Hepatitis E virus

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Hepatitis E virus (HEV), the major etiologic agent of enterically transmitted non-A, non-B hepatitis worldwide, is a spherical, non-enveloped, single stranded RNA virus that is approximately 32 to 34 nm in diameter. HEV belongs to a genus of HEV-like viruses (unassigned genus). (Reference: The Springer Index of Viruses - a comprehensive encyclopedic reference [R. Lange, ed., Springer-Verlag, Heidelberg, Germany]). Courtesy of Center for Disease Control (CDC)

Hepatitis E virus (HEV) causes self-limiting acute viral hepatitis and is the major cause of enterically transmitted non-A, non-B hepatitis. Humans are the natural hosts of HEV, but animals such as pigs (and may be other species) are considered reservoirs. HEV infection is most often seen in young to middle-aged adults (15-40 years old). A significant proportion of pregnant women infected with HEV (up to 25%) developed fatal hepatitis. The virus is transmitted primarily by the fecal-oral route and fecally contaminated drinking water is the most commonly documented vehicle of transmission.

Outbreaks of HEV are more common in regions of the world with hot climates and are rare in temperate climates. Sporadic cases of acute hepatitis E not related to travel have been reported in the United States and many other industrialized countries. A vaccine for HEV is not currently available although several studies are in progress.

HEV is a non-enveloped, spherical, 27-34 nm in diameter, positive-stranded RNA virus. HEV was thought to be a member of the family Caliciviridae. However, recent sequence comparisons and phylogenetic analyses revealed that HEV was distinct and thus leading to its removal from Caliciviridae. Currently, HEV is classified in a new family Hepeviridae, genus Hepevirus. The virus genome is approximately 7.2 kb in length and contains a 3'' poly-A tail and short 5'' and 3'' noncoding regions. There are three overlapping open reading frames (ORFs), each expressing different proteins. ORF1 is located at the 5'' end of the genome and codes for a polyprotein that is presumably cleaved into multiple non-structural proteins required for virus replication. ORF2 is located at the 3'' end of the genome that encodes for a capsid protein, the principal structural protein. ORF3 overlaps with the ORF2 and codes for an immunogenic phosphoprotein. It is generally believed that there exists a single genotype of HEV. The recently discovered swine and avian strains of HEV genetically and antigenically related to human strains of HEV. Swine HEV is considered as a zoonotic pathogen.