microbiology 2 MBBS REFER APURB SHASTRI MUHS EXAM ORITNTED detail answer of questions, colour diagrams as well for exam important points for muhs exam cover all 1. Hepatitis B - laboratory diagnosis 2. Rhabdoviruses** - immunoprophylaxis**, dosage schedule, non-neural vaccines and schedule 3. Influenza Virus and HIV - diagram 4. Type-A Influenza Virus - antigenic variations and significance 5. Merits and demerits of Salk's and Sabin's vaccines 6. Classify Herpesviridae, mention virus included in subfamilies and one infection caused by each 7. HIV** - pathogenesis, mention two opportunistic infections*; laboratory diagnosis; HIV Testing in India - strategies 8. Four Oncogenic Viruses 9. Epstein-Barr Virus LAQ 1. HIV** - define window period, laboratory diagnosis**, etiology, pathogenesis, diagram of HIV; Enumerate organisms causing STDs* 2. Hepatitis***** - classify, laboratory diagnosis****, pathogenesis of HBV*; morphology*, enumerate serological markers; enumerate viruses, mode of transmission; prophylaxis 3. Herpes Virus* - classification, Varicella zoster - clinical features, laboratory diagnosis; Herpes simplex - lesions, laboratory diagnosis 4. Polio Viruses - pathogenicity, immunoprophylaxis, laboratory diagnosis 5. Influenza Viruses** - morphology**, antigenic variations*, pathogenesis of Influenza; classification; Antigenic Shift - mechanism, significance
Reading File
general-purpose
You are a medical microbiology expert helping a 2nd MBBS student prepare for MUHS exams. Search the medical textbook library database for detailed content on the following virology topics. Use query_library_db with FTS searches. Search for each of these topics and return ALL relevant content (full paragraphs, mechanisms, diagrams references): 1. Hepatitis B - laboratory diagnosis, serological markers, HBsAg, anti-HBs, HBeAg, anti-HBc, window period 2. Rhabdovirus / Rabies - immunoprophylaxis, vaccine dosage schedule, non-neural vaccines (HDCV, PCECV), pre-exposure and post-exposure prophylaxis 3. Influenza Virus - morphology, antigenic variation, antigenic drift, antigenic shift, pandemic, epidemic, pathogenesis 4. HIV - structure/morphology, pathogenesis, CD4 cells, opportunistic infections, laboratory diagnosis, ELISA, Western blot, HIV testing strategies in India (Strategy I, II, III) 5. Polio virus - pathogenicity, Salk vaccine, Sabin vaccine, merits and demerits 6. Herpesviridae - classification, subfamilies (alphaherpesvirinae, betaherpesvirinae, gammaherpesvirinae), HSV, VZV, CMV, EBV 7. Epstein-Barr virus - infectious mononucleosis, lab diagnosis, oncogenic potential 8. Oncogenic viruses - HPV, EBV, HBV, HTLV-1 Use these SQL queries: ```sql SELECT book_title, section_heading, '/textbooks/' || block_file_path AS file_path, line_start, line_end, snippet(paragraphs_fts, 0, '>>>', '<<<', '...', 40) as snippet FROM paragraphs_fts WHERE paragraphs_fts MATCH 'hepatitis B laboratory diagnosis serological markers' ORDER BY rank LIMIT 5 ``` Run multiple parallel searches. For each search result, use read_file to get full content from the file_path at the indicated line_start/line_end (read 80-100 lines around each result). Return a structured summary of ALL content found for each topic, including exact text from the textbooks that would be useful for exam answers.
general-purpose
You are a medical microbiology expert helping a 2nd MBBS student prepare for MUHS exams (Apurb Shastri reference). Search the medical textbook library database for detailed virology content. Use query_library_db tool with these specific searches: Search 1 - Find microbiology books available: ```sql SELECT isbn, title, speciality FROM v_book_overview WHERE speciality LIKE '%microbio%' OR title LIKE '%microbio%' ORDER BY title LIMIT 20 ``` Search 2 - Hepatitis B: ```sql SELECT book_title, section_heading, '/textbooks/' || block_file_path AS file_path, line_start, line_end, snippet(paragraphs_fts, 0, '>>>', '<<<', '...', 50) as snippet FROM paragraphs_fts WHERE paragraphs_fts MATCH '"hepatitis B" AND "laboratory diagnosis"' ORDER BY rank LIMIT 5 ``` Search 3 - HIV pathogenesis and diagnosis: ```sql SELECT book_title, section_heading, '/textbooks/' || block_file_path AS file_path, line_start, line_end, snippet(paragraphs_fts, 0, '>>>', '<<<', '...', 50) as snippet FROM paragraphs_fts WHERE paragraphs_fts MATCH 'HIV pathogenesis "opportunistic infections"' ORDER BY rank LIMIT 5 ``` Search 4 - Rabies immunoprophylaxis: ```sql SELECT book_title, section_heading, '/textbooks/' || block_file_path AS file_path, line_start, line_end, snippet(paragraphs_fts, 0, '>>>', '<<<', '...', 50) as snippet FROM paragraphs_fts WHERE paragraphs_fts MATCH 'rabies vaccine immunoprophylaxis schedule' ORDER BY rank LIMIT 5 ``` Search 5 - Influenza antigenic variation: ```sql SELECT book_title, section_heading, '/textbooks/' || block_file_path AS file_path, line_start, line_end, snippet(paragraphs_fts, 0, '>>>', '<<<', '...', 50) as snippet FROM paragraphs_fts WHERE paragraphs_fts MATCH 'influenza "antigenic shift" "antigenic drift"' ORDER BY rank LIMIT 5 ``` Search 6 - Herpes classification: ```sql SELECT book_title, section_heading, '/textbooks/' || block_file_path AS file_path, line_start, line_end, snippet(paragraphs_fts, 0, '>>>', '<<<', '...', 50) as snippet FROM paragraphs_fts WHERE paragraphs_fts MATCH 'herpesviridae classification alphaherpesvirinae' ORDER BY rank LIMIT 5 ``` Search 7 - Polio Salk Sabin vaccine: ```sql SELECT book_title, section_heading, '/textbooks/' || block_file_path AS file_path, line_start, line_end, snippet(paragraphs_fts, 0, '>>>', '<<<', '...', 50) as snippet FROM paragraphs_fts WHERE paragraphs_fts MATCH 'Salk Sabin vaccine polio merits demerits' ORDER BY rank LIMIT 5 ``` Search 8 - Oncogenic viruses: ```sql SELECT book_title, section_heading, '/textbooks/' || block_file_path AS file_path, line_start, line_end, snippet(paragraphs_fts, 0, '>>>', '<<<', '...', 50) as snippet FROM paragraphs_fts WHERE paragraphs_fts MATCH 'oncogenic virus HPV EBV' ORDER BY rank LIMIT 5 ``` For each search result with a file_path, use read_file to read the content at those line numbers (read 100 lines starting from line_start - 5). Return ALL the textbook content you find, organized by topic. Include actual text from the books.
