Hepatitis D Delta Virus
On this page
Direct answer
Hepatitis D is a liver infection caused by the delta virus, a defective RNA virus that needs hepatitis B surface antigen to replicate. It arises as coinfection with hepatitis B or as superinfection of a chronic carrier, and superinfection is the more severe form. Diagnosis rests on anti-HDV antibody testing with HDV RNA detection, and hepatitis B vaccination prevents it.
What you must remember
- Dependence on HBsAg: the delta virus needs hepatitis B surface antigen to package its genome, so it never infects without hepatitis B.
- Coinfection: simultaneous acute hepatitis B and D, which often resolves, with IgM anti-HDV positive during the acute phase.
- Superinfection: delta virus added to a chronic hepatitis B carrier, which often leads to rapid progression to cirrhosis.
- Serology: anti-HDV antibody shows exposure, while HDV RNA shows active replication.
- Severe course: superinfection is linked to rapid cirrhosis and hepatocellular carcinoma, and fulminant hepatitis is a recognised risk.
- Treatment: pegylated interferon-alpha has been the established option, with bulevirtide licensed in parts of Europe; availability varies by country.
- Prevention: hepatitis B vaccination, since hepatitis D cannot occur without hepatitis B.
Coinfection or superinfection: how the course differs
A 35-year-old man with known chronic hepatitis B has a flare with jaundice and a rising bilirubin, and his HBsAg is positive. The examiner asks whether delta virus is present and how it changes the prognosis. Coinfection and superinfection look similar at first, but their outcomes differ sharply.
| Feature | Coinfection | Superinfection |
|---|---|---|
| Timing | Simultaneous acute infection | Added to chronic hepatitis B |
| Serology | IgM anti-HDV, falling | Persistent anti-HDV with HDV RNA |
| Chronicity | Often resolves | Often chronic |
| Outcome | Usually self-limited | Rapid cirrhosis |
Timing is the key distinction, and it changes both prognosis and the expected course. Anti-HDV serology confirms exposure, while HDV RNA shows active replication and guides treatment decisions.
Clinically, a superinfected carrier often presents with a flare of transaminases or decompensation rather than classic acute hepatitis, which is why the diagnosis is easily missed. Prevalence varies widely across regions, so testing is targeted at HBsAg-positive patients with severe or unexplained disease. Liver stiffness measurement or biopsy helps stage fibrosis, and cirrhosis then changes surveillance for hepatocellular carcinoma.
Where the exam tests the hepatitis D trap
Hepatitis D is commonly missed because routine hepatitis B testing does not include it.
- Trap: assuming a positive HBsAg excludes a second virus Correct: every HBsAg-positive patient with a flare should be tested for anti-HDV, since the delta component is otherwise missed.
- Trap: calling anti-HDV IgM alone proof of chronic infection Correct: IgM suggests recent infection but can persist in chronic disease, so HDV RNA with persistent antibody establishes chronicity.
- Trap: treating hepatitis D with hepatitis B antivirals alone Correct: nucleos(t)ide analogues suppress hepatitis B but do not clear the delta virus.
Frequently asked questions
Why can hepatitis D not occur without hepatitis B?
Hepatitis D cannot occur without hepatitis B because the delta virus needs hepatitis B surface antigen to package its genome and enter hepatocytes. This dependence means that vaccinating against hepatitis B also prevents hepatitis D.
What distinguishes hepatitis D coinfection from superinfection?
Coinfection is simultaneous acute infection with hepatitis B and D, and it often resolves, whereas superinfection adds the delta virus to a chronic hepatitis B carrier. Superinfection is the more severe form, with a higher risk of rapid progression to cirrhosis.
Which test confirms active hepatitis D infection?
Detection of HDV RNA in serum confirms active hepatitis D infection, while anti-HDV antibody shows past or current exposure. IgM anti-HDV suggests recent infection (it can persist in chronic disease), and quantifying HDV RNA guides monitoring and treatment decisions.
Why are standard hepatitis B antivirals not enough for hepatitis D?
Nucleos(t)ide analogues suppress hepatitis B but have little effect on the delta virus, so they do not clear hepatitis D. Pegylated interferon-alpha has been the established option, and bulevirtide is licensed in parts of Europe, though availability varies by country.