Zoonotic Diseases Practice Questions

Q: A veterinary doctor had pyrexia of unknown origin. Blood culture in special laboratory media was positive for Gram-negative, oxidase-positive short bacilli. Which one of the following is the likely organism grown in culture?

Brucella spp.. ### Explanation The clinical presentation of **Pyrexia of Unknown Origin (PUO)** in a high-risk professional (veterinary doctor) strongly suggests **Brucellosis**, a classic zoonotic infection. **1. Why Brucella spp. is correct:** * **Occupational Risk:** Veterinarians, farmers, and slaughterhouse workers are at high risk through contact with infected animals or unpasteurized dairy. * **Microbiology:** *Brucella* are small, Gram-negative coccobacilli (short bacilli) that are **oxidase-positive** and catalase-positive. * **Culture:** They are fastidious and require **special media** (e.g., Castaneda’s biphasic medium) for growth. They are notorious for causing "culture-negative" endocarditis if standard media are used or if incubation is too short. **2. Why the other options are incorrect:** * **Pasteurella spp.:** While Gram-negative and oxidase-positive, it is typically associated with **animal bites** (cats/dogs) causing cellulitis, not prolonged PUO. * **Francisella spp.:** Causes Tularemia. While it is a Gram-negative coccobacillus, it is typically **oxidase-negative** and requires cysteine-enriched media (BCYE agar). * **Bartonella spp.:** Causes Cat Scratch Disease or Trench Fever. It is a fastidious Gram-negative rod but is **oxidase-negative**. **3. High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Bone marrow culture (higher yield than blood culture). * **Standard Serology:** Standard Agglutination Test (SAT); titers >1:160 are significant. * **Rose Bengal Plate Test:** Used as a rapid screening tool. * **Treatment:** WHO recommends **Rifampicin + Doxycycline** for 6 weeks. * **Complication:** Osteoarticular involvement (sacroiliitis) is the most common complication.

Q: A patient presented with pyrexia of unknown origin. Blood culture in special laboratory media was positive for gram-negative short bacilli that were oxidase-positive. Which one of the following is the likely organism grown in culture?

Brucella spp.. ### Explanation **Correct Answer: D. Brucella spp.** **Why Brucella is the correct answer:** Brucellosis is a classic cause of **Pyrexia of Unknown Origin (PUO)**, often presenting as "undulant fever." The organism is a small, **Gram-negative coccobacillus** (short bacilli) that is **oxidase-positive** and catalase-positive. A key diagnostic feature is its growth characteristics: it is a fastidious aerobe that requires **special laboratory media** (e.g., Castaneda’s biphasic medium) and often takes prolonged incubation (up to 2-4 weeks) to grow. **Analysis of Incorrect Options:** * **A. Pasteurella spp.:** While these are Gram-negative, oxidase-positive bacilli, they are typically associated with **animal bites** (cats/dogs) and cause acute cellulitis or abscesses rather than chronic PUO. * **B. Francisella spp.:** *Francisella tularensis* (Tularemia) is a Gram-negative coccobacillus, but it is characteristically **oxidase-negative**. It also requires cysteine-enriched media (like BCYE) for growth. * **C. Bartonella spp.:** These are Gram-negative bacilli but are typically **oxidase-negative**. They cause Cat Scratch Disease or Bacillary Angiomatosis and are extremely difficult to culture on standard blood media. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Bone marrow culture (higher yield than blood culture). * **Culture Media:** **Castaneda’s Medium** is the traditional biphasic medium used to reduce the risk of laboratory-acquired infections. * **Serology:** The **Standard Agglutination Test (SAT)** detects antibodies; a titer >1:160 is significant. * **Treatment:** The WHO recommends **Rifampicin + Doxycycline** for 6 weeks. * **Occupational Hazard:** It is the most common laboratory-acquired infection; samples must be handled in Biosafety Level 3 (BSL-3) cabinets.

Q: Which of the following is NOT a zoonotic disease?

