compromised and in other high-risk groups including male homosexuals and intravenous drug abusers. In parts of Asia and Africa, chronic carriage occurs in up to 50% of the population. Worldwide there are about 300 million chronic carriers of hepatitis B virus and it is the most important cause of primary hepatocellular carcinoma.
Interferon alfa (see p. 263) given for 4—6 months gives long-term clearance of hepatitis B virus from the plasma in 25-40% of patients. The effect is characteristically preceded by elevations in serum transamininases which reflects immune-mediated destruction of virus-infected hepatocytes; if liver function is impaired prior to therapy use of interferon alfa should be monitored carefully because it may precipitate hepatic failure.
Lamivudine, a nucleoside analogue, inhibits replication of hepatitis B virus DNA and reduces hepatic inflammation. The serum of about 17% of patients converts from positive to negative for antibodies to hepatitis B after one year of therapy. Long-term treatment is probably necessary and the drug is well tolerated.
Hepatitis B vaccine (inactivated B virus surface antigen adsorbed on aluminium hydroxide adjuvant) provides active immunity against hepatitis B infection, and in countries of low endemicity it is given to individuals at high risk, including healthcare professionals. Immunity is conferred for at least 5 years and can be supplemented by booster injections.
Hepatitis B immunoglobulin (pooled plasma selected for high titres of antibodies to the virus) provides passive immunity for post-exposure prophylaxis e.g. after accidental needlestick injury.
In countries with high prevalence of hepatitis B the virus is transmitted vertically (from mother to baby). Passive immunoprophylaxis with immune globulin given to the baby at birth, followed by vaccination, is effective at preventing chronic carriage. Mass vaccination should lead to a reduction in the incidence of primary hepatocellular carcinoma, but cannot yet be implemented in third world countries for want of funding.
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