Zoonotic Diseases Practice Questions

Q: Which disease is transmitted by lice?

Epidemic typhus. **Explanation:** The correct answer is **Epidemic typhus**. This disease is caused by *Rickettsia prowazekii* and is uniquely transmitted by the **human body louse** (*Pediculus humanus corporis*). The transmission occurs when louse feces containing the bacteria are rubbed into bite wounds or mucous membranes by scratching. **Analysis of Options:** * **Epidemic Typhus (A):** Transmitted by lice. It is characterized by high fever, headache, and a rash that spreads from the trunk to the extremities. It can recur years later as **Brill-Zinsser disease**. * **Endemic Typhus (B) & Murine Typhus (C):** These terms are synonymous. Both are caused by *Rickettsia typhi* and are transmitted to humans by the **rat flea** (*Xenopsylla cheopis*). * **Rickettsial pox (D):** Caused by *Rickettsia akari*, this disease is transmitted by **mites** associated with common house mice. It is clinically distinguished by an initial eschar at the bite site followed by a papulovesicular rash. **High-Yield NEET-PG Pearls:** * **Vector Mnemonic:** "Louse-borne is Lousy (Epidemic/Prowazekii)" vs. "Flea-borne is Endemic (Typhi)." * **Weil-Felix Test:** Epidemic and Endemic typhus both show a positive reaction with **OX-19**. * **Drug of Choice:** Doxycycline is the gold standard treatment for all rickettsial infections. * **Scrub Typhus:** Often confused with the above, it is caused by *Orientia tsutsugamushi* and transmitted by **trombiculid mites (chiggers)**; it shows a positive **OX-K** on Weil-Felix.

Q: A labourer involved with repair-work of sewers was admitted with fever, jaundice, and renal failure. What is the most appropriate test to diagnose the infection in this patient?

Microscopic agglutination. **Explanation:** The clinical presentation of fever, jaundice, and renal failure in a patient with occupational exposure to sewage (rodent urine) is classic for **Weil’s Disease**, the severe form of **Leptospirosis**. **1. Why Microscopic Agglutination Test (MAT) is correct:** MAT is the **gold standard** serological test for diagnosing Leptospirosis. It involves mixing the patient's serum with live antigens from various *Leptospira* serovars and observing for agglutination under a dark-field microscope. It is highly specific and can identify the infecting serovar. While PCR and blood cultures are useful in the first week (leptospiremic phase), MAT becomes the investigation of choice from the second week onwards (immune phase). **2. Why other options are incorrect:** * **Dark field microscopy (DFM):** While *Leptospira* can be visualized via DFM of blood or urine, it has very low sensitivity and a high rate of false positives due to artifacts (like fibrin threads), making it unreliable for definitive diagnosis. * **Paul Bunnell test:** This is a heterophile antibody test used to diagnose Infectious Mononucleosis caused by the Epstein-Barr virus (EBV). * **Micro immunofluorescence (MIF):** This is the gold standard for diagnosing *Chlamydia* infections, not Leptospirosis. **Clinical Pearls for NEET-PG:** * **Transmission:** Contact with water/soil contaminated by urine of infected rodents (rats). * **Biphasic illness:** Initial febrile/septicemic phase followed by an immune phase. * **Weil’s Syndrome Triad:** Jaundice, Renal failure (often non-oliguric), and Hemorrhage (e.g., epistaxis or pulmonary hemorrhage). * **Culture:** Uses **EMJH medium** or **Fletcher’s medium** (growth takes weeks). * **Drug of Choice:** Doxycycline (prophylaxis/mild cases) or IV Penicillin G (severe cases).

Q: Which infection causes acute febrile illness with jaundice and conjunctivitis?

