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Published online by Cambridge University Press: 07 December 2009
The virus
Hepatitis B virus (HBV) is a member of the Hepadnaviridae family of viruses, and has a double-stranded circular DNA and a DNA polymerase enzyme. It has two major proteins: hepatitis B surface antigen (HBs Ag), which is an outer protein expressed in excess when the virus replicates in the liver; and hepatitis B core antigen, an inner protein, which is expressed only within hepatocytes in the liver. A third protein, hepatitis B e antigen (HBe Ag), is also shed in the blood when the virus replicates, and its presence is associated with high infectivity.
Hepatitis D virus (HDV) is a defective RNA virus, which cannot replicate in humans in the absence of HBV. Patients can be co-infected with HBV and HDV, or HBV infected patients can be super-infected with HDV.
Epidemiology
Route of spread
The routes of transmission are
parenteral (blood exposure)
sexual
vertical (from mother to baby).
Prevalence
Hepatitis B virus infection occurs worldwide with prevalence of infection varying between <2% to 15%, with 80% of the global population having a 60% lifetime risk of infection.
Incubation period
Infection can develop from 6 weeks to 6 months after exposure to the virus.
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