Hepatitis B is a viral infection of the liver usually transmitted by inoculation of infected blood or blood products. However, the antigen has been found in most body secretions, and it is known that the disease can be spread by oral or sexual contact. Hepatitis B virus (HBA) is highly prevalent in homosexuals and intravenous drugs abusers. Other group at high risk include patients and staff at hemodialysis centers, physicians, dentists, nurses and personnel working in clinical and pathologic laboratories. Approximately 5-10% of infected individuals become carriers, providing a substantial reservoir of infection. 40-70% of infants born to HBsAg-positive mothers will develop antigens to hepatitis B in the bloodstream. Fecal-oral transmission of virus B has also been documented. The incubation period of hepatitis B is 6 weeks to 6 months. Clinical features of hepatitis A and B are similar; however, the onset in hepatitis B tends to be more insidious.
Hepatitis B virus is pleomorphic and occurs in spherical and tubular forms of different sizes. The largest of these, the Dane particle, is thought to be the complete infectious virus. The 42-nm Dane particle is composed of a core (27-rim particle) found in the nucleus of infected liver cells, and a double-shelled surface particle found in the cytoplasm. The other particles form an excess coating of the virus and contain no nucleic acid.
There are 3 distinct antigen-antibody systems that relate to HBV infection. In addition, DNA polymerase activity can be measured as a sensitive index of viral replication and infectivity.
The surface antigen (HBsAg) is the antigen routinely measured in blood. HBsAg is unaffected by repeated freezing and thawing or by heating at 56 degrees centigrade overnight or at 60 degrees centigrade for l hour. It is inactivated by heating between 85 and 100 degrees centigrade for 15 to 30 minutes. HBsAg can exist in serum as 3 antigenically identical forms: (1) the outer coat of the intact Dane particle; (2) a spherical 22-nm particle; and (3) elongated tubular particles, The spherical and tubular particles do not contain nucleic acid and are not infectious. Four major antigenic subtypes of HBAg have been recognized. Subtyping of HBsAg if primarily of epidemiologic importance. The presence of GBsAg is the first manifestation of HBV infection occurring before biochemical evidence of liver disease. HBsAg persists throughout the clinical illness, persistence of HBsAg is usually associated with clinical and laboratory evidence of chronic hepatitis. The presence of HBsAg establishes infection with HBV and implies infectivity. Specific antibody to HBsAg (anti-HBs) occurs in most individuals after clearance of HBsAg. Anti-HBs is usually delayed after clearance of HBsAg. During this serologic gap, infectivity has been demonstrated. Development of anti-HBs signals recovery from HBV, noninfectivity, and protection from HBV infection.
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