HEPADNAVIRIDAE

• STRUCTURE: Circular DNA, partially double-stranded, partially single-stranded.

• REPLICATION: DNA replication with an RNA intermediate, utilizing Reverse Transcriptase.

  • Upon entry of virus into cell, the viral DNA-Polymerase repairs the single-stranded end of the molecule, forming a supercoiled dsDNA genome.

  • Host-cell RNA Polymerase then forms mRNA's from the DNA genome:

    • Full-length (+) mRNA

    • Subgenomic mRNA's, from which structural and non-structural proteins are made.

  • The full-length mRNA gets enclosed around a core-capsid.

  • Inside the core, viral DNA Polymerase then serves as a Reverse Transcriptase, to make DNA out of the full-length mRNA.

    • cDNA is formed, forming a DNA:RNA hybrid. The RNA is then degraded, and then a complementary DNA strand is formed, making dsDNA.

  • dsDNA progeny genome is then put out of cell, taking outer envelope with it as it leaves host cell.

• HEPATITIS-B VIRUS (HBV):

  • STRUCTURE:

    • Dane Particle: The entire infectious virion, including nucleocapsid, core antigens, and surface antigens.

    • HBV Surface Antigen (HBsAg): 4 phenotypes, useful for epidemiology: adw, ayw, adr, ayr.

  • TRANSMISSION: Sexual, fecal-oral, or intravenous or by exposure to blood products.

  • DIAGNOSIS:

• MANIFESTATIONS: Cell-mediated immunity is responsible for the symptoms.

  • Acute Infection: Acute infection may or may not lead to persistent infection. HBsAg and Anti-HBc will show up in blood.

  • Chronic (Persistent) Infection: Hepatitis-B virus is still being produced. 5-10% of HBV can be expected to develop an HBV carrier state.

    • Vasculitis, arthralgia, rash, and kidney problems can all result from immune-complex disease involving immune complexes of the HBsAg.

    • Primary Hepatocellular Carcinoma: 80% of primary hepatomas are due to HBV infection.

• Other Hepatitis Infections:

  • Hepatitis-A (HAV): Enterovirus-72

  • Hepatitis-C (HCV): Flavivirus.

  • HEPATITIS-D (Delta Agent): Hepatitis-B is required in order for this virus to infect.

    • STRUCTURE: ss circular RNA that resembles an intron. RNA encodes the delta antigen, which is in turn enveloped by the HBsAg.

    • MANIFESTATIONS: Should be tested for as co-infection with HBV. Course is more severe and prognosis is poorer when Delta agent is present.

  • Hepatitis-E (HEV): Calicivirus

• VACCINE: It consists of the Hepatitis-B Surface Antigen, to which we then make protective antibodies. Thus presence of Anti-HBs is indicative of previous vaccination.

Category: Microbiology Notes