Reading File
Reading File
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
Reading File
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Loading Image
Loading Image
Loading Image
Reading File
Reading File
Reading File
Reading File
Reading File
Reading File
Reading File
Reading File
Reading File
Reading File
Reading File
Reading File
Finding Sources
Finding Sources
Reading File
Reading File
Finding Sources
Finding Sources
Reading File
Reading File
answer
Here is the complete, exam-oriented answer for your MUHS 2nd MBBS Microbiology paper, based on Apurb Shastri and standard references (Jawetz, Sherris & Ryan, Murray, Robbins).
๐ฆ MICROBIOLOGY โ VIROLOGY
MUHS 2nd MBBS Exam-Oriented Notes
Reference: Apurb Shastri | Jawetz | Sherris & Ryan | Murray
SECTION A โ SHORT ANSWER QUESTIONS (SAQ)
1. HEPATITIS B โ LABORATORY DIAGNOSIS โญโญโญโญโญ
๐ฌ Serological Markers of HBV
| Marker | Full Name | Significance |
|---|---|---|
| HBsAg | Hepatitis B surface antigen | First marker to appear; indicates active infection |
| HBeAg | Hepatitis B e antigen | Marker of active viral replication + high infectivity |
| HBcAg | Hepatitis B core antigen | Found only in hepatocyte nuclei (NOT in serum) |
| Anti-HBs | Antibody to HBsAg | Protective antibody; marker of recovery or vaccination |
| Anti-HBc IgM | IgM to core antigen | Marker of acute infection; present during window period |
| Anti-HBc IgG | IgG to core antigen | Marker of past or chronic infection; NOT induced by vaccine |
| Anti-HBe | Antibody to HBeAg | Seroconversion = reduced infectivity, better prognosis |
| HBV DNA | Viral genome | Gold standard for active replication; guides antiviral therapy |
๐ Serological Interpretation Table (MOST IMPORTANT FOR MUHS)
| Clinical State | HBsAg | Anti-HBs | Anti-HBc IgM | Anti-HBc IgG | HBeAg |
|---|---|---|---|---|---|
| Acute infection | โ | โ | โ | โ | โ |
| Window period | โ | โ | โ | โ | ยฑ |
| Recovery / Past infection | โ | โ | โ | โ | โ |
| Chronic carrier (low replication) | โ | โ | โ | โ | โ |
| Chronic active (high replication) | โ | โ | โ | โ | โ |
| Vaccinated (no prior infection) | โ | โ | โ | โ | โ |
โญ WINDOW PERIOD (High-Yield MUHS Point)
- Period between disappearance of HBsAg and appearance of Anti-HBs
- HBsAg is undetectable; Anti-HBs not yet produced
- ONLY marker present = IgM Anti-HBc โ This is the diagnostic clue
- May last weeks to months
Temporal Sequence in Acute Self-Limiting HBV Infection:
EXPOSURE
|
โ 1โ12 weeks incubation
HBsAg appears (first marker) โ HBeAg + HBV DNA appear
|
โ Symptoms (if any)
IgM Anti-HBc appears
|
โ HBsAg disappears
--- WINDOW PERIOD --- (only IgM Anti-HBc positive)
|
โ
Anti-HBs appears + IgG Anti-HBc
Anti-HBe appears (seroconversion)
|
โ Recovery
Anti-HBs + Anti-HBc IgG persist lifelong
Laboratory Methods
| Test | Purpose |
|---|---|
| ELISA / CMIA | Detection of HBsAg, HBeAg, Anti-HBs, Anti-HBc (routine) |
| PCR (HBV DNA) | Quantitative viral load; guides therapy |
| Liver biopsy | Grading and staging of liver disease |
| Liver function tests | ALT/AST elevated; indirect marker |
| Serum bilirubin | Elevated in icteric phase |
Prevention (Prophylaxis)
- Vaccine: Recombinant HBsAg (yeast-expressed) โ Engerix-B, Recombivax HB
- Schedule: 0, 1, 6 months (IM into deltoid)
- Efficacy: >90% protection; immunity lasts ~20 years
- HBIG: Hepatitis B Immunoglobulin โ passive immunization for post-exposure or neonates of HBsAg-positive mothers
- Neonate of HBsAg+ mother: HBIG at birth + HBV vaccine within 24 hours โ prevents vertical transmission
2. RHABDOVIRUSES โ IMMUNOPROPHYLAXIS, DOSAGE SCHEDULE, NON-NEURAL VACCINES โญโญโญ
Quick Recap of Rabies Virus
- Family: Rhabdoviridae | Genus: Lyssavirus
- Morphology: Bullet-shaped, (-) ssRNA, helical nucleocapsid
- Pathognomonic: Negri bodies (eosinophilic intracytoplasmic inclusions in Purkinje cells / hippocampal neurons)
WHO Categories of Exposure
| Category | Nature of Contact | Action |
|---|---|---|
| I | Touching / feeding animal; lick on intact skin | None required |
| II | Minor scratches/abrasions without bleeding; nibbling | Wound care + Vaccine only |
| III | Transdermal bite/scratch; lick on broken skin; mucous membrane contact; bat contact | Wound care + Vaccine + RIG |
๐งด Local Wound Treatment (First Priority)
- Wash with soap and water for 15 minutes under running tap
- Apply 70% alcohol / povidone-iodine / 0.01% aqueous iodine
- Do NOT suture immediately (if needed, delay 24โ48 h, with minimum sutures under RIG cover)
- Anti-tetanus prophylaxis + antibiotics as needed
"Local wound treatment alone can reduce rabies risk by up to 80%"
๐ฉบ Post-Exposure Prophylaxis (PEP) Schedules
(A) Essen Regimen โ 5 doses
Days: 0, 3, 7, 14, 28 โ 1 dose IM (deltoid) each
(B) Zagreb / Abbreviated Regimen โ 4 doses (2-1-1)
| Day | Doses |
|---|---|
| Day 0 | 2 doses โ one in each deltoid |
| Day 7 | 1 dose |
| Day 21 | 1 dose |
(C) Updated 4-dose Regimen
Days: 0, 3, 7, 14 โ for healthy immunocompetent individuals receiving RIG + wound care
Pre-Exposure Prophylaxis (PrEP) โ for high-risk individuals
Days: 0, 7, 21 or 28 โ 3 doses IM
๐ Non-Neural Rabies Vaccines (Cell-Culture Vaccines = CCEEVs)
| Vaccine | Cell Line Used |
|---|---|
| HDCV (Human Diploid Cell Vaccine) | Human diploid cells (MRC-5) |
| PCECV (Purified Chick Embryo Cell Vaccine) | Primary chick embryo cells |
| PVRV (Purified Vero Cell Rabies Vaccine) | Vero cells (African green monkey kidney) |
| PDEV (Purified Duck Embryo Vaccine) | Embryonated duck eggs |
| PHKSV (Purified Hamster Kidney Cell Vaccine) | Syrian hamster kidney cells |
Why non-neural vaccines replaced nerve tissue vaccines (NTV):
