Although the taxonomic classification of caliciviruses has improved with the availability of full-length gene sequences and robust phylogenetic methods [42] , the increase in genetic diversity introduced by novel caliciviruses would necessitate further taxonomic revisions within the family. The International Committee on Taxonomy of Viruses has adopted a systematic polythetic approach towards virus taxonomy, but classification at or below the genus level may be complicated by the specific biology of diverse viruses. As a case in point, the proposed assignment of the novel bat virus to the genus Sapovirus might be opposed on the basis of an increased genomic G+C content, the different reading frame of ORF2, and the increased length of the 39 UTR. On the other hand, the polythetic criteria for inclusion in the genus are not fully clear, and phylogenetic distances between viral gene sequences have assumed overriding importance in previous and current classifications. It should be noted that even phylogenetic analysis may be confounded by other factors such as the cleavage pattern of ORF1 polyprotein, which has not been determined experimentally for many caliciviruses.