Leptospirosis. ### Explanation **Correct Option: A. Leptospirosis** Leptospirosis, caused by the spirochete *Leptospira interrogans*, typically presents in two phases. The initial **septicemic phase** is characterized by high-grade fever, headache, and myalgia. A hallmark clinical sign is **conjunctival suffusion** (redness without inflammatory exudate). In severe cases, known as **Weil’s Disease**, the infection progresses to an icteric phase involving hepatic dysfunction (jaundice), renal failure, and hemorrhages. The combination of fever, jaundice, and conjunctival suffusion is a classic diagnostic triad for this condition. **Why Incorrect Options are Wrong:** * **B. Malaria:** While it causes acute febrile illness and jaundice (due to hemolysis), it does not typically present with conjunctival suffusion. Splenomegaly is a more prominent feature. * **C. Pertussis:** Also known as "Whooping Cough," this is a respiratory infection characterized by paroxysmal coughing fits and an inspiratory "whoop." It does not cause jaundice. * **D. Typhoid:** Caused by *Salmonella Typhi*, it presents with "step-ladder" fever, bradycardia (Faget's sign), and abdominal symptoms. Jaundice is rare and usually signifies a complication rather than a primary feature. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Contact with water or soil contaminated by the urine of infected rodents (occupational hazard for farmers/sewer workers). * **Diagnosis:** **Microscopic Agglutination Test (MAT)** is the gold standard. Dark-field microscopy can visualize the "question mark" shaped spirochetes. * **Treatment:** Doxycycline is the drug of choice for prophylaxis and mild cases; IV Penicillin G is used for severe cases. * **Culture:** Grown on specialized media like **EMJH** or **Fletcher’s medium**.

Q: What is the primary reservoir for Leptospira?

Rat. **Explanation:** **Leptospirosis** is a worldwide zoonotic infection caused by the spirochete *Leptospira interrogans*. **Why Rat is the Correct Answer:** The **Rat (specifically the brown rat, *Rattus norvegicus*)** is the most important primary reservoir and maintenance host globally. The bacteria colonize the **renal tubules** of the rodents and are excreted in their **urine** for long periods without causing disease in the host. Human infection occurs through direct contact with infected urine or indirectly through contaminated water and soil (often during floods), entering via skin abrasions or mucous membranes. **Analysis of Incorrect Options:** * **A. Cat:** While cats can technically be infected, they are resistant to the bacteria and are rarely implicated in human transmission. * **B. Dog:** Dogs can act as incidental hosts and reservoirs for specific serovars (like *L. canicola*), but they are not the *primary* global reservoir compared to rodents. * **D. Monkey:** Monkeys are not significant reservoirs in the epidemiological cycle of Leptospirosis. **High-Yield Clinical Pearls for NEET-PG:** * **Occupational Hazard:** Common in sewage workers, farmers, and miners. * **Weil’s Disease:** The severe icteric form characterized by the triad of **Jaundice, Renal Failure, and Hemorrhage**. * **Biphasic Illness:** Consists of an initial febrile/leptospiremic phase followed by an immune phase (meningitis, uveitis). * **Diagnosis:** **Microscopic Agglutination Test (MAT)** is the Gold Standard. For early diagnosis (first week), blood culture in **EMJH medium** or Fletcher’s medium is used. * **Drug of Choice:** Doxycycline (prophylaxis/mild cases) or Penicillin G (severe cases).

Q: A 50-year-old man presented with flu-like symptoms. He was treated with penicillin and sent home. A week later, he returned feeling worse, complaining of fever, night sweats, persistent cough, weight loss, and lethargy. He is a rancher with a history of congenital heart disease and rheumatic fever. The physician suspected subacute bacterial endocarditis. Blood cultures were negative, but serum analysis showed positive antibodies against a specific bacterium. Treatment with doxycycline was initiated, leading to improvement. What is the most likely causative organism?