- NTVs (Semple vaccine) used sheep/goat brain tissue โ contained myelin basic protein โ risk of demyelinating encephalomyelitis (neuroparalytic accident) / Guillain-Barrรฉ-like reaction
- CCEEVs are myelin-free, have higher immunogenicity, fewer adverse effects
Rabies Immunoglobulin (RIG)
- Purpose: Passive immunization to bridge gap until active vaccine-induced immunity develops
- Dose: 20 IU/kg body weight (Human RIG = HRIG) or 40 IU/kg (Equine RIG = ERIG)
- Route: Maximum infiltrated around wound + remainder IM (anatomically distant from vaccine)
- Timing: Day 0 ONLY (simultaneously with first vaccine dose, different site)
Previously vaccinated patients: Give only Day 0 and Day 3 doses โ NO RIG needed
3. INFLUENZA VIRUS AND HIV โ DIAGRAMS โญโญโญ
๐จ DIAGRAM 1: Structure of Influenza A Virus
INFLUENZA A VIRUS โ STRUCTURE
โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ
โ HA (Hemagglutinin trimer) = spike โ โ Binds sialic acid; target of
โ NA (Neuraminidase tetramer) โ neutralizing antibodies
โ โ โ โ Cleaves sialic acid; aids
โ โโโโโโโโโโโโโโโโโโโโโโโโโโ โ release
โ โ Lipid Envelope โ โ
โ โ โโโโโโโโโโโโโโโโโโโโ โ โ
โ โ โ M2 ion channel โ โ โ โ Target of Amantadine
โ โ โโโโโโโโโโโโโโโโโโโโ โ โ
โ โ M1 (matrix protein) โ โ โ Type-specific antigen
โ โ โโโโโโโโโโโโโโโโโโโโ โ โ
โ โ โ Nucleoprotein(NP)โ โ โ โ Type-specific antigen
โ โ โ PB1, PB2, PA โ โ โ โ RNA polymerase complex
โ โ โ 8 RNA segments โ โ โ โ (-) ssRNA
โ โ โโโโโโโโโโโโโโโโโโโโ โ โ
โ โโโโโโโโโโโโโโโโโโโโโโโโโโ โ
โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ
Surface glycoproteins: HA (18 types) + NA (11 types)
Current circulating: H1N1, H3N2, H5N1 (avian)
๐จ DIAGRAM 2: Structure of HIV
HIV VIRION โ STRUCTURE
โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ
โ โ
โ gp120 โโโ โโโ (surface knobs) โ โ Binds CD4 receptor
โ gp41 โโโ ||| (transmembrane) โ โ Fusion with host cell
โ โ
โ โโโโโโโ Lipid bilayer โโโโโโโ โ
โ โ p17 (matrix protein) โ โ โ Lines inside envelope
โ โ โโโโโโโโโโโโโโโโโโโโโโ โ โ
โ โ โ p24 (capsid = cone)โ โ โ โ Most abundant antigen
โ โ โ โโโโโโโโโโโโโโ โ โ โ Detected in ELISA
โ โ โ โ 2 copies โ โ โ โ
โ โ โ โ (+) ssRNA โ โ โ โ โ Diploid genome
โ โ โ โ p7 (NCp7) โ โ โ โ โ Nucleocapsid protein
โ โ โ โ Reverse โ โ โ โ โ RT (p51/p66)
โ โ โ โTranscriptaseโ โ โ โ
โ โ โ โ Integrase โ โ โ โ โ p32
โ โ โ โ Protease โ โ โ โ โ p10
โ โ โ โโโโโโโโโโโโโโ โ โ โ
โ โ โโโโโโโโโโโโโโโโโโโโโโ โ โ
โ โโโโโโโโโโโโโโโโโโโโโโโโโโโโโ โ
โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ
Genes: gag (core) | pol (enzymes) | env (envelope)
Accessory: tat, rev, nef, vif, vpu, vpr
4. TYPE-A INFLUENZA VIRUS โ ANTIGENIC VARIATIONS AND SIGNIFICANCE โญโญโญ
Surface Glycoproteins (Basis of Variation)
- Hemagglutinin (HA): 18 subtypes (H1โH18) โ binds sialic acid on host cells; major target of neutralizing antibodies
- Neuraminidase (NA): 11 subtypes (N1โN11) โ cleaves sialic acid; aids viral release
- Nomenclature: Influenza A / H3N2 = Type A, HA subtype 3, NA subtype 2
๐ ANTIGENIC DRIFT
| Feature | Details |
|---|---|
| Mechanism | Accumulation of point mutations in HA and NA genes |
| Change | Gradual / minor antigenic change |
| Viruses affected | All three types: A, B, and C |
| Epidemiologic impact | Seasonal epidemics / local outbreaks |
| Frequency | Every 2โ3 years |
| Selection pressure | Pre-existing herd immunity selects mutant strains that evade antibodies |
| Need for vaccine update | Yes โ influenza vaccine is updated annually |
๐ ANTIGENIC SHIFT
| Feature | Details |
|---|---|
| Mechanism | Genetic reassortment between different influenza A strains (human + animal/avian) |
| Change | Abrupt / major change in HA and/or NA subtypes |
| Viruses affected | Influenza A only (B and C restricted to humans; no animal reservoir) |
| Epidemiologic impact | Pandemics (worldwide spread) |
| Frequency | Irregular (unpredictable) |
| Why pandemic: | New HA/NA = no pre-existing immunity in population |
๐ Comparison Table: Drift vs. Shift
| Feature | Antigenic Drift | Antigenic Shift |
|---|---|---|
| Mechanism | Point mutations | Genetic reassortment |
| Rate of change | Gradual | Abrupt |
| Magnitude | Minor | Major |
| Virus types | A, B, C | A only |
| Result | Epidemics | Pandemics |
| Immunity pre-existing | Partial | None (naive population) |
| Vaccine update | Annual | New vaccine needed |
Major Pandemics Due to Antigenic Shift
| Year | Pandemic Name | Subtype | Origin |
|---|---|---|---|
| 1918 | Spanish flu (worst ever) | H1N1 | Avian/human |
| 1957 | Asian flu | H2N2 | Avian + H1N1 reassortment |
| 1968 | Hong Kong flu | H3N2 | H2N2 + avian HA reassortment |
| 2009 | Swine flu | H1N1 (pdm09) | Swine + human + avian triple reassortment |
Significance of Antigenic Variations
- Vaccines must be updated annually (due to drift)
- Pandemics are unpredictable and require new vaccines (due to shift)
- Herd immunity is rapidly lost โ entire population may be susceptible to a shift variant
- H5N1 (avian influenza) โ pandemic potential if acquires human-to-human transmission genes via shift
- Explains why influenza continues to cause morbidity/mortality despite available vaccines
5. MERITS AND DEMERITS OF SALK'S AND SABIN'S VACCINES โญโญโญ
IPV (Salk's Vaccine) โ Inactivated Polio Vaccine
| Feature | Detail |
|---|---|
| Type | Formalin-inactivated; killed vaccine |
| Route | Intramuscular (IM) |
| Contains | All 3 poliovirus serotypes |
โ Merits of IPV
- No risk of vaccine-associated paralytic polio (VAPP) โ cannot revert to virulence
- Safe in immunocompromised patients and their household contacts
- Stable โ does not require very strict cold chain
- No interference from intestinal enteroviruses
- Good systemic immunity (serum IgG + IgM)
- Can be combined with other vaccines (DPT, etc.)
