Zoonotic Diseases Practice Questions

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

Epidemic typhus. ***Epidemic typhus*** - **Epidemic typhus** is caused by **Rickettsia prowazekii** and transmitted by the **human body louse (Pediculus humanus corporis)**, consistent with the history of a louse bite. - The classic presentation includes **fever, chills**, and a **maculopapular rash** that starts on the trunk and spreads centrifugally, sparing the palms and soles [1]. *Endemic typhus* - **Endemic typhus** (murine typhus) is caused by **Rickettsia typhi** and transmitted by the **rat flea**, not a louse [1]. - While it also presents with fever and rash, the distinct vector and, typically, milder course differentiate it from epidemic typhus. *Rickettsial pox* - **Rickettsialpox** is caused by **Rickettsia akari** and transmitted by the **mite** from house mice, not a louse. - It is characterized by an **eschar** at the bite site followed by a generalized papulovesicular rash, which is different from the maculopapular rash described. *Scrub typhus* - **Scrub typhus** is caused by **Orientia tsutsugamushi** and transmitted by the **chigger mite** larvae, not a louse [1]. - Similar to rickettsialpox, it typically presents with an **eschar** at the bite site and can cause generalized rash, but the vector is different [1].

Q: Bartonella henselae causes which disease -

Bacillary peliosis. ***Bacillary peliosis*** - **Bartonella henselae** is a gram-negative rod that causes **bacillary peliosis** (peliosis hepatis), particularly in immunocompromised individuals such as AIDS patients. - This condition is characterized by **blood-filled cystic spaces** in the liver and spleen. - *Note: Bartonella henselae* most commonly causes **Cat Scratch Disease** in immunocompetent individuals, but bacillary peliosis is the specific disease entity among the given options. *Spirillum fever* - **Spirillum fever** is caused by **Spirillum minus** (a different bacterial genus) and is characterized by a relapsing fever after a rat bite. - Its clinical presentation and causative agent differ from those of *Bartonella henselae* infections. *Chancre redux* - **Chancre redux** is not a standard medical term and does not represent a recognized disease entity. - It does not correspond to any disease caused by *Bartonella henselae*. *Rat bite fever* - **Rat bite fever** is caused by either **Streptobacillus moniliformis** or **Spirillum minus**, both of which are distinct from *Bartonella henselae*. - While *Bartonella henselae* is transmitted by cat scratches or bites, it does not cause rat bite fever.

Q: "Endemic" typhus is caused by:

Rickettsia mooseri. ***Rickettsia mooseri (Rickettsia typhi)*** - **Endemic (murine) typhus** is caused by *Rickettsia typhi*, also known as *Rickettsia mooseri*. - This form of typhus is typically transmitted to humans through contact with **feces of infected rat fleas** (*Xenopsylla cheopis*). - Clinical features include fever, headache, and maculopapular rash. *Coxiella burnetii* - *Coxiella burnetii* is the causative agent of **Q fever**, which presents differently from typhus. - Q fever is primarily transmitted by inhaling **aerosols from infected animals**, particularly livestock (cattle, sheep, goats). - It does not cause endemic typhus. *Ehrlichia chafeensis* - *Ehrlichia chafeensis* causes **human monocytic ehrlichiosis** (HME), a tick-borne disease. - This condition is characterized by fever, headache, and myalgia, but it is distinct from typhus. - Transmitted by the **lone star tick** (*Amblyomma americanum*), not by fleas. *Rickettsia prowazekii* - *Rickettsia prowazekii* causes **epidemic (louse-borne) typhus**, which is a distinct form of typhus. - Epidemic typhus is transmitted by the **human body louse** (*Pediculus humanus corporis*). - Historically associated with overcrowded, unsanitary conditions, war, and famine.

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 vector for Lyme disease transmission is -

Ticks. ***Ticks*** - **Lyme disease** is caused by the bacterium *Borrelia burgdorferi* and is primarily transmitted to humans through the bite of infected black-legged ticks, also known as **deer ticks** (*Ixodes scapularis* in the eastern and midwestern U.S., and *Ixodes pacificus* in the Pacific Coast). - Ticks are the **definitive vector** for Lyme disease, serving as both a reservoir and a means of transmission. *Rat flea* - **Rat fleas** (*Xenopsylla cheopis*) are primarily known as vectors for diseases such as **bubonic plague** (caused by *Yersinia pestis*) and **murine typhus** (caused by *Rickettsia typhi*). - They are not associated with the transmission of Lyme disease. *Sand fly* - **Sand flies** (e.g., *Phlebotomus* species) are vectors for diseases such as **leishmaniasis**, **sandfly fever**, and **Bartonellosis**. - They are not responsible for transmitting *Borrelia burgdorferi* or Lyme disease. *Mosquito* - **Mosquitoes** are significant vectors for numerous diseases including **malaria**, **dengue fever**, **Zika virus**, and **West Nile virus**. - While they transmit many pathogens, mosquitoes do not transmit the bacteria responsible for Lyme disease.

