Zoonotic Diseases Practice Questions

Q: A farmer presents with fever, malaise, and diarrhea. There is a history of exposure to livestock. Which of the following organisms is most likely responsible for the illness?

Coxiella burnetii. ***Coxiella burnetii*** - This organism causes **Q fever**, a common zoonosis transmitted primarily through aerosols generated from the births or products of infected livestock, such as **sheep, goats, and cattle**, which aligns with the patient being a farmer. - Acute Q fever typically presents with non-specific severe symptoms including high fever, headache, significant **malaise**, and sometimes gastrointestinal issues like **diarrhea**. *Rickettsia rickettsii* - This organism is responsible for **Rocky Mountain spotted fever (RMSF)**, which is associated with a history of **tick bite** exposure, not direct livestock aerosol exposure. - RMSF classically presents with a prominent rash, often **petechial**, starting on the wrists and ankles and spreading centripetally, which is a key differentiating feature. *Rickettsia typhi* - This pathogen causes **murine typhus** (endemic typhus), transmitted through exposure to rat fleas, making it less likely given the farmer's exposure to livestock. - Murine typhus generally causes a milder presentation compared to epidemic typhus, often presenting with fever, headache, and a **truncal rash**. *Orientia tsutsugamushi* - This organism causes **scrub typhus**, found primarily in the Asia-Pacific region and transmitted by the bite of a **chigger** (mite larva). - A distinguishing feature of scrub typhus is the presence of a painless **eschar** (black, necrotic lesion) at the site of the chigger bite.

Q: Which of the following is the vector responsible for transmitting Orientia tsutsugamushi?

Mite. ***Mite***- *Orientia tsutsugamushi*, the causative agent of **scrub typhus**, is transmitted to humans by the bite of the **larval stage** (chiggers) of mites belonging to the Trombiculidae family, such as *Leptotrombidium deliense*. - Mites are crucial in the infectious cycle because they maintain the pathogen through **transovarial transmission**, acting as both the **vector** and the **reservoir**. *Tick* - Ticks are the vectors for other rickettsial diseases, most notably **Rocky Mountain spotted fever** (*Rickettsia rickettsii*) and tularaemia. - Tick-borne infections typically involve different reservoirs (e.g., small mammals, deer) and produce distinct clinical syndromes from scrub typhus. *Louse* - Lice (specifically the body louse) are the vectors for **epidemic typhus** (*Rickettsia prowazekii*) and trench fever. - Transmission of louse-borne pathogens involves scratching infectious feces into the skin, which is not the mechanism for *Orientia tsutsugamushi*. *Flea* - Fleas, particularly the oriental rat flea, transmit **murine typhus** (*Rickettsia typhi*) and **plague** (*Yersinia pestis*). - This type of vector is typically associated with peridomestic rodents, contrasting with the outdoor, vegetation-associated exposure risk characteristic of **scrub typhus**.

Q: A cattle farmer presented with a lesion on the arm. Gram staining showed gram-positive rods with square ends with a central spore. Identify the organism.

Bacillus anthracis. ***Bacillus anthracis***- The microscopic finding of large, non-motile, **Gram-positive rods** with characteristic **square ends** (often described as 'boxcar' shapes) and a central spore is the classic description of *Bacillus anthracis*.- The clinical history of a **cattle farmer** with a skin lesion strongly suggests **cutaneous anthrax**, the most common form of anthrax acquired through exposure to infected livestock.*Bacillus cereus*- While also a Gram-positive, spore-forming rod, *B. cereus* is generally **motile** and typically causes severe food poisoning (emetic or diarrheal types).- It usually lacks the distinctive **square ends** seen in *Bacillus anthracis*.*Pseudomonas aeruginosa*- This organism is a **Gram-negative rod**, which directly contradicts the finding of a Gram-positive rod in the staining.- Furthermore, *P. aeruginosa* is **non-spore-forming**, ruling it out based on the finding of a central spore.*Brucella abortus*- *Brucella* species are small, obligate intracellular, **Gram-negative coccobacilli** or short rods, not large Gram-positive rods.- They are **non-spore-forming** and typically cause systemic illness (**brucellosis** or undulant fever) rather than localized cutaneous lesions matching this description.

Q: A farmer presents with an ulcerative skin lesion showing signs of necrosis. Smear from the ulcer stained with polychrome methylene blue reveals capsulated bacilli that are McFadyean reaction positive. What is the most likely causative organism?

