Hepatitis A virus (HAV) infection is a significant cause of morbidity and attendant economic loss in many parts of the world. The virus is present worldwide and rates of infection are inversely associated with levels of environmental sanitation and personal hygiene. Improvements in sanitation and hygiene can reduce the transmission of HAV. However, in less developed countries, an improvement in sanitary conditions may result in an increase in the burden of clinical disease as peak rates of infection shift from early childhood, when infection is largely asymptomatic, to older age groups in which it is more often symptomatic.
Viral hepatitis type B is a major health problem occurring endemically in all parts of the world, more than 2000 million people having been infected with the hepatitis B virus (HBV). The disease is characterized by a relatively long incubation period, high carrier rate, and diverse manifestations, including the serious consequences associated with cirrhosis and hepatocellular carcinoma. More than 80% of all cases of the latter are attributable to HBV, making it second only to tobacco among the known causes of human cancer. In some regions of the world, co-infection and superinfection with hepatitis delta virus have been associated with high morbidity and mortality in HB-positive individuals. although rate in infants and children, severe fulminant hepatitis B with hepatic failure and coma may develop in adults. Approximately 300 million people, most of whom live in developing countries, are lifelong chronic carriers of HBV.