Zoonotic Diseases Practice Questions

Q: A fourteen-year-old boy is admitted with a history of fever, icterus, conjunctival suffusion, and hematuria for twenty days. Which of the following serological tests can be of diagnostic utility?

Microscopic Agglutination Test. ### Explanation The clinical presentation of **fever, icterus (jaundice), conjunctival suffusion, and hematuria** (suggesting renal involvement) is a classic triad for **Weil’s Disease**, the severe form of **Leptospirosis**. Conjunctival suffusion (redness without inflammatory exudate) is a pathognomonic sign of Leptospirosis. **Why the Correct Answer is Right:** The **Microscopic Agglutination Test (MAT)** is the **gold standard** serological investigation for Leptospirosis. It involves mixing the patient's serum with live leptospiral antigens (various serovars) and observing for agglutination under a dark-ground microscope. A four-fold rise in titer or a single high titer (usually >1:160 or 1:80 in endemic areas) confirms the diagnosis. **Why Other Options are Incorrect:** * **A. Widal test:** Used for diagnosing **Enteric fever** (Typhoid). While it presents with fever, it does not typically cause conjunctival suffusion or acute renal failure. * **C. Paul Bunnell test:** A non-specific heterophile antibody test used to diagnose **Infectious Mononucleosis** (EBV). It presents with fever, lymphadenopathy, and pharyngitis. * **D. Weil-Felix reaction:** A heterophile agglutination test used for diagnosing **Rickettsial infections** (Typhus group). It utilizes *Proteus* antigens to detect cross-reacting antibodies. **High-Yield Clinical Pearls for NEET-PG:** * **Causative Agent:** *Leptospira interrogans* (spirochete with hooked ends/question mark shape). * **Transmission:** Contact with water/soil contaminated by the **urine of infected rodents** (rats). * **Biphasic Nature:** Leptospiremic phase (first week - blood/CSF culture) followed by Immune phase (second week onwards - urine culture and MAT). * **Drug of Choice:** Doxycycline (prophylaxis/mild cases) or IV Penicillin G (severe cases).

Q: Leptospira icterohemorrhagica infection is transmitted by:

Rats. **Explanation:** **Leptospirosis** is a worldwide zoonotic infection caused by the spirochete *Leptospira interrogans*. 1. **Why Rats are Correct:** The primary reservoir for *Leptospira icterohemorrhagica* (the serogroup responsible for severe disease) is the **Rat**. The bacteria colonize the proximal convoluted tubules of the rat's kidneys and are shed in their **urine**. Humans are accidental hosts, typically infected through direct contact with contaminated water or soil (often during floods) via skin abrasions or mucous membranes. 2. **Analysis of Incorrect Options:** * **Bats:** While bats are reservoirs for viruses like Rabies, Nipah, and Ebola, they are not the primary epidemiological source for *Leptospira*. * **Birds:** Birds are generally not reservoirs for Leptospirosis; they are more commonly associated with *Chlamydia psittaci* or Cryptococcosis. * **Dogs:** While dogs can carry *Leptospira* (specifically serovar *Canicola*), the question specifies *L. icterohemorrhagica*, which is classically associated with rodents (rats). 3. **High-Yield Clinical Pearls for NEET-PG:** * **Weil’s Disease:** This is the severe triad of Leptospirosis consisting of **Jaundice, Renal Failure, and Hemorrhage**. * **Clinical Feature:** Look for **conjunctival suffusion** (redness without discharge) and calf muscle tenderness in clinical vignettes. * **Diagnosis:** **Microscopic Agglutination Test (MAT)** is the gold standard. For early diagnosis (first week), blood or CSF culture on **EMJH or Fletcher’s medium** is used. * **Treatment:** Doxycycline is the drug of choice for prophylaxis and mild cases; IV Penicillin G is used for severe cases.

Q: A farmer working in poultry developed acute onset of fever with chills. On physical examination, there is hepatosplenomegaly and lymphadenopathy. Blood culture shows Brucella. He must have got the infection through all the following ways, EXCEPT:

