Zoonotic Diseases Practice Questions

Q: What is the causative organism of Weil disease?

Leptospira interrogans. **Explanation:** **Leptospirosis** is a zoonotic infection caused by spirochetes of the genus *Leptospira*. The correct answer is **Leptospira interrogans** because it is the primary pathogenic species responsible for human leptospirosis, including its most severe form, **Weil disease**. * **Why A is correct:** *Leptospira interrogans* is the pathogenic complex. Weil disease (icterohemorrhagic leptospirosis) is the severe manifestation characterized by the triad of **jaundice, acute kidney injury (renal failure), and hemorrhage** (often pulmonary). It is typically transmitted through contact with water or soil contaminated by the urine of infected rodents. * **Why B, C, and D are incorrect:** These species belong to the **saprophytic** (non-pathogenic) or intermediate groups of Leptospira. *Leptospira biflexa* is the classic free-living saprophyte found in surface waters and does not cause disease in humans. *L. wolhachii* and *L. inadai* are generally considered non-pathogenic or of low clinical significance in the context of classic Weil disease. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Thin, tightly coiled spirochetes with characteristic **hooked ends** (often described as "C" or "S" shaped). * **Microscopy:** They are too thin to be seen under light microscopy; **Dark-field microscopy** is required. * **Culture:** They are obligate aerobes grown on specialized media like **EMJH** (Ellinghausen-McCullough-Johnson-Harris) or **Fletcher’s medium**. * **Diagnosis:** The **Microscopic Agglutination Test (MAT)** is the gold standard serological test. * **Clinical Phases:** It is a biphasic illness (Septicemic phase followed by the Immune phase). Jaundice in Weil disease is unique because it is often associated with **conjunctival suffusion** (redness without discharge).

Q: The Weil-Felix test is useful in the diagnosis of which of the following conditions, except?

Trench fever. **Explanation:** The **Weil-Felix test** is a heterophile agglutination test used for the diagnosis of Rickettsial diseases. It relies on a cross-reaction between antibodies produced during certain rickettsial infections and the somatic (O) antigens of specific strains of **Proteus vulgaris (OX-19, OX-2)** and **Proteus mirabilis (OX-K)**. **Why Trench Fever is the correct answer:** Trench fever is caused by ***Bartonella quintana***. Unlike Rickettsia, Bartonella species do not share cross-reactive antigens with Proteus strains. Therefore, the Weil-Felix test is **negative** in Trench fever. Other Rickettsial diseases that are Weil-Felix negative include Q fever (*Coxiella burnetii*) and Rickettsialpox (*R. akari*). **Analysis of Incorrect Options:** * **Epidemic typhus (*R. prowazekii*):** Characteristically shows a strongly positive reaction with **OX-19**. * **Scrub typhus (*Orientia tsutsugamushi*):** This is the only major rickettsial disease that reacts exclusively with **OX-K**. * **Rocky Mountain Spotted Fever (*R. rickettsii*):** Being part of the Spotted Fever Group, it typically shows positive reactions with both **OX-19 and OX-2**. **High-Yield Clinical Pearls for NEET-PG:** * **Summary Table:** * **Typhus Group** (Epidemic/Endemic): OX-19 (+++), OX-2 (+) * **Spotted Fever Group**: OX-19 (+), OX-2 (+++) * **Scrub Typhus**: OX-K (+++); OX-19 and OX-2 are negative. * **Limitations:** The test lacks high sensitivity and specificity; definitive diagnosis is now preferred via Immunofluorescence Assay (IFA) or PCR. * **Mnemonic:** "K" for **K**atayama/Scrub (OX-K).

Q: Which of the following organisms is known to cause severe encephalitis with direct transmission from pigs to humans?

