Hepatitis A Virus- An Overview


Hepatitis A virus (HAV) is a member of the picornavirus family, which are small, non-enveloped, single-stranded RNA viruses that cause various human and animal diseases. HAV is the causative agent of hepatitis A, an acute and self-limiting infection of the liver that is transmitted by the fecal-oral route. Hepatitis A is a global public health problem, especially in regions with poor sanitation and hygiene.

The structure of HAV is similar to other picornaviruses, but with some distinctive features. The virus has a spherical particle with icosahedral symmetry, measuring about 27 to 32 nm in diameter . The capsid consists of 60 copies of each of the three main proteins: VP1 (also known as 1D), VP2 (1B), and VP3 (1C) . These proteins form a stable shell that protects the viral RNA genome from degradation.

The genome of HAV is a linear single-stranded RNA molecule with positive polarity, meaning that it can act as a messenger RNA for protein synthesis . The genome is about 7.5 kb long and has a low G+C content compared to other picornaviruses. The genome has three main parts: a 5` noncoding region (NCR) that comprises about 10% of the genome and is covalently linked to a viral protein VPg; a single open reading frame (ORF) that encodes all of the viral proteins, with regions designated as P1 for capsid proteins and P2 and P3 for nonstructural proteins; and a short 3` NCR that terminates in a poly(A) tail .

The P1 region contains four segments for structural proteins that make up the capsid: 1A-VP4, 1B-VP2, 1C-VP3, and 1D-VP1 . The P2 and P3 regions comprise seven nonstructural proteins that are involved in viral replication and processing: 2A, 2B, 2C, 3A, 3B (VPg), 3C (a cysteine protease), and 3D (an RNA-dependent RNA polymerase) .

The structure of HAV is important for understanding its replication cycle, pathogenesis, and immune response. The capsid proteins mediate the attachment and entry of the virus into host cells, as well as the assembly and release of new virions . The nonstructural proteins orchestrate the synthesis and processing of viral RNA and proteins, as well as the modulation of host cell functions. The genome structure and sequence determine the antigenicity and variability of the virus, as well as its interaction with cellular factors.

In summary, HAV is a small RNA virus with a simple but stable structure that enables it to infect human liver cells and cause hepatitis A. The virus has a single-stranded RNA genome with three main parts: a 5` NCR linked to VPg, an ORF encoding capsid and nonstructural proteins, and a 3` NCR with a poly(A) tail. The capsid consists of three main proteins: VP1, VP2, and VP3. The nonstructural proteins include seven proteins: 2A, 2B, 2C, 3A, 3B (VPg), 3C (a protease), and 3D (a polymerase).