Zoonotic Diseases Practice Questions

Q: Which of the following characterizes Q fever?

Is an acute febrile illness caused by Coxiella burnetii.. **Explanation:** **Q fever** is a zoonotic disease caused by **_Coxiella burnetii_**, an obligate intracellular Gram-negative bacterium. It is unique among Rickettsial organisms because it does not require an arthropod vector for human transmission; instead, it is primarily acquired through the **inhalation of contaminated aerosols** or dust from infected livestock (cattle, sheep, and goats). * **Why Option B is correct:** Q fever typically presents as an **acute febrile illness**. While many cases are asymptomatic, symptomatic patients often experience high fever, severe headache, malaise, and atypical pneumonia. * **Why Option A is incorrect:** The incubation period is typically **2 to 3 weeks** (range 10–40 days), not four to six weeks. * **Why Option C is incorrect:** It is not confined to the upper respiratory tract. It is a systemic illness that frequently involves the **lower respiratory tract** (pneumonia) and the **liver** (granulomatous hepatitis). * **Why Option D is incorrect:** Q fever has a **worldwide distribution** (except New Zealand) and is not specifically restricted to tropical regions. **High-Yield Clinical Pearls for NEET-PG:** * **Reservoir:** Placenta of infected animals (contains high concentrations of the bacteria). * **Morphology:** It forms **spore-like variants** that are highly resistant to environmental stressors (heat, drying, and many disinfectants). * **Diagnosis:** Serology is the gold standard. It exhibits **Antigenic Variation**: * **Phase II antibodies** are high in **acute** infection. * **Phase I antibodies** are high in **chronic** infection (e.g., culture-negative endocarditis). * **Weil-Felix Test:** Q fever is **Weil-Felix negative** (unlike most other Rickettsial diseases). * **Treatment:** Doxycycline is the drug of choice for acute cases.

Q: Leptospira canicola infection usually presents as?

Aseptic meningitis. **Explanation:** Leptospirosis is a zoonotic infection caused by the spirochete *Leptospira interrogans*. The clinical presentation varies significantly depending on the specific serovar involved. **Why Aseptic Meningitis is correct:** *Leptospira canicola* is the serovar typically hosted by dogs. In humans, infection with *L. canicola* usually results in a milder, anicteric (non-jaundiced) form of the disease. The most characteristic clinical feature of this milder form is **aseptic meningitis**, which occurs during the second (immune) phase of the illness. Patients present with headache, neck stiffness, and CSF pleocytosis, but the prognosis is generally favorable. **Analysis of Incorrect Options:** * **B. Jaundice:** While jaundice is a hallmark of **Weil’s Disease**, it is specifically associated with the serovar ***L. icterohaemorrhagiae*** (hosted by rats). *L. canicola* rarely causes significant hepatic dysfunction or jaundice. * **C. Diarrhoea and vomiting:** While these may occur as non-specific prodromal symptoms during the initial leptospiremic phase, they are not the defining clinical presentation of *L. canicola*. * **D. Lobar pneumonia:** Leptospirosis can cause pulmonary hemorrhage in severe cases, but it does not typically present as classic lobar pneumonia (which is usually bacterial, e.g., *S. pneumoniae*). **High-Yield Clinical Pearls for NEET-PG:** * **Reservoirs:** *L. icterohaemorrhagiae* (Rats), *L. canicola* (Dogs), *L. pomona* (Pigs/Cattle). * **Weil’s Syndrome:** A triad of jaundice, renal failure, and hemorrhage (caused by *L. icterohaemorrhagiae*). * **Diagnosis:** **Korthof’s** or **EMJH** medium for culture; **Microscopic Agglutination Test (MAT)** is the Gold Standard. * **Treatment:** Doxycycline (mild cases) or Penicillin G (severe cases).

Q: Which of the following causes epidemic typhus?