Q: True about endemic typhus

Flea is a vector of disease. ***Flea is a vector of disease*** - Endemic typhus, also known as murine typhus, is transmitted to humans primarily through the bite of infected **fleas**, usually the **rat flea (Xenopsylla cheopis)**. - The fleas become infected by feeding on **rodents (rats)**, which serve as the primary reservoir for the causative organism, *Rickettsia typhi*. *A rash developing into an eschar is characteristics of the disease* - The development of a **rash** is common in endemic typhus, but an **eschar (a scab-like lesion)** at the site of inoculation is **not characteristic**; eschars are more typical of **scrub typhus** or **rickettsialpox**. - The rash of endemic typhus typically appears as **maculopapular lesions** on the trunk and spreads outwards, but it does **not commonly become an eschar**. *Man is the only reservoir of infection* - **Rodents**, particularly **rats**, are the primary natural **reservoirs** for *Rickettsia typhi*, the causative agent of endemic typhus. - While humans can be infected, they are **not the primary reservoir** and do not typically play a significant role in maintaining the natural transmission cycle. *Culture is diagnostic* - **Culturing *Rickettsia typhi*** is **difficult and dangerous**, requiring specialized biosafety level 3 laboratories, and is **not routinely used for diagnosis**. - Diagnosis typically relies on **serological tests** (e.g., indirect immunofluorescence assay, Weil-Felix agglutination) to detect antibodies against *Rickettsia typhi*, or **molecular tests** like PCR.

Q: Undulant fever is caused by -

Brucella melitensis. ***Brucella melitensis*** - **Brucellosis** is characterized by an **undulant fever**, meaning the fever waxes and wanes over days or weeks, giving it a wave-like pattern. - *Brucella melitensis* is one of the most common species causing human brucellosis, typically acquired through contact with infected animals or contaminated animal products like unpasteurized milk. *Bordetella* - *Bordetella pertussis* causes **whooping cough**, a severe respiratory infection characterized by paroxysmal cough followed by an inspiratory "whoop." - While it causes fever, it does not typically present with the classic undulant fever pattern seen in brucellosis. *Bartonella* - *Bartonella* species can cause various diseases, such as **cat scratch disease** (*Bartonella henselae*), trench fever (*Bartonella quintana*), and Carrion's disease (*Bartonella bacilliformis*). - These infections can present with fever but do not specifically cause an "undulant fever" pattern. *Borrelia recurrentis* - *Borrelia recurrentis* is a spirochete that causes **louse-borne relapsing fever**, characterized by recurrent episodes of high fever separated by afebrile periods. - While it causes episodic fever, the pattern is one of distinct relapses rather than the continuous, undulating pattern of brucellosis.

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.

Question 1

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

Accepted Answer

Epidemic typhus

Answer

Endemic typhus

Answer

Rickettsial pox

Answer

Scrub typhus

Question 2

Bartonella henselae causes which disease -

Accepted Answer

Bacillary peliosis

Answer

Spirillum fever

Answer

Chancre redux

Answer

Rat bite fever

Question 3

"Endemic" typhus is caused by:

Accepted Answer

Rickettsia mooseri

Answer

Coxiella burnetii

Answer

Ehrlichia chafeensis

Answer

Rickettsia prowazekii

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 young man, home on leave from the military, went camping in the woods to detect deer movement for future hunting. Ten days later, he developed fever, malaise, and myalgia. Leukopenia and thrombocytopenia were observed, as well as several tick bites. Which of the following statements best describes human monocytic ehrlichiosis (HME)?

Accepted Answer

Diagnosis is usually made serologically but morulae may be seen in the cytoplasm of monocytes

Answer

It is a fatal disease transmitted by the bite of a dog

Answer

Clinical diagnosis is based on the presence of erythema migrans (EM)

Answer

Symptoms include vomiting and paralysis

Question 6

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 7

Most important vector for Lyme disease transmission is -

Accepted Answer

Ticks

Answer

Rat flea

Answer

Sand fly

Answer

Mosquito

Question 8

True about endemic typhus

Accepted Answer

Flea is a vector of disease

Answer

A rash developing into an eschar is characteristics of the disease

Answer

Man is the only reservoir of infection

Answer

Culture is diagnostic

Question 9

Undulant fever is caused by -

Accepted Answer

Brucella melitensis

Answer

Bartonella

Answer

Bordetella

Answer

Borrelia recurrentis

Question 10

Most important reservoir of leptospira is:

Accepted Answer

Rat

Answer

Man

Answer

Pig

Answer

Monkey

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

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