The natural history of hepatitis B.

Hepatitis B infection is acquired through contact with the blood of a person carrying the hepatitis B virus. The carrier rate of HBsAg varies world-wide. In many endemic areas, infection is largely acquired perinatally, while in other areas of high prevalence, transmission occurs during childhood, with intrafamilial spread being particularly important. Subclinical hepatitis B attacks are extremely frequent. The unusual clinical episode diagnosed in the adult tends to be more severe than that for virus A or non-A, non-B infection although the overall picture is similar. A fulminant course may be related to an enhanced immune response, and in such instances, HBsAg titres may be low or undetectable. About 10% of patients suffering an acute attack, more commonly males, will not clear the virus and will become chronic carriers. These may remain 'healthy' or suffer from various grades of chronic hepatitis and cirrhosis. Chronicity is related to impairment of humoral and cell-mediated immunity. There are two phases of hepatitis B infection, the replicative and the integrated, the former being recognized by the presence of hepatitis B viral DNA in serum. Relapses of chronic hepatitis B may be related to conversion from replicative to integrated stages, to spontaneous reactivation, or to super-added virus infection, especially with delta virus.