Zoonotic Diseases Practice Questions

Q: True about scrub typhus is?

Transmitted by larva of trombiculid mite. ***Transmitted by larva of trombiculid mite*** - Scrub typhus is transmitted to humans through the bite of the **larval form of trombiculid mites**, commonly known as chiggers. - These chiggers carry the bacteria *Orientia tsutsugamushi* within their salivary glands. - This is the **correct answer**. *Incubation period is 3-4 days* - The typical incubation period for scrub typhus ranges from **6 to 21 days**, with an average of 10 to 12 days. - An incubation period of 3-4 days is generally **too short** for scrub typhus. *Caused by Rickettsia typhi* - Scrub typhus is caused by **Orientia tsutsugamushi**, an obligate intracellular bacterium. - *Rickettsia typhi* is the causative agent of **murine typhus**, a different rickettsial disease. *Eschar is pathognomonic and diagnostic on its own* - An **eschar** is a characteristic and highly suggestive finding in scrub typhus, appearing at the site of the chigger bite in 50-80% of cases. - However, eschar is **not pathognomonic** - it can occur in other rickettsial diseases and conditions. - Definitive diagnosis requires laboratory confirmation such as **IgM ELISA**, **PCR**, or **serological tests** (Weil-Felix test) to identify *Orientia tsutsugamushi*.

Q: Wells' disease is caused by?

Leptospira. ***Leptospira*** - **Wells' disease**, also known as severe leptospirosis, is caused by infection with bacteria belonging to the genus **Leptospira**. - This zoonotic disease is transmitted through contact with infected animal urine or contaminated water and can cause a wide range of symptoms, from mild flu-like illness to severe organ damage. *Mycoplasma* - **Mycoplasma** are bacteria known to cause various infections such as atypical pneumonia, urinary tract infections, and genital infections. - They are not associated with Wells' disease or leptospirosis. *Legionella* - **Legionella** is a bacterium notorious for causing **Legionnaires' disease**, a severe form of pneumonia, and Pontiac fever. - These infections are typically acquired through inhalation of contaminated aerosols from water systems, not from animal urine or contaminated water in the context of Wells' disease. *Listeria* - **Listeria monocytogenes** is a bacterium that causes **listeriosis**, a serious infection typically contracted from contaminated food. - It primarily affects pregnant women, newborns, older adults, and immunocompromised individuals, and is not responsible for Wells' disease.

Q: Q fever is caused by -

Coxiella burnetii. ***Coxiella burnetii*** - **Q fever** is an infectious disease caused by the gram-negative bacterium **Coxiella burnetii**. - This bacterium is highly resistant and can survive in the environment, primarily transmitted through **inhalation of contaminated aerosols from infected animals** (e.g., cattle, sheep, goats). *Pseudomonas* - **Pseudomonas aeruginosa** is a common opportunistic pathogen known for causing a wide range of infections, particularly in hospitalized or immunocompromised individuals. - It is often associated with **nosocomial infections**, such as pneumonia, urinary tract infections, and wound infections, and is not the causative agent of Q fever. *Rickettsia typhi* - **Rickettsia typhi** is the causative agent of **endemic (murine) typhus**, a common rickettsial disease. - It is transmitted to humans through the bite of **fleas** that have fed on infected rodents. *Francisella* - The genus **Francisella** includes **Francisella tularensis**, the bacterium responsible for **tularemia**, also known as "rabbit fever." - Tularemia is a zoonotic disease transmitted to humans through contact with infected animals, insect bites, or inhalation, but it is distinct from Q fever.

Q: A girl from Shimla presented to OPD with fever, hypotension, malaise and axillary and inguinal lymphadenopathy. Culture in glucose broth shows stalactite growth. Most likely causative organism is?

Yersinia pestis. ***Yersinia pestis*** - The combination of **fever**, **hypotension**, **malaise**, and **inguinal and axillary lymphadenopathy** (buboes) is highly characteristic of **bubonic plague**, caused by *Yersinia pestis*. - **Stalactite growth** in broth culture is a classic identifying feature of *Yersinia pestis* when incubated without agitation, due to the organism's **lipid A-modified LPS** which allows self-aggregation. *Brucella abortus* - *Brucella abortus* causes **brucellosis**, which presents with **undulant fever**, **arthralgia**, and **hepatosplenomegaly**, but typically not with prominent acute lymphadenopathy and hypotension to this degree. - While it is a **facultative intracellular pathogen**, it does not exhibit stalactite growth in glucose broth. *Coxiella burnetii* - *Coxiella burnetii* causes **Q fever**, which is characterized by **fever**, **headache**, and **pneumonia**, often without prominent lymphadenopathy. - It is an **obligate intracellular bacterium** and cannot be cultivated in standard glucose broth, much less show stalactite growth. *Francisella tularensis* - *Francisella tularensis* causes **tularemia**, which can manifest with **fever**, **lymphadenopathy** (ulceroglandular form), and **malaise**. - However, it typically requires **specialized culture media** like cysteine-enriched agar and does not exhibit stalactite growth in glucose broth.

