The elusive hepatitis C virus.

Specific laboratory tests are generally available now for three hepatitis viruses: hepatitis A (infectious or epidemic hepatitis), hepatitis B (previously referred to as serum hepatitis), and hepatitis D (the delta virus). A fourth virus, which causes enterically transmitted non-A, non-B hepatitis (or epidemic non-A hepatitis) has been seen by electron microscopy and has morphological and biophysical characteristics that suggest that it is a member of the calicivirus group. Serological tests are under development, and molecular cloning of this virus is in progress. Other viruses that cause an acute hepatitis include the Epstein-Barr virus, cytomegalovirus, yellow fever virus, and the more exotic haemorrhagic fever viruses such as Lassa fever virus, the Marburg agent, Ebola virus, and Rift Valley fever virus, but the diseases caused by these viruses are not generally included in the term viral hepatitis. As specific diagnosis of the different types of viral hepatitis became possible some 10 years ago it became apparent that there was one form, previously unrecognised and unrelated to hepatitis A, B, or D, that was transmitted principally by the parenteral route. This became known as non-A, non-B hepatitis. Results obtained from several carefully conducted surveys of posttransfusion hepatitis in the United States and elsewhere provided strong epidemiological evidence of "guilt by association." This form of non-A, non-B hepatitis has been found in every country in which it has been sought; and it shares several features with hepatitis B. In countries where all blood donations are screened for hepatitis B surface antigen by very sensitive techniques non-A, non-B hepatitis may account for as many as 90% of all cases of posttransfusion hepatitis. Outbreaks of non-A, non-B hepatitis have also been reported after treatment with blood clotting factors VIII and IX. Non-A, non-B hepatitis has occurred in haemodialysis and other specialist units, among drug addicts, and after accidental inoculation with contaminated needles and other sharp objects. Mother to infant transmission has been reported.' In Britain and in several other countries some cases are not associated with transfusion, and such sporadic cases of non-A, non-B hepatitis account for 10-25% of all adult patients with clinical viral hepatitis. The route of infection or the source of infection cannot be identified in many of these patients, but sexual transmission is a strong candidate. Although in general the illness is mild and often subclinical or anicteric, severe hepatitis with jaundice does occur, and non-A, non-B hepatitis accounts for a substantial …