📚 Viral Hepatitis: Structure, Diagnosis, and Control

Source Information: This study material has been compiled from a lecture audio transcript and supplementary copy-pasted text, covering key aspects of viral hepatitis.

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🎯 Learning Objectives

Upon completing this study material, you should be able to:

• Describe the structure and nature of the main hepatitis viruses.
• Understand and correctly interpret viral hepatitis diagnostic results.
• Be familiar with the methods used to control hepatitis viral infections.

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1. Introduction to Viral Hepatitis: A Global Health Challenge 🌍

Viral hepatitis refers to inflammation of the liver caused by a viral infection. It represents a significant global health challenge, contributing to mortality rates comparable to or exceeding those of HIV, malaria, and tuberculosis. A critical issue is that a large proportion of individuals with chronic hepatitis viral infections remain unaware of their status.

1.1 Patterns of Hepatic Injury 🩹

Hepatic injury can occur through several mechanisms:

1. Direct, Toxic Effects: Caused by chemicals or their metabolites.
2. Indirect, Immunologically Mediated Damage: The body's immune response to an infection causes damage to liver cells (hepatocytes). Viral hepatitis primarily falls into this category.
3. Effects of Bile Retention: Damage due to impaired bile flow.

1.2 Clinical Features of Acute Viral Hepatitis 🤒

Acute viral hepatitis often presents with symptoms similar to other liver injuries:

• Onset: Slow/insidious
• Jaundice: Lasts weeks to months
• Stool Color: Pale
• Urine Color: Dark
• Other Symptoms: Fatigue, itchiness

To confirm a diagnosis, specific tests are essential. Patient history can provide crucial clues, such as:

• Regular alcohol consumption
• Tattoos acquired abroad
• Intravenous drug use
• Travel to regions with higher prevalence (e.g., Dubai)

1.3 Global Impact 📊

Estimates from the WHO (2016-2021) highlight the severe impact of viral hepatitis:

• HBV: Out of 879,724 positive tests, 3,667 (52%) were new diagnoses.
• HCV: Out of 1,060,035 positive tests, 831 (52%) were new diagnoses. This indicates a significant hidden burden of chronic infections.

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2. The Five Main Hepatitis Viruses 🦠

There are five primary hepatitis viruses, each with distinct characteristics regarding acute and chronic infection potential:

• Hepatitis A (HAV)
• Hepatitis B (HBV)
• Hepatitis C (HCV)
• Hepatitis D (HDV)
• Hepatitis E (HEV)

2.1 Hepatitis A Virus (HAV)

• Nature: Non-enveloped RNA virus.
• Transmission: Primarily faecal-oral route 💩.
• Serotype: One serotype worldwide.
• Mortality: Global estimates range from 15,000 to 28,000 deaths per year, often linked to poor sanitary conditions.
• Disease Outcome: Age significantly influences disease outcome; older individuals may experience more severe symptoms.
  • Example: US data (1983-1991) showed varying case rates and mortality across age groups, with higher mortality per 1000 cases in older individuals.
• Diagnosis:
  • Typical test looks for anti-HAV IgM (current/recent infection) and IgG (historical infection) in patient sera.
  • Interpretation:
    • High IgM, Negative/Low IgG: Possible infection – seek PCR confirmation.
    • High IgM, High IgG: HAV infected.
    • Low/Negative IgM, High IgG: Historical HAV infection.
  • 💡 NICE Guidance: Use PCR if available (not routine). If serology is taken within the first 7-10 days of symptoms, repeat 2 weeks later.
• Prevention & Control:
  • Vaccination ✅
  • Improved sanitation and hygiene 🧼
  • Isolation of infected individuals
  • Targeted vaccination programs
  • Post-exposure vaccination can prevent disease up to 2 weeks after exposure.
  • At-risk individuals may also be offered human normal immunoglobulin.