R. prowazekii. **Explanation:** **Epidemic typhus** is caused by ***Rickettsia prowazekii***. The underlying medical concept involves the transmission of the bacteria via the **human body louse** (*Pediculus humanus corporis*). It typically occurs in crowded, unsanitary conditions (wars, refugee camps), where the louse feces containing the pathogen are scratched into the skin. **Analysis of Options:** * **Option A: *R. typhi*** causes **Endemic (Murine) typhus**, which is transmitted to humans by the **rat flea** (*Xenopsylla cheopis*). * **Option C: *R. rickettsii*** is the causative agent of **Rocky Mountain Spotted Fever (RMSF)**, primarily transmitted by **Dermacentor ticks**. * **Option D: *R. tsutsugamushi*** (now *Orientia tsutsugamushi*) causes **Scrub typhus**, transmitted by the bite of **larval mites (chiggers)**. It is characterized by a pathognomonic **eschar** at the bite site. **High-Yield Clinical Pearls for NEET-PG:** * **Weil-Felix Test:** A heterophile agglutination test used for diagnosis. *R. prowazekii* reacts with **OX-19**. * **Brill-Zinsser Disease:** A recrudescent (latent) form of epidemic typhus that occurs years after the primary infection, usually milder and without the need for a louse vector. * **Drug of Choice:** Doxycycline is the gold standard treatment for all Rickettsial diseases. * **Mnemonic:** "Pro-War-Zekii" (Prowazekii) occurs during **War** (Epidemics).

Q: Which organism is implicated in cellulitis following animal bites?

Pasteurella. **Explanation:** The correct answer is **Pasteurella** (specifically *Pasteurella multocida*). **1. Why Pasteurella is correct:** *Pasteurella multocida* is a small, Gram-negative coccobacillus that exists as normal flora in the oropharynx of many animals, particularly **cats (70-90%) and dogs (20-50%)**. Following a bite or scratch, it is the most common pathogen to cause rapidly progressing cellulitis, often appearing within **3 to 24 hours** of the injury. A key clinical feature is the rapid onset of inflammation and potential progression to tenosynovitis or osteomyelitis. **2. Why the other options are incorrect:** * **Staphylococcus aureus:** While it is the most common cause of *general* skin and soft tissue infections (cellulitis/abscesses), it is not the specific organism associated with the initial presentation of animal bites. * **Pseudomonas:** This is typically associated with puncture wounds through the soles of shoes (leading to osteochondritis) or "hot tub folliculitis," but not primary animal bites. * **Klebsiella:** This is a common cause of pneumonia (in alcoholics) and UTIs, but it is not a primary pathogen in animal bite-related cellulitis. **3. NEET-PG High-Yield Pearls:** * **Drug of Choice:** The preferred treatment for *Pasteurella* infections is **Amoxicillin-Clavulanate** (Augmentin). It covers both *Pasteurella* and anaerobic co-pathogens. * **Morphology:** Look for **"Bipolar staining"** (safety-pin appearance) on Wayson or Giemsa stain. * **Cat vs. Dog:** While both carry the organism, cat bites are more likely to result in infection because their long, sharp teeth cause deep puncture wounds that "seed" the bacteria into bones and joints. * **Other Bite Organisms:** Remember *Eikenella corrodens* for human bites and *Capnocytophaga canimorsus* for sepsis following dog bites (especially in asplenic patients).

Q: What is the most common mode of transmission of Pasteurella multocida?

Animal bites or scratches. **Explanation:** *Pasteurella multocida* is a small, Gram-negative coccobacillus that exists as a commensal in the oral cavity and upper respiratory tract of many domestic and wild animals, most notably **cats (50–90%) and dogs (25–50%)**. **1. Why Option A is Correct:** The primary mode of transmission to humans is through **animal bites, scratches, or licks** on pre-existing skin lesions. Because cats have sharp, thin teeth, they often cause deep puncture wounds that inoculate the bacteria into the periosteum or joint spaces, leading to rapid-onset cellulitis (often within 24 hours). **2. Why the Other Options are Incorrect:** * **Option B (Aerosols):** While rare cases of respiratory tract colonization occur in patients with underlying chronic lung disease (COPD), it is not the *most common* mode. * **Option C (Contaminated tissue):** This is more characteristic of *Francisella tularensis* (Tularemia) or *Bacillus anthracis* (Anthrax). * **Option D (Human to human):** *Pasteurella* is a zoonotic pathogen; human-to-human transmission is virtually non-existent. **High-Yield Clinical Pearls for NEET-PG:** * **Rapid Onset:** It is the fastest-growing wound infection after a bite, typically manifesting within **2–12 hours**. * **Morphology:** It shows **bipolar staining** (safety-pin appearance) with Wayson or Giemsa stains. * **Culture:** It grows well on Blood Agar (showing a characteristic **musty odor** due to indole production) but **does not grow on MacConkey agar**. * **Drug of Choice:** **Penicillin G** is the treatment of choice (unlike many other Gram-negative rods). Amoxicillin-Clavulanate is used for empirical bite wound management.

