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Answer me very short answers

Answer me from 20 to 25 for viva

Here are short viva answers for Q20–25:

20) Classification of Streptococcus

Lancefield grouping (A–V) based on C-carbohydrate antigen
Hemolysis: α (partial/green), β (complete/clear), γ (none)
Key species: S. pyogenes (Group A), S. agalactiae (Group B), S. pneumoniae (α-hemolytic, no Lancefield group)

21) Hanta virus

Family: Bunyaviridae; enveloped, ssRNA virus
Reservoir: rodents (transmitted via urine/feces/saliva aerosols)
Causes HFRS (hemorrhagic fever with renal syndrome) & HPS (hantavirus pulmonary syndrome)
No human-to-human transmission (except Andes virus)

22) Agents of Bioterrorism (CDC Classification)

Category A (highest risk): Anthrax, Smallpox, Plague, Botulism, Tularemia, Viral hemorrhagic fevers
Category B: Brucellosis, Q fever, Ricin, Salmonella
Category C: Emerging pathogens (Nipah, Hanta)

23) ESKAPE Pathogens

Multidrug-resistant organisms:

E - Enterococcus faecium
S - Staphylococcus aureus (MRSA)
K - Klebsiella pneumoniae
A - Acinetobacter baumannii
P - Pseudomonas aeruginosa
E - Enterobacter spp.

24) Antigenic Shift vs Antigenic Drift

	Antigenic Drift	Antigenic Shift
Mechanism	Point mutations	Reassortment of gene segments
Change	Minor	Major
Result	Epidemics	Pandemics
Virus	Influenza A & B	Influenza A only

25) Organisms with Oncogenic Potential

Organism	Cancer
HPV (16,18)	Cervical, oropharyngeal ca
EBV	Burkitt's lymphoma, Nasopharyngeal ca
HBV/HCV	Hepatocellular carcinoma
HTLV-1	Adult T-cell leukemia
HHV-8	Kaposi's sarcoma
H. pylori	Gastric adenocarcinoma, MALT lymphoma
S. haematobium	Bladder carcinoma
Clonorchis sinensis	Cholangiocarcinoma

Fungi with oncogenic potential

Fungi with oncogenic potential are rare but include:

1) Aspergillus flavus / A. parasiticus

Produce Aflatoxin B1 (most potent natural carcinogen)
Causes hepatocellular carcinoma (HCC)
Acts by mutating p53 tumor suppressor gene (codon 249)

2) Fusarium spp. / Penicillium spp.

Produce mycotoxins (fumonisin, ochratoxin)
Fumonisins linked to esophageal carcinoma
Ochratoxin A linked to renal carcinoma

3) Candida spp. (indirect/controversial)

Chronic mucocutaneous candidiasis may predispose to oral squamous cell carcinoma
Nitrosamines produced by Candida are carcinogenic

Key point for viva: The main fungus asked in exams is Aspergillus (Aflatoxin B1) → Liver cancer (HCC). The mechanism is aflatoxin B1 → epoxide metabolite → binds DNA → G to T transversion at p53 codon 249.

Explain 24th answer

Antigenic Shift vs Antigenic Drift

Antigenic DRIFT 🌊

What happens: Small, gradual changes in surface antigens due to random point mutations in genes coding for Haemagglutinin (H) or Neuraminidase (N).

Example:

H3N2 → slight mutation → H3N2 (slightly different)
The virus looks "similar but changed"

Result:

Partial immunity in population
Causes seasonal epidemics every year
Affects Influenza A & B

Analogy: A person slowly changing their hairstyle - still recognizable but slightly different.

Antigenic SHIFT 💥

What happens: Sudden, major change when two different influenza viruses infect the same host cell and their gene segments reassort (mix and match).

Example:

Human H1N1 + Avian H5N1 → new H5N1 (with human genes)
2009 Swine flu: H1N1 with pig + bird + human segments

Result:

Population has zero immunity
Causes pandemics (worldwide spread)
Affects Influenza A only (because it infects multiple species)

Analogy: Two people swapping organs - completely new entity.

Key Differences Table

Feature	Drift	Shift
Mechanism	Point mutation	Gene reassortment
Change	Minor	Major
Frequency	Continuous	Occasional
Immunity	Partial	None
Outcome	Epidemic	Pandemic
Virus	A & B	A only
Intermediate host	Not needed	Needed (pig)

Viva tip: Reassortment needs a mixing vessel - the pig is classic because it has receptors for both human and avian influenza viruses.

Can you sinplify

Antigenic Drift

Small changes in H or N antigen
Caused by point mutations
Happens slowly, continuously
Causes epidemics
Influenza A & B

Antigenic Shift

Big sudden change in H or N antigen
Caused by gene reassortment (two viruses mix genes)
Happens suddenly
Causes pandemics
Influenza A only

Simple way to remember:

Drift = Small change = Epidemic Shift = Big change = Pandemic

Mixing vessel = Pig (has receptors for both human & bird flu, so genes can mix inside it)

What are a and b virus

Influenza A vs B

Influenza A

Infects humans, birds, pigs, horses
Has subtypes (H1N1, H3N2, H5N1 etc.)
Causes epidemics + pandemics
More severe
Can do both drift & shift

Influenza B

Infects humans only
No subtypes (only lineages - Victoria & Yamagata)
Causes epidemics only
Less severe
Only drift (no shift)

Simple Memory:

A = Animals + humans = more dangerous B = humans only = less dangerous

Abswer 20 better

Classification of Streptococcus

Two ways to classify:

1) By HEMOLYSIS (on blood agar)

Type	What happens	Example
α (alpha)	Partial hemolysis - green zone	S. pneumoniae, Viridans
β (beta)	Complete hemolysis - clear zone	S. pyogenes, S. agalactiae
γ (gamma)	No hemolysis	Enterococcus

