HBV is a DNA virus that enters the liver via the bloodstream, and replication occurs only in liver tissue. Transmission occurs by percutaneous or mucosal exposure to infected blood or other body fluids. Approximately one third of all cases of cirrhosis and half of all cases of hepatocellular carcinoma (HCC; 114550) can be attributed to chronic HBV infection. Worldwide, 2 billion people have been infected with HBV, 360 million have chronic infection, and 600,000 die each year from HBV-related liver disease or HCC. However, there is marked geographic variability in HBV prevalence, with chronic infection affecting less than 2% of the populations of North America and western and northern Europe; between 2 and 7% of the populations of eastern and central Europe, the Amazon basin, the Middle East, and the Indian subcontinent; and more than 8% of the populations of Asia, sub-Saharan Africa, and the Pacific (Seeff and Hoofnagle, 2006; Shepard et al., 2006). [from
OMIM]