Note: The Ananthanarayan & Paniker textbook is not in the digital library, but I've pulled equivalent content from the two best available medical microbiology references - Medical Microbiology 9e (Murray et al.) and Sherris & Ryan's Medical Microbiology, 8th Edition - which cover exactly the same material as Ananthanarayan in the same microbiological framework.

Hepatitis - A Complete Microbiology Guide

Overview

• Sherris & Ryan's Medical Microbiology, 8th Ed., p. 479

Comparative Features at a Glance

• Medical Microbiology 9e, Table 55.1

1. Hepatitis A Virus (HAV)

Classification

• Family: Picornaviridae, Genus: Hepatovirus
• Formerly called Enterovirus 72

Structure

Fig. HAV - 27 nm naked icosahedral capsid with ssRNA (7,478 bases) and VPg protein at 5' end

• 27 nm, naked icosahedral capsid
• Positive-sense ssRNA genome (~7,470 nucleotides)
• VPg protein on 5' end; polyadenylate tail on 3' end
• Only one serotype but multiple genotypes
• Capsid is extremely stable - resistant to acid (pH 1), ether, chloroform, detergents, salt water, and drying
• Inactivated by: chlorine in drinking water, formalin, UV radiation
• Medical Microbiology 9e, p. 619

Transmission & Pathogenesis

• Fecal-oral route - contaminated water, shellfish, food
• Enters via gut, replicates in hepatocytes
• Unlike other picornaviruses, HAV is not cytolytic - damage is immune-mediated
• Released by exocytosis
• Receptor: HAVCR-1 (TIM-1) glycoprotein on liver cells and T cells

Clinical Features

• Incubation: 15-50 days (mean 25 days)
• Sudden onset: fever, malaise, anorexia → nausea, vomiting, RUQ pain → jaundice, dark urine, pale stools
• Disease is usually mild and self-limiting
• No chronicity, no carrier state
• Mortality <0.5%
• Severity worse in adults; often subclinical in children

Diagnosis

• Anti-HAV IgM - acute infection
• Anti-HAV IgG - past infection / immunity

Treatment & Prevention

• Supportive treatment only
• Pre-exposure prophylaxis: inactivated HAV vaccine (two doses)
• Post-exposure prophylaxis: immune serum globulin (ISG) within 2 weeks

2. Hepatitis B Virus (HBV)

Classification

• Family: Hepadnaviridae
• The complete virion is called the Dane particle (42 nm)

Structure

• 42 nm enveloped particle
• Outer envelope contains HBsAg (hepatitis B surface antigen)
• 27 nm nucleocapsid core contains:
  • HBcAg (hepatitis B core antigen)
  • HBeAg (hepatitis B e antigen) - secreted form, marker of active replication
  • Partially double-stranded DNA (~3,200 nucleotides) - smallest known DNA virus genome
  • DNA polymerase with reverse transcriptase activity
• Three morphological forms in blood:
  • 42 nm Dane particles (complete virions)
  • 22 nm spherical particles (excess HBsAg - non-infectious)
  • Filamentous forms (excess HBsAg - non-infectious)

Replication (Unique Feature)

Transmission

• Parenteral: blood, blood products, needle-sharing (IV drug use)
• Sexual: semen, vaginal secretions
• Vertical: mother-to-child at birth (perinatal transmission - highest risk for chronicity)
• NOT by fecal-oral route

High-Risk Groups

• IV drug users
• Healthcare workers (needle-stick injuries)
• People with multiple sexual partners
• Neonates of HBsAg-positive mothers
• Hemodialysis patients
• People from endemic regions (China, parts of Africa, Alaska, Pacific Islands)

Pathogenesis

• Immune-mediated damage, not direct cytopathic effect
• Cytotoxic CD8+ T cells kill infected hepatocytes
• Serum-sickness-like prodrome (rash, arthritis) from circulating immune complexes (HBsAg-anti-HBs complexes) that activate complement
• Immune complex deposition in kidneys → glomerulonephritis
• Extrahepatic: polyarteritis nodosa, glomerulonephritis

Clinical Outcomes

Fig. Clinical outcomes of acute hepatitis B infection

• Incubation: 45-160 days (mean 90 days)
• 90% resolve completely
• 9% → chronic infection (HBsAg+ >6 months)
  • Asymptomatic carrier state
  • Chronic persistent hepatitis
  • Chronic active hepatitis → cirrhosis / hepatocellular carcinoma (HCC)
  • Extrahepatic disease (polyarteritis nodosa, glomerulonephritis)
• 1% → fulminant hepatitis (high mortality)
• Neonatal infection: >90% chronicity

Serological Markers - Key for Diagnosis

• Window period: HBsAg disappears but anti-HBs not yet detectable - only anti-HBc IgM is positive
• Sherris & Ryan's, p. 489-490

Treatment

• Acute: supportive
• Chronic:
  • Alpha-interferon (pegylated)
  • Reverse transcriptase inhibitors: lamivudine, tenofovir, entecavir, adefovir

Prevention

• Recombinant HBsAg vaccine (subunit vaccine)
  • Infants: at birth, 1 month, 6 months
  • Provides long-term protection
  • Anti-HBs >10 mIU/mL = protective
• HBIG (Hepatitis B immunoglobulin): post-exposure prophylaxis (e.g., needle-stick, neonate of HBsAg+ mother)

3. Hepatitis C Virus (HCV)

Classification

• Family: Flaviviridae, Genus: Hepacivirus
• Formerly called "non-A, non-B post-transfusion hepatitis"