โ Demerits of IPV
- No mucosal (secretory IgA) immunity โ does not protect gut; virus can still replicate in intestine
- No herd immunity โ vaccinated person can still shed virus in stools
- More expensive to produce and administer
- Requires trained personnel for injection
- More painful; risk of injection-site reactions
- Requires strict sterility
OPV (Sabin's Vaccine) โ Oral Polio Vaccine
| Feature | Detail |
|---|---|
| Type | Live attenuated; oral |
| Route | Oral (2 drops) |
| Contains | All 3 serotypes (Sabin 1, 2, 3); trivalent |
โ Merits of OPV
- Produces mucosal (secretory IgA) immunity โ protects the intestinal mucosa; eliminates virus from gut
- Herd immunity โ vaccine virus spreads to unvaccinated contacts via fecal-oral route
- Cheap and easy to administer โ no injection required
- Mimics natural infection โ longer lasting immunity
- Stimulates all arms of immunity (IgM, IgG, IgA, cell-mediated)
- Ideal for eradication campaigns (Pulse Polio Programme)
โ Demerits of OPV
- VAPP (Vaccine-Associated Paralytic Poliomyelitis) โ reversion to neurovirulence: ~1 per 2 million doses
- Contraindicated in immunocompromised individuals and household contacts
- VDPVs (Vaccine-Derived Polioviruses) โ can circulate and cause outbreaks in under-vaccinated populations
- Requires very strict cold chain (heat-sensitive)
- Intestinal interference โ can be blocked by other enteroviruses (reduced efficacy in tropical countries)
- Sabin type 3 > type 2 > type 1 in frequency of reversion
๐ Head-to-Head Comparison Table
| Feature | IPV (Salk) | OPV (Sabin) |
|---|---|---|
| Type | Killed | Live attenuated |
| Route | IM injection | Oral |
| Serum IgG/IgM | โ Yes | โ Yes |
| Secretory IgA (gut) | โ No | โ Yes |
| Herd immunity | โ No | โ Yes |
| VAPP risk | โ Zero | โ ~1/2 million |
| Immunocompromised | โ Safe | โ Contraindicated |
| Cost | Expensive | Cheap |
| Storage | Easier | Strict cold chain |
| Used in India (NIP) | Both (IPV + bOPV) | bOPV (types 1+3) |
Current India strategy: Switch from tOPV to bOPV (bivalent = types 1+3) + at least 1 dose of IPV (to cover type 2 after OPV type 2 withdrawal)
6. CLASSIFY HERPESVIRIDAE โ SUBFAMILIES, VIRUSES, AND ONE INFECTION EACH โญโญโญ
General Properties of Herpesviridae
- ds DNA virus (largest DNA viruses)
- Icosahedral capsid enclosed in a tegument, surrounded by lipid envelope
- Key feature: Latency โ after primary infection, virus remains latent in specific cell types and can reactivate
๐ Classification of Human Herpesviruses
FAMILY: HERPESVIRIDAE
โ
โโโ SUBFAMILY: ALPHAHERPESVIRINAE
โ โโโ Variable host range
โ โโโ Short replication cycle
โ โโโ Latency: SENSORY NEURONS (dorsal root ganglia / trigeminal ganglia)
โ โ
โ โโโ HHV-1 โ Herpes Simplex Virus 1 (HSV-1)
โ โโโ HHV-2 โ Herpes Simplex Virus 2 (HSV-2)
โ โโโ HHV-3 โ Varicella-Zoster Virus (VZV)
โ
โโโ SUBFAMILY: BETAHERPESVIRINAE
โ โโโ Restricted host range
โ โโโ LONG replication cycle (7โ14 days)
โ โโโ Latency: SECRETORY GLANDS, KIDNEYS, LYMPHOID TISSUE
โ โ
โ โโโ HHV-5 โ Cytomegalovirus (CMV)
โ โโโ HHV-6 โ Human Herpesvirus 6
โ โโโ HHV-7 โ Human Herpesvirus 7
โ
โโโ SUBFAMILY: GAMMAHERPESVIRINAE
โโโ Restricted host range
โโโ Variable replication cycle
โโโ Latency: B LYMPHOCYTES / LYMPHOID TISSUE
โ
โโโ HHV-4 โ Epstein-Barr Virus (EBV)
โโโ HHV-8 โ Kaposi Sarcoma-Associated Herpesvirus (KSHV)
Summary Table: All 8 Human Herpesviruses
| HHV # | Common Name | Subfamily | Latency Site | Key Infection |
|---|---|---|---|---|
| HHV-1 | HSV-1 | Alpha | Trigeminal ganglion | Herpes labialis (cold sores) / Encephalitis |
| HHV-2 | HSV-2 | Alpha | Sacral ganglia | Genital herpes / Neonatal herpes |
| HHV-3 | VZV | Alpha | Dorsal root ganglia | Chickenpox (1ยฐ) / Herpes zoster (reactivation) |
| HHV-4 | EBV | Gamma | B lymphocytes | Infectious mononucleosis / Burkitt lymphoma |
| HHV-5 | CMV | Beta | Mononuclear cells / glands | Congenital CMV / CMV retinitis (AIDS) |
| HHV-6 | HHV-6 | Beta | T lymphocytes | Roseola infantum (Exanthem subitum) |
| HHV-7 | HHV-7 | Beta | T lymphocytes | Roseola infantum (less common) |
| HHV-8 | KSHV | Gamma | B lymphocytes | Kaposi sarcoma (in AIDS patients) |
Key Distinguishing Features
- "Owl-eye inclusions" = CMV (intranuclear + intracytoplasmic inclusions)
- Cowdry type A inclusions = HSV, VZV, CMV
- EBV infects via CD21 (complement receptor CR2)
- CMV replication in cell culture takes 7โ14 days (slowest)
- HSV-1 is leading cause of sporadic viral encephalitis
- Acyclovir target = viral thymidine kinase (present in Alpha only)
7. HIV โ PATHOGENESIS, OPPORTUNISTIC INFECTIONS, LABORATORY DIAGNOSIS, TESTING STRATEGIES IN INDIA โญโญโญโญโญ
Etiology
- Family: Retroviridae | Genus: Lentivirus
- Types: HIV-1 (global pandemic) and HIV-2 (West Africa; less virulent)
- Genome: (+) ssRNA, diploid (2 copies); ~9.7 kb
- Key enzymes: Reverse Transcriptase, Integrase, Protease
๐ด PATHOGENESIS OF HIV
Step-by-Step Mechanism:
STEP 1: ENTRY
gp120 binds CD4 receptor on T-helper cells / macrophages / dendritic cells
โ
Co-receptor binding:
โข CCR5 (macrophage-tropic, R5 = early infection)
โข CXCR4 (T-tropic, X4 = late infection, more cytopathic)
โ
gp41 undergoes conformational change โ membrane fusion โ viral entry
STEP 2: REVERSE TRANSCRIPTION
(+) ssRNA โ (via RT) โ dsDNA (proviral DNA)
RT is error-prone โ ~1 mutation per replication cycle โ viral diversity
STEP 3: INTEGRATION
Integrase inserts proviral DNA randomly into host chromosome
โ Integrated provirus = LATENT RESERVOIR (cannot be eliminated)
STEP 4: ACTIVATION AND REPLICATION
NF-ฮบB activation (by cytokines, co-infections) โ viral transcription
RNA exported โ structural proteins made โ assembly at cell membrane
STEP 5: BUDDING AND MATURATION
Protease cleaves gag-pol polyprotein โ mature virion
~10 billion particles produced per day
STEP 6: CD4 T-CELL DEPLETION
โข Direct cytopathic effect
โข Syncytia formation (multinucleated giant cells)
โข CTL-mediated killing
โข Bystander apoptosis
โข Immune activation and exhaustion
โข Virus in GALT โ massive CD4+ memory T-cell depletion early
Disease Progression
| Stage | CD4 Count | Features |
|---|---|---|
| Acute retroviral syndrome | Transient drop | Mononucleosis-like: fever, rash, lymphadenopathy (2โ4 weeks) |
| Clinical latency | 500โ200/ฮผL | Asymptomatic; high viral replication in lymph nodes |
| Symptomatic HIV | 200โ500/ฮผL | PGL, minor OIs, constitutional symptoms |
| AIDS | <200/ฮผL | Major opportunistic infections + AIDS-defining illnesses |
โญ Two Important Opportunistic Infections in AIDS
