Hepatitis D Virus (HDV)
Prepared by: Upendra Thapa Shrestha
- Group: Group V (-ssRNA)
- Order: Unassigned
- Family: Unassigned
- Genus: Deltavirus
- Species: Hepatitis delta virus
Hepatitis D virus (HDV) causes an acute and chronic inflammatory disease of the liver. It is an incomplete virus, requiring Hepatitis B Virus (HBV) for replication and hepatocyte infection. HDV infection is exclusive to HBV-infected individuals.
- Small, spherical virus (~36 nm in diameter).
- Genomic RNA is circular, single-stranded, and negative-sense.
- Encapsulated within **delta antigen**, which is surrounded by HBV envelope proteins (HBsAg).
- Delta antigen exists in two forms: **small (24 kDa) and large (27 kDa)**.
- Uses a **circle-rolling replication mechanism**.
HDV replication occurs in hepatocytes and involves host cellular RNA polymerases rather than viral RNA-dependent polymerase. It generates genomic, antigenomic, and mRNA forms through a rolling-circle mechanism.
HDV transmission occurs through coinfection (HBV + HDV simultaneous infection) or superinfection (HDV infecting an existing chronic HBV carrier). Spread occurs via blood, sexual contact, and perinatal transmission.
- Acute hepatitis D (coinfection with HBV) mimics acute HBV infection.
- Superinfection leads to **chronic HDV infection**, often progressing to cirrhosis.
- Severe cases may result in **fulminant hepatitis**, liver failure, and hepatic encephalopathy.
HDV infection is diagnosed through **serological (anti-HD IgG & IgM)** and **molecular (RT-PCR for HDV RNA)** testing. HDAg detection is rare due to antigen-antibody complex formation.
- **Cirrhosis:** More aggressive in HDV-superinfected HBV patients.
- **Hepatocellular carcinoma (HCC):** HDV enhances oncogenic clusterin gene expression.
- **Acute-on-chronic liver failure:** Leads to ascites and encephalopathy.
No specific antiviral therapy is available. HBV vaccination prevents HDV infection, and patients with HBV should avoid HDV-contaminated blood products.
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