Nipah virus. **Explanation:** The correct answer is **Nipah virus (NiV)**, a highly pathogenic zoonotic paramyxovirus. In the initial 1998 outbreak in Malaysia, pigs acted as the **intermediate hosts**. The virus was transmitted to humans through direct contact with infected pigs or their contaminated tissues/fluids. Clinically, Nipah virus presents as severe, rapidly progressing encephalitis with a high fatality rate (40–75%). While the natural reservoir is the *Pteropus* fruit bat, the pig-to-human route is a classic epidemiological hallmark of this virus. **Analysis of Incorrect Options:** * **Poliovirus:** Transmitted via the fecal-oral route. It primarily affects the anterior horn cells of the spinal cord, leading to flaccid paralysis rather than primary encephalitis. * **Measles virus:** Transmitted via respiratory droplets. While it can cause Subacute Sclerosing Panencephalitis (SSPE) as a late complication, it does not involve pigs in its transmission cycle. * **West Nile virus:** An arbovirus transmitted to humans primarily through the bite of infected **Culex mosquitoes**. Birds are the natural reservoir; pigs are not the primary source of human infection. **High-Yield Clinical Pearls for NEET-PG:** * **Reservoir:** *Pteropus* species (Fruit bats). * **Transmission (India/Bangladesh):** Consumption of raw date palm sap contaminated with bat saliva/urine and human-to-human transmission are more common than the porcine route. * **Diagnosis:** RT-PCR or ELISA for IgM/IgG antibodies. * **Histopathology:** Characterized by systemic vasculitis and syncytia (multinucleated giant cells) formation in the brain and lungs.

Q: Which of the following statements regarding anthrax is true?

McFadyean reaction is positive for the capsule.. **Explanation:** **1. Why Option A is Correct:** The **McFadyean reaction** is a classic diagnostic test for *Bacillus anthracis*. When a smear of blood or tissue from an infected animal is stained with polychrome methylene blue, the **polypeptide capsule** (composed of poly-D-glutamic acid) appears as a ragged, purple-pink halo surrounding the blue-stained bacilli. This reaction is highly specific for identifying the capsule in clinical specimens. **2. Why Other Options are Incorrect:** * **Option B:** Humans are **not resistant**; they are highly susceptible hosts. Anthrax is a significant zoonotic disease, primarily affecting those in contact with infected livestock or animal products (e.g., hides, wool). * **Option C:** The infectious dose for pulmonary anthrax (Woolsorter’s disease) is relatively high. It is estimated that **8,000 to 50,000 spores** are required to initiate an infection via inhalation, not fewer than 100. * **Option D:** *B. anthracis* produces **non-bulging, central or subterminal spores**. The spores do not swell the mother cell. "Bulging spores" are characteristic of *Clostridium* species (e.g., *C. tetani* with drumstick appearance). **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Large, Gram-positive, non-motile bacilli with "Bamboo stick" appearance (chains) and "Medusa head" colonies on agar. * **Capsule:** Unique because it is **polypeptide** (Poly-D-glutamic acid), whereas most bacterial capsules are polysaccharide. * **String of Pearls Reaction:** Occurs when grown on solid media containing low concentrations of penicillin. * **Virulence Factors:** Encoded on plasmids **pXO1** (Toxins: Edema factor, Lethal factor, Protective antigen) and **pXO2** (Capsule).

Q: A sewer worker presents with high-grade fever, neck rigidity, and signs of meningismus. Laboratory findings are suggestive of renal failure and elevated liver enzymes. What is your diagnosis?