Q: A bird seller developed fever with chills and severe body pain. Investigation confirms the disease as ornithosis. Causative agent is:

Chlamydia psittaci. ***Chlamydia psittaci*** - **Ornithosis**, also known as psittacosis, is caused by *C. psittaci* and is transmitted to humans through contact with infected birds (e.g., parrots, parakeets, pigeons). The patient's occupation as a **bird seller** is a key clue. - Clinical manifestations include **fever, chills, and severe body pain**, mimicking severe influenza or atypical pneumonia. *Coxiella burnetii* - This bacterium causes **Q fever**, primarily transmitted from livestock (cattle, sheep, goats) through aerosols from birth products. - While Q fever can cause similar flu-like symptoms and atypical pneumonia, the patient's **bird exposure** points away from this diagnosis. *Borrelia* - Different species of *Borrelia* cause diseases such as **Lyme disease** (*B. burgdorferi*) and **relapsing fever** (*B. recurrentis*, *B. hermsii*). - These infections are typically transmitted by ticks or lice and are not associated with avian exposure or ornithosis. *Burkholderia pseudomallei* - This bacterium causes **melioidosis**, an infection prevalent in tropical and subtropical regions, particularly Southeast Asia and northern Australia. - It is acquired through contact with contaminated soil or water, not typically through avian exposure, and often presents with pneumonia, abscesses, or septicemia.

Q: A person working in an abattoir presented with malignant pustule on hand. What is the causative agent?

Bacillus anthracis. **Bacillus anthracis** - The presence of a **malignant pustule** on the hand, especially in an individual working in an **abattoir** (exposure to animals/animal products), is highly characteristic of **cutaneous anthrax**. - **Bacillus anthracis** is a **spore-forming bacterium** that causes anthrax, and the cutaneous form typically presents as a painless ulcer that develops into a black eschar. *Clostridium botulinum* - This bacterium causes **botulism**, a severe **neuroparalytic disease** characterized by flaccid paralysis. - It does not cause cutaneous lesions like a malignant pustule and is typically associated with **food poisoning** or wound infections leading to toxin production. *Streptococcus pyogenes* - This bacterium is a common cause of various infections, including **strep throat**, **impetigo**, **erysipelas**, and **necrotizing fasciitis**. - While it can cause skin infections, it does not typically present as a "malignant pustule" with the characteristic eschar seen in anthrax. *Clostridium perfringens* - This bacterium is a common cause of **gas gangrene** (myonecrosis) and **food poisoning**. - While it can cause severe tissue infections, it does not present as a malignant pustule.

Q: Scrub typhus is transmitted by:

Mite. ***Mite*** - Scrub typhus is caused by **Orientia tsutsugamushi**, which is transmitted to humans by the bite of infected larval trombiculid mites, also known as **chiggers**. - These mites typically inhabit areas with **dense vegetation** and are commonly found in rural or forested regions. - The **eschar** (black necrotic lesion) at the bite site is a characteristic feature of scrub typhus. *Louse* - **Lice** are known vectors for diseases such as **epidemic typhus** (caused by Rickettsia prowazekii) and **relapsing fever** (caused by Borrella recurrentis). - They do not transmit **scrub typhus**. *Tick* - **Ticks** are vectors for a variety of rickettsial diseases, including **Rocky Mountain spotted fever** (R. rickettsii), **Indian tick typhus** (R. conorii), and **ehrlichiosis**. - While ticks transmit other typhus-like illnesses, they are not responsible for transmitting **scrub typhus**. *Flea* - **Fleas** are vectors for **murine typhus** (caused by Rickettsia typhi) and **plague** (caused by Yersinia pestis). - They do not transmit **scrub typhus**, which is specifically transmitted by mites.

Q: A patient presents with a bullseye rash after a tick bite. Which organism is most likely responsible for this condition?

Borrelia burgdorferi. ***Correct: Borrelia burgdorferi*** - **Lyme disease**, caused by *Borrelia burgdorferi*, is classically characterized by an **erythema migrans** rash, which is often described as a **"bullseye"** or target-like lesion, developing after a tick bite. - This **spirochete** is transmitted to humans through the bite of infected *Ixodes* ticks and is the most common cause of vector-borne disease in the United States. *Incorrect: Rickettsia rickettsii* - This organism causes **Rocky Mountain spotted fever**, which typically presents with a **maculopapular rash** that begins on the ankles and wrists and spreads centrally. - While also transmitted by ticks, it does not typically cause a bullseye-shaped erythema migrans rash. *Incorrect: Treponema pallidum* - This bacterium is the causative agent of **syphilis** and is transmitted through sexual contact, not tick bites. - The primary lesion of syphilis is a **chancre**, a painless ulcer, which is distinct from a bullseye rash. *Incorrect: Leptospira interrogans* - This spirochete is responsible for **leptospirosis**, contracted through contact with contaminated water or animal urine. - It can cause severe systemic symptoms, including fever, headache, muscle pain, and jaundice, but it does not produce a bullseye rash.

