The primary purpose of this phase 1, double-blind, cohort study is to evaluate the safety, tolerability, and pharmacokinetics of escalating doses of MGAWN1 administered as a single intravenous (IV) infusion to healthy adults. Subjects will be enrolled sequentially into one of 5 dose-level cohorts, with 8 subjects in each cohort. Six subjects in each cohort will receive MGAWN1 (a Neutralizing, Humanized, Monoclonal Antibody (IgG1k) to West Nile Virus) and 2 will receive a saline control.