| OI | Pathogen | CD4 Threshold | Feature |
|---|---|---|---|
| Pneumocystis pneumonia (PCP) | Pneumocystis jirovecii | <200/ฮผL | Dry cough, dyspnoea, bilateral interstitial infiltrates; treat with TMP-SMX |
| Toxoplasmosis | Toxoplasma gondii | <100/ฮผL | Ring-enhancing brain lesions; seizures, focal neurological deficits |
Other important OIs: CMV retinitis (<50/ฮผL), MAC (M. avium complex), Cryptococcal meningitis, Cerebral toxoplasmosis, Oesophageal candidiasis, Kaposi sarcoma (HHV-8)
๐ฌ LABORATORY DIAGNOSIS OF HIV
Screening Test
- ELISA (4th generation): Detects both HIV antibodies (anti-gp120, anti-p24) + p24 antigen simultaneously
- Sensitivity >99.5%; can detect infection as early as 2โ4 weeks post-exposure
- 4th gen ELISA reduces window period to ~18 days
Confirmatory Test
- Western Blot: Detects antibodies to specific HIV proteins (gp160, gp120, gp41, p24, p17)
- Positive: Bands at 2 of 3 (gp41, gp120/gp160, p24) โ WHO criteria
- Specificity >99.99%
Supplementary / Other Tests
| Test | Purpose |
|---|---|
| CD4+ T-cell count | Staging; indicates degree of immunosuppression; <200 = AIDS |
| Viral load (HIV RNA PCR) | Predicts disease progression; monitors treatment response |
| p24 antigen | Early marker; detectable before antibodies |
| HIV DNA PCR | Diagnosis in neonates (maternal antibodies interfere with ELISA) |
| Rapid antibody tests | Point-of-care; used in field settings |
๐ฎ๐ณ HIV TESTING IN INDIA โ THREE STRATEGIES (NACO)
| Strategy | When Used | Protocol |
|---|---|---|
| Strategy I | Blood/organ donation safety screening | Single test: If reactive on one ELISA/rapid test โ reject unit; if non-reactive โ accept |
| Strategy II | Surveillance in low-prevalence populations | Two tests: Test 1 (A1); if reactive โ Test 2 (A2 = different antigen); both reactive = positive |
| Strategy III | Diagnostic testing in symptomatic patients | Three tests: A1 reactive โ A2 โ A3 (three different kits); all 3 reactive = positive; discordant = indeterminate (repeat after 2 weeks) |
Key Rule:
- Strategy I = for blood banks (1 test)
- Strategy II = for surveillance (2 tests)
- Strategy III = for clinical diagnosis (3 tests using 3 different kits/antigens)
Organisms Causing STDs (Enumerate) โญ
| Category | Organism | Disease |
|---|---|---|
| Bacterial | Treponema pallidum | Syphilis |
| Neisseria gonorrhoeae | Gonorrhoea | |
| Chlamydia trachomatis | Chlamydia / LGV | |
| Haemophilus ducreyi | Chancroid | |
| Calymmatobacterium granulomatis | Granuloma inguinale | |
| Viral | HIV-1, HIV-2 | AIDS |
| HSV-2 (HSV-1) | Genital herpes | |
| HPV (types 6, 11, 16, 18) | Warts / Cervical Ca | |
| HBV | Hepatitis B | |
| HCV | Hepatitis C | |
| HTLV-1 | ATL | |
| Parasitic | Trichomonas vaginalis | Trichomoniasis |
| Ectoparasites | Phthirus pubis | Pubic lice |
8. FOUR ONCOGENIC VIRUSES โญโญโญ
Definition
Oncogenic (tumour) viruses carry or activate genes that cause uncontrolled cell proliferation โ malignancy.
4 Key Oncogenic Viruses
1. Human Papillomavirus (HPV)
- High-risk types: HPV-16, HPV-18
- Associated cancers: Cervical carcinoma, vulval, penile, oropharyngeal carcinoma
- Mechanism:
- E6 protein โ binds and degrades p53 โ no apoptosis; also activates TERT โ immortalization
- E7 protein โ binds and inactivates Rb โ releases E2F โ uncontrolled S-phase entry; also inactivates p21
- In cancers: HPV DNA integrates into host genome โ overexpression of E6/E7
2. Epstein-Barr Virus (EBV / HHV-4)
- Associated cancers: Burkitt lymphoma, Nasopharyngeal carcinoma, Hodgkin lymphoma, B-cell lymphomas in AIDS
- Mechanism:
- Uses CD21 receptor to infect B cells
- LMP-1 mimics constitutively active CD40 โ NF-ฮบB activation โ B-cell proliferation + anti-apoptosis
- EBNA-2 โ activates cyclin D, MYC
- Burkitt lymphoma: t(8;14) translocation โ MYC dysregulation
3. Hepatitis B Virus (HBV)
- Associated cancer: Hepatocellular carcinoma (HCC) โ 70โ85% of HCC worldwide
- Mechanism:
- Chronic inflammation โ hepatocyte death โ regeneration โ DNA damage accumulation
- HBx protein โ transcriptional transactivator โ NF-ฮบB โ anti-apoptosis
- Integration of HBV DNA near proto-oncogenes
- Cirrhosis โ major predisposing factor
4. Human T-Cell Lymphotropic Virus Type 1 (HTLV-1)
- Associated cancer: Adult T-Cell Leukaemia/Lymphoma (ATLL)
- Mechanism:
- Tax protein โ activates NF-ฮบB + IL-2/IL-2R pathway โ T-cell proliferation โ genomic instability โ ATLL
- No viral oncogene; transformation by Tax-mediated host gene deregulation
- Latency period: 40โ60 years (longest of any oncovirus)
- Monoclonal integration of provirus in tumour cells
Quick Summary Table
| Virus | Cancer | Key Oncoprotein | Mechanism |
|---|---|---|---|
| HPV-16/18 | Cervical carcinoma | E6, E7 | Degrade p53, inactivate Rb |
| EBV | Burkitt lymphoma, NPC | LMP-1, EBNA-2 | NF-ฮบB, MYC translocation |
| HBV | Hepatocellular carcinoma | HBx protein | Chronic inflammation + transactivation |
| HTLV-1 | Adult T-cell leukaemia | Tax protein | NF-ฮบB, IL-2 loop, genomic instability |
9. EPSTEIN-BARR VIRUS (EBV) โญโญโญ
Classification
- Family: Herpesviridae | Subfamily: Gammaherpesvirinae
- HHV-4 | Lymphocryptovirus
- ds DNA virus; infects B lymphocytes via CD21 (complement receptor CR2)
Primary Infection โ Infectious Mononucleosis (IM)
- Synonyms: "Kissing disease", Glandular fever
- Incubation period: 30โ50 days
- Classic triad: Fever + Tonsillopharyngitis + Lymphadenopathy (posterior cervical)
- Additional features: Splenomegaly (50%), hepatomegaly, macular rash
- Rash with ampicillin/amoxicillin (maculopapular rash in 95% โ classic marker)
Laboratory Diagnosis of EBV / IM
| Test | Details |
|---|---|
| Paul-Bunnell test | Detects heterophile antibodies (agglutinate sheep RBCs) |
| Monospot test (rapid) | Horse RBC agglutination; 90% sensitivity by week 3 |
| Peripheral blood film | Atypical lymphocytes (Downey cells) >10% โ pathognomonic |
| FBC | Leukocytosis with lymphocytosis |
| LFTs | Elevated ALT/AST (transient hepatitis) |
| EBV-specific antibodies | VCA IgM (acute), VCA IgG (past), EBNA (convalescence) |
EBV Serology Interpretation
| Antibody | Acute IM | Past Infection | Vaccinated (No EBV vaccine exists) |
|---|---|---|---|
| VCA IgM | โ Present | โ Absent | โ |
| VCA IgG | โ Present | โ Present | โ |
| EA (Early antigen) | โ Present | โ Absent | โ |
| EBNA | โ Absent | โ Present | โ |
Key: EBNA appears only after 3โ6 months (convalescence); its absence in acute disease helps confirm recent primary infection.
