Zoonotic Diseases — MCQs

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?

Q28Easy

Schistosomiasis is an example of which type of zoonotic disease?

Q29Medium

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?

Q30Easy

Seal finger and whale finger are clinical manifestations associated with which organism?

Zoonotic Diseases Indian Medical PG Practice Questions and MCQs

Question 21: Which of the following is NOT an anthropozoonosis?

A. Dracunculiasis (Correct Answer)
B. Rabies
C. Plague
D. Hydatid cyst

Explanation: ### Explanation The core of this question lies in the definition of **Anthropozoonosis**. Anthropozoonoses are infectious diseases that are naturally transmitted from vertebrate animals to humans. In these cycles, humans are usually "accidental" hosts, and the disease can be maintained in nature without human intervention. **Why Dracunculiasis is the correct answer:** **Dracunculiasis (Guinea worm disease)** is considered an **anthropozoonosis** (or more specifically, a human-specific infection). The life cycle involves humans and a crustacean intermediate host (*Cyclops*), but it lacks a vertebrate animal reservoir. Because there is no vertebrate animal involved in the natural transmission cycle to humans, it does not meet the definition of a zoonosis. **Analysis of Incorrect Options:** * **Rabies:** A classic viral anthropozoonosis transmitted to humans via the bite of infected vertebrate animals (dogs, bats, monkeys). * **Plague:** A bacterial zoonosis caused by *Yersinia pestis*. The natural reservoir is wild rodents (vertebrates), with transmission to humans occurring via flea bites. * **Hydatid Cyst:** Caused by *Echinococcus granulosus*. It is a parasitic zoonosis where dogs are the definitive hosts and sheep/cattle are intermediate hosts. Humans are accidental "dead-end" hosts. **NEET-PG High-Yield Pearls:** * **Definitions:** * *Anthropozoonosis:* Animal $\rightarrow$ Man (e.g., Rabies, Plague, Anthrax). * *Zooanthroponosis:* Man $\rightarrow$ Animal (e.g., Human Tuberculosis to cattle). * *Amphixenosis:* Transmission in both directions (e.g., Salmonellosis). * **Eradication Status:** Dracunculiasis is on the verge of global eradication. India was certified Guinea worm-free by the WHO in February 2000. * **Vector:** The intermediate host for *Dracunculus medinensis* is the **Cyclops** (Water flea). Filtering water is the primary preventive measure.

Question 22: Which of the following are direct zoonoses?

A. Rabies and Taeniasis
B. Rabies
C. Rabies and Hydatid disease
D. Rabies and Brucellosis (Correct Answer)

Explanation: ### Explanation **Concept of Direct Zoonoses** Zoonoses are classified based on their life cycle and mode of transmission. **Direct Zoonoses** are diseases transmitted from an infected vertebrate host to a susceptible human host by direct contact, contact with a fomite, or by a mechanical vector. Crucially, the agent undergoes **no essential developmental change or propagation** during transmission. **Why Option D is Correct:** * **Rabies:** Transmitted directly via the bite of an infected animal (saliva). The virus does not require an intermediate host or developmental cycle outside the vertebrate host. * **Brucellosis:** Transmitted through direct contact with infected animal tissues, secretions, or the consumption of unpasteurized milk. * *Other examples include: Anthrax, Leptospirosis, and Q fever.* **Analysis of Incorrect Options:** * **Options A & C (Taeniasis and Hydatid disease):** These are classified as **Cyclozoonoses**. These diseases require more than one vertebrate host (e.g., humans and cattle for *T. saginata*; humans and dogs for *E. granulosus*) to complete their life cycle, but no invertebrate host. * **Option B:** While Rabies is a direct zoonosis, this option is incomplete as Brucellosis also fits the definition provided in the context of the question. **NEET-PG High-Yield Pearls:** 1. **Metazoonoses:** Require both a vertebrate and an **invertebrate host** (e.g., Plague, Malaria, Kala-azar). 2. **Saprozoonoses:** Require a vertebrate host and a **non-animal environmental reservoir** like soil or plants (e.g., Tetanus, Histoplasmosis). 3. **Ornithosis:** A term often used for Psittacosis (Chlamydia psittaci), which is a direct zoonosis transmitted from birds.

Question 23: Which of the following diseases is associated with rats?

A. Leptospirosis (Correct Answer)
B. Measles
C. Tetanus
D. Influenza

Explanation: **Explanation:** **Leptospirosis** is a classic zoonotic disease caused by the spirochete *Leptospira interrogans*. Rats (specifically *Rattus norvegicus*) are the most important reservoir hosts. The bacteria colonize the renal tubules of the rodents and are excreted in their **urine**. Human infection occurs through direct contact with infected urine or, more commonly, through water and soil contaminated by it. Entry is typically via abraded skin or mucous membranes, often following heavy rainfall or flooding. **Analysis of Incorrect Options:** * **Measles:** A highly contagious viral infection caused by the Rubeola virus. It is an exclusively human disease with no animal reservoir. * **Tetanus:** Caused by *Clostridium tetani*. It is not a zoonosis in the traditional sense; the bacteria are found in soil and animal feces (as spores) and enter the body through contaminated wounds. * **Influenza:** While some strains are zoonotic (birds/pigs), the standard seasonal influenza is primarily a human-to-human respiratory infection. Rats are not a significant reservoir for Influenza. **NEET-PG High-Yield Pearls:** * **Weil’s Disease:** The severe form of Leptospirosis characterized by the triad of **jaundice, renal failure, and hemorrhage**. * **Occupational Hazard:** Common in sewage workers, rice field farmers, and veterinarians. * **Diagnosis:** **Microscopic Agglutination Test (MAT)** is the gold standard. In the first week, the organism can be isolated from blood/CSF; after the first week, it is found in the urine. * **Drug of Choice:** Doxycycline (prophylaxis/mild cases) or IV Penicillin G (severe cases).

