Hepatitis B Virus

Introduction

Hepatitis B Virus (HBV) is a serious viral infection that attacks the liver and can cause both acute and chronic diseases. It belongs to the Hepadnaviridae family and is unique among DNA viruses because it replicates through reverse transcription. HBV remains one of the leading causes of liver-related illness and death worldwide, but it is preventable through vaccination.

Key Facts

• Virus Type: Enveloped, partially double-stranded DNA virus
• Family: Hepadnaviridae
• Genome Size: ~3.2 kb
• Transmission: Blood, body fluids, and mother-to-child
• Global Impact: ~254 million chronic cases (as of 2022)
• Prevention: Safe vaccine and hygiene practices
• Treatment: Antivirals such as tenofovir and entecavir

Characteristics

HBV is an enveloped virus with an icosahedral nucleocapsid containing partially double-stranded circular DNA. Inside the host cell, this DNA converts into covalently closed circular DNA (cccDNA), serving as a template for replication. The virus multiplies using reverse transcription of a pregenomic RNA, similar to retroviruses.

This replication strategy allows HBV to persist in liver cells for a long time, leading to chronic infection in some individuals.

Epidemiology

Hepatitis B is a global health challenge. According to the World Health Organization (WHO), around 254 million people live with chronic HBV infection. The Western Pacific and African regions have the highest number of cases, with Asia also showing a high burden.
Every year, HBV contributes to around 1.1 million deaths due to complications like cirrhosis and liver cancer (Hepatocellular Carcinoma, HCC).

Transmission varies by region:

• In Asia and Africa, mother-to-child and early-childhood infections are most common.
• In developed regions, sexual contact and unsafe injections are major transmission routes.

Transmission

HBV spreads through contact with infected blood or body fluids. Common routes include:

• Perinatal transmission: from infected mother to child during birth.
• Sexual contact: unprotected sex or multiple partners.
• Parenteral exposure: contaminated needles, tattoos, or medical instruments.
• Household exposure: sharing razors or toothbrushes.

Because the virus is present in saliva and other fluids, even intimate contact may pose a risk.

Pathogenesis

Liver injury in HBV infection is mainly caused by the immune response, not the virus itself.

• Cytotoxic T cells (CTLs) attack infected liver cells displaying viral antigens (HBsAg, HBcAg).
• Cytokines like interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) help suppress viral replication but also trigger inflammation.
• Over time, continuous immune attack can lead to fibrosis, cirrhosis, and liver cancer in chronic cases.

Immunity and Chronic Infection

• People who recover from acute HBV infection develop protective antibodies (anti-HBs) and long-term immunity.
• The infection becomes chronic if HBsAg remains positive for more than six months.
• Age plays a key role:
• Infants: 90–95% chance of chronic infection
• Adults: less than 5% become chronic carriers

Successful immune control is marked by loss of HBeAg and development of anti-HBe antibodies.

Symptoms and Clinical Features

The symptoms of HBV infection vary widely:

Acute Infection

• Fatigue
• Loss of appetite
• Nausea and vomiting
• Joint pain and rash
• Jaundice (yellowing of skin and eyes)

Some individuals, especially children, may show no symptoms at all. Rarely, acute infection can lead to fulminant hepatitis, a life-threatening condition.

Chronic Infection

Chronic HBV can remain silent for years. Over time, it may cause:

• Chronic hepatitis (persistent inflammation)
• Cirrhosis (scarring of liver tissue)
• Hepatocellular carcinoma (HCC)

Symptoms may include persistent fatigue, right upper abdominal pain, and swelling from fluid accumulation.

Diagnosis

Diagnosis is based on blood tests and serologic markers:

• HBsAg – active infection
• Anti-HBc IgM – recent or acute infection
• HBeAg – high viral replication
• Anti-HBe – reduced viral activity
• Anti-HBs – immunity after infection or vaccination
• HBV DNA (PCR) – measures viral load

A chronic infection is confirmed when HBsAg persists for over six months. Liver enzyme tests (ALT, AST) and imaging help assess liver damage.

Treatment

Acute HBV

Most adults recover without antiviral therapy. Treatment focuses on rest, hydration, and monitoring. Antivirals like tenofovir or entecavir may be used for severe cases.

Chronic HBV

The main goal is to prevent cirrhosis and liver cancer by controlling viral replication.
First-line therapies include:

• Pegylated interferon-α
• Tenofovir disoproxil fumarate (TDF)
• Entecavir (ETV)

These drugs have a high resistance barrier and can achieve long-term viral suppression. Many patients need ongoing treatment and regular monitoring.

Prevention

HBV is completely preventable through safe and effective vaccines.

Key Preventive Measures:

1.     Vaccination:

o    Given in three doses (birth, 1 month, and 6 months).

o    Offers over 95% protection.

2.     Newborn prophylaxis:

o    Infants born to infected mothers should receive HBV vaccine + HBIG within 12 hours of birth.

3.     Blood safety:

o    Screen all blood donations for HBV.

4.     Safe medical practices:

o    Use sterile equipment and avoid needle reuse.

5.     Safe sex:

o    Use condoms and avoid risky sexual behaviours.

Conclusion

Hepatitis B remains a major global health concern, especially in developing countries. With widespread vaccination, early screening, and antiviral therapy, HBV-related deaths can be significantly reduced. Public awareness and preventive healthcare are key to controlling this vaccine-preventable liver disease.