Coxiella burnetii. **Explanation:** The clinical presentation points toward **Q fever**, caused by **_Coxiella burnetii_**. The patient’s occupation as a **rancher** is a classic high-yield clue, as _C. burnetii_ is a zoonotic pathogen found in cattle, sheep, and goats. While it typically causes a self-limiting flu-like illness (Acute Q fever), it can progress to **Chronic Q fever**, which most commonly manifests as **Culture-Negative Endocarditis**, especially in patients with pre-existing valvular heart disease or congenital heart defects. **Why the other options are incorrect:** * **_Chlamydophila psittaci_:** Causes Psittacosis (ornithosis). While it presents with fever and cough, the history would typically involve exposure to **birds/parrots**, not cattle or ranching. * **_Chlamydophila pneumoniae_:** A common cause of atypical pneumonia and bronchitis. It does not typically cause endocarditis or correlate with ranching exposure. * **_Chlamydia trachomatis_:** Primarily causes urogenital infections, lymphogranuloma venereum (LGV), or trachoma; it is not a cause of endocarditis. **NEET-PG High-Yield Pearls:** * **Culture-Negative Endocarditis:** _Coxiella burnetii_ is the most common cause worldwide. Other causes include _HACEK_ organisms, _Bartonella_, and _Brucella_. * **Diagnosis:** Since it is an obligate intracellular bacterium, it does not grow on routine blood cultures. Diagnosis relies on **Serology (IFA)**. * **Phase Variation:** In acute infection, antibodies to **Phase II antigen** are higher. In chronic infection (endocarditis), antibodies to **Phase I antigen** are significantly elevated (IgG > 1:800). * **Treatment:** Doxycycline is the drug of choice. For chronic endocarditis, a combination of Doxycycline and Hydroxychloroquine is used for 18+ months.

Q: Fresh water swimming can lead to which of the following infections?

Leptospirosis. **Explanation:** **Leptospirosis** is a zoonotic infection caused by the spirochete *Leptospira interrogans*. The bacteria are shed in the **urine of infected animals** (most commonly rodents, dogs, and livestock) [1]. These spirochetes can survive for weeks in **fresh water and moist soil** [1]. Human infection occurs through direct contact with contaminated water or soil via skin abrasions or mucous membranes. Activities like **freshwater swimming**, kayaking, or wading in floodwaters are classic risk factors frequently tested in exams [1]. **Analysis of Incorrect Options:** * **A. Brucellosis:** Primarily transmitted through the consumption of unpasteurized dairy products or direct contact with infected livestock (cattle, goats, sheep). It is an occupational hazard for veterinarians and slaughterhouse workers, not associated with swimming. * **C. Babesiosis:** A malaria-like illness caused by *Babesia microti*. It is transmitted by the bite of the **Ixodes tick** (the same vector for Lyme disease). * **D. Lassa Fever:** A viral hemorrhagic fever transmitted through contact with food or household items contaminated with the urine or feces of infected **Mastomys rats** (multimammate rats), primarily in West Africa. **High-Yield Clinical Pearls for NEET-PG:** * **Weil’s Disease:** The severe form of Leptospirosis characterized by the triad of **Jaundice, Renal failure, and Hemorrhage**. * **Clinical Feature:** Look for **conjunctival suffusion** (redness without exudate), which is a highly specific sign. * **Biphasic illness:** It typically presents with an initial septicemic phase followed by an immune phase (meningitis/uveitis). * **Treatment:** **Doxycycline** is the drug of choice for prophylaxis and mild cases; IV **Penicillin G** is preferred for severe disease.

Q: Which rickettsiae are able to grow in cell-free media?

