**4. Pathogenesis and clinical features of HBV infection**

Hepatitis B virus gets entry into the bloodstream and targets the liver cells [24]. The hepatocytes which are infected are distended, and the cytoplasm assumes a ground appearance that is glassy. The virus is not cytopathic, and injury of the liver in HBV chronic infection is due to immunological responses [8, 25]. Although, the virus has a long incubation period of 45–180 days, replication starts few days after infection. The infection can be acute, an unexpected sickness with a mild-tosevere course followed by comprehensive resolve [26]. On the other hand, if the cell-mediated immune reaction is feeble, the infection does not resolve, and chronic hepatitis arises with an extended course of active disease or silent asymptomatic infection [27].

About 30–80% adults of acute HBV infection shows symptoms (1% fulminant hepatitis), whereas less than 1 year old children shows no symptoms [28]. Symptoms of HBV infection include malaise, dark urine, fever, nausea, jaundice, pale stools, right upper quadrant pain, and anorexia. The risk of chronic infection of HBV is hinged on the duration of acquisition [26]. About 90% of infected neonates, 30–50% of children aged 1–4 years, and 1–10% of acutely infected adults result to persistent infection. There are approximately 15–40% with persistent infection that leads to advanced liver disease, cirrhosis, and/or HCC [8, 29].