Q: What is the pathogen that causes pneumonia in patients exposed to rabbits?

Francisella tularensis. **Explanation:** The correct answer is **Francisella tularensis**, the causative agent of **Tularemia**. This is a highly infectious, Gram-negative coccobacillus. It is a classic zoonotic pathogen often associated with **rabbits, hares, and rodents** (hence the name "Rabbit Fever"). Transmission occurs through direct contact with infected animal tissues, tick/deerfly bites, or inhalation of contaminated aerosols. When inhaled, it causes **pneumonic tularemia**, a severe form of atypical pneumonia characterized by fever, cough, and hilar lymphadenopathy. **Analysis of Incorrect Options:** * **Chlamydia psittaci:** Causes Psittacosis (Ornithosis). The key epidemiological link here is exposure to **birds** (parrots, pigeons, or poultry), not rabbits. * **Histoplasma capsulatum:** A dimorphic fungus associated with **bird or bat droppings** (caves, chicken coops). It causes a granulomatous lung disease mimicking tuberculosis. * **Coxiella burnetii:** The agent of **Q fever**. It is typically transmitted via inhalation of aerosols from **birth products or excreta of livestock** (cattle, sheep, and goats). **High-Yield Clinical Pearls for NEET-PG:** * **Infectious Dose:** *F. tularensis* is extremely virulent; as few as 10 organisms can cause disease. It is classified as a **Category A Bioterrorism Agent**. * **Clinical Forms:** The most common form is **Ulceroglandular** (skin ulcer + regional lymphadenopathy). The most lethal is **Pneumonic**. * **Diagnosis:** Culturing is difficult and hazardous (requires Biosafety Level 3). Diagnosis is usually via serology (Agglutination tests). * **Treatment:** **Streptomycin** or Gentamicin are the drugs of choice.

Q: Bacillary angiomatosis is caused by which organism?

Bartonella henselae. **Explanation:** **Bacillary Angiomatosis (BA)** is a vascular proliferative disease caused by Gram-negative rickettsial organisms of the genus *Bartonella*. It primarily affects immunocompromised individuals, particularly those with HIV/AIDS (CD4 count <200 cells/mm³). 1. **Why Option A is correct:** The primary causative agents are **Bartonella henselae** (transmitted via cat scratches/bites) and **Bartonella quintana** (transmitted via the human body louse). These bacteria induce endothelial cell proliferation, leading to the characteristic "mulberry-like" friable, red-to-purple vascular papules and nodules that can mimic Kaposi Sarcoma. 2. **Why other options are incorrect:** * **Option B (Hansen’s bacillus):** This refers to *Mycobacterium leprae*, the causative agent of Leprosy, characterized by hypopigmented patches and nerve thickening. * **Option C (Koch’s bacillus):** This refers to *Mycobacterium tuberculosis*, which causes Tuberculosis (e.g., Lupus vulgaris or Scrofuloderma in the skin). * **Option D (Haemophilus ducreyi):** This is the causative agent of **Chancroid**, characterized by painful genital ulcers and inguinal lymphadenopathy (buboes). **High-Yield Clinical Pearls for NEET-PG:** * **Histopathology:** Shows lobular proliferation of capillaries with **neutrophilic infiltrate** and "amphophilic granular clumps" (which are the bacteria). * **Special Stain:** **Warthin-Starry silver stain** is used to visualize the bacilli. * **Differential Diagnosis:** Must be distinguished from **Kaposi Sarcoma** (which shows a lymphocytic infiltrate and spindle cells). * **Treatment of Choice:** **Erythromycin** or Doxycycline.

Q: A farmer rearing sheep presents with complaints of fever and weakness for the last one month. There is generalised lymphadenopathy and associated hepatomegaly. Biopsy of the liver shows non-caseating granuloma. This clinical presentation is most likely due to infection with which of the following agents?

