Phylogenetic analysis of the genus Calicivirus in the family Caliciviridae based on the nucleotide and amino acid sequences of human and animal calicivirus 3D RNA-dependent RNA polymerase (approximately 470nt) and capsid hypervariable regions (approximately 1,200nt) to generate phylogenetic trees indicates that there are five separate genogroups:
Primate studies indicate faecal-oral (waterborne) transmission of the virus. HEV is endemic in S.E. Asia, ex 'USSR', India, Mid-East, Africa and C. America. ~1% of US blood donors have anti-HEV antibodies. Large epidemics with person to person spread have been known to occur. Normal course of infection seems to be an acute but relatively benign illness (c.f. HAV), except during pregnancy - 15-30% mortality. Recombinant vaccines are currently being prepared.
A closely related virus, swine hepatitis E virus (swine HEV), was recently identified in pigs. Swine HEV crossreacts with antibody to the human HEV capsid antigen & is a ubiquitous agent in pigs. The putative capsid gene (ORF2) of swine HEV shares about 80% sequence identity at the nucleotide level and 90-92% identity at the amino acid level with human HEV strains. The possible medical significance of this finding remains unclear at present.