MAHE 2006 Hepatitis B
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You are here: Home » MAHE 2006 MCQs » MAHE 2006 Hepatitis B
- adw
- ayr
- ada
- ayw
Hepatitis B Virus
HBV, the only member of the family Hepadnaviridae that infects humans, has a diameter of 42 nm and consists of a 28 nm core surrounded by a protein coat; the core contains protein, circular double-stranded DNA, and DNA polymerase . Immunofluorescent antibody studies have detected HBV in the nuclei of infected liver cells. The core moves through the nuclear membrane into the cytoplasm, where it acquires its surface coat. HBV is found in the serum of almost all patients early in the course of acute HBV infection.
Two additional particles appear in the liver cell cytoplasm and serum of patients with HBV: a 22 nm-diameter sphere and a rod-shaped filament of the same diameter. These particles are found at the onset of jaundice in nearly all patients with acute HBV infection. The surface coat of the hepatitis B virion and the spheres and filaments are composed of pre-S1, pre-S2, and S polypeptides, in both glycosylated and unglycosylated forms. The S polypeptide is the major hepatitis B surface antigen (HBsAg).
Although there is only one major serotype of HBV, HBsAg has five major subtype determinants, termed a, d, y, w, and r, which are primarily of epidemiologic interest. All HBsAg-positive sera contain determinant a; determinants d and y are mutually exclusive, as are w and r. Hence, four subtype patterns are possible: adw, ayw, adr, and ayr. The first three subtype patterns occur frequently; ayr is rare. Many studies have attempted to correlate subtype with clinical course. It appears, however, that the subtypes are associated with different geographic distributions of HBV rather than with different degrees of virulence. Subtype adw is most common in the Americas and Europe; adr prevails in most of the Far East.
HBV can be classified into seven genotypes (A to G) on the basis of an intergroup divergence of 8% or more in the complete nucleotide sequence.
Genotypes A (serotype adw) and D (ayw) are most common in the United States and Europe;
genotypes B (adw) and C (adr) are most frequent in China and Southeast Asia.
There are also several variations or mutations in the nucleotide sequence of HBV. Core promoter and precore variants produce HBV virions that do not produce hepatitis B e antigen (HBeAg). These variants are most commonly seen in patients with genotypes B, C, and D. These differences in genotypes and the presence or absence of variants may account for variations in clinical manifestations of chronic HBV infection in the United States and other parts of the world.
Category: MAHE 2006 MCQs
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