<qa>  What is the name of the prototype Norwalk virus?Noroviruses are single-stranded, positive-sense RNA viruses that cause acute gastroenteritis in humans. The prototype Norwalk virus NV was identified in a large outbreak of acute gastroenteritis in an elementary school in Norwalk, Ohio, in 1968. Since then, many strains have been described and named by the locations of their first isolation. Genetically, Noroviruses belong to one of four genera within Caliciviridae CV. Phylogenetic analysis has shown that the Norovirus genus is divided into five genogroups and each genogroup can be further divided into genetic clusters; at least 30 genetic clusters of Noroviruses have been identified. 