Bacillus anthracis. ***Bacillus anthracis*** - The combination of a necrotic skin ulcer (eschar) in an exposed individual (farmer) and the specific laboratory findings is diagnostic for **Cutaneous Anthrax**. - The **McFadyean reaction** is a specific test for *Bacillus anthracis*, where the D-glutamic acid polypeptide capsule is stained **pink/purple** against the blue bacilli using **Polychrome Methylene Blue (PMB)** stain. *Clostridium perfringens* - This organism typically causes **gas gangrene** (clostridial myonecrosis) characterized by severe tissue destruction and gas production (crepitus), not usually a single necrotic ulcer. - Although it is a Gram-positive bacillus, it is an **anaerobe**, unlike the aerobic *Bacillus anthracis*, and the McFadyean reaction is not used for its identification. *Yersinia pestis* - This Gram-negative organism causes **plague** and typically presents with painful, swollen lymph nodes called **buboes** (buboes plague). - It is classified as a small, pleomorphic, non-capsulated bacillus and does not exhibit a positive McFadyean reaction with Polychrome Methylene Blue. *Francisella tularensis* - This causative agent of **tularemia** often causes an ulceroglandular syndrome, but it is a small, Gram-negative coccobacillus and does not have the macroscopic capsule visualized by the McFadyean reaction. - It requires specialized culture media like **cysteine-glucose-blood agar** due to its fastidious nature, differentiating it from *Bacillus* species.

Q: Match the following: Vector/agent : 1. Louse - 2. Tick - 3. Mite - 4. Poxvirus Diseases caused : A. Epidemic typhus - B. Rocky Mounted Spotted Fever (RMSF) - C. Scrub typhus - D. Molluscum contagiosum

1-A, 2-B, 3-C, 4-D. ***1-A, 2-B, 3-C, 4-D*** - **1-A (Louse - Epidemic typhus):** Epidemic typhus is caused by *Rickettsia prowazekii*, transmitted to humans via the bite or feces of the **human body louse** (*Pediculus humanus corporis*). This is a classic louse-borne rickettsial disease. - **2-B (Tick - Rocky Mountain Spotted Fever):** RMSF is caused by *Rickettsia rickettsii* and transmitted by **hard ticks**, primarily *Dermacentor* species. It is the most severe tick-borne rickettsial illness in the United States. - **3-C (Mite - Scrub typhus):** Scrub typhus is caused by *Orientia tsutsugamushi*, transmitted by the bite of infected **larval mites** (chiggers) of the *Leptotrombidium* genus. It is endemic in the Asia-Pacific region. - **4-D (Poxvirus - Molluscum contagiosum):** Molluscum contagiosum is a benign viral skin infection caused by the **Molluscum contagiosum virus**, a member of the Poxviridae family. It spreads through direct contact, not via arthropod vectors. *1-B, 2-A, 3-C, 4-D* - The match **1-B** is incorrect: **Louse** transmits **Epidemic typhus (A)**, not Rocky Mountain Spotted Fever (B), which is tick-borne. - The match **2-A** is incorrect: **Tick** transmits **Rocky Mountain Spotted Fever (B)**, not Epidemic typhus (A), which is louse-borne. *1-D, 2-B, 3-C, 4-A* - The match **1-D** is incorrect: **Louse** is an arthropod vector for **Epidemic typhus (A)**, while **Molluscum contagiosum (D)** is a viral disease spread by direct contact, not lice. - The match **4-A** is incorrect: **Poxvirus** causes **Molluscum contagiosum (D)**, while **Epidemic typhus (A)** is a rickettsial infection transmitted by lice, not a poxvirus disease. *1-C, 2-B, 3-A, 4-D* - The match **1-C** is incorrect: **Louse** transmits **Epidemic typhus (A)**, not **Scrub typhus (C)**, which is transmitted by larval mites. - The match **3-A** is incorrect: **Mites** transmit **Scrub typhus (C)**, not **Epidemic typhus (A)**, which is a louse-borne disease.