2.2 Hepatitis B Virus (HBV)

• Nature: Enveloped DNA virus.
• Transmission: Contact with blood, sexual transmission, perinatal routes 🩸.
• Genotypes: Ten genotypes exist, influencing treatment and disease progression.
• Prevalence: 254 million HBV carriers worldwide (WHO 2024).
• Mortality (2016 estimates):
  • 100,300 deaths due to fulminant hepatitis.
  • 349,500 deaths due to HBV-related hepatocellular carcinoma (HCC).
  • 365,600 deaths due to cirrhosis.
• Chronicity: Age at acquisition significantly influences the likelihood of chronic infection (> 6 months):
  • Under 1 year: 90% become chronic.
  • 1-5 years: 30% become chronic.
  • Adults: 0-2% become chronic.
• Diagnosis (Serology - Complicated!): Involves detecting viral antigens and corresponding antibodies.
  • Antigens secreted by virus: C (Core), E (Envelope), S (Surface).
  • Antibodies:
    • HBcAb (antibody to Core antigen): Indicates current or past infection.
    • HBeAb (antibody to E antigen): Suggests an adaptive immune response suppressing viral replication, but not sterilizing immunity.
    • HBsAb (antibody to S antigen): Indicates sterilizing immunity (e.g., from vaccination or resolved infection). Recombinant S antigen is used in the HBV vaccine.
  • HBsAg (Surface antigen): Presence in serum indicates viremia (active infection).
  • Acute HBV Infection Progression: Levels of HBsAg, HBeAg, DNA, IgM anti-HBc, IgG anti-HBc, anti-HBe, anti-HBs, ALT, jaundice, and symptoms change over months post-infection.
• Chronic HBV Infection Stages (Four phases over time):
  1. Immune Tolerance Phase: High HBV DNA, HBeAg positive, normal ALT.
  2. Immune Clearance Phase: High HBV DNA, HBeAg positive, elevated ALT, risk of cirrhosis.
  3. Immune Control Phase: Low/undetectable HBV DNA, HBeAg negative, anti-HBe positive, normal ALT.
  4. Immune Escape Phase: Variable HBV DNA, HBeAg negative, anti-HBe positive, elevated ALT, increased risk of cirrhosis.
• Treatment:
  • Only for chronically infected individuals, typically when cirrhosis risk is high.
  • First-line: Interferon-alpha.
  • Alternatives: Nucleoside inhibitors.
  • Treatment usually suppresses viral replication, not eradicates the virus.
  • ⚠️ Interferon-alpha is not recommended for decompensated liver disease or pregnancy.
• Prevention & Control:
  • Vaccination (at birth in high-prevalence areas) ✅
  • Public health awareness (e.g., needle exchange programs)
  • Screening programs to identify chronically infected individuals + education
  • Treatment of chronically infected individuals to reduce viral loads and prevent transmission.
  • If mother is HBV positive, antivirals are given in the third trimester.

2.3 Hepatitis D Virus (HDV)

• Nature: Unique "piggyback" virus; requires HBV structural proteins to package its genome.
• Association: Combined HBV + HDV infection is associated with a poorer prognosis than HBV alone.
• Diagnosis: Detection of antibodies to Hepatitis Delta Antigen (HDAg).
• Prevention & Control: Exactly the same as for HBV, as HDV cannot exist independently.

2.4 Hepatitis C Virus (HCV)

• Nature: Enveloped RNA virus, discovered in 1989.
• Transmission: Primarily parenteral (blood-to-blood contact) 💉.
• Prevalence: Approximately 3% of the world's population infected.
• Vaccine: No vaccine available for HCV.
• Mortality: About 240,000 deaths per year due to HCV-associated HCC and cirrhosis.
• Disease Progression:
  • Incubation Period: 15-150 days.
  • Acute Phase: 60-70% are asymptomatic.
  • Chronicity: 80% of newly infected patients progress to chronic infection.
  • Long-term: Over 20 years, chronic infection can lead to cirrhosis (15-30% of cases) and liver cancer (5-10% of cases).
• Treatment: HCV is curable with combination therapy! 💊
  • Classes of drugs: Polymerase inhibitors, Protease inhibitors, NS5A inhibitors.
• Diagnosis: Use of PCR to detect the virus in an infected patient's blood.
• Prevention & Control:
  • Public health awareness (e.g., needle exchange programs)
  • Screening programs to identify chronically infected individuals
  • Treatment of chronically infected individuals to prevent further transmission.

2.5 Hepatitis E Virus (HEV)

• Nature: Four main genotypes that infect humans.
• Transmission: Predominantly faecal-oral route 💧.
• Prevalence: 20 million HEV infections worldwide per year.
• Mortality: Estimated to cause 44,000 deaths per year.
• High-Risk Groups:
  • Pregnant Women: High mortality (~30%) in infected pregnant women (restricted to genotype 1).
  • Chronic Liver Disease: Individuals with chronic liver disease are also at risk (all genotypes).
  • UK Specific: Predominantly seen in men over 50, mainly genotype 3.
• Genotype Characteristics:
  • Genotypes 1 & 2: Found in humans (Asia, Africa, Mexico, West Africa). Water-borne transmission, cause epidemics. No inter-species transmission.
  • Genotypes 3 & 4: Widespread (North America, Europe, Asia). Known for animal-to-human transmission (pigs, wild boar, deer) and can be food-borne. Can cause chronicity in immunocompromised persons.
• Diagnosis:
  • Usually based on the presence of IgM antibodies to viral proteins.
  • RT-PCR detection of virus in blood and stools can also be used.
• Prevention & Control:
  • Public health (improved sanitation/hygiene) 🧼
  • Treatment of chronically infected patients with ribavirin (questionable efficacy).
  • Vaccination: An HEV vaccine is currently only licensed in China.

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3. General Control and Prevention Measures 🛡️

Effective control of viral hepatitis relies on a multi-faceted approach:

• Vaccination: Available for HAV and HBV (and indirectly for HDV).
• Public Health Awareness: Education on transmission routes, safe practices (e.g., safe sex, clean needles).
• Improved Sanitation and Hygiene: Crucial for faecal-oral transmitted viruses (HAV, HEV).
• Screening Programs: To identify chronically infected individuals, especially for HBV and HCV, enabling early treatment and preventing further transmission.
• Treatment: Suppressing viral loads (HBV) or curing the infection (HCV) reduces disease progression and transmission.

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4. Online Resources 🌐

For more detailed information, the World Health Organization (WHO) provides helpful fact sheets for each hepatitis virus:

• WHO Hepatitis A Fact Sheet (and links therein for other types)