Person-to-person transmission. **Explanation:** Brucellosis (also known as Malta fever or Undulant fever) is a classic **zoonotic infection** caused by *Brucella* species. The primary reservoir includes domestic animals like cattle (*B. abortus*), goats/sheep (*B. melitensis*), and pigs (*B. suis*). **Why Option C is the correct answer:** Human-to-human transmission of Brucella is **extremely rare** and is not considered a significant route of infection. While rare cases of transmission via breast milk, sexual contact, or bone marrow transplantation have been documented, it is practically non-existent in a clinical or community setting. Therefore, it is the "Except" option. **Why the other options are incorrect (Modes of Transmission):** * **Ingestion (Options A & B):** This is the most common route. Consuming **unpasteurized milk**, dairy products, or undercooked **infected meat** allows the bacteria to enter via the gastrointestinal mucosa. * **Direct Contact (Option D):** Farmers, veterinarians, and slaughterhouse workers are at high risk. The bacteria can enter through skin abrasions or conjunctiva when handling **infected fetuses**, placentae, or uterine discharges (as Brucella has a predilection for the reproductive tract of animals due to the presence of **Erythritol**). * **Inhalation:** Laboratory workers can acquire the infection via aerosolization of cultures. **Clinical Pearls for NEET-PG:** * **Clinical Triad:** Fever (Undulant/wave-like), Hepatomegaly, and Splenomegaly. * **Diagnosis:** **Standard Agglutination Test (SAT)** is the most common; a titer of >1:160 is significant. * **Culture:** Blood culture in **Castaneda’s medium** (biphasic medium) is the gold standard. * **Treatment:** WHO recommends **Doxycycline + Rifampicin** for 6 weeks. For complicated cases (e.g., endocarditis), Streptomycin is added.

Q: A 15-year-old girl has swollen, painful lymph nodes in her right axilla. Physical examination reveals multiple scratches on her right arm, with a papule associated with one of the scratch marks. She states the scratches occurred about 5 days ago. What type of animal is the most likely source of the infection?

Cat or kitten. **Explanation:** The clinical presentation of regional lymphadenopathy (axillary), a primary inoculation papule, and a history of animal scratches strongly points to **Cat-Scratch Disease (CSD)**. **1. Why Cat or Kitten is Correct:** The causative agent of CSD is ***Bartonella henselae***, a fastidious Gram-negative rod. It is typically transmitted to humans via the scratch or bite of a domestic cat, particularly **kittens**, which are more likely to be bacteremic. The infection begins as a small papule at the site of inoculation, followed 1–3 weeks later by painful, suppurative regional lymphadenopathy (most commonly axillary or cervical). **2. Why Other Options are Incorrect:** * **Chicken:** Associated with *Campylobacter jejuni* (diarrhea) or *Chlamydia psittaci* (psittacosis/pneumonia), not localized lymphadenopathy from scratches. * **Dog or puppy:** While dog bites can cause infections (e.g., *Pasteurella multocida* or *Capnocytophaga canimorsus*), these typically present as acute, rapidly progressing cellulitis rather than subacute regional lymphadenitis with a primary papule. * **Horse:** Associated with *Glanders* (*Burkholderia mallei*), which is rare and presents with more severe systemic symptoms or localized nodules that ulcerate. **3. High-Yield Clinical Pearls for NEET-PG:** * **Causative Agent:** *Bartonella henselae*. * **Stain of Choice:** **Warthin-Starry silver stain** is used to visualize the bacilli in lymph node biopsies. * **Histopathology:** Characterized by **stellate (star-shaped) necrotizing granulomas**. * **Bacillary Angiomatosis:** In immunocompromised (HIV) patients, *B. henselae* causes vascular proliferative lesions that can mimic Kaposi Sarcoma. * **Treatment:** Most cases are self-limiting; however, **Azithromycin** is the drug of choice to reduce lymph node volume.

Q: A group of social activists cleaning sewers develop fever and headaches. On examination, a non-catalase, non-glucose fermenting organism is isolated from them. Which of the following organisms is most likely responsible?

Leptospira. **Explanation:** The clinical scenario describes a classic presentation of **Leptospirosis**, an occupational hazard for sewer workers, farmers, and those in contact with water contaminated by animal urine (typically rats). **Why Leptospira is correct:** * **Occupational Exposure:** Sewer workers are at high risk due to exposure to rodent urine. * **Biochemical Profile:** *Leptospira interrogans* is a spirochete. Unlike many common bacteria, it is **catalase-negative** and **does not ferment glucose** (it utilizes long-chain fatty acids as its primary energy and carbon source). * **Clinical Presentation:** Fever and headache are the initial symptoms of the bacteremic phase. **Why the other options are incorrect:** * **A. Pseudomonas:** While common in moist environments and sewers, *Pseudomonas aeruginosa* is **catalase-positive** and **oxidase-positive**. It utilizes glucose via oxidative pathways (O/F test), not fermentation, but the catalase-positive status rules it out. * **C. Chlamydia:** These are obligate intracellular bacteria that do not grow on standard culture media and are not typically associated with sewer-related outbreaks of acute fever. * **D. Actinomyces:** These are Gram-positive anaerobic filamentous bacteria. They are part of the normal oral flora and typically cause chronic "lumpy jaw" abscesses with sulfur granules, not acute febrile illness in sewer workers. **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**. * **Culture:** Grown on specialized media like **EMJH** (Ellinghausen-McCullough-Johnson-Harris) or **Fletcher’s medium**. * **Microscopy:** Cannot be seen under light microscopy; requires **Dark Ground Microscopy (DGM)**. * **Serology:** **Microscopic Agglutination Test (MAT)** is the gold standard for diagnosis.

