Zoonotic Diseases Practice Questions

Q: Which of the following statements about non-typhoidal Salmonella is FALSE?

Humans are the only reservoirs.. **Explanation:** The correct answer is **A**. The genus *Salmonella* is divided into typhoidal and non-typhoidal (NTS) groups. While *Salmonella Typhi* and *Paratyphi* are strictly human pathogens (no animal reservoir), **Non-Typhoidal Salmonella (NTS)**, such as *S. Enteritidis* and *S. Typhimurium*, are **zoonotic**. They have a wide host range, including poultry, cattle, rodents, and reptiles. **Analysis of Options:** * **Option A (False):** Humans are NOT the only reservoirs. NTS is primarily acquired from animal sources. This distinguishes it from Typhoid fever, where humans are the sole source of infection. * **Option B (True):** The most common route of transmission is the consumption of contaminated animal products, particularly **undercooked eggs, poultry, and meat**, as well as unpasteurized milk. * **Option C (True):** NTS infections are more severe and prone to bacteremia in **immunocompromised individuals**, especially those with HIV/AIDS, sickle cell disease (predisposes to osteomyelitis), and malaria. * **Option D (True):** While fluoroquinolones were once the mainstay of treatment, there is a significant global rise in **fluoroquinolone resistance** (and multidrug resistance), necessitating the use of third-generation cephalosporins or azithromycin. **High-Yield Clinical Pearls for NEET-PG:** * **Most common presentation:** Self-limiting gastroenteritis (incubation period 6–72 hours). * **Sickle Cell Anemia Connection:** NTS is the most common cause of **osteomyelitis** in patients with Sickle Cell Disease. * **Rose Spots:** These are characteristic of Typhoid fever, NOT non-typhoidal salmonellosis. * **Antibiotic Policy:** Antibiotics are generally avoided in uncomplicated NTS gastroenteritis as they may prolong fecal shedding; they are reserved for invasive disease or high-risk patients.

Q: Which human infection spreads through urine?

Leptospira. **Explanation:** **Leptospirosis** is a zoonotic disease caused by the spirochete *Leptospira interrogans*. The pathogen colonizes the renal tubules of reservoir animals (primarily rodents, dogs, and livestock) and is shed in their **urine**. Humans acquire the infection through direct contact with infected urine or, more commonly, via water and soil contaminated with it. The bacteria enter the human body through mucous membranes or abraded skin. **Analysis of Options:** * **Leptospira (Correct):** It is the classic example of a "urine-borne" zoonosis. In humans, leptospires can also be found in the urine during the second week of illness (leptospiruria), though human-to-human transmission is rare. * **Legionella:** Spread via **inhalation** of contaminated aerosols from water systems (e.g., AC cooling towers, showers). It is not shed in urine. * **Plague (*Yersinia pestis*):** Primarily transmitted via the **bite of an infected rat flea** (*Xenopsylla cheopis*) or through respiratory droplets (pneumonic plague). * **Diphtheria (*Corynebacterium diphtheriae*):** Transmitted via **respiratory droplets** or direct contact with skin lesions. **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.** * **Biphasic Nature:** It presents in two phases: the *Leptospiremic phase* (blood/CSF) followed by the *Immune phase* (urine). * **Culture Media:** Uses specialized media like **EMJH** (Ellinghausen-McCullough-Johnson-Harris) or **Fletcher’s medium**. * **Microscopic Agglutination Test (MAT):** The gold standard for serological diagnosis.

Q: Which species of Brucella is acquired from contact with goats and sheep?

B. melitensis. **Explanation:** Brucellosis is a zoonotic infection caused by small, Gram-negative coccobacilli. Humans are accidental hosts, acquiring the infection through direct contact with infected animals or consumption of unpasteurized dairy products. **1. Why B. melitensis is correct:** * **B. melitensis** is the most common and virulent species causing human brucellosis worldwide. Its primary reservoirs are **goats and sheep**. It is highly prevalent in the Mediterranean, Middle East, and parts of India. **2. Why the other options are incorrect:** * **B. suis:** The primary reservoir is **pigs (swine)**. It is known for causing chronic infections and localized suppurative lesions. * **B. abortus:** The primary reservoir is **cattle**. While it causes "contagious abortion" in cows, it generally causes a milder form of the disease in humans compared to *B. melitensis*. * **B. canis:** The primary reservoir is **dogs**. Human infections are rare and usually result in mild symptoms. **3. High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Characterized by **Undulant fever** (fever that rises and falls like waves), profuse malodorous sweating, and splenomegaly. * **Diagnosis:** * **Standard Agglutination Test (SAT):** Detects antibodies; a titer of 1:160 or more is significant. * **Castaneda’s Medium:** A biphasic culture medium used for blood cultures (though automated systems like BACT/ALERT are now preferred). * **Rose Bengal Test:** A rapid screening test. * **Treatment:** The WHO recommends a combination of **Rifampicin and Doxycycline** for 6 weeks. * **Occupational Hazard:** It is a significant risk for veterinarians, slaughterhouse workers, and laboratory personnel (highly infectious via aerosols).