R. quintana. **Explanation:** The correct answer is **R. quintana** (now reclassified as *Bartonella quintana*). **1. Why the correct answer is right:** Most members of the order Rickettsiales are **obligate intracellular parasites**, meaning they lack certain metabolic pathways and must reside within a host cell to replicate. However, **R. quintana** is the notable exception. It is the only rickettsial agent that can be grown on **cell-free media**, specifically blood agar or enriched agar (like chocolate agar), under 5% CO2. Due to this unique characteristic and genetic differences, it was moved from the genus *Rickettsia* to *Bartonella*. **2. Why the incorrect options are wrong:** * **B. R. rickettsii:** The causative agent of Rocky Mountain Spotted Fever. It is an obligate intracellular pathogen that requires living host cells (like yolk sacs of embryonated eggs or cell cultures) for growth. * **C. R. typhi:** The agent of Endemic (Murine) Typhus. Like other true Rickettsia, it cannot synthesize sufficient ATP to survive outside a host cell. * **D. R. tsutsugamushi:** (Now *Orientia tsutsugamushi*), the agent of Scrub Typhus. It is also an obligate intracellular bacterium and lacks a peptidoglycan cell wall, making it even more dependent on host cell environments. **3. NEET-PG High-Yield Pearls:** * **Disease:** *Bartonella quintana* causes **Trench Fever**, characterized by a 5-day relapsing fever. * **Vector:** It is transmitted by the **human body louse** (*Pediculus humanus corporis*). * **Clinical Association:** In HIV/immunocompromised patients, it can cause **Bacillary Angiomatosis** and endocarditis. * **Staining:** Rickettsiae are best visualized using **Giemsa** or **Gimenez** stains; they stain poorly with Gram stain.

Q: A 40-year-old bank officer was diagnosed with ileocecal tuberculosis, confirmed to be of bovine origin after thorough investigation. He stated that no one in his family had tuberculosis. What is the most likely source of his infection?

Infected milk. **Explanation:** The clinical presentation of **ileocecal tuberculosis** caused by a **bovine strain** (*Mycobacterium bovis*) is a classic textbook scenario for zoonotic transmission via the oral route. **1. Why "Infected milk" is correct:** *Mycobacterium bovis* is the primary cause of bovine tuberculosis. In humans, infection occurs most commonly through the **ingestion of raw, unpasteurized milk** from infected cows. Once ingested, the bacilli penetrate the intestinal mucosa, typically targeting the lymphoid tissue of the **ileocecal region** (Peyer’s patches), leading to primary abdominal tuberculosis. This explains why a bank officer with no family history of respiratory TB (human-to-human transmission) would develop an extrapulmonary, bovine-origin infection. **2. Why the other options are incorrect:** * **Infected client:** This implies droplet nuclei transmission of *M. tuberculosis* (human strain), which typically causes pulmonary TB, not bovine ileocecal TB. * **Contaminated vessel/Polluted water:** While general hygiene is important, *M. bovis* is not a water-borne pathogen. It requires a specific animal reservoir (cattle) and a lipid-rich medium like milk to remain viable for transmission to humans. **High-Yield Clinical Pearls for NEET-PG:** * **Organism:** *Mycobacterium bovis* is a member of the *M. tuberculosis* complex. * **Distinguishing Feature:** *M. bovis* is **intrinsically resistant to Pyrazinamide**. * **Culture:** It is microaerophilic and inhibited by glycerol (unlike *M. tuberculosis*, which is enhanced by it). It grows better on **Pyruvate-based Lowenstein-Jensen (LJ) medium**. * **Prevention:** The primary preventive measure for bovine TB in humans is the **pasteurization of milk**.

Q: What is the diagnostic method of choice for leptospirosis?