Q: A patient presented with rashes all over the body, sparing the palms and soles. The patient does not have a history of animal exposure. This condition may be associated with which of the following?

Epidemic typhus. **Explanation:** The clinical presentation of a generalized rash that **spares the palms and soles** is a classic diagnostic hallmark of **Epidemic Typhus**, caused by *Rickettsia prowazekii*. **1. Why Epidemic Typhus is correct:** In Epidemic Typhus (transmitted by the human body louse), the rash typically begins on the trunk/axilla and spreads centrifugally to the extremities. Crucially, it **spares the face, palms, and soles**. The question also mentions "no animal exposure," which fits the human-louse-human cycle of *R. prowazekii*, unlike other rickettsial diseases which are zoonotic. **2. Why the other options are incorrect:** * **Rocky Mountain Spotted Fever (RMSF):** Caused by *R. rickettsii*, the rash typically begins on the wrists and ankles and spreads centripetally. Most importantly, it **involves the palms and soles** in 80% of cases. * **Q Fever:** Caused by *Coxiella burnetii*, this condition is unique among rickettsial diseases because it **does not present with a rash**. It typically presents as interstitial pneumonia or hepatitis. * **Rickettsialpox:** Caused by *R. akari*, it is characterized by a distinctive **eschar** at the site of the mite bite, followed by a papulovesicular rash that looks like chickenpox. **High-Yield Clinical Pearls for NEET-PG:** * **Centrifugal spread (Trunk to extremities):** Epidemic and Endemic Typhus. * **Centripetal spread (Extremities to trunk):** Rocky Mountain Spotted Fever (RMSF). * **Palms and Soles involvement:** RMSF, Secondary Syphilis, Hand-Foot-Mouth Disease (Coxsackie A), and Erythema Multiforme. * **Drug of Choice:** Doxycycline is the treatment of choice for all rickettsial infections. * **Weil-Felix Test:** *R. prowazekii* reacts with OX-19.

Q: Which of the following statements about Brucella is false?

It is a strict anaerobe.. **Explanation:** The correct answer is **D (It is a strict anaerobe)** because *Brucella* species are actually **strict aerobes**. They require oxygen for growth and do not ferment carbohydrates in conventional media. Some species, notably *Brucella abortus*, are capnophilic, requiring 5–10% $CO_2$ for initial isolation. **Analysis of Options:** * **Option A:** *Brucella* causes **Brucellosis**, clinically known as **Undulant fever** (due to the characteristic rising and falling temperature pattern), **Malta fever**, or **Mediterranean fever**, reflecting its geographical prevalence and historical discovery. * **Option B:** Morphologically, *Brucella* are small, non-motile, non-sporing, **Gram-negative coccobacilli**. They often appear as "fine grains of sand" under the microscope. * **Option C:** *Brucella* is highly susceptible to heat. **Pasteurization** of milk is the most effective public health measure to eliminate the transmission of bovine brucellosis to humans. **High-Yield Clinical Pearls for NEET-PG:** * **Zoonosis:** It is primarily a zoonotic disease transmitted via unpasteurized dairy or direct contact with infected animal tissues (placenta/secretions). * **Intracellular Pathogen:** It is a **facultative intracellular** organism, surviving within macrophages, which leads to chronicity and granuloma formation. * **Diagnosis:** The **Standard Agglutination Test (SAT)** is commonly used; a titer of 1:160 or more is significant. * **Culture:** **Castaneda’s medium** (biphasic medium) is the traditional method for blood culture to reduce the risk of laboratory-acquired infection. * **Treatment:** The WHO recommends **Doxycycline + Rifampicin** for 6 weeks.

Q: All of the following are characteristic of Brucella species except:

2-mercaptoethanol (2ME) is used to detect IgA antibodies.. **Explanation:** **Why Option D is the correct answer (The "Except"):** The 2-mercaptoethanol (2ME) test is used to detect **IgG** antibodies, not IgA. In Brucellosis, IgM appears early but declines with treatment. IgG persists in chronic or relapsing cases. 2-mercaptoethanol acts by breaking the disulfide bonds of IgM molecules, neutralizing them. Therefore, any residual agglutination observed after 2ME treatment is attributed solely to **IgG**, making it a crucial marker for monitoring treatment response and identifying chronic infection. **Analysis of Incorrect Options:** * **Option A:** *B. abortus* is indeed **capnophilic**, requiring 5–10% CO₂ for primary isolation, unlike *B. melitensis* or *B. suis*. * **Option B:** While ingestion of unpasteurized dairy is the most common route, **aerosol transmission** is a significant risk, especially in laboratory settings (making it a Tier 1 select agent/biothreat). * **Option C:** Brucella is highly heat-sensitive; standard **pasteurization** effectively kills the bacteria in milk. **Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Bone marrow culture (more sensitive than blood culture). * **Culture Media:** Castaneda’s medium (biphasic medium) is classically used. * **Serology:** The Standard Agglutination Test (SAT) detects antibodies against *B. abortus*, *B. suis*, and *B. melitensis*, but **not** *B. canis*. * **Drug of Choice:** Doxycycline + Rifampicin (or Streptomycin). * **Rose Bengal Test:** A rapid screening card test used in field settings.

