I noticed a posting from Jackson County Vector Control that it would be spraying pesticides on Leonard Avenue off Delta Waters Road in Medford. What were they spraying for? What safety precautions should I take?

I noticed a posting from Jackson County Vector Control that it would be spraying pesticides on Leonard Avenue off Delta Waters Road in Medford. What were they spraying for? What safety precautions should I take?

— Greg F., Medford

The spraying was done Thursday morning by a spray truck from the department in response to neighbors calling about a mosquito problem in that area, Greg.

"It's not anything unusual," explained Eugene Papineau, vector control manager. "We get thousands of calls every year from people asking us to spray.

"We post the area when we are doing a large area," he added.

In this case, laboratories at Oregon State University confirmed that mosquitoes trapped Aug. 10 in northeast Medford, including the Delta Waters area, were carrying the West Nile virus.

West Nile symptoms include high fever, aches, pain behind the eyes and overall lethargy. However, it can be fatal for people who have weakened immune systems or other underlying health problems. Fewer than 1 percent of people infected become seriously ill.

The department uses Anvil, a pesticide commonly used to control mosquitoes in residential areas. It contains a man-made pyrethroid related to naturally occurring pyrethrins, a bug toxin found in chrysanthemum seed cases. Pyrethrins and pyrethroids are common in household pest-control products.

"But it is a pesticide, so you treat it with care and caution," Papineau said, although noting it poses a low risk to people.

Residents are encouraged to avoid the area where spraying occurs for about 30 minutes. They should close windows and doors and turn off window air-conditioning units before spraying begins, officials recommend. The only known dangers are from short-term exposures to high levels of the active ingredients and its solvent base.

As mosquito season begins to wane, one human case of West Nile has been found in Malheur County, the only one in Oregon this year. Last year, 69 cases were confirmed in Oregon, including one in Jackson County.

For more information on the local spray program, check out jacksonvectorcontol.org online.

Send questions to "Since You Asked," Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by e-mail to youasked@mailtribune.com.