Zoonotic Diseases Practice Questions

Q: Which of the following is true about Endemic typhus?

Vector is flea. ***Vector is flea*** - **Endemic typhus**, also known as **murine typhus**, is transmitted to humans by the **rat flea** (*Xenopsylla cheopis*). - The flea becomes infected by feeding on rodents (primarily rats) that carry the causative bacteria. *Reservoir is humans* - The primary **reservoir** for **endemic typhus** is **rodents**, particularly rats, not humans. - Humans are considered **accidental hosts** and do not typically perpetuate the transmission cycle. *Cause is Rickettsia prowazekii* - The causative agent of **endemic typhus** is **Rickettsia typhi**. - **Rickettsia prowazekii** is the causative agent of **epidemic typhus**, which is distinct from endemic typhus. *Tetracycline is not useful for treatment* - **Tetracyclines**, particularly **doxycycline**, are the **first-line treatment** for endemic typhus and are highly effective. - Other effective antibiotics include **chloramphenicol** and **fluoroquinolones**.

Q: An army jawan posted in a remote forest area presented with fever and headache. His fever was 104°F and pulse was 70 per minute. He had an erythematous lesion of about 1 cm on the leg surrounded by small vesicles, along with generalized lymphadenopathy at the time of presentation to the referral hospital. His blood sample was collected to perform serology for the diagnosis of Rickettsial disease. Which one of the following results in the Weil-Felix reaction will be diagnostic in this clinical setting?

High OX - K. **High OX - K** - The clinical presentation (fever, headache, erythematous lesion with vesicles, rural exposure) is highly suggestive of **Scrub typhus**, which is caused by *Orientia tsutsugamushi*. - A **high OX-K titer** in the Weil-Felix reaction is characteristic for **Scrub typhus**, as this rickettsial species shares antigens with *Proteus mirabilis* OX-K. *High OX - 19 and OX - 2* - A high titer for both OX-19 and OX-2 would generally suggest **typhus group rickettsiae** (e.g., epidemic or endemic typhus), which is less likely given the specific lesion described (eschar with vesicles) and the forest setting. - This combination is not typically associated with the classic presentation of **Scrub typhus**. *High OX - 2* - A high OX-2 titer alone is less specific and can be elevated in some cases of **spotted fever group rickettsiae**, but it is not the primary indicator for Scrub typhus. - It would not definitively diagnose the clinical picture, which points strongly to Scrub typhus due to the characteristic skin lesion and rural exposure. *High OX - 19* - A high OX-19 titer is primarily indicative of **typhus group rickettsiae** like **epidemic typhus** (*Rickettsia prowazekii*) or **murine typhus** (*Rickettsia typhi*). - This finding is not consistent with the typical presentation of Scrub typhus, which is associated with the OX-K antigen.

Q: A patient presents to the emergency room with vomiting, diarrhea, high fever, and delirium. Upon physical examination, you notice large buboes, which are painful on palpation, and purpura and ecchymoses suggestive of disseminated intravascular coagulation. Gram stain on aspirate of a bubo reveals gram-negative rods with bipolar staining. Which of the following antibiotics is the drug of choice for empiric therapy?

Streptomycin. ***Streptomycin*** - The clinical presentation (high fever, delirium, **buboes**, purpura, ecchymoses, and **bipolar staining gram-negative rods**) is highly suggestive of **septicemic** or **bubonic plague** caused by *Yersinia pestis* [1]. - **Streptomycin** and **gentamicin** are the **drugs of choice** for treating plague, especially in severe forms [1]. *Penicillin* - **Penicillin** is effective against many gram-positive bacteria and some gram-negative cocci, but generally **not effective** against *Yersinia pestis*, a gram-negative rod. - Using penicillin would likely lead to treatment failure and worsening of the patient's condition given the severity of plague. *Ceftazidime* - **Ceftazidime** is a **third-generation cephalosporin** effective against a broad spectrum of gram-negative bacteria, including *Pseudomonas aeruginosa*. - While it has gram-negative coverage, it is **not considered the first-line empiric therapy** for suspected plague; aminoglycosides like streptomycin are preferred due to their established efficacy [1]. *Chloramphenicol* - **Chloramphenicol** is an effective antibiotic that can be used for plague, particularly in cases of **meningitis** due to its good central nervous system penetration. - However, for initial empiric therapy of **bubonic or septicemic plague**, **streptomycin** or **gentamicin** are generally preferred over chloramphenicol [1].