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

Microscopic agglutination test. **Explanation:** The clinical presentation of fever, jaundice, and renal failure in a sewer worker is a classic description of **Weil’s Disease**, the severe form of **Leptospirosis**. Leptospires are excreted in the urine of infected rodents; sewer workers are at high risk due to exposure to contaminated water. **Why the correct answer is right:** The **Microscopic Agglutination Test (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. **Analysis of incorrect options:** * **Weil-Felix test:** Used for the diagnosis of **Rickettsial infections** (Typhus group). It uses *Proteus* antigens to detect cross-reacting antibodies. * **Paul Bunnell test:** A screening test for **Infectious Mononucleosis** (Epstein-Barr Virus) that detects heterophile antibodies. * **Microimmunofluorescence (MIF) test:** The gold standard for diagnosing **Chlamydial infections** (e.g., *C. psittaci*, *C. pneumoniae*). **High-Yield Clinical Pearls for NEET-PG:** * **Triad of Weil’s Disease:** Jaundice, Renal failure (azotemia), and Hemorrhage (often subconjunctival suffusion). * **Specimen Timing:** In the first week (leptospiremic phase), the organism is best isolated from **Blood or CSF**. After the first week (immune phase), it is isolated from **Urine**. * **Culture Media:** Korthof’s medium, Fletcher’s medium, or EMJH medium. * **Drug of Choice:** Doxycycline (mild cases/prophylaxis) or Penicillin G (severe cases).

Question 1

A fourteen-year-old boy is admitted with a history of fever, icterus, conjunctival suffusion, and hematuria for twenty days. Which of the following serological tests can be of diagnostic utility?

Accepted Answer

Microscopic Agglutination Test

Answer

Widal test

Answer

Paul Bunnell test

Answer

Weil Felix reaction

Question 2

Leptospira icterohemorrhagica infection is transmitted by:

Accepted Answer

Rats

Answer

Bats

Answer

Birds

Answer

Dogs

Question 3

Which of the following is a dead-end host for humans?

Accepted Answer

Bubonic plague

Answer

Malaria

Answer

Typhoid

Answer

Filaria

Question 4

A farmer working in poultry developed acute onset of fever with chills. On physical examination, there is hepatosplenomegaly and lymphadenopathy. Blood culture shows Brucella. He must have got the infection through all the following ways, EXCEPT:

Accepted Answer

Person-to-person transmission

Answer

Infected meat

Answer

Ingestion of raw milk

Answer

Contact with infected fetuses

Question 5

A 15-year-old girl has swollen, painful lymph nodes in her right axilla. Physical examination reveals multiple scratches on her right arm, with a papule associated with one of the scratch marks. She states the scratches occurred about 5 days ago. What type of animal is the most likely source of the infection?

Accepted Answer

Cat or kitten

Answer

Chicken

Answer

Dog or puppy

Answer

Horse

Question 6

A group of social activists cleaning sewers develop fever and headaches. On examination, a non-catalase, non-glucose fermenting organism is isolated from them. Which of the following organisms is most likely responsible?

Accepted Answer

Leptospira

Answer

Pseudomonas

Answer

Chlamydia

Answer

Actinomyces

Question 7

A patient presented with rashes all over the body, sparing the palms and soles. The patient does not have a history of animal exposure. This condition may be associated with which of the following?

Accepted Answer

Epidemic typhus

Answer

Q fever

Answer

Rocky Mountain spotted fever (RMSF)

Answer

Rickettsialpox

Question 8

Which of the following statements about Brucella is false?

Accepted Answer

It is a strict anaerobe.

Answer

It causes undulant, Malta, or Mediterranean fever.

Answer

It is a gram-negative coccobacillus.

Answer

It can be killed by pasteurization.

Question 9

All of the following are characteristic of Brucella species except:

Accepted Answer

2-mercaptoethanol (2ME) is used to detect IgA antibodies.

Answer

B. abortus is capnophilic.

Answer

Transmission by aerosol can occur.

Answer

Pasteurization destroys Brucella.

Question 10

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

Accepted Answer

Microscopic agglutination test

Answer

Weil Felix test

Answer

Paul Bunnell test

Answer

Microimmunofluorescence test

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

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