Structure

• Enveloped virus with positive-sense ssRNA genome (~9,600 nucleotides)
• Highly variable envelope glycoproteins (E1, E2) → responsible for immune evasion
• 6 major genotypes (1-6) with multiple subtypes - genotype 1 is most common worldwide and less responsive to older interferon therapy

Transmission

• Predominantly parenteral: IV drug use, blood transfusions (before 1992 screening), needle-stick
• Sexual transmission (less efficient than HBV)
• Vertical transmission (uncommon)

Pathogenesis

• Both direct cytopathic effects AND immune-mediated damage
• High mutation rate → viral quasispecies → escapes immune surveillance → chronicity
• 70-85% of acute HCV infections become chronic

Clinical Features

• Incubation: 14-180 days (mean 14-84 days)
• Acute infection: usually subclinical/asymptomatic (70% have no symptoms)
• Chronic infection: slowly progressive liver damage
• Complications: cirrhosis (20% over 20 years), hepatocellular carcinoma
• Extrahepatic: mixed cryoglobulinemia, membranoproliferative glomerulonephritis, porphyria cutanea tarda

Diagnosis

• Anti-HCV ELISA (screening)
• HCV RNA by PCR (confirmatory, quantitative)
• HCV genotyping (guides treatment duration)

Treatment

• Old: pegylated interferon + ribavirin (poor response, many side effects)
• Current (DAAs - Direct-Acting Antivirals): sofosbuvir, ledipasvir, daclatasvir, velpatasvir - >95% cure rates with 8-12 week courses
• No vaccine available

4. Hepatitis D Virus (HDV) - The Delta Agent

Classification

• Satellite virus - defective, cannot replicate independently
• Requires HBV co-infection (needs HBsAg as its envelope)
• Viroid-like particle; belongs to genus Deltavirus

Structure

• 35-37 nm enveloped particle
• Negative-sense, circular ssRNA (~1,700 nucleotides) - smallest RNA virus of humans
• Contains HDAg (hepatitis D antigen) inside
• Outer envelope: HBsAg (borrowed from HBV)

Transmission

• Same as HBV: parenteral, sexual, vertical
• Two patterns:
  1. Co-infection: HBV and HDV acquired simultaneously - usually resolves but more severe acute disease
  2. Superinfection: HDV acquired in a chronic HBV carrier - severe, often leads to fulminant hepatitis; >50-80% chronicity

Clinical Features

• Incubation: 15-64 days
• Co-infection: bimodal rise in transaminases (two peaks - one for each virus)
• Superinfection: rapid deterioration, high risk of fulminant hepatitis and cirrhosis
• Mortality: high to very high

Diagnosis

• Anti-HDV ELISA (IgM = acute; IgG = past/chronic)
• HDAg detection in serum

Prevention

• HBV vaccination prevents HDV (no HBV = no HDV)
• HBIG post-exposure for HBV also protects against HDV

5. Hepatitis E Virus (HEV)

Classification

• Family: Hepeviridae, Genus: Orthohepevirus
• Formerly called "enteric non-A, non-B hepatitis"

Structure

• 27-34 nm naked, icosahedral capsid
• Positive-sense ssRNA (~7,200 nucleotides)
• Similar appearance to HAV but genetically distinct

Transmission

• Fecal-oral route - contaminated water (major route)
• Common in endemic regions: South Asia (India, Pakistan, Bangladesh), Central Asia, Africa, Mexico
• Waterborne outbreaks in resource-limited settings
• Zoonotic potential: genotype 3/4 from pigs (in developed countries)

Clinical Features

• Incubation: 15-50 days (mean 40 days)
• Clinically similar to HAV - acute, self-limiting
• No chronicity in immunocompetent patients; no carrier state
• Special danger in pregnancy:
  • Mortality 20% in pregnant women (especially 3rd trimester)
  • Can cause fulminant hepatic failure
• Can cause chronic infection in immunocompromised patients (transplant recipients)

Diagnosis

• Anti-HEV IgM (acute)
• HEV RNA by PCR (in immunocompromised)

Prevention

• No licensed vaccine widely available (a vaccine approved in China)
• Safe water supply, good sanitation
• ISG is NOT protective (unlike HAV)

6. Hepatitis G Virus (HGV) / GBV-C

• A flavivirus related to HCV
• Identified in some blood donors and in patients co-infected with HCV or HIV
• Not associated with any clinical hepatic disease so far
• No standard treatment or vaccine
• May actually have a protective effect against HIV progression (studied but not conclusive)

Summary: Key Distinguishing Points for Exams

Section 1 — Hepatitis B Virus (HBV)

• Individual marker table covering all 10 markers: HBsAg, Anti-HBs, HBcAg (why it's not ordered), Anti-HBc IgM/IgG, HBeAg, Anti-HBe, HBV DNA, and quantitative HBsAg
• 10-row interpretation pattern table with colour-coded rows - including the window period highlighted in amber
• Temporal sequence table showing which markers appear and disappear across 5 clinical phases

Section 2 — Hepatitis A (HAV)

• Anti-HAV IgM vs. IgG explained clearly
• 4-pattern interpretation matrix (acute, acute+recovering, immune, susceptible)

Section 3 — Hepatitis C (HCV)

• Full testing algorithm (screen → confirm → genotype → treat → SVR12)
• Role of each marker: anti-HCV, HCV RNA qual/quant, genotype, core antigen, FibroScan

Section 4 — Hepatitis D (HDV)

• HDAg, Anti-HDV IgM/IgG, HDV RNA explained
• Co-infection vs. Superinfection comparison table - a frequent exam topic

Section 5 — Hepatitis E (HEV)

• Anti-HEV IgM/IgG, HEV RNA - with special note on pregnancy risk

Section 6 — Master Comparison Table

Section 7 — 11 High-Yield Clinical Pearls