Q: Mammalian reservoir for R. prowazekii ?

Humans. ***Humans*** - Humans are the primary reservoir for **epidemic typhus**, caused by *Rickettsia prowazekii*. - The disease is typically transmitted among humans by the human **body louse** (*Pediculus humanus corporis*). *Rodents* - Rodents are common reservoirs for other rickettsial diseases, such as **murine typhus** (*R. typhi*), which is transmitted by **fleas**. - While some **flying squirrels** are noted reservoirs for sylvatic typhus caused by *R. prowazekii*, humans remain the main reservoir for epidemic forms. *Cattle* - Cattle are generally not considered a mammalian reservoir for *Rickettsia prowazekii*. - They are more commonly associated with diseases like **Q fever** caused by **Coxiella burnetii**, which is a related but distinct pathogen. *Dog* - Dogs are not a known reservoir for *Rickettsia prowazekii*. - They can be infected with other rickettsial species, such as *Rickettsia rickettsii* (Rocky Mountain spotted fever) or *Ehrlichia canis*, but not epidemic typhus.

Q: Scrub typhus is caused by:

Orientia tsutsugamushi. ***R.tsutsugamushi*** - **Scrub typhus** is specifically caused by **Orientia tsutsugamushi**, which was formerly classified as *Rickettsia tsutsugamushi*. - This organism is transmitted by the bite of infected **chiggers** (larval mites) found in certain geographical areas. *R.akari* - *Rickettsia akari* is the causative agent of **rickettsialpox**, a mild rickettsial disease characterized by an eschar and a vesicular rash. - It is transmitted by the bite of an infected **mite**, specifically the house mouse mite, *Liponyssoides sanguineus*. *R.typhi* - *Rickettsia typhi* is responsible for **murine typhus** (also known as endemic typhus), a rickettsial disease. - This bacterium is transmitted to humans by the bite of an infected **flea**, typically the rat flea (*Xenopsylla cheopis*). *R. conorii* - *Rickettsia conorii* causes **Mediterranean spotted fever**, also known as boutonneuse fever or Israeli spotted fever. - It is transmitted by the bite of infected **ticks**, primarily the dog tick (*Rhipicephalus sanguineus*).

Q: A 16-year-old girl presents with a painfully enlarged lymph node in her right axilla and low grade fever. Peripheral blood counts are within normal limits. The lymph node is biopsied, and numerous granulomas filled with neutrophils and necrotic debris are observed. Which of the following organisms could produce this disease?

Bartonella henselae. ***Bartonella henselae*** - This organism causes **cat scratch disease (CSD)**, which typically presents with **lymphadenopathy** (often in the axilla) following a cat scratch or bite. - The characteristic histological finding in CSD is **suppurative granulomas** (granulomas with central necrosis and neutrophils), or **stellate microabscesses**, in the affected lymph nodes. *Chlamydia psittaci* - This bacterium causes **psittacosis**, primarily a respiratory illness (pneumonia) acquired from birds. - While it can cause systemic symptoms like **fever**, it is not typically associated with localized, painful suppurative lymphadenopathy or granulomas in the axilla. *Coxiella burnetii* - This organism is the causative agent of **Q fever**, which can present as an acute febrile illness, pneumonia, or hepatitis, often from exposure to infected farm animals. - It does not typically cause localized painful lymphadenopathy with suppurative granulomas in the axilla. *Borrelia burgdorferi* - This bacterium causes **Lyme disease**, characterized by an expanding erythematous rash (erythema migrans), followed by joint, cardiac, and neurological manifestations. - Primary findings do not include suppurative granulomas in lymph nodes, although general lymphadenopathy can occur.

