Section V. HEPATITIS B VIRUS
7-18. VIRUS STRUCTURE
The hepatitis B virus (HBV) consists of a central core containing the core antigen
(HBcAg) and a surrounding envelope containing the surface antigen (HBsAg).
(figure 7-5). DNA, hepatitis Be antigen (HBeAg), and an enzyme (DNA polymerase)
required to help the DNA reproduce are also located in the central core. The intact virus
particle containing these components is referred to as the "Dane particle" and is
considered the infectious virus. Hepatitis B belongs to the hepadna class of viruses.
Figure 7-5. Structure of HBV.
7-19. MODE OF TRANSMISSION
Hepatitis B virus is predominantly transmitted via the parenteral route.
Parenteral transmission occurs mainly through exposure to contaminated blood or blood
products (blood transfusions, dialysis patients, hemophiliacs, infected needles, and so forth).
Though transmission appears to be primarily parenteral, HBV can also be transmitted
through a number of nonparenteral routes such as close intimate contact.
7-20. INCUBATION PERIOD AND INFECTIVITY
The length of the incubation period for HBV correlates inversely with the amount
of virus to which the individual is exposed. (Large dose of HBV = short incubation time.)
The average incubation period for hepatitis B is about 45 days with a typical range from
30 to 120 days. Hepatitis B is potentially highly infectious. As long as HBsAg is
detectable, the individual should be considered infectious. A chronic carrier state does
exist for hepatitis B infections.