Q: The life cycle shown below is of:

Nipah virus. ***Nipah virus*** - The diagram clearly illustrates the transmission pathways characteristic of Nipah virus, involving **fruit bats (flying foxes)** as primary reservoirs, **pigs as intermediate hosts**, and human infection through direct contact with infected animals or consumption of **contaminated date palm sap**. - The described "rapid pig-to-pig transmission" and "people consume contaminated date palm sap" are key epidemiological features of Nipah virus outbreaks in Southeast Asia. *Japanese encephalitis* - Japanese encephalitis is primarily transmitted by **mosquitoes** (Culex species) and involves **water birds** as primary reservoirs, and pigs as amplifying hosts. - The life cycle shown does not depict mosquito vectors or water birds, which are central to Japanese encephalitis transmission. *Chandipura virus* - Chandipura virus is an arbovirus transmitted by **sandflies** and often associated with seasonal outbreaks of acute encephalitis, primarily affecting children. - Its transmission cycle does not involve bats, pigs, or contaminated date palm sap as depicted in the image. *Influenza* - Influenza viruses circulate mainly among **humans, birds, and pigs**, with transmission primarily through **respiratory droplets** or direct contact. - While pigs can play a role in certain influenza strains (e.g., swine flu), the involvement of bats and consumption of contaminated sap is not characteristic of human influenza transmission.

Q: Match List-I with List-II and select the correct answer using the code given below the Lists:

A→3 B→4 C→2 D→1. ***A→3 B→4 C→2 D→1*** - **Epidemic typhus** is caused by *Rickettsia prowazekii*, primarily transmitted by the **human body louse**. - **Murine typhus** is caused by *Rickettsia typhi*, transmitted by **fleas typically found on rodents**. - **Scrub typhus** is caused by *Orientia tsutsugamushi* (formerly *Rickettsia tsutsugamushi*), transmitted by the bite of **chiggers (larval mites)**. - **Indian tick typhus** is a form of spotted fever group rickettsiosis, often caused by *Rickettsia conorii*, transmitted by **ticks.** *A→2 B→4 C→1 D→3* - This option incorrectly associates Epidemic typhus with *Rickettsia tsutsugamushi* and Indian tick typhus with *Rickettsia prowazekii*. - Epidemic typhus is caused by *Rickettsia prowazekii*, and *Rickettsia tsutsugamushi* causes Scrub typhus. *A→1 B→4 C→3 D→2* - This option incorrectly identifies *Rickettsia conorii* as the agent for Epidemic typhus and *Rickettsia tsutsugamushi* for Indian tick typhus. - *Rickettsia conorii* is associated with Mediterranean spotted fever (a form of tick typhus), and *Rickettsia tsutsugamushi* causes Scrub typhus. *A→4 B→1 C→3 D→2* - This option incorrectly matches Epidemic typhus with *Rickettsia typhi* and Scrub typhus with *Rickettsia prowazekii*. - *Rickettsia typhi* causes Murine typhus, and *Rickettsia prowazekii* causes Epidemic typhus.

Q: An organism produces cutaneous disease (malignant pustule or eschar) at the site of inoculation in handlers of animal skins. Most likely organism is:

Bacillus anthracis. ***Bacillus anthracis*** - This description is classic for **cutaneous anthrax**, characterized by a **malignant pustule** or **eschar** that develops at the site of inoculation. - The context of handling **animal skins** (e.g., wool-sorter's disease) is a key epidemiological clue for _Bacillus anthracis_ infection. *Neisseria meningitidis* - Primarily causes **meningitis** and **meningococcemia**, involving a petechial or purpuric rash, not a single eschar or malignant pustule. - There is no direct association with handling animal skins. *Pseudomonas aeruginosa* - This bacterium is often associated with **opportunistic infections** in immunocompromised individuals, burn patients, or those with indwelling medical devices. - While it can cause skin lesions (e.g., **ecthyma gangrenosum**), these are distinct from the anthrax eschar and are not linked to animal skin exposure. *Cryptococcus neoformans* - A **fungus** that primarily causes **cryptococcal meningitis** or pulmonary infections, especially in immunocompromised individuals. - Skin manifestations, when they occur, are typically papules, nodules, or ulcers, not the classic **cutaneous anthrax eschar**.