Q: A man presents with fever and chills 2 weeks after a louse bite. There was a maculo-papular rash on the trunk which spread peripherally. The cause of this infection can be

Epidemic typhus. ***Epidemic typhus*** - This condition is characterized by **fever**, **chills**, and a **maculopapular rash** that spreads centrally to peripherally, often following a **louse bite**. - It is caused by **Rickettsia prowazekii** and transmitted by the human body louse (Pediculus humanus corporis), making it common in crowded, unhygienic conditions. *Scrub typhus* - Scrub typhus is typically transmitted by the bite of **chiggers (larval mites)** and is caused by **Orientia tsutsugamushi**. - A characteristic feature is an **eschar** at the site of the bite, which is not mentioned in the patient's presentation. *Endemic typhus* - Also known as **murine typhus**, this disease is caused by **Rickettsia typhi** and transmitted by the **rat flea**. - While it causes fever and rash, its transmission vector (**flea**) and typical epidemiology (associated with rodents) differ from the louse bite described. *Rickettsial pox* - Rickettsial pox is caused by **Rickettsia akari** and transmitted by the **house mouse mite**. - It presents with an initial **papule** at the bite site that develops into an eschar, followed by fever and a **vesicular rash**, which is different from the maculopapular rash described.

Q: The following is the etiological agent of Rocky Mountain spotted fever:

Rickettsia rickettsii. ***Rickettsia rickettsii*** - This bacterium is the definitive **causative agent** of **Rocky Mountain spotted fever (RMSF)**. - RMSF is a severe **tick-borne disease** endemic to the Americas, characterized by fever, headache, and a distinctive rash. *Coxiella burnetii* - This bacterium causes **Q fever**, an acute or chronic infectious disease often presenting with flu-like symptoms or pneumonia. - Unlike *Rickettsia rickettsii*, it is **not transmitted by ticks** in the same way and does not cause a spotted rash. *Rochalimaea quintana* - Now known as **Bartonella quintana**, this bacterium is the etiologic agent of **trench fever** and can cause chronic bacteremia in individuals experiencing homelessness. - It is primarily transmitted by **body lice** and does not cause RMSF. *Rickettsia tsutsugamushi* - This bacterium is the causative agent of **scrub typhus**, a common febrile illness in Asia and the Pacific. - **Scrub typhus** is transmitted by infected chiggers and is characterized by a distinctive eschar, which is not typical for RMSF.

Q: A clinically depressed farmer complains of extreme weakness, a daily rise and fall in fever, and night sweats. Small gram-negative rods are isolated from blood cultures after a 2-week incubation period. Which of the following organisms is the most likely etiologic agent?

Brucella melitensis. ***Brucella melitensis*** - This organism is known to cause **brucellosis**, which presents with **undulant fever** (daily rise and fall), night sweats, and fatigue, consistent with the patient's symptoms. The profession of a **farmer** puts him at higher risk due to exposure to infected livestock. - **Neuropsychiatric manifestations** including depression, fatigue, and malaise are well-recognized features of chronic brucellosis, explaining the patient's clinical depression. - **_Brucella_ species** are characteristic for their slow growth, often requiring **extended incubation periods** (up to 2 weeks) in blood cultures, and appear as small gram-negative rods. *Campylobacter jejuni* - This bacterium is a common cause of **gastroenteritis**, leading to **diarrhea**, abdominal cramps, and fever. While it can cause bacteremia, it typically presents with more prominent gastrointestinal symptoms. - _C. jejuni_ is a **curved or spiral-shaped** gram-negative rod, distinct from the small rods described, and does not typically cause an undulant fever pattern. *Francisella tularensis* - This agent causes **tularemia**, which can manifest with fever, chills, and fatigue, but often includes a characteristic **skin lesion (ulceroglandular)** and prominent lymphadenopathy. - Although it is a small gram-negative rod, the specific **undulant fever pattern** and the farmer's exposure history are more indicative of brucellosis. *Salmonella enteritidis* - This bacterium commonly causes **food poisoning** with symptoms like diarrhea, fever, and vomiting. While it can lead to bacteremia, it is less likely to present with the prolonged, **undulant fever** seen in brucellosis. - **_Salmonella_ species** are typically readily isolated from blood cultures within a few days, unlike the prolonged incubation needed for _Brucella_.

