Cure could be almost as bad as the disease

Mosquito sprays can be harmful to some

By Mark Schleifstein
Staff writer/The Times-Picayune

Although the pesticides being used to kill mosquitoes pose only a small risk to humans, experts recommend that pregnant women, children and those sensitive to chemicals should go inside when the spray truck or plane comes near.

And in areas where mosquito-control workers are using hand-held sprayers to treat ditches and ponds, parents are advised to keep children away because the chemical can cause skin irritation.

"The chemicals they've selected are the latest recommended ways of dealing with any mosquito-borne disease where viral transmission is the issue," said Bill Hartley, a toxicologist at Tulane University School of Public Health.

"But if I had a child or someone with concerns about chemical exposure, I would recommend reducing their exposure even more," Hartley said. "If you know when your area is being fogged or truck-sprayed, go inside the house. And if you have a window air conditioner, cut it off during the spraying. That will reduce the major part of your exposure."

Further, experts suggest that parents bring in toys before the fogging truck comes by and wipe down play areas after it passes.

Whenever an area is faced with a health problem such as this year's West Nile outbreak, officials are forced to weigh the risk of poisons against the increased risk of disease that would result from not using the pesticides, Hartley said.

Throughout Louisiana, mosquito-control agencies are using a half-dozen chemical and biological poisons to attack mosquitoes.

To kill adult mosquitoes, malathion and naled are being applied by air at a rate of less than 3 ounces per acre. Both chemicals kill mosquitoes by interfering with the insect's nervous system. Both also can affect humans in the same way, but usually only in large doses not associated with aerial spraying, Hartley said.

"That exposure is somewhere between 100 and 10,000 times below what we would consider an amount where there would be health concerns," Hartley said.

But direct exposure to the chemicals can cause problems.

"At very low levels, it can cause nausea, dizziness and confusion," Hartley said. High exposures, such as from an accidental spill of a large amount of the pesticides, can cause paralysis and kill people by shutting down their respiratory systems.

Fogger trucks in the area are most often using resmethrin, a pesticide that attacks the insect's central nervous system. Resmethrin is an artificial version of the natural insect-killing chemical formed by dandelions.

Again, Hartley said, the amount used is minimal, though he encouraged the same precautions when the truck comes by.

Mosquito-control officials are applying two other pesticides by hand to target mosquito eggs and larvae in ditches, ponds and backyard containers.

Bacillus sphericus, a bacterial poison that attacks the insect's stomach, is naturally occurring and does not have a similar effect on mammals or humans, Hartley said.

Methoprene is a chemical that kills by disrupting the growth cycle of insects. In humans, it can cause skin and eye irritation, and children should be kept away from treated areas, Hartley said.

Beyond Pesticides recommends that Louisiana communities follow the lead of cities in New York, New Jersey and Florida in announcing when and where pesticides will be applied so families can take those precautions.

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Mark Schleifstein can be reached at or (504) 826-3327


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