The objective of this research is to better define the extent and timing of Rift Valley Fever (RVF) virus transmission and its related chronic disease/infection attack rate, during an interepidemic period in a high-risk region that has seen repeated RVF outbreaks. The results will be used to develop and refine predictive algorithms for RVF Virus transmission, based on epidemiological, environmental, and remote sensing data, with the ultimate goal of providing improved early detection of significant RVF outbreaks. It is expected that the analysis of test-performance characteristics will determine the best use of serologic assays in Kenya's next RVF epizootic/epidemic. The primary outcome measure will be the current RVF-specific seropositivity profile for a cross-sectional survey population in Ijara District in northeast Kenya. The secondary outcome measures to be studied will be: 1) an assessment of the behavioral factors associated with risk of seropositivity (previous infection) in the study population; and 2) the association of selected long-term ophthalmological and clinical outcomes with seropositivity. The study design for this protocol involves questionnaire administration to consenting participants of Ijara District, followed by performance of medical exams, ophthalmologic exams, and phlebotomy on all participants. ELISA testing for RVF will then be performed on the blood samples obtained, and all ELISA screen-positive samples will have confirmatory testing by plaque-reduction neutralizing antibody testing.