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

Background and Objective: West Nile Virus (WNV) is an RNA arbovirus in the family Flaviviridae. Most human infections are asymptomatic with less than one percent of patients exhibiting severe symptoms including encephalitis, paralysis, and death. To test the hypothesis that the recent decline in WNV cases in Fremont County is correlated to widespread exposure, serosurveys were conducted for two years. Methods: Serum samples were drawn and tested for the presence of WNV IgG and IgM antibodies using Enzyme Linked Immunosorbant Assays. The presence of high titers of IgG antibodies is indicative of past exposures; IgM indicates more recent exposure. Results: In 2011, of 85 subjects 16.5% (95% CI: 8.9%-24.1%) were positive for IgG and 9.4% (95% CI: 3.2%-15.6%) were for IgM. In 2012, 95 subjects were tested. 10.5% (95% CI: 4.34%-16.66%) were positive for IgG and 5.3% (95% CI: 0.8%- 9.8%) for IgM. Discussions and Conclusions: These results indicate that most residents of Fremont County have been exposed to WNV and the recent decline in cases is not correlated to widespread exposure.