Brucella melitensis. **Explanation:** The clinical presentation of prolonged fever (undulant fever), weakness, generalized lymphadenopathy, and hepatosplenomegaly in a **sheep farmer** strongly suggests **Brucellosis**. **1. Why Brucella melitensis is correct:** Brucellosis is a zoonotic infection transmitted through direct contact with infected animals or consumption of unpasteurized dairy. *Brucella melitensis* is the most common and virulent species globally, primarily infecting **sheep and goats**. Pathologically, Brucella is an intracellular pathogen that survives within macrophages, leading to the formation of **non-caseating granulomas** in the reticuloendothelial system (liver, spleen, bone marrow). **2. Why other options are incorrect:** * **Yersinia pestis:** Causes Plague. It typically presents acutely with painful lymphadenopathy (buboes) or pneumonia, not a chronic one-month history of granulomatous hepatitis. * **Brucella canis:** While it causes human brucellosis, its reservoir is **dogs**, not sheep. It is also less common and generally causes milder disease than *B. melitensis*. * **Francisella tularensis:** Causes Tularemia. While it can cause granulomas and lymphadenopathy, it is usually associated with contact with **rabbits** or tick bites and often presents with a localized skin ulcer (ulceroglandular form). **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Bone marrow culture (highest yield). * **Standard Culture:** Blood culture using **Castaneda’s medium** (biphasic medium). * **Serology:** Standard Agglutination Test (SAT) detects antibodies; a titer >1:160 is significant. * **Treatment:** Doxycycline + Rifampicin for 6 weeks (WHO regimen). * **Rose Bengal Test:** A rapid screening test used in clinics.

Question 1

Which of the following characterizes Q fever?

Accepted Answer

Is an acute febrile illness caused by Coxiella burnetii.

Answer

Has an incubation period of four to six weeks.

Answer

Is an illness confined to the upper respiratory tract.

Answer

Is most commonly found in the tropical region.

Question 2

Leptospira canicola infection usually presents as?

Accepted Answer

Aseptic meningitis

Answer

Jaundice

Answer

Diarrhoea and vomiting

Answer

Lobar pneumonia

Question 3

Which of the following causes epidemic typhus?

Accepted Answer

R. prowazekii

Answer

R. typhi

Answer

R. rickettsii

Answer

R. tsutsugamushi

Question 4

Which organism is implicated in cellulitis following animal bites?

Accepted Answer

Pasteurella

Answer

Staphylococcus aureus

Answer

Pseudomonas

Answer

Klebsiella

Question 5

About rickettsiae, all are true except -

Accepted Answer

Cephalosporins are drugs of choice

Answer

These are transmitted by arthropod vectors

Answer

Eschar is not seen in RMSF

Answer

Weil-Felix reaction may be diagnostic

Question 6

What is the most common mode of transmission of Pasteurella multocida?

Accepted Answer

Animal bites or scratches

Answer

Aerosols or dust

Answer

Contaminated tissue

Answer

Human to human

Question 7

What is the pathogen that causes pneumonia in patients exposed to rabbits?

Accepted Answer

Francisella tularensis

Answer

Chlamydia psittaci

Answer

Histoplasma capsulatum

Answer

Coxiella burnetii

Question 8

A 44-year-old farmer presented with high-grade fever for 4 days. On examination, an ulcer was found at the right-hand region along with painful cervical lymphadenopathy. The patient reported a bite by an animal 4 days prior, after which a papule formed and later progressed to an ulcer. The patient also had an erythematous, maculopapular rash all over the body and erythema nodosum on the lower limbs. Swabs from the ulcer and biopsy from the lymph nodes were collected. Gram staining was performed, and cultures showed growth on chocolate agar, BCYE agar, and media supplemented with cysteine. What is the drug of choice for the organism identified?

Accepted Answer

Streptomycin

Answer

Doxycycline

Answer

Amikacin

Answer

Gentamycin

Question 9

Bacillary angiomatosis is caused by which organism?

Accepted Answer

Bartonella henselae

Answer

Hansen's bacillus

Answer

Koch's bacillus

Answer

Haemophilus ducreyi

Question 10

A farmer rearing sheep presents with complaints of fever and weakness for the last one month. There is generalised lymphadenopathy and associated hepatomegaly. Biopsy of the liver shows non-caseating granuloma. This clinical presentation is most likely due to infection with which of the following agents?

Accepted Answer

Brucella melitensis

Answer

Yersinia pestis

Answer

Brucella canis

Answer

Francisella tularensis

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

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