Microscopic Agglutination Test (MAT). **Explanation:** **Leptospirosis** is a zoonotic infection caused by the spirochete *Leptospira interrogans*. The **Microscopic Agglutination Test (MAT)** is considered the **Gold Standard** diagnostic method by the WHO. **Why MAT is the Correct Answer:** MAT is a highly specific serological test that involves mixing the patient's serum with live antigens (cultures of various *Leptospira* serovars). The mixture is examined under a **Dark Ground Microscope (DGM)** to observe for agglutination. It is the reference method because it can identify the specific infecting serovar and determine the antibody titer, which is crucial for epidemiological surveillance and definitive diagnosis. **Analysis of Incorrect Options:** * **A. Cold agglutination test:** This is used to diagnose *Mycoplasma pneumoniae* (Primary Atypical Pneumonia) and certain hemolytic anemias, not leptospirosis. * **B. MAT for small animals:** While leptospirosis affects animals, the standard diagnostic reference for human clinical diagnosis is simply the "Microscopic Agglutination Test." This option is a distractor. * **D. Latex agglutination test:** This is a rapid screening test. While useful for bedside or field diagnosis due to its simplicity, it lacks the sensitivity and specificity of MAT and is not the "method of choice" for confirmation. **High-Yield Clinical Pearls for NEET-PG:** * **Specimen Timing:** In the first week (Septicemic phase), the organism is best isolated from **Blood or CSF**. After the first week (Immune phase), it is best isolated from **Urine**. * **Culture Media:** *Leptospira* are grown on specialized media like **EMJH (Ellinghausen-McCullough-Johnson-Harris)** or **Fletcher’s medium**. * **Weil’s Disease:** A severe form of leptospirosis characterized by the triad of **Jaundice, Renal failure, and Hemorrhage**. * **Drug of Choice:** Doxycycline (prophylaxis/mild cases) or Penicillin G (severe cases).

Question 1

Which disease is transmitted by lice?

Accepted Answer

Epidemic typhus

Answer

Endemic typhus

Answer

Murine typhus

Answer

Rickettsial pox

Question 2

A labourer involved with repair-work of sewers was admitted with fever, jaundice, and renal failure. What is the most appropriate test to diagnose the infection in this patient?

Accepted Answer

Microscopic agglutination

Answer

Dark field microscopy

Answer

Paul Bunnell test

Answer

Micro immunofluorescence

Question 3

Which infection causes acute febrile illness with jaundice and conjunctivitis?

Accepted Answer

Leptospirosis

Answer

Malaria

Answer

Pertussis

Answer

Typhoid

Question 4

What is the primary reservoir for Leptospira?

Accepted Answer

Rat

Answer

Cat

Answer

Dog

Answer

Monkey

Question 5

Which of the following statements about Rickettsiae are true?

Accepted Answer

Respond to tetracycline therapy

Answer

Multiply only within living cells

Answer

Produce typhus fever of epidemic type only

Answer

Transmitted by arthropod vectors

Question 6

A 50-year-old man presented with flu-like symptoms. He was treated with penicillin and sent home. A week later, he returned feeling worse, complaining of fever, night sweats, persistent cough, weight loss, and lethargy. He is a rancher with a history of congenital heart disease and rheumatic fever. The physician suspected subacute bacterial endocarditis. Blood cultures were negative, but serum analysis showed positive antibodies against a specific bacterium. Treatment with doxycycline was initiated, leading to improvement. What is the most likely causative organism?

Accepted Answer

Coxiella burnetii

Answer

Chlamydophila psittaci

Answer

Chlamydophila pneumoniae

Answer

Chlamydia trachomatis

Question 7

Fresh water swimming can lead to which of the following infections?

Accepted Answer

Leptospirosis

Answer

Brucellosis

Answer

Babesiosis

Answer

Lassa fever

Question 8

Which rickettsiae are able to grow in cell-free media?

Accepted Answer

R. quintana

Answer

R. rickettsii

Answer

R. typhi

Answer

R. tsutsugamushi

Question 9

A 40-year-old bank officer was diagnosed with ileocecal tuberculosis, confirmed to be of bovine origin after thorough investigation. He stated that no one in his family had tuberculosis. What is the most likely source of his infection?

Accepted Answer

Infected milk

Answer

Infected client

Answer

Contaminated vessel

Answer

Polluted water

Question 10

What is the diagnostic method of choice for leptospirosis?

Accepted Answer

Microscopic Agglutination Test (MAT)

Answer

Cold agglutination test

Answer

Microscopic Agglutination Test (MAT) for small animals

Answer

Latex agglutination test

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

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