The hepatitis E virus (HEV) is the causative agent of

hepatitis E Hepatitis E is inflammation of the liver caused by infection with the hepatitis E virus (HEV); it is a type of viral hepatitis. Hepatitis E has mainly a fecal-oral transmission route that is similar to hepatitis A, although the viruses are unrel ...

. It is of the species ''Orthohepevirus A.'' Globally, approximately 939 million corresponding to 1 in 8 individuals have ever experienced HEV infection. About 15–110 million individuals have recent or ongoing HEV infection. The virus particle was first seen in 1983, but was only molecularly cloned in 1989.

Genome and proteome

''Orthohepevirus A'' can be classified into eight different genotypes from different geographical regions: genotype 1 (Asia), genotype 2 (Africa and Mexico), genotype 3 (Europe and North America), genotype 4 (Asia); genotypes 5 and 6 have been detected in Asian wild boar and genotypes 7 and 8 in camels.Schlauder, G. G. & Mushahwar, I. K. (2001) Genetic heterogeneity of hepatitis E virus. J Med Virol 65, 282–92 The viral genome is a single strand of positive-sense RNA that is about 7200 bases in length. The three open-reading frames (ORF1, ORF2 and ORF3) encode for three proteins (O1, O2, O3), two of which are polyproteins, that is, they are cleaved into fragments which carry out the actual functions of the virus (see figure). The O1 protein consists of seven such fragments, namely Met (

methyltransferase Methyltransferases are a large group of enzymes that all methylate their substrates but can be split into several subclasses based on their structural features. The most common class of methyltransferases is class I, all of which contain a Ross ...

), Y (Y-domain), Plp (

papain-like protease Papain-like proteases (or papain-like (cysteine) peptidases; abbreviated PLP or PLCP) are a large protein family of cysteine protease enzymes that share structural and enzymatic properties with the group's namesake member, papain. They are found ...

), V (proline-rich variable region), X (X-domain, macro-domain), Hel (

helicase Helicases are a class of enzymes thought to be vital to all organisms. Their main function is to unpack an organism's genetic material. Helicases are motor proteins that move directionally along a nucleic acid phosphodiester backbone, separatin ...

), and Rdrp ( RNA-dependent RNA polymerase). The Pvx domain is a fusion protein consisting of the Plp, V, and X domains. The O3 protein is encoded by a single open-reading frame (ORF3). The O2 protein encodes the capsid, which is composed of three domains, namely the shell domain (S) and two protruding domains (P1, P2). Numbers in the figure indicate positions in the RNA sequence. Hepatitis E Virus genome and encoded proteins

Hepatitis E Virus genome and encoded proteins

Interactome

The protein-protein

interactome In molecular biology, an interactome is the whole set of molecular interactions in a particular cell. The term specifically refers to physical interactions among molecules (such as those among proteins, also known as protein–protein interactions, ...

among ''Orthohepevirus A'' proteins has been mapped by Osterman et al. (2015), who found 25 interactions among the 10 proteins studied. Almost all (24) of these interactions were considered as of "high quality".

Structure

The viral particles are 27 to 34 nanometers in diameter and are not enveloped.

Taxonomy

It was previously classified in the family ''

Caliciviridae The ''Caliciviridae'' are a family of "small round structured" viruses, members of Class IV of the Baltimore scheme. Caliciviridae bear resemblance to enlarged picornavirus and was formerly a separate genus within the picornaviridae. They are p ...

''. However, its

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...

more closely resembles

rubella virus Rubella virus (RuV) is the pathogenic agent of the disease rubella, transmitted only between humans via the respiratory route, and is the main cause of congenital rubella syndrome when infection occurs during the first weeks of pregnancy. Rube ...

. It is now classified as a member of the genus ''

Orthohepevirus ''Orthohepevirus'' is a genus of viruses assigned to the family ''Hepeviridae''. ''Orthohepevirus'' is a fairly isolated viral genus in which the virions are characterized by round, non-enveloped and isometric capsids with a diameter of 27–34 ...

'' in the family ''

Hepeviridae ''Hepeviridae'' is a family of viruses. Human, pig, wild boar, sheep, cow, camel, monkey, some rodents, bats and chickens serve as natural hosts. There are two genera in the family. Diseases associated with this family include: hepatitis; high ...

''.

Evolution

The strains of HEV that exist today may have arisen from a shared ancestor virus 536 to 1344 years ago. Another analysis has dated the origin of Hepatitis E to ~6000 years ago, with a suggestion that this was associated with domestication of pigs. At some point, two

clades A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

may have diverged — an anthropotropic form and an enzootic form — which subsequently evolved into genotypes 1 and 2 and genotypes 3 and 4, respectively. Whereas genotype 2 remains less commonly detected than other genotypes, genetic evolutionary analyses suggest that genotypes 1, 3, and 4 have spread substantially during the past 100 years.Izopet J, Abravanel F, Dalton H, Nassim RK (2014) Hepatitis E Virus Infection. Clin Micro Reviews 27 (1) 116–138

Notes

References

External links

* * * {{DEFAULTSORT:Hepatitis E Virus Hepeviridae Viral hepatitis