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: 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: A 23 year old male patient presented with abrupt onset of fever, headache and myalgia followed by petechial rash and arthritis 2 to 10 days after exposure to a rat bite. He is diagnosed with Rat-bite fever. What is the causative organism of this disease?

Streptobacillus moniliformis. ***Streptobacillus moniliformis*** - This organism is a common cause of rat-bite fever (also known as **Haverhill fever** or **streptobacillary fever**) in North America. - Clinical features of fever, headache, myalgia, polyarthralgia, and **maculopapular** or **petechial rash** occurring 2-10 days post-exposure to a rat bite are characteristic of infection with this bacterium. *Erysipelothrix rhusiopathiae* - This bacterium primarily causes **erysipeloid**, a localized skin infection seen in individuals handling animal products (e.g., butchers, fishermen). - While it can cause systemic infection, **arthritis** and **petechial rash** as prominent features after a rat bite are less typical for *Erysipelothrix rhusiopathiae*. *Eikenella corrodens* - This organism is part of the normal oral flora and is commonly associated with infections following **human bites** or **clenched fist injuries**. - It typically causes localized cellulitis, abscesses, or osteomyelitis, rather than the systemic symptoms of rat-bite fever with prominent rash and arthritis. *Klebsiella granulomatis* - This bacterium is the causative agent of **donovanosis (granuloma inguinale)**, a sexually transmitted infection characterized by chronic, progressive genital ulcers. - Its clinical presentation is entirely different from rat-bite fever, lacking associations with animal bites or the described systemic symptoms.

Q: Most important reservoir of leptospira is:

Rat. ***Rat*** - **Rats** are considered the most important and widespread natural reservoirs for pathogenic *Leptospira* species due to their chronic renal carriage and shedding of leptospires in urine. - Their ubiquity, especially in environments frequented by humans, greatly contributes to the transmission cycle of **leptospirosis**. *Man* - Humans can develop leptospirosis but are generally considered **dead-end hosts**, meaning they rarely transmit the infection to others. - They do not typically contribute to the long-term maintenance or spread of the bacterium in the environment. *Pig* - **Pigs** can be important reservoirs for certain serovars of *Leptospira*, particularly those associated with livestock. - While significant in some agricultural settings, they are not globally as primary a reservoir as rats for human leptospirosis. *Monkey* - **Monkeys** can be infected with *Leptospira*, but they are not considered a primary or major reservoir for human leptospirosis globally. - Their role in environmental transmission is generally less significant compared to rodents or domestic animals.

Q: A 30-year-old man develops a pustular lesion at the site of a cat scratch on his forearm. This is followed 1 week later by malaise, fever, and lymphadenopathy. On examination, he has tender axillary lymph nodes. Which of the following is the most likely causative organism?

Bartonella henselae. ***Bartonella henselae*** - This organism is the definitive cause of **cat scratch disease**. The patient's presentation with a **pustular lesion at the site of a cat scratch**, followed by malaise, fever, and regional **lymphadenopathy (tender axillary lymph nodes)**, is classic for this infection. - *B. henselae* is transmitted to humans through scratches or bites from infected cats, especially kittens. *Bartonella quintana* - This bacterium is primarily associated with **trench fever** and **bacillary angiomatosis** in immunocompromised individuals. - It is transmitted by the human body louse, not typically from cat scratches. *Bartonella bacilliformis* - This organism is the causative agent of **Carrion's disease**, which presents in two stages: an acute febrile hemolytic anemia (**Oroya fever**) and a chronic verrucous skin eruption (**verruga peruana**). - It is transmitted by the **sand fly (Lutzomyia species)** and is endemic to certain Andean regions. *Coxiella burnetii* - This bacterium causes **Q fever**, a zoonotic infection typically transmitted through inhalation of aerosols from infected animals (cattle, sheep, goats). - Q fever commonly presents with **flu-like symptoms**, pneumonia, or hepatitis, and does not typically involve a pustular lesion at a scratch site with regional lymphadenopathy.

Q: Fever of unknown origin in a farmer who raises goats would most likely be caused by which of the following organisms?

Brucella melitensis. ***Brucella melitensis*** - **Brucellosis** is a zoonotic infection commonly acquired through contact with infected animals or consumption of unpasteurized dairy products. - ***Brucella melitensis* is specifically associated with goats and sheep**, making it the most likely organism in this clinical scenario. - It classically presents as **fever of unknown origin (FUO)** due to its varied and non-specific clinical manifestations, including undulating fever, malaise, myalgia, arthralgia, and hepatosplenomegaly. *T. pallidum* - *Treponema pallidum* is the causative agent of **syphilis**, a sexually transmitted infection. - While syphilis can cause fever, its primary modes of transmission (sexual contact, vertical transmission) and clinical manifestations (e.g., chancres, rash, mucous patches) are distinct from the scenario described. - Not associated with occupational goat exposure. *Histoplasma capsulatum* - *Histoplasma capsulatum* causes **histoplasmosis**, a fungal infection associated with exposure to **bird or bat droppings**, particularly in endemic areas (e.g., Ohio and Mississippi River valleys). - Although it can cause disseminated disease and fever, the epidemiological context (exposure to goats, not birds/bats) makes it unlikely in this scenario. *Clostridium novyi* - *Clostridium novyi* is an anaerobic bacterium known to cause **gas gangrene** (clostridial myonecrosis) and occasionally **black disease** in livestock. - It is not typically associated with human fever of unknown origin in the context of occupational animal contact described. - More relevant to wound infections or animal disease rather than systemic FUO in farmers.

