Hepatitis viruses: a pandora's box?

The term hepatitis virus is reserved for those viruses that are predominantly hepatotropic, although several new agents have been assigned to this category in the absence of hepatotropism and clinical disease. The hepatitis viruses can be broadly divided into those transmitted via the fecal-oral route, and those by blood, blood products and body fluids. Hepatitis A (picornaviridae), hepatitis B (hepadnaviridae) and hepatitis C (flaviviridae) represent the major public health problems. The epidemiology of hepatitis A virus (HAV) and hepatitis B virus (HBV) is changing in response to vaccination. In the case of HAV, older age groups are now deemed at risk, particularly of fulminant hepatitis if exposed over the age of 50. Chronic hepatitis B in some regions is now predominantly of the so-called precore mutant type where high levels of HBV replication persist in the presence of anti-hepatitis B virus (HBe) antibodies. The HBV vaccination is among the most cost-effective health care measures. The epidemiological significance of mutations found increasingly in the HBV S gene isolated from vaccinated children is unclear. Evidence that hepatitis G and TT virus are significant causes of hepatitis is lacking. Of interest, however, is the finding that the related GBV-B agent of monkeys may be a model for developing new antiviral agents against HCV. Animal models of hepatitis infections are providing new insights into the pathogenesis of hepatitis in humans. Indeed it is possible that hepatitis E is primarily an agent of pigs and other domesticated livestock. Intriguingly, the new TT virus shares many properties with the circoviruses, significant pathogens of chickens and pigs. The challenge in the next decade will be to assess the significance of these new agents in terms of public health and resources. Value judgements will have to be made in assessing the risks associated with blood containing trace amounts of these adventitious agents.