Infectious Diseases in an Age of Change The Impact of Human Ecology and Behavior on Disease Transmission (1995) / Chapter Skim
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Hepatitis Viruses: Changing Patterns of Human Disease
Hepatitis Viruses: Changing Patterns of Human Disease
Pages 59-76
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From page 59... ...
] are spread principally by exposure to blood, although HBV is frequently spread by unprotected sex.
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From page 60... ...
or in common-source epidemics caused by contamination of food or water. Viremia occurs during the incubation period and the early acute phase of hepatitis A, and transmission by transfusion or recently by contaminated commercial factor VIII (3)
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From page 61... ...
When serologic tests for HAV infection became available, HAV was identified as the principal cause of these epidemics, and until the 1980s it remained the type of viral hepatitis most frequently reported to the Centers for Disease Control. Since the last epidemic in the early 1970s, HAV has diminished in importance in the United States but recently has leveled off and is still responsible for ~30% of reported clinical hepatitis in this country (8~.
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From page 62... ...
This unique vaccine was prepared from viral envelope protein "hepatitis B surface antigen (HBsAg)
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From page 63... ...
Changing Patterns Since serologic tests for the detection of HBV infection were first applied in the mid-1960s the incidence of hepatitis B progressively increased until the mid-1980s, when it reached a plateau and began to decrease slightly, probably as a result of intensive efforts to control the spread of human immunodeficiency virus (HIV) in the same high-risk populations.
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From page 64... ...
cases increased from ~65% before screening for HBV markers was instituted to >90% as HBV carriers were excluded from the blood donor population (16~. The "new" hepatitis had an average incubation period of ~7-10 weeks, which is intermediate between those of hepatitis A and hepatitis B and similar to the mean incubation period of all cases of transfusion-associated hepatitis in the 1950s and 1960s, suggesting that NANB hepatitis had also been the principal cause of transfusion-associated hepatitis in the
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From page 65... ...
This suggests that multiple serotypes of HCV exist, but the lack of a convenient in vitro assay system and the failure to demonstrate lasting immunity following infection of chimpanzees, even when the virus used for rechallenge is the same as the original inoculum, suggest that serotypic variation is a prominent feature of HCV. The infectivity titer of HCV in the blood may be as high as 106 infectious doses per ml but is usually much lower, especially in cases of chronic infection, apparently because of complexing of virus to antibody (22, 23~.
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From page 66... ...
Transfusion-associated NANB hepatitis is virtually disappearing as a result of the current comprehensive screening program that tests specifically for infections with HBV, HCV, and HIV and excludes all who identify themselves as members of high-risk populations. Intravenous drug use as a risk factor has also diminished in relative importance, probably because of efforts to control AIDS in such populations.
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From page 67... ...
HEPATITIS D VIRUS History The first evidence for the existence of HDV came in 1978 when a previously unrecognized intranuclear antigen was detected by immunofluorescence in liver biopsies from Italian patients with chronic HBV infection. First thought to be another antigenic specificity of HBV, the antigen was eventually shown to be associated with the capsid protein of a previously unrecognized virus, subsequently called "hepatitis delta virus" (HDV)
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From page 68... ...
will continue to be at risk of contracting hepatitis D HEPATITIS E VIRUS History Hepatitis E was not recognized as a unique human disease until 1980, when serologic tests for the diagnosis of hepatitis A and hepatitis B were applied to stored clinical samples collected during waterborne epidemics of viral hepatitis in India (43, 441.
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From page 69... ...
Indeed, virtually 100% of stored serum samples from such epidemics were found to contain IgG anti-HAV but not IgM anti-HAV strong evidence for past HAV infection with resultant immunity and therefore evidence for the existence of a previously unrecognized hepatitis agent as the cause of the epidemics. HEV was first visualized in 1983 and transmitted to a human volunteer and cynomolgus monkeys, thus establishing its etiologic role in enterically transmitted NANB (ET-NANB)
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From page 70... ...
The infectivity titer of HEV in feces probably does not exceed 107 infectious doses per g, 2 orders of magnitude less than peak fecal titers of HAV. A viremia occurs during the incubation period of hepatitis E, but the titer of virus present has not been determined.
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From page 71... ...
It will be important to determine age-specific antibody profiles for populations of currently industrialized countries to determine if this can be confirmed and to determine if the anti-HEV currently detected in such populations represents the traces of a former time. More recent interactions between changing human culture and HEV were seen in epidemics of hepatitis E that occurred among refugees living under substandard conditions in Ethiopia and Somalia in the 1980s (50~.
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From page 72... ...
More convincing evidence for an additional, waterborne hepatitis agent has come from recent studies in Asia, where at least two waterborne epidemics of hepatitis appear not to have been caused by any of the recognized hepatitis viruses (53, 54~. Thus, the epidemiology of viral hepatitis continues to evolve.
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From page 73... ...
Each of the five recognized hepatitis viruses belongs to a different virus family, and each has a unique epidemiology. The medical impact of these viruses on society has been strongly influenced by changes in human ecology.
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From page 74... ...
Hepatitis Surveillance Report No. 16 (Communicable Disease Center, Atlanta)
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From page 75... ...
(1983) in Viral Hepatitis and Delta Infection, eds.
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