Q: The primary site of multiplication of rickettsial organisms is in the

Endothelial cells of small vessels. ***Endothelial cells of small vessels*** - Rickettsial organisms are **obligate intracellular bacteria** and have a strong tropism for the **endothelial cells** lining small blood vessels. - This tropism leads to **vasculitis**, which causes the characteristic rash and systemic symptoms seen in rickettsial infections. *Media of arteries* - While rickettsiae infect blood vessels, their primary site of multiplication is not the **media of arteries**, which mainly consists of smooth muscle cells. - The **endothelium**, the innermost layer, is the critical target for replication and subsequent host cell damage. *Parenchymal cells of the liver* - Although some rickettsial infections can cause liver dysfunction, the **parenchymal cells (hepatocytes)** of the liver are not their primary site of multiplication. - Liver involvement is often secondary to systemic vasculitis rather than direct hepatocyte infection. *Adventitia of all blood vessels* - The **adventitia** is the outermost layer of blood vessels and is composed mainly of connective tissue. - Rickettsial organisms primarily target the **endothelial cells** lining the lumen, not the adventitial layer.

Question 1

A farmer presents with fever, malaise, and diarrhea. There is a history of exposure to livestock. Which of the following organisms is most likely responsible for the illness?

Accepted Answer

Coxiella burnetii

Answer

Rickettsia typhi

Answer

Orientia tsutsugamushi

Answer

Rickettsia rickettsii

Question 2

Which of the following is the vector responsible for transmitting Orientia tsutsugamushi?

Accepted Answer

Mite

Answer

Flea

Answer

Tick

Answer

Louse

Question 3

A cattle farmer presented with a lesion on the arm. Gram staining showed gram-positive rods with square ends with a central spore. Identify the organism.

Accepted Answer

Bacillus anthracis

Answer

Bacillus cereus

Answer

Pseudomonas aeruginosa

Answer

Brucella abortus

Question 4

A farmer presents with an ulcerative skin lesion showing signs of necrosis. Smear from the ulcer stained with polychrome methylene blue reveals capsulated bacilli that are McFadyean reaction positive. What is the most likely causative organism?

Accepted Answer

Bacillus anthracis

Answer

Yersinia pestis

Answer

Francisella tularensis

Answer

Clostridium perfringens

Question 5

Match the following: 
Vector/agent : 1. Louse - 2. Tick - 3. Mite - 4. Poxvirus
Diseases caused : A. Epidemic typhus - B. Rocky Mounted Spotted Fever (RMSF) - C. Scrub typhus - D. Molluscum contagiosum

Accepted Answer

1-A, 2-B, 3-C, 4-D

Answer

1-B, 2-A, 3-C, 4-D

Answer

1-D, 2-B, 3-C, 4-A

Answer

1-C, 2-B, 3-A, 4-D

Question 6

The life cycle shown below is of:

Accepted Answer

Nipah virus

Answer

Japanese encephalitis

Answer

Chandipura virus

Answer

Influenza

Question 7

Match List-I with List-II and select the correct answer using the code given below the Lists:

Accepted Answer

A→3  B→4  C→2  D→1

Answer

A→2  B→4  C→1  D→3

Answer

A→1  B→4  C→3  D→2

Answer

A→4  B→1  C→3  D→2

Question 8

A 28-year-old man presents to the physician because of dizziness and palpitations for the past 12 hours and fever, malaise, headache, and myalgias for the past week. The patient traveled into the woods of Massachusetts 4 weeks ago. He has no known chronic medical conditions, and there is no history of substance use. His temperature is 38.3°C (100.9°F), pulse is 52/min, respirations are 16/min, and blood pressure is 126/84 mm Hg. His physical examination shows a single, 10-cm, round, erythematous lesion with a bull’s-eye pattern in the right popliteal fossa. His electrocardiogram shows Mobitz I second-degree atrioventricular (AV) block. The complete blood cell count and serum electrolyte levels are normal, but the erythrocyte sedimentation rate is 35 mm/hour. What is the most likely cause of the patient’s cardiac symptoms?

Accepted Answer

Spirochete infection

Answer

Systemic fungal infection

Answer

Viral infection transmitted by Aedes aegypti mosquito bite

Answer

Sexually transmitted bacterial infection

Answer

Mycoplasma infection

Question 9

An organism produces cutaneous disease (malignant pustule or eschar) at the site of inoculation in handlers of animal skins. Most likely organism is:

Accepted Answer

Bacillus anthracis

Answer

Neisseria meningitidis

Answer

Pseudomonas aeruginosa

Answer

Cryptococcus neoformans

Question 10

The primary site of multiplication of rickettsial organisms is in the

Accepted Answer

Endothelial cells of small vessels

Answer

Media of arteries

Answer

Parenchymal cells of the liver

Answer

Adventitia of all blood vessels

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

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