2) By LANCEFIELD GROUPING (A–V)

Based on C-carbohydrate antigen on cell wall

Group	Species	Disease
A	S. pyogenes	Strep throat, Rheumatic fever, PSGN
B	S. agalactiae	Neonatal meningitis
C, G	S. dysgalactiae	Pharyngitis
D	Enterococcus	UTI, Endocarditis

Special: S. pneumoniae

α-hemolytic
No Lancefield group
Classified by Quellung reaction (capsular swelling)
Causes: Pneumonia, Meningitis, Otitis media

Memory tip:

Group A = Throat Group B = Baby (neonates) Group D = Dirty urine (UTI)

Answer 13 to 19

Q13–19 Short Answers

13) Gas Gangrene

Caused by Clostridium perfringens (most common)
Toxin: Alpha toxin (lecithinase/phospholipase C)
Spreads through muscle, produces gas (CO2 + H2)
Features: Crepitus, foul smell, necrosis
Treatment: Surgical debridement + Penicillin + Hyperbaric O2

14) Mycetoma Foot

Chronic granulomatous infection of foot/leg
Two types:
- Eumycetoma - fungal (Madurella mycetomatis)
- Actinomycetoma - bacterial (Nocardia, Actinomadura)
Features: Swelling, sinuses discharging grains, painless
Grains color helps identify causative agent

15) Nipah Virus

Family: Paramyxoviridae
Reservoir: Fruit bats (Pteropus)
Transmission: Bats → pigs → humans / date palm sap
Causes: Encephalitis + respiratory illness
High mortality (40-75%)
No approved vaccine; Treatment: Ribavirin (supportive)

16) Zygomycosis

Caused by Rhizopus, Mucor, Absidia
Affects immunocompromised (diabetics - DKA esp.)
Types:
- Rhinocerebral (most common)
- Pulmonary, Cutaneous, GI
Hyphae: Broad, aseptate, right angle branching
Treatment: Amphotericin B + surgery

17) Free Living Amoebae

Organism	Disease
Naegleria fowleri	PAM (Primary Amoebic Meningoencephalitis) - fatal
Acanthamoeba	GAE (Granulomatous Encephalitis) + Keratitis
Balamuthia mandrillaris	GAE

Naegleria: enters via cribriform plate while swimming
Treatment: Amphotericin B (mostly fatal despite treatment)

18) Lymphogranuloma Venereum (LGV)

Caused by Chlamydia trachomatis (L1, L2, L3 serovars)
STI affecting lymphatics
Stages:
1. Small painless ulcer (heals fast)
2. Painful inguinal lymphadenopathy (buboes)
3. Fibrosis, elephantiasis, rectal stricture
Diagnosis: Frei test (skin test), CFT
Treatment: Doxycycline 3 weeks

19) Human Papilloma Virus (HPV)

dsDNA virus, non-enveloped
Oncogenic types: 16, 18 (high risk) → Cervical cancer
Low risk types: 6, 11 → Genital warts (condyloma acuminata)
Mechanism: E6 inhibits p53, E7 inhibits Rb
Vaccine: Gardasil (4-valent), Cervarix (2-valent), Gardasil-9
Pap smear for screening

Memory for HPV: 16 & 18 = Cancer | 6 & 11 = Warts

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Answer 20 to 25

Q20–25 Short Answers

20) Heterophile Antigens

Antigens shared between unrelated species
Example: Forssman antigen - found in guinea pig kidney, sheep RBC, but NOT in rabbit/rat
Paul-Bunnell test - heterophile antibodies in Infectious Mononucleosis (EBV) agglutinate sheep RBCs
Weil-Felix reaction: Proteus antigens cross-react with Rickettsia antibodies

21) Endotoxin vs Exotoxin

Feature	Endotoxin	Exotoxin
Source	Gram negative	Gram positive & negative
Chemical nature	LPS (lipopolysaccharide)	Protein
Heat stability	Stable	Labile
Toxoid formation	No	Yes
Potency	Low	High
Fever	Yes	Yes
Example	E. coli, Salmonella	Tetanus, Cholera, Diphtheria

22) Bacterial Capsule

Made of polysaccharide (except B. anthracis - polyglutamic acid)
Functions:
- Anti-phagocytic (virulence factor)
- Protects from complement
Detection: Quellung reaction, India ink stain, Anthony's stain
Examples: S. pneumoniae, K. pneumoniae, H. influenzae, N. meningitidis

23) Lyme Disease

Caused by Borrelia burgdorferi
Vector: Ixodes tick (deer tick)
Stages:
1. Early localized: Erythema migrans (bull's eye rash)
2. Early disseminated: Facial palsy, carditis
3. Late: Arthritis, encephalopathy
Diagnosis: ELISA + Western blot
Treatment: Doxycycline

24) 6 Viruses Causing Diarrhea in Children

Virus	Key Point
Rotavirus	Most common, winter, wheel-shaped
Norovirus	Cruise ship outbreaks
Astrovirus	Star-shaped, young children
Adenovirus (40,41)	Enteric adenovirus
Calicivirus	Small round structured virus
Coronavirus	Rare, neonates

Rotavirus = #1 cause of viral diarrhea in children under 5

25) Stool Concentration Techniques

Used to concentrate parasites (cysts, eggs, larvae) in stool

Two types:

A) Flotation (Float up):

Zinc sulfate flotation (most common)
Parasites float to top due to high specific gravity of ZnSO4
Good for cysts and eggs

B) Sedimentation (Sink down):

Formol-ether (Ritchie's) method - most widely used
Parasites settle at bottom
Good for all parasites including operculated eggs

Sedimentation > Flotation in sensitivity

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