Oncogenic Potential of EBV
| Tumor | Population | Mechanism |
|---|---|---|
| Burkitt lymphoma | African children | t(8;14) โ MYC overexpression |
| Nasopharyngeal carcinoma (NPC) | Southern Chinese, Inuit | LMP-1, EBERs |
| Hodgkin lymphoma (mixed cellularity) | General | EBV in Reed-Sternberg cells |
| EBV+ B-cell lymphomas | Immunosuppressed (AIDS, transplant) | Polyclonal โ monoclonal B-cell expansion |
| NK/T-cell lymphoma | Asian populations | EBV in NK cells |
SECTION B โ LONG ANSWER QUESTIONS (LAQ)
LAQ 1. HIV โ WINDOW PERIOD, LAB DIAGNOSIS, ETIOLOGY, PATHOGENESIS, DIAGRAM โญโญโญโญโญ
(Full detailed answer covered in SAQ 7 above โ integrate here for LAQ)
Window Period โ Definition
The window period is the interval between initial HIV infection and the time when detectable antibodies appear in the blood. During this period, the person is highly infectious but serological tests (antibody-based) are negative.
| Test | Window Period Duration |
|---|---|
| HIV antibody ELISA (1st/2nd gen) | 6โ12 weeks |
| 3rd gen ELISA (IgM + IgG) | 3โ4 weeks |
| 4th gen ELISA (Ag + Ab combined) | ~18 days |
| HIV RNA PCR | ~10โ12 days |
Only p24 antigen and HIV RNA PCR can diagnose infection during the window period.
(See complete pathogenesis, diagram, lab diagnosis, and strategies in SAQ 7 above)
LAQ 2. HEPATITIS โ CLASSIFY, LAB DIAGNOSIS, PATHOGENESIS OF HBV, MORPHOLOGY, SEROLOGICAL MARKERS, VIRUSES + TRANSMISSION, PROPHYLAXIS โญโญโญโญโญ
Classification of Hepatitis Viruses
| Virus | Family | Genome | Transmission | Chronicity | Vaccine |
|---|---|---|---|---|---|
| HAV | Picornaviridae | (+) ssRNA | Fecal-oral | No | Yes (killed) |
| HBV | Hepadnaviridae | Partially ds DNA | Parenteral, sexual, vertical | Yes (~10%) | Yes (recombinant) |
| HCV | Flaviviridae | (+) ssRNA | Parenteral (mainly) | Yes (~85%) | No |
| HDV | Deltavirus | (-) ssRNA (defective) | Parenteral (needs HBV) | Yes (co-inf vs. super-inf) | HBV vaccine protects |
| HEV | Hepeviridae | (+) ssRNA | Fecal-oral (waterborne) | No (except pregnant) | Yes (HEV 239, China) |
| HGV/GBV-C | Flaviviridae | (+) ssRNA | Parenteral | Unclear | No |
Morphology of HBV (Dane Particle)
HBV DANE PARTICLE (42 nm)
โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ
โ โ
โ โ โ โ HBsAg (surface) โ 22 nm โ
โ โโโโโ spherical + tubular particles โ
โ โ
โ โโโโโโโโโ Lipid envelope (HBsAg) โโโโโโโ
โ โ โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ โโ
โ โ โ Icosahedral capsid (HBcAg) โ โโ
โ โ โ โโโโโโโโโโโโโโโโโโโโโโโโโโโโ โโ
โ โ โ โ Partially ds DNA โโ โโ
โ โ โ โ HBeAg (soluble, secreted)โโ โโ
โ โ โ โ DNA polymerase (RT) โโ โโ
โ โ โ โโโโโโโโโโโโโโโโโโโโโโโโโโโโ โโ
โ โ โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ โโ
โ โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ
โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ
Forms in serum:
1. 42 nm DANE PARTICLE (complete infectious virion)
2. 22 nm spherical particles (excess HBsAg โ non-infectious)
3. 22 nm tubular particles (excess HBsAg โ non-infectious)
Pathogenesis of HBV
HBV ENTRY โ Hepatocyte via NTCP (Na+/taurocholate cotransporting polypeptide)
โ
Partial ds DNA โ Complete dsDNA (cccDNA) in nucleus
โ
cccDNA acts as template โ pregenomic RNA + mRNAs
โ
Core particles assemble โ RT converts pgRNA โ partially ds DNA
โ
Envelopment with HBsAg โ secretion of Dane particles
IMMUNE RESPONSE:
โข Hepatocyte damage is IMMUNE MEDIATED (CTL kill infected hepatocytes)
โข HBV itself is NOT directly cytopathic
โข Strong CTL response โ acute hepatitis + viral clearance (acute self-limiting)
โข Weak/absent CTL response โ failure to clear โ CHRONIC INFECTION
CHRONIC HBV:
Immune tolerance โ immune activation โ immune clearance โ low-replication phase
โ Chronic inflammation โ cirrhosis โ HCC (hepatocellular carcinoma)
Prophylaxis of Hepatitis
| Virus | Prophylaxis |
|---|---|
| HAV | Inactivated vaccine (2 doses, 6 months apart) + IVIG for post-exposure |
| HBV | Recombinant vaccine (0, 1, 6 months) + HBIG for post-exposure; neonatal immunization |
| HCV | No vaccine; avoid blood exposure; DAAs for treatment |
| HDV | HBV vaccination prevents HDV (HDV needs HBV) |
| HEV | Safe water; HEV 239 vaccine (licensed in China) |
(Complete serological markers and lab diagnosis covered in SAQ 1)
LAQ 3. HERPES VIRUS โ CLASSIFICATION, VZV (VARICELLA ZOSTER), HERPES SIMPLEX โญโญโญ
(Classification covered in SAQ 6)
Varicella-Zoster Virus (VZV / HHV-3)
Primary Infection: VARICELLA (Chickenpox)
- Transmission: Respiratory droplets + direct contact; highly contagious
- Incubation: 14โ21 days
- Clinical features:
- Fever, malaise โ centripetal rash (starts on trunk, spreads to face + limbs)
- Rash: macule โ papule โ vesicle โ pustule โ crust (all stages simultaneously present = "starry night" appearance)
- Pruritic lesions
- Complications: secondary bacterial infection (S. aureus), pneumonia (adults), encephalitis, Reye's syndrome (with aspirin)
Lab Diagnosis of Varicella
| Test | Finding |
|---|---|
| Tzanck smear (from vesicle base) | Multinucleated giant cells (Tzanck cells) โ also positive in HSV |
| Electron microscopy | Herpesvirus particles |
| DFA (Direct Fluorescent Antibody) | VZV antigens in vesicle cells |
| PCR | Most sensitive; detects VZV DNA in vesicle fluid/CSF |
| Serology (ELISA) | VZV IgM (acute) / IgG (past or vaccination) |