Question 1

Which of the following is true about Endemic typhus?

Accepted Answer

Vector is flea

Answer

Reservoir is humans

Answer

Cause is Rickettsia prowazekii

Answer

Tetracycline is not useful for treatment

Question 2

An army jawan posted in a remote forest area presented with fever and headache. His fever was 104°F and pulse was 70 per minute. He had an erythematous lesion of about 1 cm on the leg surrounded by small vesicles, along with generalized lymphadenopathy at the time of presentation to the referral hospital. His blood sample was collected to perform serology for the diagnosis of Rickettsial disease. Which one of the following results in the Weil-Felix reaction will be diagnostic in this clinical setting?

Accepted Answer

High OX - K

Answer

High OX - 19 and OX - 2

Answer

High OX - 2

Answer

High OX - 19

Question 3

A patient presents to the emergency room with vomiting, diarrhea, high fever, and delirium. Upon physical examination, you notice large buboes, which are painful on palpation, and purpura and ecchymoses suggestive of disseminated intravascular coagulation. Gram stain on aspirate of a bubo reveals gram-negative rods with bipolar staining. Which of the following antibiotics is the drug of choice for empiric therapy?

Accepted Answer

Streptomycin

Answer

Penicillin

Answer

Ceftazidime

Answer

Chloramphenicol

Question 4

Mammalian reservoir for R. prowazekii ?

Accepted Answer

Humans

Answer

Rodents

Answer

Cattle

Answer

Dog

Question 5

You are explaining to your patient about epidemic typhus. He wants to know how he could have gotten infected with the disease. All the following are TRUE regarding transmission of epidemic typhus, EXCEPT:

Accepted Answer

It may be transmitted by getting bitten by an infected louse

Answer

It may be transmitted by self-inoculation due to an infected louse being crushed due to scratching

Answer

It may be transmitted by inhalation of infected louse feces

Answer

It may be transmitted by self-inoculation of infected louse feces while scratching

Question 6

Scrub typhus is caused by:

Accepted Answer

Orientia tsutsugamushi

Answer

R.akari

Answer

R.typhi

Answer

R.conorii

Question 7

A 16-year-old girl presents with a painfully enlarged lymph node in her right axilla and low grade fever. Peripheral blood counts are within normal limits. The lymph node is biopsied, and numerous granulomas filled with neutrophils and necrotic debris are observed. Which of the following organisms could produce this disease?

Accepted Answer

Bartonella henselae

Answer

Chlamydia psittaci

Answer

Coxiella burnetii

Answer

Borrelia burgdorferi

Question 8

A man presents with fever and chills 2 weeks after a louse bite. There was a maculo-papular rash on the trunk which spread peripherally. The cause of this infection can be

Accepted Answer

Epidemic typhus

Answer

Scrub typhus

Answer

Endemic typhus

Answer

Rickettsial pox

Question 9

The following is the etiological agent of Rocky Mountain spotted fever:

Accepted Answer

Rickettsia rickettsii

Answer

Coxiella burnetii

Answer

Rochalimaea quintana

Answer

Rickettsia tsutsugamushi

Question 10

A clinically depressed farmer complains of extreme weakness, a daily rise and fall in fever, and night sweats. Small gram-negative rods are isolated from blood cultures after a 2-week incubation period. Which of the following organisms is the most likely etiologic agent?

Accepted Answer

Brucella melitensis

Answer

Campylobacter jejuni

Answer

Francisella tularensis

Answer

Salmonella enteritidis

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

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