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Microbiology · Other DNA viruses

Hepatitis B virus !

  • Virus
  • Enveloped
  • Exam priority: high

A virus that infects the liver; it may clear or become chronic and lead to cirrhosis and liver cancer. A vaccine is given from birth.

Updated 2026-11-01

Also called: HBV

At a glance

Shape
Spherical (Dane particle) with an HBsAg-bearing envelope
Genome
Circular, partially double-stranded DNA (replicates with reverse transcriptase)
Envelope
Enveloped
Family
Hepadnaviridae
Size
About 42 nm

Morphology

  • Complete particle (Dane particle): envelope with HBsAg and nucleocapsid with HBcAg
  • Infected blood also holds many empty HBsAg particles without genome
  • HBeAg is a secreted protein that goes with active replication

Transmission

  • Perinatal, mother to child at birth (the main route in endemic areas)
  • Sexual
  • Parenteral: shared needles, unsafe injections, needlestick injuries in health care
  • Close household contact in childhood (wounds, sharp objects)

Reservoir: Humans

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Life cycle

  1. The virus enters the hepatocyte through the bile-salt receptor NTCP.
  2. The genome reaches the nucleus and is repaired into covalently closed circular DNA (cccDNA), which persists.
  3. Messenger RNAs and a pregenomic RNA are transcribed.
  4. Inside the capsid, reverse transcriptase copies the pregenomic RNA into DNA.
  5. Nucleocapsids are enveloped in the endoplasmic reticulum and leave without killing the cell.

Virulence factors

  • Liver damage comes mainly from cytotoxic T cells attacking infected hepatocytes, not from the virus itself
  • Nuclear cccDNA explains why antivirals control but rarely cure
  • Integration of viral DNA and chronic inflammation favour hepatocellular carcinoma, even without cirrhosis
  • The HBx protein disturbs cell regulation and adds to oncogenesis

Diseases it causes

Clinical picture

  • Acute infection may be silent or cause jaundice, dark urine, fatigue and very high transaminases
  • The chance of chronic infection depends on age: the rule in newborns, the exception in adults
  • Co-infection or superinfection with hepatitis delta virus (HDV), which only replicates when HBsAg is present and worsens disease

Diagnosis

  • HBsAg positive: current infection (acute or chronic), the person is infectious
  • IgM anti-HBc positive: recent or acute infection; it can also appear in severe flares
  • Total anti-HBc positive with HBsAg negative and anti-HBs positive: past, resolved infection
  • Anti-HBs positive alone (anti-HBc negative): immunity from vaccination
  • HBeAg positive: active replication and high infectivity; conversion to anti-HBe usually marks lower replication
  • Window period: HBsAg has gone and anti-HBs is not yet detectable; IgM anti-HBc is the key marker (anti-HBe may also be present)
  • Viral load (HBV DNA) by PCR to decide on and follow treatment

Treatment

Acute infection is usually managed with supportive care. Chronic infection is treated with high-barrier nucleoside or nucleotide analogues (tenofovir, entecavir), which suppress but rarely eliminate the virus; pegylated interferon alfa is another option. Lamivudine is no longer preferred because resistance is common.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Recombinant HBsAg vaccine, with the first shot within hours of birth
  • HBsAg screening in every pregnancy
  • Newborn of an HBsAg-positive mother: vaccine plus hepatitis B immune globulin within 12 hours
  • Screened blood, sterile equipment, condoms and post-exposure prophylaxis at work

Vaccine: Recombinant vaccine (HBsAg). In Colombia's PAI: a birth dose, then within the combined vaccine of the first year of life.

Test yourself

Think of the answer, then tap the question to see it.

Which serologic pattern fits a vaccinated person with no past infection?

HBsAg negative, total anti-HBc negative and anti-HBs positive.

Which marker shows infection during the hepatitis B window period?

IgM anti-HBc: HBsAg has disappeared and anti-HBs is not yet detectable.

What does a positive HBeAg mean in chronic hepatitis B?

Active viral replication, a high viral load and greater infectivity, including perinatal transmission.

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Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: Hepatitis B (WHO, 2025); Clinical Testing and Diagnosis for Hepatitis B (CDC, 2025); Recommendations for Identification and Public Health Management of Persons with Chronic Hepatitis B Virus Infection (CDC (MMWR), 2008); Clinical Overview of Perinatal Hepatitis B (CDC, 2025).

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Representative model, for educational purposes only.