Viral type A and type B hepatitis: morphology, biology, immunology and epidemiology--a review.

Viral hepatitis is one of the most serious infectious diseases in the United States and is of great concern to the public health agencies, hospitals and research laboratories. Progress in our knowledge of this disease has been based on cooperation between specialists in many diverse scientific disciplines employing sophisticated scientific instruments and technics. Close cooperation between clinical pathologists and clinicians is of great importance in diagnosis. Biologic, immunologic, epidemiologic and morphologic studies have resulted in the demonstration that the disease is the result of infection with at least two different viruses, described as type A and type B hepatitis viruses. The first induces type A hepatitis (infectious or epidemic, or MS-2 strain) of longer incubation period, is transmitted parenterally and apparently by inhalation or ingestion of virus-containing material, by venereal means as well as by other means. Extremely sensitive methods are now available for the detection of hepatitis type B infection, based on the results of biochemical, biophysical and immunoelectronmicroscopic studies that resulted in our knowledge of structure and composition of type B virus, and our knowledge of host immune responses to the various components of this virus. Thus it is now known that two antigen-antibody systems are associated with viral hepatitis type B: hepatitis B surface antigen (HBsAg) and antibody (HBsAb) and hepatitis B core antigen (HBcAg) and antibody to it (HBcAb). The test for antibody to HBcAg appears to be a sensitive indicator of viral replication when only subdetectable amounts of HBsAg are circulated. Since the recent discovery and characterization of type A hepatitis virus, great progress has been made in our understanding of the relationship between type A and type B hepatitis viruses. There is no cross immunity between the two viruses, and as is now suspected, there may be at least another virus, described as type C virus, which may play an etiologic role in viral hepatitis. There is no doubt now that type A and type B hepatitis viruses can be transmitted to monkeys; type A to marmosets and chimpanzees, type B to chimpanzees and rhesus monkeys. The two viruses are serologically and immunologically distinct. This knowledge and the results of biologic experiments have laid a solid foundation of meaningful diagnostic procedures for the two types of viral hepatitis. Advances in biophysical and biochemical procedures of treatment of sera of hepatitis B patients have resulted in availability of viral material, noninfectious but immunogenic, for vaccination of chimpanzees. Protective efficacy trials of the vaccine in chimpanzees have demonstrated the vaccine to be fully protective against high doses of infectious hepatitis B virus...