 The discovery of Norovirus receptors provides new opportunities to evaluate the pathogenesis and epidemiology of Noroviruses. A host genetic factor involving Norovirus infection was originally suggested by many researchers before the cloning of Noroviruses in the 1990s because about 20-30 of individuals who did not have antibodies against Noroviruses were never infected following a challenge with NV, and in outbreaks, individuals who remained healthy were clustered in families that had the same exposure to Noroviruses as the ill families. Further, pre-existing antibodies against NV were not protective against NV infection, while individuals who had high levels of antibodies against NV were more susceptible to NV than individuals who did not have the antibodies. These observations indicate that, in addition to immune responses, there must be another factors that controls the host-specificity of Norovirus infection. 