Perinatal transmission of hepatitis B.

Viral hepatitis is caused by four or more different viruses or groups of viruses: hepatitis A, hepatitis B; the more recently identified forms of hepatitis, non-A, non-B hepatitis which are caused by more than two viruses and probably by several different viruses; epidemic non-A hepatitis (previously referred to as epidemic non-A, non-B hepatitis); and the delta virus. Hepatitis A and hepatitis B can be differentiated by sensitive laboratory tests for specific antigens and antibodies and the viruses have been characterised. Specific laboratory tests are available for the delta agent, a defective virus which replicates in subjects infected with hepatitis B virus.