Leptospirosis. **Explanation:** The clinical presentation of a **sewer worker** (occupational exposure) with high-grade fever, signs of meningitis (neck rigidity), and multi-organ involvement (**renal failure and jaundice/elevated liver enzymes**) is a classic description of **Weil’s Disease**, the severe form of **Leptospirosis**. 1. **Why Leptospirosis is correct:** *Leptospira interrogans* is transmitted through water contaminated with the urine of infected rodents (common in sewers). The disease is characteristically biphasic: the initial septicemic phase presents with fever and **conjunctival suffusion** (a high-yield sign), followed by an immune phase involving the liver (jaundice), kidneys (uremia), and CNS (aseptic meningitis). 2. **Why other options are incorrect:** * **Borrelia recurrentis:** Causes Relapsing Fever, characterized by recurring febrile episodes due to antigenic variation, but typically lacks the specific renal-hepatic failure triad seen here. * **Diphtheria:** Primarily presents as a pseudomembranous pharyngitis with potential bull-neck lymphadenopathy and myocarditis; it does not cause this systemic febrile-icteric-renal syndrome. * **Plague:** Caused by *Yersinia pestis*, it presents as painful lymphadenopathy (Buboes) or severe pneumonia, usually following a flea bite. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Microscopic Agglutination Test (MAT). * **Culture Media:** EMJH (Ellinghausen-McCullough-Johnson-Harris) or Fletcher’s medium. * **Morphology:** Tightly coiled spirochetes with "hooked ends" (Question-mark shape). * **Drug of Choice:** Doxycycline (prophylaxis/mild cases) or IV Penicillin G (severe cases).

Q: A 45-year-old veterinary surgeon presented with a black eschar on the left hand. There was extensive swelling around the ulcer but it was not painful. There were few vesicular lesions surrounding the ulcer. He presented a history of injury to the hand while handling animals. What would be the presumptive diagnosis on the basis of history and culture smear of fluid from the vesicles?

Cutaneous anthrax. ### Explanation The clinical presentation described is classic for **Cutaneous Anthrax**, caused by *Bacillus anthracis*. **1. Why Cutaneous Anthrax is correct:** * **Occupational History:** The patient is a veterinary surgeon with a history of handling animals, making this a "Hide Porter’s disease" scenario. * **The Lesion:** The pathognomonic feature is a **painless, itchy papule** that rapidly evolves into a vesicle and then a **depressed black eschar** (necrotic center) surrounded by extensive **non-pitting edema**. * **Microscopy:** A culture smear from the vesicle fluid would typically show large, Gram-positive, non-motile, spore-forming bacilli in chains (Bamboo-stick appearance). **2. Why the other options are incorrect:** * **Actinomycetoma:** Presents as a chronic, localized, swelling with multiple discharging sinuses and "sulfur granules." It is usually painful in later stages and lacks the acute black eschar. * **Clostridium infection (Gas Gangrene):** While it involves trauma, it is characterized by **excruciating pain**, crepitus (gas in tissues), and systemic toxemia, unlike the painless lesion of anthrax. * **Extrapulmonary nocardiosis:** Usually presents as chronic abscesses or cellulitis in immunocompromised patients; it does not typically present as an acute black eschar with massive edema. **High-Yield Clinical Pearls for NEET-PG:** * **Virulence Factors:** Encapsulated (Poly-D-glutamic acid capsule) and produces Anthrax Toxin (Edema Factor, Lethal Factor, and Protective Antigen). * **McFadyean’s Reaction:** Used for presumptive identification (polychrome methylene blue staining shows purple capsules). * **Medusa Head Appearance:** Characteristic colony morphology on nutrient agar. * **String of Pearls Reaction:** Seen on agar containing penicillin. * **Treatment:** Ciprofloxacin or Doxycycline are the first-line agents.

Q: Cat scratch disease is characterized by?

