A number of viruses have been found to primarily infect hepatocytes, though not all cause clinically relevant disease. The classically recognized hepatotropic viruses are the hepatitis A, B, C, D, E, and G viruses. Of clinically apparent acute and chronic hepatitis, 10% to 20% is cryptogenic in nature and is thought to be caused by as yet unidentified viruses.
Hepatitis viruses A and E are transmitted via the fecal-oral route, whereas B, C, and D are spread primarily via contact with infected blood or other body fluid. Hepatitis G is transferred by either route, but is not proven to cause clinical disease. Fecal-oral transmission of the A and E viruses is responsible for most acute outbreaks, whereas B and C constitute a major chronic public health burden.
Hepatitis A virus (HAV) infection accounts for approximately 25,000 cases of acute hepatitis annually in the United States, with as many as 40% of the urban population having serologic evidence of past infection. Outbreaks often affect clusters of persons exposed to a single source, such as a food handler or contaminated central water supply.
Persons infected with hepatitis B virus (HBV) carry the virus in all bodily fluids (blood, breast milk, saliva, semen, and urine). HBV can cause both acute and chronic hepatitis, the latter conferring risk of cirrhosis and hepatocellular carcinoma. It is estimated that 200 million people worldwide are chronically infected with HBV.