Zoonotic Diseases Practice Questions

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_.

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: Mammalian reservoir of Rickettsial pox -

Mice. ***Mice*** - The primary **mammalian reservoir** for *Rickettsia akari*, which causes **rickettsialpox**, is **mice** (specifically the house mouse, *Mus musculus*). - The disease is transmitted to humans by the bite of the **mouse mite** (*Liponyssoides sanguineus*), which is the vector. *Cattle* - **Cattle** are not known reservoirs for *Rickettsia akari* or agents causing **rickettsialpox**. - They are more commonly associated with other zoonotic diseases such as **anthrax** or **Q fever** (*Coxiella burnetii*). *Goat* - **Goats** are not considered reservoirs for *Rickettsia akari* or the transmission of **rickettsialpox**. - They can be reservoirs for diseases like **brucellosis** or **Q fever**, but not for rickettsialpox. *Human* - **Humans** are occasional and **dead-end hosts** for *Rickettsia akari*, meaning they can get the disease but do not typically transmit it further to maintain the natural cycle. - Humans become infected when bitten by an infected **mouse mite** but do not act as the reservoir.

Q: Jail fever is related to

Rickettsia prowazekii. ***Rickettsia prowazekii*** - **Jail fever** is another name for **epidemic typhus**, which is caused by *Rickettsia prowazekii*. - This disease is historically associated with crowded, unsanitary conditions like those found in jails or during wartime. *Rickettsia conorii* - This bacterium causes **Mediterranean spotted fever** (boutonneuse fever), which is characterized by a distinctive skin rash and eschar. - It is transmitted by dog ticks, and is not associated with the term "jail fever." *Rickettsia typhi* - *Rickettsia typhi* is responsible for **murine typhus** (endemic typhus), which is typically transmitted by fleas, mainly from rats. - While it is a rickettsial disease, it is not referred to as jail fever. *Rickettsia akari* - This species causes **rickettsialpox**, a mild rickettsial infection characterized by an initial papule that develops into an eschar, followed by a generalized papulovesicular rash. - It is transmitted by mites found on house mice and is distinct from jail fever.

Q: Rickettsialpox is caused by?

Rickettsia akari. ***Rickettsia akari*** - **Rickettsia akari** is the specific etiologic agent responsible for causing **rickettsialpox**. - This Rickettsia species is transmitted to humans by the bite of the **mouse mite**, particularly *Liponyssoides sanguineus*. *Rickettsia conorii* - **Rickettsia conorii** is the pathogen that causes **Mediterranean spotted fever** (also known as boutonneuse fever), which is distinct from rickettsialpox. - It is typically transmitted by ticks, such as *Rhipicephalus sanguineus*. *Rickettsia rickettsii* - This bacterium is the causative agent of **Rocky Mountain spotted fever**, a severe and potentially fatal tick-borne disease. - It is not associated with rickettsialpox, which presents with different clinical features and epidemiology. *Rickettsia typhi* - **Rickettsia typhi** is the cause of **murine (endemic) typhus**, a flea-borne disease primarily associated with rats. - Murine typhus has different clinical manifestations and epidemiology compared to rickettsialpox.

Q: Rickettsia rickettsii is responsible for which disease -

Rocky mountain spotted fever. ***Rocky mountain spotted fever*** - **Rickettsia rickettsii** is the specific etiologic agent responsible for **Rocky Mountain Spotted Fever (RMSF)**, a severe tick-borne illness. - RMSF is characterized by a distinctive **rash** that typically begins on the ankles and wrists and spreads inwards, affecting the palms and soles. *Endemic typhus* - Endemic typhus, also known as **murine typhus**, is caused by **Rickettsia typhi**, not Rickettsia rickettsii. - It is typically transmitted by fleas, particularly those found on rodents, and is less severe than RMSF. *Scrub typhus* - Scrub typhus is caused by **Orientia tsutsugamushi**, a different rickettsial species. - This disease is transmitted by the bite of infected chiggers (larval mites) and is prevalent in rural Asia and the Pacific. *Epidemic typhus* - Epidemic typhus is caused by **Rickettsia prowazekii** and is transmitted by the human body louse. - It is historically associated with crowded, unsanitary conditions and can cause severe systemic illness.