Q: Cat scratch disease is caused by

Bartonella. ***Correct: Bartonella*** - **Cat scratch disease** is caused by the bacterium **Bartonella henselae**, which is transmitted through the scratch or bite of an infected cat. - The infection primarily manifests as **lymphadenopathy** (swollen lymph nodes) near the site of inoculation. *Incorrect: Moraxella* - **Moraxella** species, particularly *Moraxella catarrhalis*, are common causes of upper and lower respiratory tract infections, such as **otitis media** and **bronchitis**. - They are not associated with cat scratch disease. *Incorrect: Pseudomonas* - **Pseudomonas aeruginosa** is a ubiquitous bacterium known for causing opportunistic infections in immunocompromised individuals, such as **pneumonia**, **urinary tract infections**, and **wound infections**. - It is a common cause of healthcare-associated infections but not cat scratch disease. *Incorrect: Francisella* - **Francisella tularensis** is the causative agent of **tularemia**, a zoonotic disease typically transmitted by contact with infected animals (e.g., rabbits, rodents) or vectors (e.g., ticks, flies). - Its clinical presentation involves fever, skin ulcers, and lymphadenopathy, but it is distinct from cat scratch disease and not transmitted by cats.

Q: Which of the following viral infections is transmitted by tick?

Kyasanur forest disease (KFD). ***Kyasanur forest disease (KFD)*** - KFD is a **viral hemorrhagic fever** caused by the Kyasanur Forest disease virus, a member of the *Flaviviridae* family. - It is primarily transmitted to humans through the bite of infected **ticks**, especially *Haemaphysalis spinigera*. *Ehrlichiosis* - Ehrlichiosis is a **bacterial infection** caused by *Ehrlichia* species, not a viral infection. - It is transmitted by **ticks**, primarily the **lone star tick** (*Amblyomma americanum*). *Lyme disease* - Lyme disease is a **bacterial infection** caused by *Borrelia burgdorferi*, not a viral infection. - It is transmitted by **ticks**, notably the **black-legged tick** (*Ixodes scapularis*). *Rocky Mountain spotted fever* - Rocky Mountain spotted fever (RMSF) is a **bacterial infection** caused by *Rickettsia rickettsii*, not a viral infection. - It is transmitted by **ticks**, such as the **American dog tick**, **Rocky Mountain wood tick**, and **brown dog tick**.

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

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 3

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 4

Four weeks after assisting in several calf deliveries, a farmer develops fever, weakness, muscle aches, and sweats. The fever rises in the afternoon and falls during the night. A Brucella species is isolated. Which Brucella species is a possible bioterrorism agent and is best described by one of the following?

Accepted Answer

Typically infects goats and sheep, grows well in CO2, and is not inhibited by thionine or basic fuchsin dyes

Answer

Commonly inhabits the canine respiratory tract and is an occasional pathogen for humans; strongly urease-positive

Answer

Gram-negative bipolar stained bacilli that cause diarrhea by means of a heat-stable enterotoxin, with abdominal pain that may be mistaken for appendicitis

Answer

Pits agar, grows both in carbon dioxide and under anaerobic conditions, and is part of the normal oral cavity flora

Question 5

A 23 year old male patient presented with abrupt onset of fever, headache and myalgia followed by petechial rash and arthritis 2 to 10 days after exposure to a rat bite. He is diagnosed with Rat-bite fever. What is the causative organism of this disease?

Accepted Answer

Streptobacillus moniliformis

Answer

Erysipelothrix rhusiopathiae

Answer

Eikenella corrodens

Answer

Klebsiella granulomatis

Question 6

Most important reservoir of leptospira is:

Accepted Answer

Rat

Answer

Man

Answer

Pig

Answer

Monkey

Question 7

A 30-year-old man develops a pustular lesion at the site of a cat scratch on his forearm. This is followed 1 week later by malaise, fever, and lymphadenopathy. On examination, he has tender axillary lymph nodes. Which of the following is the most likely causative organism?

Accepted Answer

Bartonella henselae

Answer

Bartonella quintana

Answer

Bartonella bacilliformis

Answer

Coxiella burnetii

Question 8

Fever of unknown origin in a farmer who raises goats would most likely be caused by which of the following organisms?

Accepted Answer

Brucella melitensis

Answer

T. pallidum

Answer

Histoplasma capsulatum

Answer

Clostridium novyi

Question 9

Cat scratch disease is caused by

Accepted Answer

Bartonella

Answer

Moraxella

Answer

Pseudomonas

Answer

Francisella

Question 10

Which of the following viral infections is transmitted by tick?

Accepted Answer

Kyasanur forest disease (KFD)

Answer

Ehrlichiosis

Answer

Lyme disease

Answer

Rocky Mountain spotted fever

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

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