Regional lymphadenopathy is prominent. **Explanation:** **Cat Scratch Disease (CSD)** is a bacterial infection caused by **_Bartonella henselae_**, a fastidious, pleomorphic Gram-negative bacillus. It is typically transmitted to humans through the scratch or bite of an infected domestic cat (the primary reservoir), often involving kittens. 1. **Why Option B is correct:** The hallmark of CSD is **subacute regional lymphadenopathy**. Following an initial skin papule or pustule at the inoculation site, the draining lymph nodes (most commonly axillary, epitrochlear, or cervical) become significantly enlarged, tender, and occasionally suppurative. This is the most prominent clinical feature, occurring in nearly 90% of patients. 2. **Why Option A is incorrect:** CSD is **bacterial**, not viral. While it was historically debated, the causative agent is definitively identified as *Bartonella henselae*. 3. **Why Option C is incorrect:** CSD is significantly **more common in children and adolescents** (under 20 years of age) than in adults, likely due to closer play interaction with kittens. **High-Yield Clinical Pearls for NEET-PG:** * **Stain of Choice:** *Bartonella* is best visualized in tissue sections using the **Warthin-Starry silver stain**. * **Pathology:** Lymph nodes show characteristic **stellate (star-shaped) granulomas** with central necrosis. * **Parinaud Oculoglandular Syndrome:** A specific presentation of CSD involving conjunctivitis and preauricular lymphadenopathy. * **Immunocompromised Patients:** In HIV/AIDS patients, *B. henselae* causes **Bacillary Angiomatosis** (vascular proliferative lesions) rather than typical CSD. * **Treatment:** Most cases are self-limiting, but **Azithromycin** is the drug of choice to reduce lymph node volume.

Q: What is considered the most serious form of Rickettsial disease?

Rocky Mountain spotted fever. **Explanation:** **Rocky Mountain spotted fever (RMSF)**, caused by *Rickettsia rickettsii*, is recognized as the most severe and potentially fatal rickettsial illness. The underlying medical concept is its high degree of **vasculitis**. The bacteria infect the endothelial cells lining the blood vessels, leading to widespread vascular damage, increased permeability, and subsequent organ failure (affecting the lungs, kidneys, and CNS). Without prompt treatment with Doxycycline, the mortality rate can exceed 20-30%. **Analysis of Incorrect Options:** * **Scrub typhus (*Orientia tsutsugamushi*):** While common in the "Tsutsugamushi Triangle" (including India), it is generally less virulent than RMSF. It is characterized by a pathognomonic **eschar** at the mite bite site. * **Q-fever (*Coxiella burnetii*):** This is unique because it does not cause a rash and is often transmitted via inhalation. It usually presents as a self-limiting flu-like illness or pneumonia and is rarely fatal in its acute form. * **Trench fever (*Bartonella quintana*):** Transmitted by the body louse, it causes a relapsing fever. While debilitating, it is historically known for low mortality rates compared to typhus group rickettsiae. **Clinical Pearls for NEET-PG:** * **Drug of Choice:** Doxycycline is the gold standard for all rickettsial diseases, regardless of age. * **Triad of RMSF:** Fever, headache, and a characteristic rash that begins on the **wrists and ankles** (centripetal spread) and involves the **palms and soles**. * **Weil-Felix Test:** A heterophile agglutination test used for diagnosis (though being replaced by IFA). RMSF shows a positive reaction with **OX-19 and OX-2**. * **Vector:** RMSF is transmitted by Hard Ticks (*Dermacentor* species).

Q: A 29-year-old bird collector presents with flu-like symptoms including slight fever, headache, and a dry hacking cough. He denies sputum production or hemoptysis. Physical examination reveals no crackles on auscultation, and a radiograph shows small streaks of infiltrate. The patient is diagnosed with pneumonia. What is the most likely organism causing his disease?

Chlamydophila psittaci. ### Explanation **Correct Answer: C. Chlamydophila psittaci** **1. Why it is correct:** The clinical presentation describes **Atypical Pneumonia** (walking pneumonia), characterized by a "dissociation" between physical findings (minimal crackles) and radiological findings (streaky infiltrates), along with a dry, non-productive cough. The definitive clue in this vignette is the patient’s occupation as a **bird collector**. *Chlamydophila psittaci* is the causative agent of **Psittacosis (Ornithosis)**, a zoonotic infection transmitted via the inhalation of dried bird excreta or respiratory secretions from infected birds (parrots, pigeons, etc.). **2. Why the other options are incorrect:** * **A. Chlamydophila pneumoniae:** While it causes atypical pneumonia, it is transmitted person-to-person via respiratory droplets and lacks the specific epidemiological link to birds. * **B. Haemophilus influenzae:** This typically causes **typical pneumonia**, presenting with high fever, productive cough (purulent sputum), and lobar consolidation on X-ray, often in patients with underlying COPD. * **D. Streptococcus pneumoniae:** The most common cause of community-acquired pneumonia (CAP). It presents acutely with "rusty" sputum, high-grade fever, and distinct lobar consolidation, which contradicts the "dry cough" and "streaky infiltrates" seen here. **3. NEET-PG High-Yield Pearls:** * **Horder’s Spots:** A rare clinical sign of Psittacosis—rose-colored spots on the face resembling typhoid. * **Splenomegaly:** Often present in Psittacosis, helping differentiate it from other atypical pneumonias. * **Diagnosis:** Serology (Complement Fixation Test or Microimmunofluorescence) is the gold standard. * **Treatment of Choice:** **Doxycycline** (Tetracyclines) is the first-line treatment for all *Chlamydia* species. Macrolides are used as alternatives.

