Zoonotic Diseases Practice Questions

Q: Which test cannot differentiate endemic and epidemic typhus

Weil-Felix reaction. ***Weil-Felix reaction*** - The **Weil-Felix reaction** relies on agglutination of *Proteus* antigens, a non-specific test for typhus. - It detects antibodies that cross-react with *Proteus* antigens, and these antibodies are common to both **endemic** and **epidemic typhus**, making it unable to differentiate between them. *Complement fixation test* - The **complement fixation test** can differentiate between typhus types by detecting specific antibodies to *Rickettsia prowazekii* (epidemic) and *Rickettsia typhi* (endemic), as it measures specific antigen-antibody reactions. - It uses specific antigens from each *Rickettsia* species to identify which type of typhus is present. *Immunofluorescence* - **Immunofluorescence assays (IFAs)** are highly specific and can differentiate between endemic and epidemic typhus by detecting specific antibodies against *R. prowazekii* or *R. typhi*. - They allow for the visualization of antibody binding to specific rickettsial antigens, providing differential diagnosis. *ELISA* - **ELISA** (Enzyme-Linked Immunosorbent Assay) tests can be designed with specific antigens from *R. prowazekii* and *R. typhi* to distinguish between epidemic and endemic typhus. - This method offers high sensitivity and specificity in detecting type-specific antibodies.

Q: What is the mammalian reservoir for Rickettsia prowazekii?

Humans. ***Humans*** - **Humans** are the primary and essentially sole mammalian reservoir for *Rickettsia prowazekii*, the causative agent of **epidemic typhus** - This characteristic makes **epidemic typhus** a human-to-human disease, primarily transmitted via the **human body louse** (*Pediculus humanus corporis*) - The disease can persist in human populations and reactivate years later as **Brill-Zinsser disease** (recrudescent typhus) *Rodents* - Rodents are reservoirs for other *Rickettsia* species, such as *Rickettsia typhi* (cause of **murine typhus**), but not for *Rickettsia prowazekii* - **Murine typhus** is typically transmitted by the **rat flea**, distinguishing its epidemiology from that of epidemic typhus *Dogs* - Dogs are known reservoirs for various disease-causing agents, including some rickettsial diseases like **Rocky Mountain spotted fever** (*Rickettsia rickettsii*), but not for *Rickettsia prowazekii* - Different *Rickettsia* species have specific **animal hosts** and **arthropod vectors** *Cattle* - Cattle are not typically considered a reservoir for *Rickettsia prowazekii* - They are more commonly associated with diseases like **Q fever** (*Coxiella burnetii*), which is related but distinct from typhus rickettsiae

Q: Wool-Sorter disease is caused by

Bacillus anthracis (Anthrax). ***Bacillus anthracis (Anthrax)*** - **Wool-Sorter's disease** is an alternative name for **pulmonary anthrax**, which is caused by inhaling spores of *Bacillus anthracis*. - This name originated historically from the risk of anthrax infection among workers who handled contaminated animal wool and hides. *Pseudomonas aeruginosa* - This bacterium is a common cause of **nosocomial infections**, particularly in immunocompromised patients, and can cause **pneumonia**, but it is not associated with Wool-Sorter's disease. - It is known for its **drug resistance** and often produces a characteristic **blue-green pigment** (pyocyanin) in cultures. *Vibrio parahaemolyticus* - This bacterium is primarily associated with **gastroenteritis** from consuming contaminated seafood. - Its infections are typically foodborne and do not present as a pulmonary disease like Wool-Sorter's disease. *Spirillum minus* - **Spirillum minus** is a gram-negative bacterium that causes **rat-bite fever** (also known as Sodoku), not Wool-Sorter's disease. - Symptoms usually include fever, rash, and lymphadenopathy after a rat bite.

Q: Indian tick typhus is caused by:

R conorii. ***R conorii*** - *Rickettsia conorii* is the causative agent of **Indian tick typhus**, also known as **Mediterranean spotted fever** or boutonneuse fever. - This bacterial infection is transmitted to humans through the bite of **infected ticks**. *R typhi* - *Rickettsia typhi* is the causative agent of **murine typhus**, which is transmitted by **fleas**, usually from rodents. - Its clinical presentation is generally milder than that of tick-borne rickettsial diseases and often does not involve a prominent rash. *R akari* - *Rickettsia akari* causes **rickettsialpox**, which is transmitted by the **house mouse mite**. - Key features include a primary eschar (black scab) at the bite site followed by a vesicular rash. *C burnetii* - *Coxiella burnetii* is the bacterium responsible for **Q fever**, a systemic infection often transmitted by **inhaling aerosols from infected animals** (e.g., cattle, sheep, goats). - It typically causes an acute flu-like illness, pneumonia, or hepatitis, without a characteristic rash or tick vector in most cases.

