++
- Hepatitis A–E cause most recognized cases of acute viral hepatitis; hepatitis B, C, and D cause most recognized cases of chronic viral hepatitis.
- Hepatitis A and E are transmitted by the fecal-oral route; neither causes chronic infection.
- Hepatitis B, C, and D are acquired percutaneously; all can result in chronic infection.
- Hepatitis D can occur only in a host already infected with hepatitis B.
- All five forms can cause fulminant hepatitis, but B, D, and E are common causes, whereas A and C are very rare causes.
- Diagnostic tests appropriate to different clinical situations detect specific viral antigens and antibodies in serum by sensitive enzyme immunoassay or radioimmunoassay and viral DNA/RNA by sensitive amplification assays (eg, polymerase chain reaction).
++
Although the hepatitis viruses have been characterized extensively, the pathogenesis, diagnosis, and treatment of chronic viral hepatitis continue to be the focus of research. Sensitive and specific assays are available for all five forms (A to E) of viral hepatitis (Table 39–1). Nevertheless, at least approximately 5–10% of cases of acute and chronic hepatitis cannot be attributed to any of the known forms of viral hepatitis and do not appear to result from toxic, metabolic, or genetic conditions. A specific cause cannot be identified for approximately 50% of cases of fulminant hepatitis. Whether additional unidentified viruses cause acute or chronic liver disease remains an unanswered question; to date, despite intense investigation, no other hepatitis viruses have been identified. This chapter focuses on clinical features of the five known viruses that cause almost all recognized cases of acute and chronic hepatitis (Table 39–2).
++