Q: What is the most common form of anthrax?

Cutaneous anthrax. **Explanation:** **Bacillus anthracis**, the causative agent of anthrax, is a gram-positive, spore-forming rod. The clinical presentation of anthrax depends on the route of entry of these spores into the body. **Why Cutaneous Anthrax is correct:** Cutaneous anthrax is the **most common clinical form**, accounting for more than **95% of all naturally occurring cases** worldwide. It occurs when spores enter the skin through minor abrasions or insect bites, usually during the handling of infected animal products (hides, wool, or carcasses). It typically presents as a painless "malignant pustule"—a central black eschar surrounded by significant non-pitting edema. **Why other options are incorrect:** * **Wool sorters' disease (Inhalation Anthrax):** This is a rare but severe form caused by inhaling spores (usually <5 μm) during industrial processing of animal hair or wool. While it is high-yield for exams due to its association with "mediastinal widening" on X-ray, it is far less common than the cutaneous form. * **Alimentary (Gastrointestinal) Anthrax:** This occurs after ingesting undercooked meat from infected animals. It is the rarest form of the disease but carries a high mortality rate. **NEET-PG High-Yield Pearls:** * **Virulence Factors:** Encapsulated (Poly-D-glutamic acid capsule) and produces Anthrax Toxin (composed of Protective Antigen, Edema Factor, and Lethal Factor). * **Microscopy:** "Bamboo stick" appearance; "McFadyean’s reaction" (polychrome methylene blue stain) is used to visualize the capsule. * **Culture:** Characterized by **"Medusa head" colonies** on blood agar and a "string of pearls" appearance on agar containing penicillin. * **DOC:** Ciprofloxacin or Doxycycline are the preferred treatments.

Q: Regarding Brucellosis, all of the following are true except:

Man to man transmission. **Explanation:** **Brucellosis** (also known as Undulant fever, Malta fever, or Mediterranean fever) is a classic zoonotic infection caused by Gram-negative coccobacilli of the genus *Brucella*. **1. Why Option A is the Correct Answer (The "Except"):** Human-to-human transmission of Brucellosis is **extremely rare**. While there are anecdotal reports of transmission via blood transfusion, bone marrow transplantation, or breastfeeding, it is clinically considered a "dead-end" host infection in humans. The primary mode of transmission is through direct contact with infected animal tissues or the consumption of unpasteurized dairy products. **2. Analysis of Other Options:** * **Option B (A zoonosis):** This is true. It is a systemic infection transmitted from animals (sheep, goats, cattle, pigs) to humans. * **Option C (Blood cultures):** This is true. Blood culture is the gold standard for diagnosis. Though *Brucella* is fastidious and may take weeks to grow (traditionally requiring the **Castaneda biphasic medium**), modern automated systems like BACT/ALERT usually detect it within 5–7 days. * **Option D (B. melitensis):** This is true. Among the species (*B. melitensis, B. abortus, B. suis, B. canis*), ***B. melitensis*** (from sheep/goats) is the most common and most virulent cause of human brucellosis worldwide. **Clinical Pearls for NEET-PG:** * **Rose Bengal Plate Test (RBPT):** A rapid screening test. * **Standard Agglutination Test (SAT):** Detects antibodies; a titer of >1:160 is significant. * **Treatment:** The WHO-recommended regimen is **Rifampicin + Doxycycline** for 6 weeks. * **Occupational Hazard:** It is a common laboratory-acquired infection; suspected samples must be handled in Biosafety Level 3 (BSL-3) cabinets.

Q: An organism is found to be a pleomorphic, gram-negative rod that causes a localized skin infection and is associated with an occupational disease of fishermen, fish handlers, and butchers. What is the most likely organism?

