HCV is a flavivirus that is transmitted by parenterally or sexually in the majority of cases; unlike the other members of the Flaviviridae known to infect humans, it is not transmitted by arthropods. Most new HCV infections are subclinical, and 70% to 90% develop into chronic hepatitis. Most HCV chronic cases remain without symptoms but 10% to 20% may develop to chronic active hepatitis and cirrhosis or hepatocellular carcinoma. Mixed cryoglobulinemia and glomerulonephritis complications are not uncommon with HCV (c). HAV (a) is a member of the Enterovirus genus; transmitted fecal-orally, it produces only acute disease. HBV (b), a member of the Hepadnaviridae, is transmitted similarly to HCV; it can produce acute or chronic infections. HDV (d) is a minus-sense RNA virus that can only cause infection in HBV-infected individuals. HEV is a member of the new family Hepeviridae; transmission and disease caused by HEV is similar to that of HAV, although the mortality is higher, especially in pregnant women.