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Noroviruses are members of the Caliciviridae family.The advantages of working with this system are that the capsids do not contain RNA, and thus are non-infective, and that studies have shown that these particles are similar in size, shape, appearance and antigenicity to the infective virus particles (Jiang et al., 1992).The genome is 7.7 Kb, and contains three open reading frames: VP1 (the major capsid protein), VP2 (the minor capsid protein), and a non-structural polyprotein (Jiang et al., 1993).Noroviruses (NoV) have been genetically classified into five genogroups; GII and GI are the genogroups primarily associated with human diseases, although NoV GIV has occasionally been implicated in outbreaks (Zheng et al., 2006).Straub et al. (2007) described a three-dimensional in vitro system using human embryonic intestinal epithelial cell line INT-407; however, difficulty in adapting the system to other laboratories and the length of time required for the assay has precluded its widespread adoption.

Noroviruses are members of the Caliciviridae family. There are five genera in this family, one of which is Norovirus, and one species has been identified: the Norwalk virus (ICTV, 2011). Noroviruses (NoV) have been genetically classified into five genogroups; GII and GI are the genogroups primarily associated with human diseases, although NoV GIV has occasionally been implicated in outbreaks (Zheng et al., 2006). Genogroup II.4 strains are responsible for most human NoV outbreaks, with up to 80% of infections being caused by this strain (Widdowson et al., 2004; Leon and Moe, 2006).
Despite decades of research to identify a suitable in vitro cell culture system, there has been little success. Straub et al. (2007) described a three-dimensional in vitro system using human embryonic intestinal epithelial cell line INT-407; however, difficulty in adapting the system to other laboratories and the length of time required for the assay has precluded its widespread adoption. A method developed by the same group using CaCo-2 cells was reported recently (Straub et al., 2010), but it has yet to be put into routine use. As a result, most of the information available on the structure of noroviruses has been obtained from studies conducted using recombinant norovirus-like particles that assemble spontaneously as recombinant VP1 and VP2 are expressed in insect cells (Shoemaker et al., 2010). The advantages of working with this system are that the capsids do not contain RNA, and thus are non-infective, and that studies have shown that these particles are similar in size, shape, appearance and antigenicity to the infective virus particles (Jiang et al., 1992).
Noroviruses are non-enveloped, single-stranded, positive sense RNA viruses. They are approximately 27-38 nm in diameter, with arch-like capsomeres on the capsids (Prasad et al., 1994). The genome is 7.7 Kb, and contains three open reading frames: VP1 (the major capsid protein), VP2 (the minor capsid protein), and a non-structural polyprotein (Jiang et al., 1993).