INTRODUCTION

In the context of emerging viral infections, the hepatitis viruses present a fascinating contrast of the old and the new. Although the physicians of antiquity were almost certainly aware of viral hepatitis as a disease entity associated with icterus, it is only in the past century that this has been recognized clearly to be an infectious process. Furthermore, it was almost the mid-part of the twentieth century before it was shown unequivocally that hepatitis was not a single disease, and that very similar disease processes could result from infection by very different viral agents that are incapable of eliciting cross-protective immunity. Even more striking, however, it is only in the past decade that we have gained a full appreciation of the number and diversity of the hepatitis viruses.

The era of modern hepatitis virology began with the discovery of the ‘Australia antigen’ by Blumberg and associates in 1965 and the subsequent association of this antigen with hepatitis B virus (HBV) (Blumberg et al., 1965; Prince, 1968). The identification of hepatitis A virus (HAV) came almost 8 years later, with the immune electron microscopic demonstration of HAV particles in human faecal material by Feinstone and colleagues (Feinstone et al., 1973), and the hepatitis delta virus (HDV) was discovered by Rizzetto and coworkers at the end of the 1970s (Rizzetto et al., 1980). With each of these discoveries came new serological tests and subsequent clinical studies that have redefined the epidemiological range of these infections and on more than one occasion demonstrated the existence of yet undiscovered hepatitis agent(s).