Q: A militant presents with rashes all over his body sparing the palms and soles. On examination, he was febrile and lice were noted. Which of the following is responsible for his condition?

Rickettsia prowazekii. ***Rickettsia prowazekii*** - This bacterium is the causative agent of **epidemic typhus**, which is transmitted by the **body louse** (Pediculus humanus corporis), consistent with the presence of lice. - The characteristic rash of epidemic typhus **spares the palms and soles** and often begins on the trunk, spreading centrifugally. *Rickettsia typhi* - This organism causes **murine typhus**, which is transmitted by **fleas**, particularly those found on rodents. - While it can cause a rash that typically spares the palms and soles, the transmission vector and typical setting (exposure to rodents) do not fit the clinical scenario as well as **body lice**. *Rickettsia akari* - This bacterium causes **rickettsialpox**, transmitted by **mites**. - The rash of rickettsialpox is typically papulovesicular, and a characteristic **eschar** (or black scab) is usually present at the site of the mite bite, which is not mentioned in the case. *Rickettsia conorii* - This organism causes **Mediterranean spotted fever** (also known as Boutonneuse fever), transmitted by **ticks**. - A distinguishing feature of this infection is the presence of a **tache noire** (eschar) at the site of the tick bite, which is absent in the patient's presentation.

Q: Which of the following vectors is known to transmit a disease that can be identified by the presence of spirochetes under dark-field microscopy?

Ixodes scapularis ticks. ***Ixodes scapularis ticks*** - *Ixodes scapularis* ticks are the primary vectors for **Lyme disease**, caused by the spirochete *Borrelia burgdorferi*. - **Spirochetes** can be identified in tissue samples or cultures using **dark-field microscopy** or silver staining techniques. - Direct visualization from patient samples is uncommon; diagnosis typically relies on serology and clinical presentation. *Louse* - Lice (e.g., *Pediculus humanus corporis*) transmit **relapsing fever** (*Borrelia recurrentis*) and epidemic typhus (*Rickettsia prowazekii*). - *Borrelia recurrentis* spirochetes are readily visible in **peripheral blood smears** using Wright or Giemsa stain during febrile episodes. - While this is also a spirochete disease, the question specifically refers to dark-field microscopy, which is classically associated with Lyme disease spirochete identification. *Anopheles* - The *Anopheles* mosquito is the vector for **malaria**, caused by *Plasmodium* parasites, not spirochetes. - Malaria is diagnosed by identifying ring forms, trophozoites, and schizonts within red blood cells on blood smears. *Rat flea* - The rat flea (*Xenopsylla cheopis*) is the primary vector for **bubonic plague** (*Yersinia pestis*) and murine typhus (*Rickettsia typhi*). - *Yersinia pestis* is a gram-negative coccobacillus, not a spirochete.

Q: Anaplasma phagocytophilum mainly affects -

Neutrophils (white blood cells). ***Neutrophils (white blood cells)*** - *Anaplasma phagocytophilum* specifically infects and replicates within **neutrophils**, leading to the characteristic morulae observed inside these cells. - This infection causes **human granulocytic anaplasmosis (HGA)**, primarily affecting white blood cells. *Red Blood Cells (RBCs)* - While other tick-borne diseases like **babesiosis** infect RBCs, *Anaplasma phagocytophilum* does not target red blood cells. - RBCs are responsible for oxygen transport and lack the necessary cellular machinery for *Anaplasma* replication. *Macrophages (immune cells)* - Macrophages are significant immune cells but are not the primary target cell for *Anaplasma phagocytophilum*. - Infections that primarily target macrophages include some **bacterial** and **parasitic infections** like *Leishmania*. *Platelets (thrombocytes)* - Platelets are crucial for **blood clotting** and are not directly infected by *Anaplasma phagocytophilum*. - Although **thrombocytopenia** (low platelet count) is a common finding in anaplasmosis, it is an indirect effect of the infection, not due to direct platelet invasion.

Q: Most common route of infection in pasteurella cellulitis -

Animal bites or scratches. ***Animal bites or scratches*** - *Pasteurella multocida* is a common commensal bacterium in the oral flora of **cats and dogs**. - **Animal bites or scratches** are the primary mode of transmission for *Pasteurella* infections, particularly cellulitis, due to direct inoculation. *Aerosols or dust* - Transmission via **aerosols or dust** is rare for *Pasteurella* infections, which typically require direct contact or inoculation. - While other bacteria can spread this way, *Pasteurella* cellulitis is not commonly acquired through airborne routes. *Contaminated tissue* - While possible in some contexts, **contaminated tissue** is not the most common route of infection for *Pasteurella* cellulitis. - Direct inoculation from an **animal's oral flora** is far more frequent than contact with contaminated environmental tissues. *Human to human* - *Pasteurella* infections are generally **not transmissible from human to human**. - The organism is primarily associated with animals and their bites or scratches.