Q: A patient with a cat bite presents with a swollen, tender hand and fever. A Gram stain of the wound shows gram-negative rods. What is the most likely pathogen?

Pasteurella multocida. ***Pasteurella multocida*** - ***Pasteurella multocida*** is a common commensal in the oral flora of cats and dogs, making it the most frequent cause of infection following **animal bites**. - The presentation of rapid onset of **swelling**, **pain**, and **inflammation** around a cat bite, accompanied by **gram-negative rods** on stain, is highly characteristic of ***Pasteurella*** infection. *Staphylococcus aureus* - While ***Staphylococcus aureus*** can cause skin and soft tissue infections, it typically presents with **gram-positive cocci** in clusters, not gram-negative rods. - Although common in human skin infections, it is less typical for a direct animal bite infection unless secondary contamination occurs. *Bartonella henselae* - ***Bartonella henselae*** is the causative agent of **cat scratch disease**, presenting primarily as **lymphadenopathy** often some weeks post-scratch. - It does not typically cause immediate, localized cellulitis with gram-negative rods visible on stain, as seen in this clinical scenario. *Capnocytophaga canimorsus* - ***Capnocytophaga canimorsus*** is a gram-negative rod found in the oral flora of dogs and, less commonly, cats, which can cause severe infections, particularly in immunocompromised individuals. - While it can cause rapid-onset infection from a bite, ***Pasteurella multocida*** is significantly more common in routine animal bite infections.

Q: Which of the following is the carrying agent for Lyme disease?

Ixodes scapularis ticks. ***Ixodes scapularis ticks*** - *Ixodes scapularis* ticks (deer ticks) are the primary **vectors for Lyme disease** (caused by *Borrelia burgdorferi*) in North America [1]. - In Europe, *Ixodes ricinus* is the main vector for Lyme disease. - Lyme disease presents with characteristic **erythema migrans** rash, followed by potential neurological, cardiac, and arthritic complications [1]. - Lyme arthritis commonly affects large joints, particularly the **knee**, causing inflammatory arthritis [1]. *Anopheles* - **Anopheles mosquitoes** are the primary vectors for **malaria**, not Lyme disease [2]. - Malaria is caused by *Plasmodium* parasites and presents with fever, chills, and hemolytic anemia [2]. *Louse* - **Lice** are vectors for diseases such as **epidemic typhus** (caused by *Rickettsia prowazekii*) and **relapsing fever** (caused by *Borrelia recurrentis*) [3]. - They are not associated with the transmission of Lyme disease. *Rat flea* - **Rat fleas** (e.g., *Xenopsylla cheopis*) are the primary vectors for **bubonic plague** (caused by *Yersinia pestis*) and **murine typhus**. - These insects do not transmit Lyme disease. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 389-390. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 400. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 392-393.

Question 1

True about scrub typhus is?

Accepted Answer

Transmitted by larva of trombiculid mite

Answer

Incubation period is 3-4 days

Answer

Caused by Rickettsia typhi

Answer

Eschar is pathognomonic and diagnostic on its own

Question 2

Wells' disease is caused by?

Accepted Answer

Leptospira

Answer

Mycoplasma

Answer

Legionella

Answer

Listeria

Question 3

Q fever is caused by -

Accepted Answer

Coxiella burnetii

Answer

Pseudomonas

Answer

Rickettsia typhi

Answer

Francisella

Question 4

A girl from Shimla presented to OPD with fever, hypotension, malaise and axillary and inguinal lymphadenopathy. Culture in glucose broth shows stalactite growth. Most likely causative organism is?

Accepted Answer

Yersinia pestis

Answer

Brucella abortus

Answer

Coxiella burnetii

Answer

Francisella tularensis

Question 5

A bird seller developed fever with chills and severe body pain. Investigation confirms the disease as ornithosis. Causative agent is:

Accepted Answer

Chlamydia psittaci

Answer

Coxiella burnetii

Answer

Borrelia

Answer

Burkholderia pseudomallei

Question 6

A person working in an abattoir presented with malignant pustule on hand. What is the causative agent?

Accepted Answer

Bacillus anthracis

Answer

Clostridium botulinum

Answer

Streptococcus pyogenes

Answer

Clostridium perfringens

Question 7

Scrub typhus is transmitted by:

Accepted Answer

Mite

Answer

Louse

Answer

Tick

Answer

Flea

Question 8

A patient presents with a bullseye rash after a tick bite. Which organism is most likely responsible for this condition?

Accepted Answer

Borrelia burgdorferi

Answer

Rickettsia rickettsii

Answer

Treponema pallidum

Answer

Leptospira interrogans

Question 9

A patient with a cat bite presents with a swollen, tender hand and fever. A Gram stain of the wound shows gram-negative rods. What is the most likely pathogen?

Accepted Answer

Pasteurella multocida

Answer

Staphylococcus aureus

Answer

Bartonella henselae

Answer

Capnocytophaga canimorsus

Question 10

Which of the following is the carrying agent for Lyme disease?

Accepted Answer

Ixodes scapularis ticks

Answer

Anopheles

Answer

Louse

Answer

Rat flea

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

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