- poly(A) tail.
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Type Species |
(HEV) |
Virions (27-34 nm) are icosahedral and non-enveloped (Fig. 1).
Physicochemical and Physical Properties
Virion buoyant density is 1.35 g/cm3 in CsCl and 1.29 g/cm3 in glycerol potassium tartrate gradients. Virion S20w is 183S.
The genome is a positive sense ssRNA of approximately 7.2 kb, with a 3- poly(A) tail.
Virions are constructed from a major capsid protein (CP) (predicted Mr 71 
103). A small immunoreactive protein (predicted Mr 1.5 103) of unknown function has been identified. Nonstructural proteins have limited similarity with the “alpha-like” supergroup of viruses and include domains consistent with a methyltransferase, RNA helicase, papain-like cysteine protease and RNA-dependent RNA polymerase.
None reported.
Evidence for glycosylation of the major CP in mammalian expression studies has been reported, but the biological significance is unknown.
Genome Organization and Replication
The RNA genome of Hepatitis E virus (HEV) is organized into three ORFs, with the nonstructural proteins encoded toward the 5-end of the genome and the structural protein(s) toward the 3-end. ORF1 encodes the nonstructural polyprotein. ORF2 encodes the major CP. A third ORF overlaps ORF1 and ORF2 and encodes a small protein (123 amino acids) of unknown function (Fig. 2).
A single serotype has been described, with extensive cross-reactivity among circulating strains.
HEV is associated in humans with outbreaks and sporadic cases of enterically-transmitted acute hepatitis. The virus is considered endemic in tropical and subtropical countries such as Asia, Africa, and Mexico, but antibody prevalence studies suggest global distribution of this virus, perhaps in a nonpathogenic form. Antibody prevalence studies in primates and swine have found evidence for hepatitis E virus or a related agent in animals. A HEV strain has been identified in swine that is closely related antigenically and genetically to human HEV.
List of Species Demarcation Criteria in the Genus
Not applicable.
Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus name, genome sequence accession numbers [ ], and assigned abbreviation ( ) are:
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Hepatitis E virus |
[M73218, M80581, M74506, AF011921] |
(HEV) |
Tentative Species in the Genus
None reported.
Phylogenetic Relationship with Selected Virus Families
See Fig. 3.
HEV shares similarity with the members of the family Caliciviridae in its structural morphology by electron microscopy and in its genome organization. HEV shows highest, but limited, amino acid similarity in its replicative enzymes with rubella virus and alphaviruses of the family Togaviridae and with plant furoviruses.
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