Hepatitis B Virus Infection

Detailed Overview

HBV is transmitted through contact with infectious blood or body fluids. While most adults clear the infection spontaneously, infants and young children are at a high risk (up to 90%) of developing chronic infection. Chronic HBV is characterized by phases of immune tolerance, immune clearance, inactive carrier state, and reactivation. The virus is not highly cytopathic; rather, the host's cytotoxic T-cell response against infected hepatocytes drives liver injury, fibrogenesis, and ultimately cirrhosis or hepatocellular carcinoma (HCC).

Epidemiology & Demographics

An estimated 296 million people worldwide live with chronic hepatitis B, with highest prevalence in WHO African and Western Pacific regions (>8%). Approximately 820,000 die annually from HBV-related liver diseases.

Etiological Mechanism

Infection with Hepatitis B virus (HBV).

Primary Causes

Hepatitis B virus (HBV)

• Vertical transmission: Mother-to-child transmission during birth, the most common route in endemic areas.
• Parenteral exposure: Intravenous drug use sharing contaminated needles.
• Sexual contact: Unprotected sex with an infected partner.

HBV enters hepatocytes via the NTCP receptor. Its genome is converted into covalently closed circular DNA (cccDNA) in the nucleus, serving as a template for viral replication. Hepatocyte damage is mediated by the host CD8+ T-cell response attacking viral antigens (HBsAg, HBcAg) expressed on the cell surface, leading to apoptosis, necrosis, and subsequent liver fibrosis driven by hepatic stellate cell activation.

Characteristic Clinical Presentation

• Fatigue: Profound, ongoing tiredness.
• Right upper quadrant pain: Dull ache over the liver due to capsular distension.
• Jaundice: Yellowing of the skin and sclerae.

Physical Examination Signs

• Hepatomegaly with a tender liver edge.
• Scleral icterus.
• Spider angiomata and palmar erythema in advanced chronic disease.

• Cirrhosis: Extensive liver fibrosis leading to portal hypertension.
• Hepatocellular Carcinoma: Primary liver cancer; HBV can integrate into host DNA causing oncogenesis without cirrhosis.

Diagnostic Criteria & Guidelines

Persistence of serum HBsAg for > 6 months. Acute infection is indicated by HBsAg + IgM anti-HBc.

Differential Diagnosis

• Hepatitis C, A, or E
• Autoimmune Hepatitis
• Drug-induced liver injury

Laboratory Tests & Biomarkers

• HBsAg: Positive.
• HBV DNA PCR: Elevated (e.g., > 20,000 IU/mL in HBeAg+ chronic hepatitis).
• ALT/AST: Elevated (>35 U/L in males, >25 U/L in females) during active immune clearance.

Imaging Modalities & Findings

• Abdominal Ultrasound:
• Transient Elastography (FibroScan):

• Immune tolerant phase
  HBeAg positive, high HBV DNA, normal ALT, minimal inflammation.
• Immune clearance phase
  HBeAg positive, high/fluctuating HBV DNA, elevated ALT, active inflammation.
• Inactive carrier phase
  HBsAg positive, HBeAg negative, anti-HBe positive, HBV DNA < 2,000 IU/mL, normal ALT.

Second-Line & Adjunctive Therapy

Pegylated interferon-alfa-2a 180 mcg SC weekly for 48 weeks (in highly selected non-cirrhotic patients).

Surgical & Procedural Management

Liver transplantation for decompensated cirrhosis or early-stage HCC (Milan criteria).

Recommended Lifestyle Changes

• Total abstinence from alcohol.
• Hepatitis A vaccination if non-immune.

Patient Counseling & Advice

Emphasize life-long daily medication adherence. Advise on safe sex and testing for sexual partners and household contacts.

Follow-Up & Monitoring Schedule

ALT and HBV DNA every 3-6 months. HCC surveillance with abdominal ultrasound every 6 months for cirrhotic patients and high-risk groups.

Preventive Strategies

Recombinant HBV vaccine (e.g., 3 doses at 0, 1, 6 months). Hepatitis B immune globulin (HBIG) for post-exposure prophylaxis.

Five-year survival for compensated cirrhosis is >80%. Current therapies effectively suppress viral replication but rarely achieve functional cure (HBsAg loss).