| Viral culture | Slow; VZV grows in human diploid cells |
Reactivation: HERPES ZOSTER (Shingles)
- Latent in dorsal root ganglia (or cranial nerve ganglia)
- Reactivation triggered by: stress, immunosuppression, aging
- Dermatomal distribution (unilateral, does not cross midline)
- Prodrome: pain + paraesthesia โ vesicular rash in dermatome
- Complications: Post-herpetic neuralgia (most common), Ramsay Hunt syndrome (geniculate ganglion โ facial palsy + ear vesicles), Zoster ophthalmicus (V1)
Herpes Simplex Virus (HSV-1 and HSV-2)
Lesions Caused
| Type | Location | Primary Lesion | Reactivation |
|---|---|---|---|
| HSV-1 | Orolabial | Gingivostomatitis (vesicles in mouth/gums) | Herpes labialis ("cold sores") |
| HSV-1 | Brain | Encephalitis (temporal lobe) | Recurrent encephalitis |
| HSV-1 | Eye | Keratoconjunctivitis, corneal ulcer | Recurrent keratitis โ blindness |
| HSV-2 | Genital | Genital herpes (vesicles + ulcers) | Recurrent genital lesions |
| HSV-2 | Neonate | Neonatal herpes (disseminated) | โ |
| Both | Finger | Herpetic whitlow (vesicles on finger) | Recurrence |
Lab Diagnosis of HSV
| Test | Finding |
|---|---|
| Tzanck smear | Multinucleated giant cells (cannot distinguish HSV from VZV) |
| Viral culture (gold standard) | CPE in 1โ3 days: rounding, ballooning of cells + syncytia |
| DFA (Direct Fluorescent Antibody) | Rapid, type-specific (HSV-1 vs. HSV-2) |
| PCR (CSF) | Gold standard for HSV encephalitis |
| Serology | IgM (primary), IgG (past); not useful for recurrent |
| Antigen detection ELISA | Rapid screening |
Treatment
- Acyclovir (first-line): Phosphorylated by viral thymidine kinase โ inhibits viral DNA polymerase
- Valacyclovir, Famciclovir (oral bioavailability better)
- Prophylactic acyclovir for frequent recurrences
LAQ 4. POLIO VIRUSES โ PATHOGENICITY, IMMUNOPROPHYLAXIS, LAB DIAGNOSIS โญโญโญ
Classification
- Family: Picornaviridae | Genus: Enterovirus
- Types: Poliovirus serotypes 1, 2, 3 (type 1 = Mahoney = most paralytogenic)
- (+) ssRNA, non-enveloped, icosahedral
- Receptor: CD155 (PVR = Poliovirus receptor)
Pathogenicity of Poliovirus
ORAL ROUTE โ Alimentary tract
โ
Replication in oropharynx + intestinal mucosa (Peyer's patches)
โ
Regional lymph nodes โ Viraemia (minor)
โ
Systemic spread โ Blood (major viraemia)
โ
CNS invasion via:
(a) Viraemic spread across blood-brain barrier
(b) Retrograde axonal transport via peripheral nerves
CLINICAL SPECTRUM:
>90% โ Subclinical / Asymptomatic infection
~5% โ Abortive poliomyelitis (fever, sore throat, GI symptoms โ no CNS)
1โ2% โ Non-paralytic/Aseptic meningitis (CSF pleocytosis)
0.1โ2% โ PARALYTIC POLIOMYELITIS
Paralytic Poliomyelitis
- Virus destroys anterior horn cells (lower motor neurons) of spinal cord
- Results in asymmetric, flaccid paralysis, NO sensory loss
- Maximal paralysis in 48 hours of onset
- Types:
- Spinal (most common): limb paralysis
- Bulbar (most severe): cranial nerve + respiratory centre involvement; 25โ75% mortality
- Bulbospinal: combined
- Post-polio syndrome: New muscle weakness 30โ40 years after acute infection (not virus but exhaustion of surviving neurons)
Immunoprophylaxis (covered in detail in SAQ 5)
Laboratory Diagnosis of Polio
| Specimen | Test |
|---|---|
| Stool (best specimen) | Virus isolation in cell culture (Vero, RD cells); confirm with neutralization |
| CSF | Virus isolation + RT-PCR |
| Throat swab | Virus isolation (early in disease) |
| Blood | Serology (neutralizing antibodies rise 4ร in acute vs. convalescent) |
| RT-PCR | Rapid confirmation; differentiates wild vs. vaccine-derived poliovirus |
| ITD (Intratypic differentiation) | Distinguish wild poliovirus from vaccine-derived (VDPV) |
WHO requirement: Two stool samples, 24โ48 hours apart, within 14 days of onset of paralysis, stored at -20ยฐC
LAQ 5. INFLUENZA VIRUSES โ MORPHOLOGY, ANTIGENIC VARIATIONS, PATHOGENESIS, CLASSIFICATION, ANTIGENIC SHIFT MECHANISM โญโญโญโญ
Classification
FAMILY: ORTHOMYXOVIRIDAE
โ
โโโ Genus: Alphainfluenzavirus โ Influenza A (humans, animals, birds)
โโโ Genus: Betainfluenzavirus โ Influenza B (humans only)
โโโ Genus: Gammainfluenzavirus โ Influenza C (humans; mild/asymptomatic)
โโโ Genus: Deltainfluenzavirus โ Influenza D (cattle; not human pathogen)
- Influenza A = most important clinically (pandemics + epidemics)
- Influenza B = epidemics only (no pandemics)
- Influenza C = sporadic cases only
Morphology of Influenza Virus โญโญ
INFLUENZA A VIRUS โ DETAILED MORPHOLOGY
โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ
SIZE: Roughly spherical, 80โ120 nm; some filamentous forms
SURFACE PROJECTIONS:
HA (Hemagglutinin) โ spike-shaped trimer
โข 18 subtypes (H1โH18)
โข Binds sialic acid on host respiratory epithelium
โข Major neutralizing antibody target
โข Cleaved by host proteases โ HA1 + HA2
NA (Neuraminidase) โ mushroom-shaped tetramer
โข 11 subtypes (N1โN11)
โข Cleaves sialic acid โ releases budding virions
โข Target of oseltamivir (Tamiflu), zanamivir (Relenza)
M2 (ion channel)
โข Proton pump; acidifies virion interior
โข Essential for uncoating
โข Target of amantadine, rimantadine
ENVELOPE:
Lipid bilayer (derived from host cell)
MATRIX (M1):
Lines inside of envelope; structural scaffolding
Type-specific antigen (distinguishes A/B/C)
NUCLEOCAPSID (RNP complex):
โข Helical symmetry
