The city's efforts against West Nile virus will continue Wednesday and Thursday nights with spraying in areas of the West, Northwest and Southwest sides.
Portions of the Northwest Side 36th Ward will be sprayed Wednesday night, while sections of the 23rd and 13th Wards in Austin, Clearing, West Lawn and Archer Heights will be sprayed on Thursday night, according to the Chicago Department of Public Health. Traps in all of these locations recently yielded mosquitoes carrying the virus.
"When our mosquito traps indicate that the West Nile Virus may threaten human health in a community, we take decisive action promptly," Public Health Commissioner Dr. Bechara Choucair said in a statement.
Weather permitting, the spraying will begin at about 8 p.m. on both Wednesday and on Thursday. On both nights, spraying will continue until about 1 a.m., with licensed mosquito abatement technicians in trucks dispensing an ultra-low-volume spray.
Spraying will occur starting at dusk, the peak period of mosquito activity and exposure of the northern house mosquito, the type of insect that spreads West Nile Virus.
The chemical Zenivex will be applied at a rate of 1.5 fluid ounces per acre. It is approved for use by the U.S. EPA to control disease-carrying mosquitoes and is non-persistent, decomposing rapidly in the environment, a release from the health department said.
The spray will be applied by technicians from Vector Disease Control International, the release said. Guiding the crews through the streets will be supervisors from the Department of Streets and Sanitation.
While the spray is not harmful to people or pets, and is routinely sprayed in residential areas across the nation, residents of targeted neighborhoods may choose to stay indoors and close windows while spraying is under way.
The Northern House mosquito, Culex pipiens, is the primary carrier of West Nile virus. This species thrives in water with high organic content, such as in catch basins (storm sewers), so a hot, dry summer increases the risk of infection, exactly the opposite of what many people believe.
In 2011, some 712 human cases (43 fatal) of West Nile-related illness were reported nationally. In Illinois, there were 34 reported cases (8 in Chicago), but no deaths.
Thus far in 2012, about five cases have been reported nationally, none in Illinois.