Two-Year Serosurvey of a Rural Population for West Nile Virus IgG and IgM Antibodies, A

West Nile Virus (WNV) is an RNA arbovirus in the family Flaviviridae. Birds are the primary reservoir of the virus; mosquitoes are the primary vector. Humans are a terminal host and most infections are asymptomatic. Less than one percent of patients exhibit severe symptoms including paralysis, encephalitis, and death. Since Fremont County is a hot spot for WNV, serosurveys were conducted for two years to determine the percentage of residents previously exposed to WNV. Serum samples were drawn and tested for the presence of WNV for IgG and IgM antibodies using Enzyme Linked Immunosorbant Assays (ELISA) tests. The presence of high titers of IgG antibodies are indicative of past exposures; IgM indicates more recent exposure. In 2011, 87 subjects were tested. 12.6% (95% CI: 5.7%-19.6%) were positive for IgG and 9.2% (95% CI: 3.1% to 15.3%) were positive for IgM. In 2012, 96 subjects were tested. 10.4% (95% CI: 4% to 16.8%) were positive for IgG and 6.3% (95% CI: 1.4% to 11.1%) for IgM. These surveys indicate that most of the population of Fremont County remains at risk for exposure to West Nile Virus infection and that new exposures are still occurring.