Clinical features of hepatitis D.

Hepatitis D is caused by infection with hepatitis D virus (HDV), a defective RNA virus that requires the obligatory helper function of hepatitis B virus (HBV) for its in vivo transmission. Thus, HDV is acquired only by coinfection with HBV or by superinfection of an HBV carrier. The clinical outcome of hepatitis D differs according to the modality of infection. Whereas coinfection evolves to chronicity in only 2% of the cases, superinfection results in chronic infection in over 90% of the cases. HDV is a highly pathogenic virus that causes acute, often fulminant hepatitis, as well as a rapidly progressive form of chronic viral hepatitis, leading to cirrhosis in 70 to 80% of the cases. The clinical picture of HDV disease is evolving as a consequence of a significant change in the epidemiology of HDV infection, which has led to a significant decline in incidence in Western countries, mainly as a result of universal HBV vaccination programs. However, in the face of a declining prevalence in areas of old endemicity like Europe, immigration poses a threat of HDV resurgence. The interaction of HDV with other hepatitis viruses or human immunodeficiency virus is complex and may lead to different patterns in terms of virologic expression and immunologic responses. Multiple viral infections are associated with rapid progression of liver fibrosis and eventually with the development of hepatocellular carcinoma. Hepatitis D is not a vanishing disease, and continuous efforts should be made to improve its prevention and treatment.