Malaria. **Explanation:** The core concept in this question is the definition of a **zoonosis**: a disease or infection that is naturally transmissible from vertebrate animals to humans. **Why Malaria is the correct answer:** Malaria is an **anthroponotic** disease, not a zoonotic one. While it is transmitted by a vector (the female *Anopheles* mosquito), the natural reservoir for the human-pathogenic species of *Plasmodium* (*P. falciparum, P. vivax, P. ovale, P. malariae*) is humans. The cycle of transmission is human-to-mosquito-to-human. *(Note: While P. knowlesi is a zoonosis from macaques, in the context of standard medical exams, Malaria is classified as non-zoonotic).* **Analysis of Incorrect Options:** * **Brucellosis:** A classic zoonosis transmitted to humans via direct contact with infected livestock (cattle, goats, pigs) or consumption of unpasteurized dairy products. * **Rabies:** A viral zoonosis transmitted through the bite or scratch of an infected mammal (most commonly dogs in India, or bats/raccoons globally). * **Trichinosis:** A parasitic zoonosis caused by *Trichinella spiralis*, typically acquired by consuming undercooked meat (usually pork) containing encysted larvae. **High-Yield Clinical Pearls for NEET-PG:** * **Definition Check:** If a disease requires an animal reservoir to maintain the pathogen in nature, it is a zoonosis. * **Yellow Fever:** Usually exists in two cycles—**Sylvatic (Zoonotic)** involving monkeys and **Urban (Anthroponotic)** involving humans. * **Common Zoonoses to remember:** Anthrax, Plague, Leptospirosis, Kyasanur Forest Disease (KFD), and Hydatid disease. * **Key Distinction:** Vector-borne does not always mean zoonotic. Malaria and Dengue are vector-borne but primarily anthroponotic.

Q: Which of the following organisms can cause Rat bite fever?

Spirillum minus. **Explanation:** **Rat-bite fever (RBF)** is a systemic zoonotic illness caused by two distinct bacteria, depending on the geographic region. The correct answer is **Spirillum minus**, which is the primary causative agent of the **spirillary form** of the disease (also known as **Sodoku**), predominantly seen in Asia. 1. **Why Spirillum minus is correct:** It is a Gram-negative, thick, spiral-shaped bacterium with polar flagella. It is transmitted via the bite or scratch of an infected rat. Clinically, Sodoku is characterized by the initial wound healing, followed by a sudden onset of fever, lymphadenopathy, and a characteristic "re-ulceration" or chancre-like lesion at the bite site. 2. **Why the other options are incorrect:** * **Leptospira canicola:** Causes Leptospirosis (Canicola fever), typically transmitted through water contaminated with the urine of infected dogs, not rat bites. * **Streptobacillus moniliformis:** This is the *other* cause of Rat-bite fever (the **streptobacillary form**), common in North America. However, since *Spirillum minus* is the specific organism marked as correct in this context, it is important to distinguish them: *Streptobacillus* causes "Haverhill fever" (when transmitted via contaminated milk) and usually presents with prominent polyarthralgia, which is rare in *Spirillum* infections. * **Borrelia recurrentis:** The causative agent of Louse-borne Relapsing Fever (LBRF), transmitted by the human body louse. **NEET-PG High-Yield Pearls:** * **Sodoku (Spirillum minus):** Short incubation (1–4 weeks), relapsing fever, lymphadenopathy, and site inflammation. Diagnosed via **dark-ground microscopy** or animal inoculation (cannot be cultured on artificial media). * **Streptobacillary RBF:** Short incubation (<7 days), prominent joint pain (arthritis), and maculopapular rash on palms/soles. * **Treatment:** Penicillin G is the drug of choice for both forms.

Question 1

What is the most effective natural barrier to rabies?

Accepted Answer

Water

Answer

Heat

Answer

Humidity

Answer

None of the above

Question 2

A veterinary doctor had pyrexia of unknown origin. Blood culture in special laboratory media was positive for Gram-negative, oxidase-positive short bacilli. Which one of the following is the likely organism grown in culture?

Accepted Answer

Brucella spp.

Answer

Pasteurella spp.

Answer

Francisella spp.

Answer

Bartonella spp.

Question 3

A patient presented with pyrexia of unknown origin. Blood culture in special laboratory media was positive for gram-negative short bacilli that were oxidase-positive. Which one of the following is the likely organism grown in culture?

Accepted Answer

Brucella spp.

Answer

Pasteurella spp.

Answer

Francisella spp.

Answer

Bartonella spp.

Question 4

Which of the following is NOT a zoonotic disease?

Accepted Answer

Malaria

Answer

Brucellosis

Answer

Rabies

Answer

Trichinosis

Question 5

Which of the following organisms can cause Rat bite fever?

Accepted Answer

Spirillum minus

Answer

Leptospira canicola

Answer

Streptobacillus moniliformis

Answer

Borrelia recurrentis

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

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