Hepatitis D (HDV) is caused by the hepatitis D virus, also known as delta virus or delta agent. It can affect the liver in a variety of ways and can lead to fulminant liver failure, cirrhosis, and hepatocellular carcinoma. Hepatitis D virus is a defective RNA virus requiring hepatitis B surface antigen (HBsAg) for pathogenicity (allows binding to hepatocytes and virion assembly). Thus HDV can be acquired simultaneously with hepatitis B (HBV) (coinfection) or in a previously HBsAg positive individual (superinfection). Coinfection with both HDV and HBV at the same time is associated with a more severe clinical outcome compared with HBV infection alone. Superinfection occurs when a chronically HBV-infected individual contracts HDV. Fifteen million of 350 million HBV patients are also infected with HDV.

HDV is transmitted most commonly through blood or blood products, although transmission can also occur by sexual contact and much less commonly through vertical transmission. Higher prevalence rates occur in the Mediterranean regions, central / western Africa, northern Asia, Vietnam, and Amazonian areas. Implementation of HBV vaccination programs in most high- and middle-income countries has reduced the global incidence of HDV infection as well, especially among younger patients. In Europe, rates have been increasing due to immigration from endemic areas.

Clinically, HDV infection may present asymptomatically, with symptoms of acute hepatitis, or with worsening of previously asymptomatic HBV infections. Signs and symptoms of HDV infection are nonspecific to this virus and include jaundice, pruritus, anorexia, fatigue, abdominal distention and ascites, and encephalopathy. Patients may also complain of dark-colored urine or pale stools.

Physical examination may reveal lowered blood pressure, yellow skin discoloration, spider angiomata, abdominal distention and ascites, hepatosplenomegaly, palmar erythema, Muehrcke nails, and Terry nails.

Immunocompromised patient considerations: A substantially more aggressive progression of HDV may be associated with triple infection with HIV and HBV, and screening for HDV is recommended for HIV-positive / HBV-positive patients.