Hepatitis E Viruses (HEV):

HEV has now been cloned and sequenced. The virion is a 30-32nm non-enveloped particle containing a s/s (+)sense RNA genome of ~7.5Kb. Genetic organization similar (not identical) to Caliciviruses:

In the most recent ICTV classification, HEV has been placed in its own taxonomic group within the class IV (+)sense RNA viruses, "Hepatitis E-like viruses":

The symptoms of HEV are typical of acute viral hepatitis and the infection follows a natural history that is similar to that of hepatitis A. Up to 43.5% of urban sewage samples collected in industrialized countries may be positive for HEV, suggesting that HEV may be more prevalent than previously considered in industrialized countries and that variants of the virus circulate simultaneously in most countries (Emerg Infect Dis. 2003 9(4):448-54).

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 in pregnant women where there is 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. Antibodies to HEV also indicate infection in up to 60% of rats and other rodents in the USA. The possible medical significance of these findings remains unclear at present.

A recombinant HEV vaccine has recently proved to be safe and effective in a phase 2 clinical trial (Safety and Efficacy of a Recombinant Hepatitis E Vaccine. 2007 NEJM 356: 895-903).

Expert Reviews in Molecular Medicine: Molecular biology and pathogenesis of hepatitis E virus

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