Plague as a Bioweapon — MCQs

10 questions

You are the MO in charge in a PHC and there has been a plague epidemic in your area. Which of the following measures is the LEAST appropriate for controlling epidemic?

Plague is transmitted by the bite of -

Which of the following is a Category C bioterrorism agent?

A girl from Shimla presented to OPD with fever, hypotension, malaise and axillary and inguinal lymphadenopathy. Culture in glucose broth shows stalactite growth. Most likely causative organism is?

True statement about plague is -

A farmer presents to the emergency department with painful inguinal lymphadenopathy and a history of fever and flu-like symptoms. Clinical examination reveals an ulcer on the leg. Which of the following stains should be used to detect suspected bipolar-stained organisms?

Which of the following bacteria is classified as facultative anaerobe?

A 20-year-old male patient presents to the STD clinic with a genital ulcer. The Gram stain of the smear from the ulcer shows gram-negative coccobacilli. What is the most appropriate media for culture?

The ELISA test for virulence antigen is used to diagnose which type of Escherichia coli?

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All of the following statements about Glanders are false except?

Plague as a Bioweapon Indian Medical PG Practice Questions and MCQs

Question 1: You are the MO in charge in a PHC and there has been a plague epidemic in your area. Which of the following measures is the LEAST appropriate for controlling epidemic?

A. Isolation of contacts
B. Rapid treatment of cases with streptomycin
C. Vaccination of all susceptible individuals (Correct Answer)
D. Early diagnosis and notification

Explanation: ***Vaccination of all susceptible individuals*** - While beneficial for prevention, mass vaccination during an ongoing plague epidemic is **logistically challenging** and **too slow** to effectively control the immediate spread. - The incubation period of plague is short, and an effective vaccine often requires multiple doses and time to induce immunity, making it less suitable for **rapid epidemic containment**. *Isolation of contacts* - **Isolating contacts** helps prevent the disease from spreading further by separating potentially infected individuals who may be asymptomatic or in the incubation period. - This measure is crucial in **breaking chains of transmission** and limiting the epidemic's reach. *Rapid treatment of cases with streptomycin* - **Early and rapid treatment** of confirmed plague cases with effective antibiotics like **streptomycin** is a cornerstone of epidemic control, significantly reducing mortality and infectivity. - This intervention quickly minimizes the source of infection, preventing further transmission to others. *Early diagnosis and notification* - **Early diagnosis** allows for prompt initiation of treatment and isolation, while **notification** triggers public health responses such as contact tracing and surveillance. - These steps are essential for understanding the scope of the epidemic and implementing appropriate control measures efficiently.

Question 2: Plague is transmitted by the bite of -

A. Rat flea (Correct Answer)
B. Tse-Tse fly
C. Culex mosquito
D. Body louse

Explanation: **Correct Answer: Rat flea** - Plague, caused by the bacterium *Yersinia pestis*, is primarily transmitted to humans through the bite of an infected **rat flea** (most commonly *Xenopsylla cheopis*) - The fleas acquire the bacteria by feeding on infected rodents and then transmit it to humans when they bite *Incorrect: Tse-Tse fly* - The **Tse-Tse fly** is the primary vector for **African trypanosomiasis** (sleeping sickness), caused by species of *Trypanosoma* - This fly is not associated with the transmission of plague *Incorrect: Culex mosquito* - The **Culex mosquito** is known to transmit several diseases, including **West Nile virus**, **Japanese encephalitis**, and **filariasis** - It is not a vector for the plague bacterium *Yersinia pestis* *Incorrect: Body louse* - The **body louse** (*Pediculus humanus corporis*) is a vector for diseases such as **epidemic typhus** (caused by *Rickettsia prowazekii*) and **relapsing fever** (caused by *Borrella recurrentis*) - It does not transmit plague

Question 3: Which of the following is a Category C bioterrorism agent?

