Researchers at the Illinois State Water Survey (ISWS) and the Illinois Natural History Survey (INHS) report a reliable link between weather conditions and an abundance of two mosquito species linked to outbreaks in humans and wildlife, especially birds.
The West Nile virus first appeared in Illinois in 2001. A major statewide outbreak occurred in 2002, with 66 deaths among the 884 people showing clinical signs of infection after being bitten by mosquitoes carrying the virus. Although the number of cases in humans declined in 2003 and 2004 (112 human cases and five deaths), transmission between mosquitoes and birds continues throughout the state at surprisingly high levels.
Two mosquito species -- Culex restuans, the white-spotted mosquito, and Culex pipiens, the northern house mosquito -- are believed to maintain the natural transmission cycle between birds and mosquitoes. The population of northern house mosquitoes, the primary suspect for transmission to humans, is low in spring but grows to become the dominant species later in summer, especially in urban areas.
The northern house mosquito becomes the main species in early August, on average, said INHS entomologist Robert Novak, who also is an adjunct professor of veterinary pathobiology in the College of Veterinary Medicine. He has been collecting data on summer changes in mosquito species in the Champaign-Urbana area since 1988.
Because that time period varies each year, ISWS atmospheric scientist Kenneth Kunkel, along with Novak and INHS mosquito ecologists Richard Lampman and Weidong Gu, examined whether changes in vector abundance may be related to weather conditions.