Question 24: 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?

A. Widal test
B. Microscopic Agglutination Test (Correct Answer)
C. Paul Bunnell test
D. Weil Felix reaction

Explanation: ### 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).

Question 25: Leptospira icterohemorrhagica infection is transmitted by:

A. Bats
B. Rats (Correct Answer)
C. Birds
D. Dogs

Explanation: **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.

Question 26: 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:

A. Infected meat
B. Ingestion of raw milk
C. Person-to-person transmission (Correct Answer)
D. Contact with infected fetuses

Explanation: **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.

Question 27: 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?

A. Cat or kitten (Correct Answer)
B. Chicken
C. Dog or puppy
D. Horse

Explanation: **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.

Question 28: Schistosomiasis is an example of which type of zoonotic disease?

A. Meta-zoonoses (Correct Answer)
B. Cyclo-zoonoses
C. Direct-zoonoses
D. Sporo-zoonoses

Explanation: ### Explanation **Correct Answer: A. Meta-zoonoses** **Why it is correct:** Zoonoses are classified based on the life cycle of the infecting organism. **Meta-zoonoses** are diseases that require both a vertebrate host and an **invertebrate host (vector)** for the completion of their life cycle. In the case of Schistosomiasis (*Bilharziasis*), the parasite requires a vertebrate host (humans) and an intermediate invertebrate host (freshwater snails of the genera *Biomphalaria*, *Bulinus*, or *Oncomelania*). The parasite undergoes essential developmental stages (miracidia to cercariae) within the snail before becoming infectious to humans. **Analysis of Incorrect Options:** * **B. Cyclo-zoonoses:** These require **more than one vertebrate host** but no invertebrate host to complete the life cycle. Examples include *Taenia solium* (human and pig) and *Echinococcus granulosus* (dog and sheep). * **C. Direct-zoonoses:** These are transmitted from an infected vertebrate host to a susceptible vertebrate host by direct contact, fomites, or a mechanical vector. No biological developmental change occurs during transmission. Examples include **Rabies**, Anthrax, and Brucellosis. * **D. Sapro-zoonoses:** (Often confused with Sporo-zoonoses) These require a **non-animal environmental reservoir** (like soil or decaying organic matter) for the life cycle. Examples include Tetanus and Histoplasmosis. **NEET-PG High-Yield Pearls:** * **Schistosomiasis Infective Stage:** Cercariae (penetrate unbroken skin during water contact). * **Diagnostic Stage:** Eggs in stool or urine (e.g., *S. haematobium* shows terminal spines in urine). * **Other Meta-zoonoses:** Plague (flea), Arboviruses (mosquito/tick), and Leishmaniasis (sandfly). * **Key Distinction:** If a "vector" is biological and essential for the parasite's development, it is a Meta-zoonosis.

Question 29: 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?

A. Weil Felix test
B. Paul Bunnell test
C. Microscopic agglutination test (Correct Answer)
D. Microimmunofluorescence test

Explanation: **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 30: Seal finger and whale finger are clinical manifestations associated with which organism?

A. Listeria
B. Erysipelothrix (Correct Answer)
C. Corynebacterium
D. Treponema

Explanation: **Explanation:** The correct answer is **Erysipelothrix rhusiopathiae**. **1. Why Erysipelothrix is correct:** *Erysipelothrix rhusiopathiae* is a Gram-positive, non-spore-forming, catalase-negative bacillus. It is a classic **zoonotic pathogen** primarily affecting individuals with occupational exposure to animals or animal products (butchers, veterinarians, and fishermen). * **Seal finger** and **Whale finger** are specific clinical terms for **Erysipeloid**, a localized cutaneous infection occurring in sealers and whale hunters after handling infected carcasses. * The organism enters through skin abrasions, causing a painful, pruritic, violaceous (purplish) lesion, typically on the fingers or hands. **2. Why other options are incorrect:** * **Listeria monocytogenes:** While also a Gram-positive rod, it is primarily associated with foodborne illnesses (dairy/deli meats), neonatal meningitis, and sepsis in immunocompromised hosts. It does not cause "seal finger." * **Corynebacterium:** *C. diphtheriae* causes respiratory diphtheria or cutaneous ulcers (desert sores), but is not associated with marine mammal exposure. * **Treponema:** *T. pallidum* causes syphilis. While it can cause skin lesions (chancre or rashes), it is a human-to-human spirochetal infection, not a marine zoonosis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Gram-positive bacilli that can form long filaments (resembling "hair"). * **Culture:** Produces **H₂S (Hydrogen Sulfide)** on TSI agar (a key differentiating feature from Listeria). * **Test-tube brush growth:** Characteristic pattern in gelatin stabs. * **Treatment:** **Penicillin** is the drug of choice. Note that it is intrinsically **resistant to Vancomycin**, which is a common "trap" question in exams.

Practice by Chapter

Principles of Zoonotic Transmission

Practice Questions

Viral Zoonoses

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Bacterial Zoonoses

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Parasitic Zoonoses

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Vector-Borne Zoonoses

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Foodborne Zoonoses

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Emerging Zoonotic Diseases

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One Health Approach to Zoonoses

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Prevention and Control of Zoonoses

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Occupational Exposure to Zoonoses

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Wildlife Reservoirs of Zoonotic Pathogens

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Global Impact of Zoonotic Diseases

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