(1)Virology and Viral Hepatitis Notes

Introduction to Virology and Viral Hepatitis

• Topics to Consider:

  • Genome.

  • Virus structure.

  • Host cell tropism.

  • Hijacking of host machinery.

  • Host immune response.

  • Disease outcome.

  • Transmission.

  • Available vaccines and therapeutics.

Virus Classification

• Host cell.

• Virus structure (capsid shape).

• Presence/absence of envelope.

• Type of nucleic acid:

  • DNA viruses (dsDNA, less common ssDNA).

  • RNA viruses (positive-sense ssRNA, negative-sense ssRNA, less common dsRNA).

  • Reverse transcribing (dsDNA, ssRNA).

Virus Structure

• Viral Nucleic Acid:

  • ssDNA, dsDNA, RNA.

  • Linear or circular.

• Protein Coat (Capsid):

  • Protects nucleic acid.

• Envelope:

  • Phospholipid bilayers.

Virion Structure Advantages

• Protection of nucleic acid.

• Specificity in host cell interaction.

• Genome delivery.

Viral Membrane (Envelope) Structure

• Phospholipid bilayer coat in some viruses.

General Virus Replication Cycle

1. Attachment/Entry

2. Replication/Transcription

3. Virion Assembly

4. Virion Release

Antibodies vs Antigens

• Antibodies: Neutralize foreign objects (antigens).

  • IgG: Majority of response.

  • IgM: Early stages.

• Antigens: Recognized by T cell receptors or antibodies.

  • Proteins, polysaccharides, lipids, small molecules.

Immunization

• Passive: Antibodies transferred (no memory).

• Active: Body responds to antigens (memory).

Measuring Virus Neutralization

• Plaque-forming assays quantify cytotoxic viruses.

• Plaque Reduction Neutralization Assay.

Terminology

• Plaque forming units (pfu): Measure of infectious virus particles.

• Multiplicity of infection (moi): Average number of virus particles infecting each cell.

Multiplicity \ of \ infection \ (moi) = \frac{Plaque \ forming \ units \ (pfu) \ of \ virus \ used \ for \ infection}{number \ of \ cells}

• IC_{50}: Half maximal inhibitory concentration.

Hepatitis Viruses

• Types: HAV, HBV, HCV, HDV, HEV.

• Key aspects:

  • Virion, genome, replication details.

  • Transmission.

  • Clinical aspects.

  • Immune response.

  • Lab diagnosis.

  • Treatment and prevention.

Viral Hepatitis Types

• HAV:

  • Enteral (fecal/oral).

  • Picornavirus (+ssRNA).

  • Mild, acute.

  • Vaccine available.

• HBV:

  • Parenteral.

  • Hepadnavirus (+dsDNA).

  • Severe, 5-10% chronic.

  • Incubation period- 45-160 days

  • Surface antigen- HBsAg

  • Vaccine available.

• HCV:

  • Parenteral.

  • Hepacivirus (+ssRNA).

  • Subclinical, 70% chronic.

  • Incubation period- 15-150 days

  • No vaccine.

• HDV:

  • Parenteral.

  • Deltavirus (-ssRNA).

  • Exacerbates HBV, chronic with HBV.

  • HBV vaccine works on HDV.

• HEV:

  • Enteral (fecal/oral).

  • Hepevirus (+ssRNA).

  • Mild in normal patients, severe in pregnant women, acute.

  • No vaccine.

Hepatitis A (HAV)

• Transmission: Fecal-oral route.

• Acute only. (no carrier/not a chronic condition)

• IgM detectable first, then IgG for life.

• Diagnosis: Raised IgM and IgG anti-HAV antibodies; elevated liver enzymes.

• Treatment: No specific treatment, rest.

• Prevention:

  • Passive immunization: Human gamma globulin.

  • Active immunization: Inactivated hepatitis A vaccine.

Hepatitis B (HBV)

• Transmission: Bloodborne, perinatal.

• Replicates through RNA intermediate via reverse transcriptase.

• Diagnosis: Liver function tests (ALT enzyme levels).

HBV Clinical Outcomes

1. Asymptomatic Infection

2. Acute HBV Infection

   1. HBV + HDV = Fulminant hepatitis

3. Chronic HBV Infection

• Treatment:

  • Interferon alpha.

  • Nucleoside/nucleotide analogs.

• Prevention:

  • Passive immunization: Hepatitis B immune globulin (HBIG).

  • Active immunization: Recombinant vaccines.

Hepatitis C (HCV)

• Transmission: Intravenous drug use, transfusions, tattooing.

• Diagnosis: Blood tests, genetic testing (6 genotypes), liver biopsy.

• Treatment:

  • Interferon-alpha and ribavirin.

  • Direct-acting antivirals (DAAs).

• No vaccine.

• Mutates rapidly due to high error rate of RNA-dependent RNA polymerase

Hepatitis D (HDV)

• Requires HBV for transmission (uses its surface antigens because it has none).

• Diagnosis: Blood tests (anti-delta antibodies, serum HDV RNA).

• Treatment: No effective antiviral treatment.

• Prevention: Hepatitis B vaccine protects against Hepatitis D.

Hepatitis E (HEV)

• Transmission: Fecal-oral route via contaminated water.

• Diagnosis: Specific antibodies in blood.

• Treatment: No available treatment, usually self-limiting.

• Prevention: Maintain water quality, proper waste disposal.

Study Guide

• Basic building blocks of a virus.

• Benefits of virus particle structure.

• Basic steps in virus replication cycle.

• How a plaque assay works.

• pfu and MOI

• HBV and HDV relationship.

• Hepatitis viruses: vaccines and treatments.

• Hepatitis virus transmission routes.

Here are the key points from the study guide in a non-flashcard format:

• Basic Building Blocks of a Virus: Genome, virus structure, host cell tropism, hijacking of host machinery, host immune response, disease outcome, transmission, available vaccines and therapeutics.

• Benefits of Virus Particle Structure: Protection of nucleic acid, specificity in host cell interaction, genome delivery.

• Basic Steps in Virus Replication Cycle: Attachment/Entry, Replication/Transcription, Virion Assembly, Virion Release.

• How a Plaque Assay Works: Plaque-forming assays quantify cytotoxic viruses to measure virus neutralization. Plaque Reduction Neutralization Assay.

• pfu: Plaque forming units: Measure of infectious virus particles.

• MOI: Multiplicity of infection: Average number of virus particles infecting each cell. Multiplicity of infection (moi) = $\frac{Plaque forming units (pfu) of virus used for infection}{number of cells}$

• HBV and HDV Relationship: HDV requires HBV for transmission. HBV vaccine protects against Hepatitis D.

• Hepatitis Viruses with Vaccines: HAV, HBV, HDV (HBV vaccine works on HDV).

• Hepatitis Viruses with Treatments: HCV (Treatment available, no vaccine), HBV (Interferon alpha, Nucleoside/nucleotide analogs).

• Hepatitis Virus Transmission Routes: HAV