The identification of the first murine norovirus, MNV, and its propagation in cultured cells provides a facile animal model for studies of norovirus immunity and pathogenesis [27, 28] . MNV, an enteric virus that infects tissues of the gastrointestinal tract, is spread by the fecal-oral route ( [27] and unpublished studies). The MNV genome encodes four open reading frames. ORF1 encodes a polyprotein that is cleaved into individual non-structural proteins similar to the polyprotein of HuNV [29] . ORF2 encodes the major capsid protein VP1 and ORF3 encodes a minor capsid protein.