A. Botulism
B. Nipah virus (Correct Answer)
C. Clostridium Perfringens
D. Plague

Explanation: ***Nipah virus*** - **Nipah virus** is classified as a **Category C bioterrorism agent** due to its potential for high mortality, emerging threat, and ease of genetic engineering. - These agents are emerging pathogens that could be engineered for **mass dissemination** in the future and require ongoing surveillance. *Botulism* - **Botulism**, caused by *Clostridium botulinum* toxin, is a **Category A bioterrorism agent** due to its high mortality and ease of dissemination. - Category A agents pose the greatest threat to public health and national security. *Clostridium Perfringens* - *Clostridium perfringens* is classified as a **Category B bioterrorism agent** because it can be used to contaminate food and water supplies. - Category B agents are moderately easy to disseminate and cause moderate morbidity but lower mortality than Category A agents. *Plague* - **Plague**, caused by *Yersinia pestis*, is a **Category A bioterrorism agent** because of its high mortality, potential for aerosol dissemination, and risk of causing public panic. - The CDC categorizes agents based on the risk they pose to national security.

Question 4: A girl from Shimla presented to OPD with fever, hypotension, malaise and axillary and inguinal lymphadenopathy. Culture in glucose broth shows stalactite growth. Most likely causative organism is?

A. Yersinia pestis (Correct Answer)
B. Brucella abortus
C. Coxiella burnetii
D. Francisella tularensis

Explanation: ***Yersinia pestis*** - The combination of **fever**, **hypotension**, **malaise**, and **inguinal and axillary lymphadenopathy** (buboes) is highly characteristic of **bubonic plague**, caused by *Yersinia pestis*. - **Stalactite growth** in broth culture is a classic identifying feature of *Yersinia pestis* when incubated without agitation, due to the organism's **lipid A-modified LPS** which allows self-aggregation. *Brucella abortus* - *Brucella abortus* causes **brucellosis**, which presents with **undulant fever**, **arthralgia**, and **hepatosplenomegaly**, but typically not with prominent acute lymphadenopathy and hypotension to this degree. - While it is a **facultative intracellular pathogen**, it does not exhibit stalactite growth in glucose broth. *Coxiella burnetii* - *Coxiella burnetii* causes **Q fever**, which is characterized by **fever**, **headache**, and **pneumonia**, often without prominent lymphadenopathy. - It is an **obligate intracellular bacterium** and cannot be cultivated in standard glucose broth, much less show stalactite growth. *Francisella tularensis* - *Francisella tularensis* causes **tularemia**, which can manifest with **fever**, **lymphadenopathy** (ulceroglandular form), and **malaise**. - However, it typically requires **specialized culture media** like cysteine-enriched agar and does not exhibit stalactite growth in glucose broth.

Question 5: True statement about plague is -

A. Septicemic plague is highly infectious
B. Live attenuated vaccines are used
C. Vaccine is not used to control epidemic of pneumonic plague
D. Most important measure to control epidemic is rodent control (Correct Answer)

Explanation: ***Most important measure to control epidemic is rodent control*** - **Plague** is a zoonotic disease primarily affecting rodents, with human infection occurring through flea bites from infected rodents. **Rodent control** is the fundamental and most important measure for plague control as it breaks the transmission cycle at its source. - While immediate epidemic response includes case isolation, antibiotic treatment, and contact prophylaxis, **rodent control remains the cornerstone of comprehensive plague control programs** and is essential for both preventing and controlling epidemics. - The bacterium *Yersinia pestis* is maintained in nature within **rodent populations**, making their management the primary long-term public health intervention. *Septicemic plague is highly infectious* - **Septicemic plague** is a severe form where bacteria multiply in the bloodstream but is **not infectious** from person to person - there is no person-to-person transmission. - **Pneumonic plague** (lung infection) is the only form that is highly infectious and can spread directly between humans via respiratory droplets. *Live attenuated vaccines are used* - Live attenuated vaccines for plague have been used historically but are **not currently recommended or widely available** for routine use. - Modern plague control relies on antibiotics (streptomycin, gentamicin, doxycycline) rather than vaccination. - Vaccine development continues, but no vaccine is currently licensed for general use in most countries. *Vaccine is not used to control epidemic of pneumonic plague* - While this statement is technically true, it is phrased as a negative statement and doesn't represent the most important or fundamental concept about plague control. - The question asks for the "true statement" and the positive statement about **rodent control being the most important measure** is the best answer as it represents the core principle of plague epidemiology and control.