Q: All are true about scrub typhus, except:

Adult female feeds on vertebrate hosts. ***Adult female feeds on vertebrate hosts*** - This statement is incorrect because the **larval stage** (chiggers) of the trombiculid mite is the one that feeds on vertebrate hosts (including humans) and transmits *Orientia tsutsugamushi*. - **Adult and nymphal mites** are free-living and feed on vegetation or small invertebrates, not vertebrate blood. *Causative organism is O. tsutsugamushi* - This statement is true; **scrub typhus** is caused by the obligate intracellular bacterium *Orientia tsutsugamushi*. - *O. tsutsugamushi* is transmitted to humans through the bite of infected larval mites. *Vector is trombiculid mite* - This statement is true; **trombiculid mites**, specifically their larval stage (chiggers), are the **vectors** for *Orientia tsutsugamushi*. - These mites are often found in areas with dense vegetation, making **scrubland** a risk factor for exposure. *Tetracycline is the drug of choice* - This statement is true; **tetracyclines**, such as **doxycycline**, are the drugs of choice for treating scrub typhus. - **Chloramphenicol** is an alternative in cases where tetracyclines are contraindicated, though often associated with side effects.

Q: Which of the following is transmitted by mites:

Scrub typhus. **Scrub typhus** - This disease is caused by the bacterium *Orientia tsutsugamushi* and is transmitted to humans through the bite of infected **larval mites** (chiggers). - The mites are found in rural areas, particularly in parts of Asia, and their bite often leaves a characteristic **eschar** at the inoculation site. *Endemic typhus* - Also known as murine typhus, this condition is caused by *Rickettsia typhi* and is transmitted by the **rat flea**, not mites. - It is typically associated with rodent populations. *Trench fever* - This disease is caused by *Bartonella quintana* and is transmitted by the human **body louse**, not mites. - It was historically prevalent during wartime due to crowded, unsanitary conditions. *Epidemic typhus* - Caused by *Rickettsia prowazekii*, this form of typhus is transmitted by the human **body louse**, not mites. - It is often associated with outbreaks in areas with poor hygiene and crowded living conditions.

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: Nipah virus is transmitted by

Fruit bats. ***Fruit bats*** - **Fruit bats**, particularly those of the *Pteropus* genus (flying foxes), are the **natural reservoir** for Nipah virus. - The virus is shed in their **urine**, **feces**, and **saliva**, which can then contaminate fruit and other food sources. *Pigs* - **Pigs** can act as **intermediate hosts** and amplify the Nipah virus, transmitting it to humans. - However, they are not the natural reservoir; they become infected by consuming contaminated plant products or interacting with infected bats. *Cattle* - While other livestock, such as **horses** and **goats**, have been shown to be susceptible to Nipah virus infection, **cattle are not typically primary transmitters** to humans. - Their role in Nipah virus epidemiology is generally considered minor compared to bats and pigs. *Mosquitoes* - Nipah virus is **not transmitted by mosquitoes** or other insect vectors. - It is primarily spread through direct contact with infected animals or their bodily fluids, or through contaminated food.

Question 1

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

Question 2

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 3

Mammalian reservoir of Rickettsial pox -

Accepted Answer

Mice

Answer

Cattle

Answer

Goat

Answer

Human

Question 4

Jail fever is related to

Accepted Answer

Rickettsia prowazekii

Answer

Rickettsia conorii

Answer

Rickettsia typhi

Answer

Rickettsia akari

Question 5

Rickettsialpox is caused by?

Accepted Answer

Rickettsia akari

Answer

Rickettsia conorii

Answer

Rickettsia rickettsii

Answer

Rickettsia typhi

Question 6

Rickettsia rickettsii is responsible for which disease -

Accepted Answer

Rocky mountain spotted fever

Answer

Endemic typhus

Answer

Scrub typhus

Answer

Epidemic typhus

Question 7

All are true about scrub typhus, except:

Accepted Answer

Adult female feeds on vertebrate hosts

Answer

Causative organism is O. tsutsugamushi

Answer

Vector is trombiculid mite

Answer

Tetracycline is the drug of choice

Question 8

Which of the following is transmitted by mites:

Accepted Answer

Scrub typhus

Answer

Endemic typhus

Answer

Trench fever

Answer

Epidemic typhus

Question 9

Cat scratch disease is caused by

Accepted Answer

Bartonella

Answer

Moraxella

Answer

Pseudomonas

Answer

Francisella

Question 10

Nipah virus is transmitted by

Accepted Answer

Fruit bats

Answer

Pigs

Answer

Cattle

Answer

Mosquitoes

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

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