โข 8 SEGMENTS of (โ) ssRNA (influenza A and B; 7 segments in C)
โข Each segment coated with nucleoprotein (NP)
โข NP is type-specific antigen
โข RNA polymerase complex (PB1, PB2, PA) associated with each segment
โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ
RNA SEGMENT CODING TABLE:
Segment 1 โ PB2 (polymerase)
Segment 2 โ PB1 (polymerase + PB1-F2 pro-apoptotic)
Segment 3 โ PA (polymerase)
Segment 4 โ HA (hemagglutinin)
Segment 5 โ NP (nucleoprotein)
Segment 6 โ NA (neuraminidase)
Segment 7 โ M1 + M2 (matrix proteins)
Segment 8 โ NS1 + NS2/NEP (non-structural)
Pathogenesis of Influenza
INHALATION of droplet nuclei
โ
HA binds ฮฑ-2,6-linked sialic acid (upper airways โ human strains)
โ [ฮฑ-2,3-linked = lower respiratory / avian receptor]
Receptor-mediated endocytosis โ M2 acidifies endosome โ uncoating
โ
(โ) RNA segments โ nucleus โ mRNA synthesis (PB1, PB2, PA)
โ
Viral proteins made โ new virion assembly โ budding
NA cleaves sialic acid โ release of progeny virions
โ
INFECTION of ciliated epithelial cells โ ciliary dysfunction โ impaired mucociliary clearance
โ
Necrosis of epithelium โ inflammatory cytokine storm (IL-6, TNF-ฮฑ, IFN)
โ
CLINICAL: Fever (3โ4 days), myalgia, headache, dry cough (sudden onset)
โ
Secondary bacterial pneumonia (S. aureus, S. pneumoniae, H. influenzae)
โ
Complications: Primary influenza pneumonia, ARDS, myocarditis, encephalitis
Antigenic Drift and Shift (Full Details in SAQ 4)
โญ Antigenic Shift โ Mechanism in Detail
MECHANISM OF ANTIGENIC SHIFT
SCENARIO: Human influenza A (H3N2) + Avian influenza A (H5N1)
infect same cell (Pig = "mixing vessel" โ has both human ฮฑ-2,6
AND avian ฮฑ-2,3 sialic acid receptors)
Human H3N2 Avian H5N1
(8 RNA segments) (8 RNA segments)
โ โ
Both infect same CELL (e.g., pig respiratory epithelium)
โ
RNA segments from BOTH viruses in same cell
โ
RANDOM REASSORTMENT of 8 segments
โ
NEW HYBRID VIRUS e.g., H5N2 or H3N1
(NEW HA and/or NA combination)
โ
Population has NO pre-existing immunity to new HA/NA
โ
PANDEMIC potential
KEY POINTS:
โข Only Influenza A โ has animal reservoir (birds, pigs, horses, seals)
โข Reassortment produces novel HA/NA subtypes
โข New pandemic strain: entirely different surface antigens
โข Examples: 1957 (H2N2), 1968 (H3N2), 2009 (H1N1 pdm)
โข H5N1 (avian flu) = currently monitored for pandemic potential
Significance of Antigenic Shift
- Creates novel HA/NA combinations never seen before in human population
- No pre-existing herd immunity โ rapid worldwide spread (pandemic)
- Existing vaccines become completely ineffective โ new vaccine must be developed
- Can cause high mortality โ as seen in 1918 Spanish flu (50โ100 million deaths)
- Pandemic preparedness must be maintained; WHO Global Influenza Surveillance and Response System (GISRS) monitors this
๐ MASTER HIGH-YIELD TABLE FOR MUHS EXAMS
| Topic | Single Most Important Point |
|---|---|
| HBV window period | Only IgM Anti-HBc is positive |
| HBV vaccination | Anti-HBs only (no Anti-HBc) = vaccinated |
| HBV chronic carrier | HBsAg positive >6 months |
| HBV infectivity marker | HBeAg = active replication |
| Rabies โ Category III | Vaccine + RIG |
| Rabies Essen regimen | Days 0, 3, 7, 14, 28 |
| Rabies Zagreb regimen | Day 0 (ร2) + Day 7 + Day 21 (2-1-1) |
| Non-neural vaccine type | HDCV, PCECV, PVRV = cell culture vaccines |
| NTV replaced because | Neuroparalytic accidents (demyelination) |
| Influenza antigenic drift | Point mutations; A, B, C; epidemics |
| Influenza antigenic shift | Reassortment; A only; pandemics |
| 1918 pandemic subtype | H1N1 (Spanish flu) |
| HIV co-receptor (early) | CCR5 (R5 phenotype) |
| HIV co-receptor (late) | CXCR4 (X4 phenotype) |
| HIV most abundant Ag | p24 (capsid protein) |
| HIV CD4 count for AIDS | <200/ฮผL |
| HIV India Strategy III | 3 tests โ for clinical diagnosis |
| HIV Strategy I | 1 test โ blood bank screening |
| OPV advantage | Secretory IgA + herd immunity |
| OPV contraindicated | Immunocompromised patients |
| IPV advantage | No VAPP; safe in immunocompromised |
| Herpes alpha latency | Neurons (DRG) |
| Herpes beta latency | Glands/kidneys |
| Herpes gamma latency | B lymphocytes |
| CMV inclusion | Owl-eye (intranuclear + intracytoplasmic) |
| EBV receptor | CD21 |
| EBV Burkitt lymphoma | t(8;14) โ MYC |
| EBV acute marker | VCA IgM; EBNA absent in acute |
| HPV E6 target | p53 degradation |
| HPV E7 target | Rb inactivation |
| HTLV-1 oncoprotein | Tax; causes ATLL |
| HBV โ HCC mechanism | Chronic inflammation + HBx protein |
| Tzanck smear positive | HSV, VZV (multinucleated giant cells) |
| VZV latency site | Dorsal root ganglia |
| Ramsay Hunt syndrome | VZV reactivation in geniculate ganglion |
| HSV encephalitis diagnosis | CSF PCR (gold standard) |
| Polio paralysis type | Asymmetric flaccid paralysis; NO sensory loss |
| Poliovirus gold std specimen | Stool (2 samples, 24โ48h apart, within 14 days) |
| Paul-Bunnell test | Heterophile antibodies โ EBV/IM |
| Atypical lymphocytes | Peripheral smear finding in IM (EBV) |
๐ Sources: Jawetz, Melnick & Adelberg's Medical Microbiology 28th Ed | Sherris & Ryan's Medical Microbiology 8th Ed | Murray's Medical Microbiology 9th Ed | Robbins & Kumar Basic Pathology | Park's Preventive & Social Medicine
This is a shared conversation. Sign in to Orris to start your own chat.