Hepatitis B virus - Introduction, Classification, Morphology, Genome, Properties
Classification of Hepatitis B virus
The Hepatitis B virus is classified as:
Realm: Riboviria
Kingdom: Pararnavirae
Phylum: Artverviricota
Class: Revtraviricetes
Order: Blubervirales
Family: Hepadnaviridae
Genus: Orthohepadnavirus
Species: Hepatitis B virus
4 major serotypes are present - (adr, adw, ayr, ayw) based on envelope antigen
8 genotypes are present (A-H), based on overall nucleotide sequence variation
Introduction to Hepatitis B virus
Hepatitis B Virus (HBV) is the major cause of infectious hepatitis worldwide. it shows restricted host range and limited tissue tropism. It usually causes chronic disease and is associated with hepatocellular carcinoma.
Morphology of Hepatitis B virus
The Hepatitis B virus is small (42nm in diameter), and enveloped (outer lipid envelope present). It has an icosahedral nucleocapsid core (27nm structure) and its nucleocapsid encloses the viral DNA and a DNA polymerase.
The outer envelope of Hepatitis B virus contains embedded proteins (Hbs Ag) which are involved in viral binding and entry into susceptible cells. Three morphological distinct forms exist:
Dare particle (complete virus particle- 42nm in diameter)
Spherical particles (22nm in diameter)
Filamentous particles (tubular forms of roughly 22nm diameter with varying lengths)
* Spherical and Filamentous particles are both antigenically identical and known as HbsAg
The core or nucleocapsid consists of the genome surrounded by a second protein, hepatitis B core antigen (HbcAg).
Fig: HBV morphology (Source: ResearchGate)
Genome
The Hepatitis B virus genome is DNA. It is small, circular, and has two partially dsDNA held in a circular configuration. The positive strand of the genome is incomplete (usually 50-80% full length) and the negative strand is complete which is linked to the viral DNA polymerase.
The complete negative strand possesses 4 genes: genes S, C, P, and X.
The gene S codes for BhsAg and HbeAg (hepatitis B e antigen)
Gene P codes for DNA polymerase that has reverse transcriptase activity
Gene X codes for X protein that has transcription-regulating activity
The genome is around 3200 case pairs in length and has 4 conserved ORFs.
Fig: HBV genome (Source: aimspress)
Other properties
Other properties of Hepatitis B virus includes:
Hepatitis B virus is extremely heat resistant- withstands extreme temperature and humidity
Stable when stored at -200°C for years and at room temperature for 6 months
killed at 600°C for 10 hours and 1000°C for 1 minute
HbsAg
is resistant to ultraviolet treatment
is stable at pH 2.4 for up to 6 hours
is destroyed by treatment with 0.5% sodium hypochlorite within 3 min