PEST CONTROL/Chicago responds to West Nile outbreak
In September 2001, when Illinois health officials confirmed the presence of West Nile Virus in their state, they knew the virus likely would return the following year. However, they could not have predicted that Chicago — with 175 human cases confirmed through October 2002 — would be a hot spot for the disease.
“We knew that West Nile Virus was endemic to the Chicago area after 2001,” says Dr. William Paul of the Chicago Department of Public Health. “We were prepared for it to resurface in 2002, but I don’t think anyone thought we’d see this many cases during the 2002 outbreak.”
Nevertheless, Chicago was prepared to respond. Because West Nile can overwinter in mosquitoes (i.e., mosquitoes that contract the virus in one year can reintroduce it the following year), the city began reviewing its mosquito management plan at the end of the 2001 mosquito season.
Working with Roselle, Ill.-based Clarke Mosquito Control, the Chicago Department of Public Health conducted a comprehensive survey of mosquito habitats and developed a map to assist in mosquito control. The map cataloged Chicago’s surface water sites, flood plains and retention ponds, and it was instrumental in identifying potential truck routes for adulticiding.
The department also developed an integrated mosquito management plan for 2002. In addition to calling for increased surveillance and public education, the plan covered early-season larviciding in areas where infected mosquitoes had been identified, and it lay the groundwork for adulticiding.
In Spring 2002, Chicago detected West Nile Virus in a bird and in mosquitoes. The city reported its first human case on Aug. 15, prompting the Department of Sewers to conduct citywide larviciding. That case also prompted the city to redouble its efforts to educate the public and to identify and eliminate standing water.
As the number of human cases increased rapidly, the Chicago Department of Public Health consulted with the Illinois Department of Public Health, based in Springfield, and U.S. Centers for Disease Control and Prevention, based in Atlanta, to prepare an appropriate response. In early September, Chicago rolled out the next phase of its mosquito control program: adulticiding.
The city had not used adulticides citywide since a 1975 outbreak of St. Louis Encephalitis. Preparing to address residents’ concerns about chemical spraying, Chicago’s public information officers met with all city departments and integrated their responses.
Identifying two large areas with high rates of West Nile infection, Chicago treated those areas twice a day for 10 days. Using 20 to 30 trucks each evening, crews applied ultra-low volumes of the adulticide Anvil to residential streets and alleys between dusk and dawn.
Public and media response to the adulticiding was largely positive, and the applications accomplished their intended effect. “After these adulticiding applications, we saw a substantial drop in mosquito populations in our traps, Paul says.