Prevention and Treatment

The first vaccine against hepatitis B, approved in the early 1980s, consisted of HBsAg obtained from the blood of chronic carriers; 1 ml of their blood often had enough antigen to immunize eight people! Since 1986, however, a genetically engineered vaccine produced in yeast has been available against hepatitis B and a combined vaccine against both hepatitis A and B has now been approved. Infants born to an infected mother are injected at birth with hepatitis B immune globulin (HBIG) containing a high titer of antibody to HBV. Active immunization is also started, with injections of the vaccine at one week, one month, and six months of age. Passive immunization with HBIG offers immediate, partial protection against HBV infection until active immunity is achieved from the vaccine. Vaccination against hepatitis B prevents the disease, and it can also help prevent many of the 500,000 to 1 million new liver cell cancers that occur worldwide

24.6 Viral Diseases of the Lower Alimentary System 623

each year. Education of groups at high-risk of contracting hepatitis B can help prevent the disease. Those likely to be exposed to blood are taught to consider all blood to be infectious, to wash their hands contaminated with blood, to wear gloves and protective clothing, and to handle contaminated sharp objects such as needles and scalpel blades carefully. Teaching the importance and proper use of condoms also helps limit spread of the infection. Victims are advised to avoid alcohol and other hepatic toxins. There is no curative antiviral treatment yet for hepatitis B. Remarkable improvement can be achieved in many cases, however, by giving injections of genetically engineered interferon along with an antiviral medication such as lamivudine, a reverse transcriptase inhibitor. ■ interferon, pp. 380,388

Hepatitis C

Even when blood that tested positive for HBV was excluded from transfusions, post-transfusion hepatitis continued to be common, indicating the presence of another bloodborne hepatitis virus. After a number of years of trying to isolate a non-A, non-B hepatitis virus, scientists in 1989 were able to clone parts of the genome of a transfusion-associated virus, now known as hepatitis C virus (HCV). One of the gene products of these clones proved to be an HCV antigen satisfactory for detecting antibody to HCV in the blood of prospective blood donors. By not using donated blood containing the HCV antibody, the incidence of post-transfusion hepatitis fell from about 8% to very low levels. The antibody test has revealed that more than 3 million Americans are infected with HCV and that over 30,000 new cases occur each year. It is now the most common chronic blood-borne infection in the United States.

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