Erysipelothrix. **Explanation:** The clinical presentation describes **Erysipeloid**, a localized cutaneous infection caused by **_Erysipelothrix rhusiopathiae_**. **1. Why Erysipelothrix is correct:** * **Occupational Exposure:** It is a classic zoonotic infection associated with handling fish, shellfish, poultry, and swine. It primarily affects fishermen, butchers, and veterinarians. * **Morphology:** It is a Gram-positive rod, but it is notoriously **decolorized easily**, often appearing **Gram-variable or Gram-negative** in clinical specimens. It is pleomorphic and can form long, filamentous chains. * **Clinical Presentation:** It causes a painful, purplish-red, well-demarcated skin lesion (Erysipeloid), typically on the hands, following traumatic inoculation. **2. Why other options are incorrect:** * **Brucella:** While zoonotic (farmers/vets), it typically presents as a systemic "undulant fever" rather than a localized skin infection. It is a small Gram-negative coccobacillus. * **Salmonella:** Though Gram-negative rods, they primarily cause enteric fever or gastroenteritis. Skin manifestations (Rose spots) are systemic, not localized occupational inoculations. * **Leptospira:** These are spirochetes (not rods) transmitted via water contaminated with animal urine. They cause systemic disease (Weil’s disease) rather than localized cutaneous lesions. **High-Yield Clinical Pearls for NEET-PG:** * **H2S Production:** *Erysipelothrix* is the **only** Gram-positive rod that produces **Hydrogen Sulfide (H2S)** on TSI agar (Blackening). * **Catalase Negative:** This distinguishes it from *Listeria monocytogenes* (which is Catalase positive). * **Treatment:** Penicillin is the drug of choice. Note that it is intrinsically **resistant to Vancomycin**, a rare trait for Gram-positive organisms.

Question 1

Which of the following statements regarding anthrax is INCORRECT?

Accepted Answer

Cutaneous anthrax is the most common form of the disease and is rare nowadays.

Answer

It can be caused by direct contact with infected animals or contaminated products.

Answer

Cutaneous anthrax can result from contact with infected animal hides or hair.

Answer

Pulmonary anthrax occurs through inhalation of spores.

Question 2

Which of the following statements about non-typhoidal Salmonella is FALSE?

Accepted Answer

Humans are the only reservoirs.

Answer

Transmission is most commonly associated with eggs, poultry, and undercooked meat.

Answer

Common in immunocompromised individuals.

Answer

Resistance to fluoroquinolones has emerged.

Question 3

What is true about the causative agent of Malta fever?

Accepted Answer

Patients present with undulant fevers, sweating (often with characteristic foul, moldy smell sometimes likened to wet hay), and migratory arthralgia and myalgia.

Answer

Gram-positive, motile, nonspore-forming, rod-shaped (coccobacilli) bacteria

Answer

A nasopharyngeal or an oropharyngeal swab is sent to the bacteriology laboratory for Gram stain.

Answer

Treated by macrolides.

Question 4

Which human infection spreads through urine?

Accepted Answer

Leptospira

Answer

Legionella

Answer

Plague

Answer

Diphtheria

Question 5

Which species of Brucella is acquired from contact with goats and sheep?

Accepted Answer

B. melitensis

Answer

B. suis

Answer

B. abortus

Answer

B. canis

Question 6

A 9-year-old girl presents with a week of right armpit pain. Examination reveals tender, enlarged right axillary lymph nodes. She has four linear, nearly healed abrasions on her right forearm, with a 0.5-cm erythematous nodule over one abrasion. Histologic examination of a lymph node shows stellate, necrotizing granulomas. The lymphadenopathy regresses over 2 months. Which of the following infections is most likely to have caused these findings?

Accepted Answer

Bartonella henselae

Answer

Cytomegalovirus

Answer

Epstein-Barr virus

Answer

Staphylococcus aureus

Question 7

Brucella is transmitted by all of the following except?

Accepted Answer

Man to man

Answer

Aerosol transmission

Answer

Ingestion of raw milk

Answer

Contact with aborted fetuses

Question 8

What is the most common form of anthrax?

Accepted Answer

Cutaneous anthrax

Answer

Wool sorters' disease

Answer

Alimentary anthrax

Answer

None of the above

Question 9

Regarding Brucellosis, all of the following are true except:

Accepted Answer

Man to man transmission

Answer

A zoonosis

Answer

Blood cultures are used in diagnosis

Answer

B. melitensis is the most common cause

Question 10

An organism is found to be a pleomorphic, gram-negative rod that causes a localized skin infection and is associated with an occupational disease of fishermen, fish handlers, and butchers. What is the most likely organism?

Accepted Answer

Erysipelothrix

Answer

Brucella

Answer

Salmonella

Answer

Leptospira

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

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