Hepatitis B Virus

STRUCTURE:
  1. HBV present in India is Ayw, Adr
  2. Serum from patient of hepatitis B shows three types of particles :
  • Dane particle
  • Double walled sphericle structure, 42 nm in diameter.
  • It is the complete hepatitis B virus
  • It contains.
  1. Core antigen (C antigen - HBc Ag)
  2. Surface antigen (HBs Ag)
  3. Hepatitis B `e' antigen (HBe Ag)
  • Sphericle particle (most common)
  1. 22 nm in diameter
  2. It is the surface component of HBV (HBs Ag)
  • Filamentous or tubular particle
  1. 22 nm
  2. It is identical to sphericle particle ie HBs Ag.
Genome:
  • There are four known genes encoded by the genome called C, P, S, and X.
  • The core protein is coded for by gene C (HBcAg), and its start codon is preceded by an upstream in-frame AUG start codon from which the pre-core protein is produced. 
  • HBeAg is produced by proteolytic processing of the pre-core protein. 
  • The DNA polymerase is encoded by gene P. 
  • Reverse transcriptase of HBV is coded on p gene
  • P gene is the longest DNA of hepatitis B virus 
  • Gene S is the gene that codes for the surface antigen (HBsAg)
TRANSMISSION:
  • HBV infection is transmitted by Blood is the most important source of infection.
Transfusion of blood or blood products.
  1. Sexual transmission
  2. Vertical transmission from mother to child
  3. Percutaneous transmission (eg - needle punctures)
  4. Virus is also present in saliva, breast milk, semen, vaginal secretions, urine, bile and feces. Of these, semen and saliva are known to transmit the infection.
  5. Perinatal transmission occurs mostly at the time of delivery
  • Hepatitis B virus is least likely to cross placenta
  • Highest transmission of hepatitis B from mother to fetus occurs if the mother is infected during IIIrd trimester
  • The likelihood of perinatal transmission of HBV correlates with the presence of HBeAg and high-level viral replication
  • 65%-90% of HBeAg-positive mothers but only 10-15% of anti-HBe- positive mothers transmit HBV infection to their offspring
SEROLOGICAL & VIROLOGICAL MARKERS OF HBV:
  • HBs Ag(Australian antigen)
  1. First virological marker detectable in the serum
  2. HBsAg presence precedes elevations of serum aminotransferase activity and onset of clinical illness.
  3. HBsAg become undetectable 1-2 months after the onset of jaundice and rarely persists beyond 6 months.
  4. Incubation period of HBV is 45 to 180 days
  5. Hbs Ag of HBV causes glomerulonephritis­
  6. In chronic HBV infection, HBsAg remains detectable beyond 6 months.
  7. HBsAg + HBeAg suggest highly infective stage
  • HBc Ag
  1. It is not demonstrable in the circulation because it is enclosed within the HBs Ag coat.
  2. HBc Ag remain in the hepatocyte, where it can readily be detectable by immunohistochemical staining.
  3. HBe Ag HBe Ag appears concurrently with or shortly after HBs Ag. HBe Ag is an 
  4. indicator of active intrahepatic replication and high infectivity. It is a qualitative marker of HBV replication HBs Ag carrier mothers who are HBe Ag positive almost invariably (> 90%) transmit hepatitis B infection to their offspring, where as HBs Ag carrier mothers with anti HBe rarely (10 to 15%) infect their offspring.
  5. HBe testing is indicated primarily during follow up of chronic infection.

  • Anti HBcAg
  1. Appears within the first 1 to 2 weeks after the appearance of HBs Ag.
  2. In acute or recent infection IgM anti HBc is detected.
  3. Ig G anti HBc indicates remote infection.
  4. Recumbent stage of Hepatitis B is characterized by Anti HBc
  5. Epidemiologic study of Hepatitis B is by Anti HBc
  • Anti HBs Ag
  1. It becomes detectable in blood when HBs Ag disappears.
  2. Anti HBs Ag is protective antibody.
  3. It is the only serological marker, present after immunization.
  • Anti HBeAg
  1. Disappearance of HBe Ag is followed by the appearance of anti HBe Ag
  2. Its presence indicates low infectivity and virus replication.
  • HBV DNA
  1. It is the quantitative marker of virus replication.
  • For the diagnosis of HBV infection, detection of HBs Ag in blood is all that ordinarily necessory.
  • The simultaneous presence of Ig M anti HBc indicates recent infection, while Ig G anti HBc indicates remote infection.
  • In 1-5% of patients there is a "window" or "gap" period between disappearace of HBs Ag and appearance of anti HBs Ag. During this period diagnosis is made by Ig M anti HBc Ag.
Exam Question of:
  • Serological marker present during window period in hepatitis B infection is Anti HBc
  • Anti HBs is the protective antibody present after recovery from hepatitis B or immunization.
  • First antibody to appear in plasma/blood in acute hepatitis B is Ig M Anti HBc
  • Recumbent stage of Hepatitis B is characterized by Anti HBc
  • The presence of hepatitis B surface antigen means actively replicating virus, and in the context of the history of recent needle-stick injury, this likely represents a hepatitis B
  • infection.
  • Hepatitis B virus is least likely to cross placenta
  • Highest transmission of hepatitis B from mother to fetus occurs if the mother is infected during IIIrd trimester
  • 10-15% of anti-HBe- positive mothers transmit HBV infection to their offspring
  • HBsAg + HBeAg suggest highly infective stage
  • Incubation period of HBV is 45 to 180 days
  • HBV present in India is Ayw, Adr
  • Reverse transcriptase of HBV is coded on p gene
  • P gene is the longest DNA of hepatitis B virus 
  • HBcAg is found within the nuclei of infected hepatocytes and not usually in the peripheral circulation in Hepatitis B' infection 
  • The serological marker of acute Hepatitis B infection is HBsAg+Core antibody
  • Acute Hepatitis B can be earliest diagnosed by IgM anti HBc ab
  • Epidemiologic study of Hepatitis B is by Anti HBc
  • Active replication in Hepatitis B infection is indicated by HBeAg
  • Hbs Ag a component of HBV causes glomerulonephritis­ Early diagnosis of active hepatitis B infection is done by IgM HBcAg antibody
  • Serological markers for active viral replication include HBe Ag, presence of DNA polymerase and circulating HBV DNA.
  • HBsAg is also known as australian antigen
  • E antigen (HBeAg) of hepatitis B virus is a product of C gene
  • DNA polymerase of HBV is encoded by P gene
  • Super carrier of HBV shows HbsAg + HBeAg + HBV DNA

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