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.