape the heat.

"I've never seen anything like this," McAllister said. "I can only imagine this is what Europe looked like after World War II. There are displaced people everywhere, and there are huge camps of responders everywhere, living in tents.

"So we've got huge numbers of people - responders as well as citizens - that can't get away from the mosquitoes."

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