Hepadnaviruses Hepatitis B Virus and Hepatitis D Virus

■ A hepatitis B virus (HBV) infection (see p. 385ff., replication) of the liver cells results in expression of viral antigen on the cell surface, followed by immunological cell damage with acute, possibly fulminant, chronic persistent or chronic aggressive hepatitis. The final stages can be liver cirrhosis or hepa-tocellular carcinoma. A concurrent or later superinfection by a defective, RNA-containing and HBV-dependent hepatitis D virus (HDV, delta agent) normally exacerbates the clinical course. Both viruses are transmitted in blood or body fluids, whereby even a tiny amount of blood may be enough to cause an infection.

Diagnosis: immunological antigen or antibody assay in patient serum. The antigen or antibody patterns observed provide insights on the stage and course of the disease.

Prevention: active immunization with HBV surface (HBs) antigen; concurrent postexposure passive immunization. ■

Hepatitis B pathogen. The hepatitis B virus (HBV) is the main representative of the family of hepadnaviruses, Hepadnaviridae. The name of the family is an acronym of the disease caused by the virus and its genomic type. It causes a sometimes chronic form of liver inflammation (hepatitis) and its genome consists of partially double-stranded DNA (hepadnavirus = hepatitis DNA virus). The replication cycle of the HBV includes a transient RNA phase (for details see Chapter 7, p. 385). The HBV possess an envelope made up

430 8 Viruses as Human Pathogen — Hepatitis B Virus -

430 8 Viruses as Human Pathogen — Hepatitis B Virus -

Hepadnaviruses

Fig. 8.10 The capsid, which consists of Hbc and Hbe antigens, encloses the entire DNA antisense strand, the incomplete sense strand, and the reverse transcriptase (not shown here). The envelope contains the three forms of the Hbs antigen: PreSI = complete protein, PreS2 = shortened form of PreSI, HBs antigen = HB surface antigen in the proper sense, shortened form of PreS2.

PreS1 PreS2 HBs antigen

PreS1 PreS2 HBs antigen

Fig. 8.10 The capsid, which consists of Hbc and Hbe antigens, encloses the entire DNA antisense strand, the incomplete sense strand, and the reverse transcriptase (not shown here). The envelope contains the three forms of the Hbs antigen: PreSI = complete protein, PreS2 = shortened form of PreSI, HBs antigen = HB surface antigen in the proper sense, shortened form of PreS2.

of a cellular double lipid layer in which are integrated the hepatitis B surface (HBs) antigen, a 25 kDa polypeptide, and its precursor stages PreS1 (40 kDa) and PreS2 (33 kDa). (Fig. 8.10). This envelope encloses the actual capsid, which consists of the hepatitis B core (HBc) antigen with 21 kDa and contains the genome together with the DNA polymerase (a reverse transcriptase, p. 385). The complete, infectious virion, also known as a Dane particle after its discoverer, has a diameter of 42 nm, the inner structure 27 nm. The virus 8 replicates in liver cells. The Dane particles and the HBs antigen, but not the HBc antigen, are released into the bloodstream, whereby the HBs antigen is present in two different forms, a filamentous particle approximately 22 x 100 nm and a spherical form with a diameter of about 22 nm. A further viral protein is the HBe antigen, which represents a posttranslational, truncated form of the HBc antigen and is no longer capable of spontaneous capsid formation. It is also released from the hepatic cells into the blood.

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Essentials of Human Physiology

Essentials of Human Physiology

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