Hepatitis Viruses

Acute and chronic liver disease is most commonly caused by hepatitis viruses. Liver diseases resulting from hepatitis viruses share the common characteristic of causing inflammation of the liver. Hepatitis viruses affect a significant population in the world and is a serious public health concern requiring considerable effort to ensure that the blood, water, and food supply remains free of these viruses. The early discovery of hepatitis viruses began in the mid-1960s with the discovery of hepatitis B virus (HBV) and continued in the 1970s with the discovery of hepatitis A (HAV) and D (∂) (HDV) viruses. Two other major causative agents of viral hepatitis were recognized and referred to as non-A, non-B hepatitis viruses (NANBH) for almost two decades. Advances in molecular techniques in the late 1980s especially the polymerase chain reaction (
PCR
), have ushered in the discovery of two new viruses, hepatitis C (HCV) and Hepatitis E (HEV) viruses earlier referred to as NANBH. Thus, the most common causes of viral hepatitis are hepatitis A, B, C, D, and E (
1
). Recently, the discovery of three other hepatitis viruses, two of which are referred to as GB-A and GB-B (
2
) and a third as GB-C, has been reported. All are closely related to the flavivirus family. It remains to be seen how many more will be discovered; there is a general belief at this time that Genelabs, Inc. (Redwood City, CA) has isolated a new hepatitis virus called hepatitis G virus, but there is uncertainty as to the significance of the recently discovered and less prevalent viruses. The focus of this chapter therefore is the more common hepatitis viruses. It needs to be emphasized that there are three other pathogenic viruses, Epstein-Barr virus (EBV), cytomegalovirus (CMV), and enterovirus, that are capable of causing inflammation of the liver, but as they are not primarily hepatotropic, diagnostic protocols for these viruses are discussed in detail elsewhere in this book. A schematic of the major and minor causes of viral hepatitis and the primary routes of transmission of the major hepatitis viruses is illustrated in Fig. 1 .
Fig. 1.
Schematic of the major and minor causes of viral hepatits and the primary routes of transmission of the major hepatitis viruses