Global Alert and Response (GAR)

Hepatitis A


The hepatitis A virus HAV

- Morphology and physicochemical properties
- Genome and proteins
- Antigenicity
- Stability

HAV, first identified in 1973, is a nonenveloped, spherical, positive stranded RNA virus, classified within the genus hepatovirus of the picornavirus family.18, 21-23

HAV infection does not lead to chronic or persistent hepatitis.18, 23, 40

HAV strains recovered from widely separated regions of the world are antigenically similar. In humans, a single serotype of HAV exists.18, 21, 23, 39, 40

HAV is known to produce disease in humans and non-human primates. In vitro, the wild type virus is generally difficult to grow and no cytopathic effect is observed. Attenuated HAV strains adapted to cell culture have been used to develop vaccines.18, 21, 23, 40

HAV infection induces lifelong protection against reinfection.18

Click here for: Electron Microscopy (EM) picture of HAV

Morphology and physicochemical properties
HAV is among the smallest and structurally simplest of the RNA animal viruses.

The virion is nonenveloped and, with a diameter of 27-32 nm, it is composed entirely of viral protein and RNA. Electron microscopy (EM) analyses show particles with icosahedral symmetry although no structural details could be discerned. Morphologically, HAV particles are indistinguishable from other picornaviruses.18, 22, 40

Full virions have a buoyant density of 1.32 - 1.34 g/cm3 in CsCl and a sedimentation coefficient of 156 - 160 S in neutral sucrose solutions.18, 21

Empty capsids, abundant in faeces collected during early infection, band at 1.20 and 1.29 - 1.31 g/cm3, with sedimentation coefficients ranging from 50 S to 90 S, predominantly 70 S. 18, 21

Genome and proteins
The hepatitis A genome consists of a linear, single stranded, positive-sense RNA of approximately 7.5 kb containing a 5'-nontranslated region with complex secondary and tertiary structure.18, 21, 22, 40

The 5'-end represents a noncoding region (NCR) extending over 10% of the genome, it is uncapped and covalently linked to the viral protein VPg (2.5 kD).18, 21, 22, 40

A single large polyprotein is expressed from a large open reading frame extending through most of the genomic RNA. This polyprotein is subsequently cleaved by a viral protease (3Cpro) to form three (possibly four) capsid proteins and several nonstructural proteins.18, 21-23, 40

The 3'-end terminates with a poly(A)tail of 40 - 80 nucleotides.18, 22

Hepatitis A capsids contain 60 copies of VP1 (30 to 33 kD), VP2 (24 to 30 kD) and VP3 (21 to 28 kD). Exposed parts of VP1 (residues Ser102 and Ser114) and of VP3 (residue Asp70) on the capsid surface define the conformational immunodominant antigenic site of HAV.18, 22, 23, 40

Sequences for known human HAV isolates are highly similar even when geographic and temporal origins are widely separated, yet seven distinct genotypes have been identified to date.18

HAV genomic replication occurs exclusively in the cytoplasm of the infected hepatocyte by a mechanism involving an RNA-dependent RNA polymerase.21

Click here for: Genetic map of HAV
Click here for: 5' NCR structure of HAV

Antigenicity
HAV has only one known serotype, and one neutralization site is immunodominant. Different viral strains show similar reactivity to monoclonal anti-HAV antibodies.18, 22, 39, 40

Antigens of the intact virion are conformational and different from those of isolated proteins. Antibodies to purified capsid proteins or to synthetic peptides have weak or no detectable neutralizing activity.18, 23

HAV is neutralized by both anti-HAV IgG and anti-HAV IgM.

No serologic or hybridizing cross-reactivity between HAV and other viral hepatitis agents, including hepatitis E virus (HEV), have been observed.18, 22

The nonstructural proteins of HAV are also immunogenic during natural and experimental infections.18

Stability
HAV has no lipid envelope and is stable when excreted from the infected liver to the bile to enter the gastrointestinal tract. It has been found to survive in experimentally contaminated fresh water, seawater, wastewater, soils, marine sediment, live oysters, and creme-filled cookies.

HAV is extremely resistant to degradation by environmental conditions, a property that allows its maintenance and spread within populations.18, 22, 39, 40

HAV is resistant to:

  • thermal denaturation (survives at 70°C for up to 10 min)
  • acid treatment (pH 1 for 2 h at room temperature), 20% ether, chloroform, dichlorodifluoromethane, and trichlorotrifluoroethane
  • perchloracetic acid (300 mg/l for 15 min at 20°C)
  • detergent inactivation (survives at 37°C for 30 min in 1% SDS)
  • storage at -20°C for years

HAV is inactivated by:

  • heating to 85°C for 1min
  • autoclaving (121°C for 20 min)
  • ultraviolet radiation (1.1 W at a depth of 0.9 cm for 1 min)
  • formalin (8% for 1 min at 25°C)
  • ß-propriolactone (0.03% for 72 h at 4°C)
  • potassium permanganate (30 mg/l for 5 min)
  • iodine (3 mg/l for 5 min)
  • chlorine (free residual chlorine concentration of 2.0 to 2.5 mg/l for 15 min)
  • chlorine-containing compounds (3 to 10 mg/l sodium hypochlorite at 20°C for 5 to 15 min)
  • shellfish from contaminated areas should be heated to 90°C for 4 min or steamed for 90 sec


Electron Microscopy (EM) picture

From: Centers for Disease Control and Prevention (CDC), Atlanta, USA: 10 http://www.cdc.gov/ncidod/diseases/hepatitis/slideset/hep06.gif

Electron microsopy (EM) picture of human hepatitis A virus.


Genetic structure of hepatitis A virus

Delineation, to scale, of the genome of HAV with its 5'-linked VPg protein, 5'-nontranslated region, single long open reading frame, 3'-nontranslated region and polyadenylated 3'-end. The RNA is translated into a precursor polyprotein that is cleaved to generate mature proteins.6


Proposed secondary structure of the 5' NCR of HAV RNA

From: Lemon SM and Robertson BH. Current perspectives in the virology and the molecular biology of hepatitis A virus. Seminars in Virology, 1993, 4:285-295, 25 with permission.

Proposed secondary structure of the 5' NCR of HAV RNA (strain HM175/wild-type). This model is based on a combination of phylogenetic comparisons, thermodynamic predictions, and nuclease digestions of synthetic RNA between nucleotides 300 and 735. Major structural domains are indicated by Roman numerals beginning at the 5' terminus. Domains contributing to the HAV internal ribosome entry site are included in the box, although the boundaries are not precisely determined. Sites of mutations that appear to enhance HAV replication in cell culture are indicated (arrows). Two possible pseudoknots are indicated by shaded interactions near the 5' terminus. The two initiation codons for the open reading frame (nucleotides 735 to 737 and 741 to 743) are underlined.18

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