The virus enters the cell by attaching to an unknown receptor and enters through endocytosis. The partial double-stranded DNA of the virus is transformed into full-length double-stranded DNA that is covalently closed and circular, serves as a transcription template for 4 viral mRNAs. The larger mRNA produces DNA polymerase, capsid proteins, and new copies of the genome. The long mRNA is transported back to the cytoplasm where the P protein synthesizes DNA by reverse transcription. Mechanism: HBV primarily infects the liver by replicating in liver cells known as hepatocytes. HBV binds to the host cell via the preS domain and is internalized via endocytosis. Viral clearance and hepatocellular damage are caused by the host immune response during viral infection. Cytotoxic T lymphocytes contribute to liver damage when HBV infects. Furthermore, activated platelets at the site of infection can accumulate CTLs in the liver. Transmission: HBV is transmitted through body fluids and blood exposure. The possible forms are: Vertical transmission. Contaminated syringes and needles. Sexual contact. Blood transfusions from mother to child.