Question 6: A farmer presents to the emergency department with painful inguinal lymphadenopathy and a history of fever and flu-like symptoms. Clinical examination reveals an ulcer on the leg. Which of the following stains should be used to detect suspected bipolar-stained organisms?

A. Albe's stain
B. McFadyean's stain
C. Wayson's stain (Correct Answer)
D. Ziehl-Neelsen stain

Explanation: ***Wayson's stain*** - This stain is specifically used for the detection of **Yersinia pestis**, the causative agent of **plague**, which often presents with **bipolar staining**. - Clinical features like **painful inguinal lymphadenopathy** (buboes), fever, flu-like symptoms, and an ulcer (possibly an inoculation site) are highly suggestive of **plague**. *Albe's stain* - **Albe's stain** is used for demonstrating **bacterial capsules**, not for bipolar-stained organisms. - It would not specifically identify **Yersinia pestis** in this context. *Mc Fayden's stain* - **McFadyen's stain** is primarily used to detect the capsule of **Bacillus anthracis** (anthrax) from smears. - While helpful for anthrax, it is not the specific stain for bipolar staining of **Yersinia pestis**. *Ziehl Nelson stain* - **Ziehl-Neelsen stain** is an **acid-fast stain** used to identify organisms with high mycolic acid content in their cell walls, such as **Mycobacterium tuberculosis**. - It is not suitable for visualizing gram-negative bacteria like **Yersinia pestis** or their bipolar staining characteristics.

Question 7: Which of the following bacteria is classified as facultative anaerobe?

A. Bacteroides
B. Pseudomonas
C. Escherichia (Correct Answer)
D. Clostridium

Explanation: ***Escherichia*** - *Escherichia coli* (E. coli) is a classic example of a **facultative anaerobe**, meaning it can grow in the presence or absence of oxygen. - It uses **aerobic respiration** when oxygen is available and switches to **fermentation** or **anaerobic respiration** in an anaerobic environment. *Bacteroides* - *Bacteroides* species are **obligate anaerobes**, meaning they can only survive and grow in the **complete absence of oxygen**. - They are a major component of the normal human gut flora and are sensitive to oxygen exposure. *Pseudomonas* - *Pseudomonas* species, such as *Pseudomonas aeruginosa*, are **obligate aerobes**, requiring **oxygen for growth and metabolism**. - They possess enzymes like cytochrome oxidase and catalase, which are essential for aerobic respiration. *Clostridium* - *Clostridium* species, like *Clostridium tetani* and *Clostridium perfringens*, are **obligate anaerobes**. - They lack the enzymes (e.g., superoxide dismutase, catalase) necessary to detoxify reactive oxygen species, making oxygen lethal to them.

Question 8: A 20-year-old male patient presents to the STD clinic with a genital ulcer. The Gram stain of the smear from the ulcer shows gram-negative coccobacilli. What is the most appropriate media for culture?

A. Blood agar with X & V factors
B. Tellurite blood agar
C. Thayer-Martin Medium
D. Chocolate agar with IsoVitale X (Correct Answer)

Explanation: ***Chocolate agar with IsoVitaleX*** - The presence of gram-negative coccobacilli in a genital ulcer in a young male suggests **Haemophilus ducreyi**, the causative agent of **chancroid**. - **Chocolate agar** supplemented with **IsoVitaleX** (a growth-enhancing supplement containing X and V factors, vitamins, and cofactors) is the **optimal and standard reference medium** for culturing this fastidious organism. - IsoVitaleX provides superior growth enhancement compared to X and V factors alone. *Thayer-Martin Medium* - This medium is a selective agar used primarily for the isolation of **Neisseria gonorrhoeae** and **Neisseria meningitidis**, which are gram-negative diplococci, not coccobacilli. - While it contains antibiotics to suppress normal flora, it is not suitable for the growth of **Haemophilus ducreyi**. *Blood agar with X & V factors* - **Haemophilus ducreyi** requires **both X (hemin) and V (NAD) factors** for growth, which this medium theoretically provides. - However, **chocolate agar with IsoVitaleX** is preferred because IsoVitaleX provides additional growth supplements beyond just X and V factors, and offers better selectivity and growth enhancement for this fastidious organism. - Blood agar alone would not effectively isolate **H. ducreyi** from polymicrobial samples. *Tellurite blood agar* - This selective and differential medium is used for the isolation of **Corynebacterium diphtheriae**, which forms characteristic black colonies due to tellurite reduction. - It is not appropriate for the isolation of **gram-negative coccobacilli** like **Haemophilus ducreyi**.

