West Nile virus in mosquitoes of Northern Ohio, 2001-2002.

From June 14 to August 30, 2001 and June 10 to August 22, 2002, the mosquitoes of Oberlin, Ohio were surveyed and tested for West Nile virus (WNV). Mosquitoes were trapped weekly using gravid traps and CO(2)-baited Centers for Disease Control light traps at seven sites in 2001 and eight sites in 2002 in woodlots within the city limits. A total of 12,151 mosquitoes, representing 14 species and one species group, were collected in gravid traps, with Culex pipiens/restuans being the most abundant, followed by Ochlerotatus triseriatus. In light traps, 12,510 mosquitoes were collected, with Aedes vexans being the most abundant, followed by Culex pipiens/restuans. All gravid trap collections were tested for WNV via reverse transcriptase-polymerase chain reaction. West Nile virus was first detected in July 2002. Of all species tested, the Cx. pipiens/restuans species group exhibited the highest minimum infection rate (MIR) and the greatest percentage of positive pools. Both the MIR and percent of positive pools increased significantly with the date, although abundance of Cx. pipiens/restuans in gravid trap collections did not.