Enteric hepatitis viruses

The term “hepatitis viruses” refers to a diverse group of viruses all of which have the human liver as the primary target of replication and give rise to hepatitis or inflammation of the liver. Their replication may result in mass destruction of liver cells. Consequences include failure of the liver to fulfil basic functions such as removal of bilirubin from the circulatory blood system. Bilirubin is a red pigment released from red blood cells as they break down and are replaced by new cells. Excessive accumulation of the pigment in the bloodstream is manifest as yellow coloration of sites such as the eyes and the palms of the hands. This condition is known as jaundice and is also marked by dark urine and stools resulting from the excretion of bilirubin. Another typical consequence of massive liver cell damage is release into the bloodstream of liver enzymes, including alanine transaminase (ALT) and aspartate transaminase (AST). Serum levels of these enzymes are used to diagnose hepatitis (Zuckerman & Thomas, 1993). Hepatitis may also be caused by other systemic pathogens such as cytomegalovirus, yellow fever virus, and Leptospira bacteria, although the liver is not the primary or only target of these organisms. Liver cell damage and jaundice may also be caused by toxic compounds, including alcohol. Since the clinical symptoms caused by hepatitis viruses are very similar, and some of the viruses only emerged on a large scale in recent years, distinction of different aetiological agents has been progressively accomplished only since the 1960s. The first two hepatitis viruses that were distinguished were simply