Hepatitis D virus (HDV) is an RNA virus that was discovered in 1977 and is structurally unrelated to the hepatitis A (HAV), hepatitis B (HBV), and hepatitis C (HCV) viruses. HDV causes a unique infection that requires the assistance of HBV viral particles to replicate and infect hepatocytes. [1, 2, 3, 4] Its clinical course is varied and ranges from acute, self-limited infection to acute, fulminant liver failure. Chronic liver infection can lead to end-stage liver disease and associated complications (including accelerated fibrosis, liver decompensation, and hepatocellular carcinoma). [5, 6, 7, 8, 9]

There are three known genotypes of HDV. Genotype 1 has a worldwide distribution; genotype 2 exists in Taiwan, Japan, and northern Asia; and genotype 3 is found in South America.

Simultaneous coinfection with HBV and HDV occurs in 5-15% of those with HBV [8, 10] and results in fulminant liver failure in 1% of patients. HBV-HDV coinfection is the most aggressive form of viral hepatitis. [8, 11, 12] Complete clinical recovery and clearance of HBV and HDV coinfection is the most common outcome. (See Prognosis and Workup.)

Infection with HDV in a patient who is already positive for the hepatitis B surface antigen (HBsAg) is known as superinfection and results in fulminant liver failure in 5% of patients. Approximately 80-90% develop chronic HDV infection. These patients progress more rapidly to develop cirrhosis and may develop hepatocellular carcinoma. (See Workup.)

A study from The Netherlands suggested that HDV may hinder the control of HBV. Xiridou et al used a mathematical model for the transmission of both viruses and calculated the reproduction numbers of single HBV infections and dual HBV/HDV infections. [3] The investigators looked at the endemic prevalence of both viruses and found that HDV modulates HBV epidemic severity and also hampers the impact on HBV interventions. Xiridou et al concluded that in endemic populations with HDV, control programs that ignore HDV presence may lead to an underestimation of the HBV epidemic and an overestimation of positive results, as control of HBV is dependent on the reproduction numbers of dual HBV/HDV infections. [3] (See Epidemiology.)

See the following topics for more information: