The Montgomery County Health Department will conduct two mosquito sprays in Wynnewood the night of Aug. 13 in an effort to stop the spread of West Nile Virus, according to Pat Ryan, assistant manager for Lower Merion Township.

In 2012 to date, nine mosquitoes have tested positive for West Nile Virus in Wynnewood, Ardmore and Penn Wynne. No cases have been found in other parts of Lower Merion. No human cases of West Nile Virus have been found in Pennsylvania in 2012, according to state health department records. In all of 2011, five mosquitoes tested positive for the virus in the township.

Each year, Montgomery County sets up light traps in areas where there are known mosquito infestations and empties those traps each week, shipping mosquitoes from each trap separately to the Pennsylvania Department of Health to be tested for West Nile Virus, Ryan said.

Five mosquitoes tested positive for West Nile Virus last week in Ardmore, Wynnewood and Penn Wynne—one each from five different traps. One of the traps was in an area in which Montgomery County had recently conducted a mosquito spray, according to Montgomery County communications director Frank Custer.

"The good news is that there were far fewer mosquitoes in the areas recently sprayed," Ryan said. "But some of the mosquitoes still have West Nile Virus—a dangerous disease that could cause potentially serious health problems."

Two residential areas will be sprayed on Aug. 13 between 8:30 and 11:30 p.m., with a rain date set for Aug. 14:

• All residential streets bounded by E. Wynnewood Road, Lancaster Avenue, Remington Road and Bowman Avenue
• All residential streets bounded by Morris Road, Grenox Road, Sussex Road, Athens Avenue, W. Wynnewood Road and Clothier Road

See the attached map to see the streets affected.

There will be no aerial spraying, according to a township release. Health Department employees will use a truck mounted with an Ultra Low Volume (ULV) sprayer.

In a previous interview, when asked if the sprays were harmful, Custer provided a link to this informational page about the sprays. It reads in part:

USEPA has evaluated these chemicals for this use and they have been found to pose very little risk to human health and the environment when used according to label directions. Exposure to the spray may aggravate existing respiratory conditions or affect sensitive individuals. Pyrethroids that enter the body leave quickly, mainly in the urine, but also in feces and breath.

Persons who apply pyrethroids and are accidentally exposed to very large amounts of these chemicals may experience dizziness, headache, nausea and diarrhea. Children exposed to large amounts of pyrethroids would be expected to be affected in the same way as adults. Adverse health effects would not be expected when pyrethroids are used according to label directions.

There is no evidence that pyrethroids cause birth defects in humans or affect the ability of humans to have children. Pyrethroids do not cause cancer in people.

According to Custer, the main way to reduce exposure to the chemicals is to stay indoors during spraying and for about 30 minutes afterwards.

"Generally, there is no need to leave the area during mosquito control spraying," Custer said.