Question 1

What is the causative organism of Weil disease?

Accepted Answer

Leptospira interrogans

Answer

Leptospira biflexa

Answer

Leptospira wolhachii

Answer

Leptospira inadai

Question 2

Global eradication of Lyme disease is unlikely because?

Accepted Answer

Borrelia burgdorferi can be maintained in nature indefinitely by a tick vector

Answer

Borrelia burgdorferi is resistant to antibiotics and disinfectants

Answer

Borrelia burgdorferi is resistant to environmental stresses

Answer

Human disease may reactivate after the primary infection (Brill-Zinsser disease)

Question 3

The Weil-Felix test is useful in the diagnosis of which of the following conditions, except?

Accepted Answer

Trench fever

Answer

Epidemic typhus

Answer

Scrub typhus

Answer

Rocky Mountain Spotted Fever (RMSF)

Question 4

Which of the following organisms is known to cause severe encephalitis with direct transmission from pigs to humans?

Accepted Answer

Nipah virus

Answer

Poliovirus

Answer

Measles virus

Answer

West Nile virus

Question 5

Which of the following statements regarding anthrax is true?

Accepted Answer

McFadyean reaction is positive for the capsule.

Answer

Humans are generally resistant to anthrax infection.

Answer

Fewer than 100 spores are sufficient to cause pulmonary anthrax.

Answer

Gram stain reveals organisms with bulging spores.

Question 6

A sewer worker presents with high-grade fever, neck rigidity, and signs of meningismus. Laboratory findings are suggestive of renal failure and elevated liver enzymes. What is your diagnosis?

Accepted Answer

Leptospirosis

Answer

Borrelia recurrentis

Answer

Diphtheria

Answer

Plague

Question 7

A 45-year-old veterinary surgeon presented with a black eschar on the left hand. There was extensive swelling around the ulcer but it was not painful. There were few vesicular lesions surrounding the ulcer. He presented a history of injury to the hand while handling animals. What would be the presumptive diagnosis on the basis of history and culture smear of fluid from the vesicles?

Accepted Answer

Cutaneous anthrax

Answer

Actinomycetoma

Answer

Clostridium infection

Answer

Extrapulmonary nocardiosis

Question 8

Cat scratch disease is characterized by?

Accepted Answer

Regional lymphadenopathy is prominent

Answer

Caused by a virus

Answer

More common in adults

Answer

All of the above

Question 9

What is considered the most serious form of Rickettsial disease?

Accepted Answer

Rocky Mountain spotted fever

Answer

Scrub typhus

Answer

Q-fever

Answer

Trench fever

Question 10

A 29-year-old bird collector presents with flu-like symptoms including slight fever, headache, and a dry hacking cough. He denies sputum production or hemoptysis. Physical examination reveals no crackles on auscultation, and a radiograph shows small streaks of infiltrate. The patient is diagnosed with pneumonia. What is the most likely organism causing his disease?

Accepted Answer

Chlamydophila psittaci

Answer

Chlamydophila pneumoniae

Answer

Haemophilus influenzae

Answer

Streptococcus pneumoniae

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?