Light, targeted spraying to control mosquitoes that might spread West Nile virus did not lead to raised pesticide levels in people, US researchers suggest on Thursday.

An expert at the Centers for Disease Control and Prevention said he was reassured by the studies done in three states where local health officials sprayed the insecticides.

Three separate studies done in North Carolina, Virginia and Mississippi showed that eating fresh produce and using flea and tick prevention on pets raised levels of pesticides more than the mosquito spraying did.

“These findings suggest that ultra low-volume application of naled, permethrin, and d-phenothrin is safe to humans,” the CDC said in its weekly report on death and illness.

West Nile virus Definition
West Nile virus is transmitted by mosquitos and causes an illness that ranges from mild to severe. Mild, flu-like illness is often called West Nile fever. More severe forms of disease, which can be life-threatening, may be called West Nile encephalitis or West Nile meningitis, depending on where it spreads.

“But we always worry a little bit, right?” cautioned Dr. Eduardo Azziz-Baumgartner of the CDC in Atlanta, who helped coordinate and report the findings.

“These are very specific findings on very specific pesticides,” Azziz-Baumgartner added in a telephone interview.

Older insecticides such as DDT and malathion have been well studied and their adverse effects on humans and wildlife documented. But Azziz-Baumgartner said he could find no research on newer products such as permethrin and naled.

“They tend to be associated with less problems in human populations than the older ones. In addition they tend to have shorter half-lives in the environment, also, so they tend to be friendlier to use,” he said.

But not entirely safe, the CDC said.

“Prolonged exposure to high concentrations of naled and synthetic pyrethroids can cause dermatitis (skin irritation), reactive airway disease, gastrointestinal distress, central nervous system depression, paralysis, and death,” the CDC report reads.

In September 2002, the Mississippi Department of Health planned a mosquito spraying program and contacted the CDC. CDC experts sampled 125 people in the targeted area and 67 in an area not to be sprayed.

Participants completed questionnaires describing pesticide use at home and work and provided urine samples one to four days after the spraying, the CDC report said.

Results showed metabolic traces of synthetic pesticides like permethrin varied little between mosquito control and non-mosquito control regions.

They also showed that 17 participants who used pesticides on pets had significantly higher urine levels of the compounds - although still not high enough to be of concern, Azziz-Baumgartner said.

In September 2003, after Hurricane Isabel hit North Carolina, officials there sprayed naled from aircraft and permethrin from trucks to control an expected mosquito explosion.

The CDC tested the urine of 75 people in the affected areas and found dimethylphosphate, left after the body metabolizes organophosphate pesticides such as naled, in 46 percent of urine samples before the spraying and 49 percent afterward.

“Participants who ate fresh fruits or vegetables fewer than three days before completing the pre-spray or post-spray questionnaires had significantly higher urine concentrations of dimethylthiophosphate than participants who did not,” the CDC said.

Farm workers also had significantly higher levels.

A similar study done in Virginia after Isabel hit had similar results, the CDC said.

Azziz-Baumgartner said this did not mean states should feel free to spray to control mosquitoes more often. Health experts prefer to prevent mosquitoes from breeding by controlling sources of water where they can lay eggs.