Question 9: The ELISA test for virulence antigen is used to diagnose which type of Escherichia coli?

A. ETEC
B. EIEC
C. EPEC (Correct Answer)
D. EHEC

Explanation: ***EPEC (Enteropathogenic E. coli)*** - The **ELISA test for virulence antigen** is specifically used to detect **Bundle-Forming Pilus (BFP)** and **EAF (E. coli adherence factor) plasmid antigens** in EPEC - EPEC is a major cause of **infantile diarrhea** in developing countries - The virulence antigen detection by ELISA is a **standard diagnostic method** for identifying typical EPEC strains - EPEC demonstrates **localized adherence** pattern on HEp-2 cells and possesses the **LEE (locus of enterocyte effacement) pathogenicity island** *ETEC (Enterotoxigenic E. coli)* - ETEC causes **traveler's diarrhea** by producing **heat-labile (LT)** and **heat-stable (ST) enterotoxins** - Diagnosis involves detecting these **specific toxins or their genes** using PCR or toxin-specific immunoassays - ELISA for virulence antigens is not the primary diagnostic method for ETEC *EIEC (Enteroinvasive E. coli)* - EIEC invades intestinal epithelial cells, causing **dysentery-like illness** similar to *Shigella* - Diagnosis relies on detecting **invasion plasmid antigen H (IpaH)** or demonstrating **invasive properties** in cell culture assays - Serotyping and molecular methods are preferred over ELISA for virulence antigens *EHEC (Enterohemorrhagic E. coli)* - EHEC (particularly **O157:H7**) produces **Shiga toxins (Stx1 and Stx2)** causing hemorrhagic colitis and HUS - Diagnosis focuses on detecting **Shiga toxins** using specific ELISA or **stx genes** by PCR - Sorbitol-MacConkey agar is used for initial screening of O157:H7 strains

Question 10: All of the following statements about Glanders are false except?

A. It is an acute illness which presents with mild upper respiratory tract symptoms, usually self-limited.
B. Glanders is caused by Brucella.
C. Human infection cannot be acquired from infected animals.
D. Belongs to class B bioterrorism agents according to CDC. (Correct Answer)

Explanation: **Explanation:** **Glanders** is a serious zoonotic disease caused by the Gram-negative bacterium ***Burkholderia mallei***. It primarily affects horses, mules, and donkeys. **Why Option D is Correct:** The CDC categorizes bioterrorism agents into three classes (A, B, and C) based on their potential for dissemination and severity. **Class B agents** are the second highest priority; they are moderately easy to disseminate, result in moderate morbidity rates, and low mortality rates. *Burkholderia mallei* (Glanders) and *Burkholderia pseudomallei* (Melioidosis) are both classified as **Category B** agents. **Why the other options are Incorrect:** * **Option A:** Glanders is **not** a mild, self-limited illness. It is a severe, often fatal disease characterized by pneumonia, bloodstream infections (sepsis), and chronic localized infections in the skin and muscle. * **Option B:** Glanders is caused by ***Burkholderia mallei***, not *Brucella*. *Brucella* causes Brucellosis (undulant fever). * **Option C:** Human infection **can** be acquired from infected animals. It is a zoonosis transmitted through direct contact with infected animal tissues, secretions, or inhalation of infectious aerosols. **High-Yield NEET-PG Pearls:** * **Causative Agent:** *Burkholderia mallei* (Non-motile, unlike *B. pseudomallei* which is motile). * **Strauss Reaction:** A classic diagnostic test where intraperitoneal inoculation of infected material into male guinea pigs causes severe orchitis (scrotal swelling). * **Mallein Test:** A skin test used in veterinary medicine to detect Glanders in horses. * **Category A Agents (The "Big Six"):** Anthrax, Botulism, Plague, Smallpox, Tularemia, and Viral Hemorrhagic Fevers (Ebola/Marburg). Remember these for contrast!

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