Q: In human infections, the morula form is seen in which of the following organisms?

Ehrlichia. ***Correct: Ehrlichia*** - *Ehrlichia* species are **obligate intracellular bacteria** that replicate in host immune cells, forming distinctive microcolonies known as **morulae** (mulberry-like clusters). - The presence of morulae within the cytoplasm of **white blood cells** (monocytes or granulocytes) is the **key diagnostic feature** for ehrlichiosis. - The term "morula" comes from Latin for "mulberry," describing the characteristic clustered appearance visible on microscopy. *Incorrect: Chlamydiae* - *Chlamydiae* are obligate intracellular parasites with a unique developmental cycle involving elementary bodies (infectious form) and reticulate bodies (replicative form). - They form **intracytoplasmic inclusions** within vacuoles, but these are **not morulae**. *Incorrect: Bartonella quintana* - *Bartonella quintana* is a fastidious gram-negative bacillus associated with **trench fever** and bacillary angiomatosis. - Typically seen as individual or small clusters of bacteria, but **does not form morulae** within host cells. *Incorrect: Mycoplasma hominis* - *Mycoplasma hominis* is a small, **wall-less bacterium** that can cause genitourinary infections. - It is an extracellular pathogen or adheres to host cells but **does not invade or form intracytoplasmic morulae**.

Q: What is the causative agent of Izumi fever?

Yersinia pseudotuberculosis. ***Yersinia pseudotuberculosis*** - Izumi fever (also called **Far East scarlet-like fever**) is caused by Yersinia pseudotuberculosis, particularly referring to outbreaks that occurred in Japan. - This infection presents with **fever, abdominal pain, and a scarlet fever-like rash**, often mimicking appendicitis due to mesenteric lymphadenitis. - Y. pseudotuberculosis is transmitted through **contaminated food and water**, and the Izumi fever variant is characterized by systemic manifestations including erythema and desquamation. *Yersinia enterocolitica* - While this is a closely related species that also causes **gastroenteritis and mesenteric adenitis**, it is NOT the causative agent of Izumi fever. - Y. enterocolitica typically presents with diarrhea, abdominal pain, and fever, but lacks the distinctive scarlet fever-like rash seen in Izumi fever. *Pseudomonas aeruginosa* - This bacterium is an **opportunistic pathogen** often associated with nosocomial infections, especially in immunocompromised individuals. - It causes **pneumonia**, urinary tract infections, and wound infections, but not Izumi fever. *Pasteurella multocida* - This bacterium is common in the **respiratory tracts of animals**, especially cats and dogs, and is a frequent cause of wound infections from animal bites or scratches. - It typically causes localized cellulitis, abscesses, and occasionally severe infections like meningitis or osteomyelitis, not Izumi fever.

Question 1

Which test cannot differentiate endemic and epidemic typhus

Accepted Answer

Weil-Felix reaction

Answer

Complement fixation test

Answer

Immunofluorescence

Answer

ELISA

Question 2

What is the mammalian reservoir for Rickettsia prowazekii?

Accepted Answer

Humans

Answer

Rodents

Answer

Dogs

Answer

Cattle

Question 3

Wool-Sorter disease is caused by

Accepted Answer

Bacillus anthracis (Anthrax)

Answer

Pseudomonas aeruginosa

Answer

Vibrio parahaemolyticus

Answer

Spirillum minus

Question 4

Indian tick typhus is caused by:

Accepted Answer

R conorii

Answer

R typhi

Answer

R akari

Answer

C burnetii

Question 5

A militant presents with rashes all over his body sparing the palms and soles. On examination, he was febrile and lice were noted. Which of the following is responsible for his condition?

Accepted Answer

Rickettsia prowazekii

Answer

Rickettsia typhi

Answer

Rickettsia akari

Answer

Rickettsia conorii

Question 6

Which of the following vectors is known to transmit a disease that can be identified by the presence of spirochetes under dark-field microscopy?

Accepted Answer

Ixodes scapularis ticks

Answer

Anopheles

Answer

Louse

Answer

Rat flea

Question 7

Anaplasma phagocytophilum mainly affects -

Accepted Answer

Neutrophils (white blood cells)

Answer

Red Blood Cells (RBCs)

Answer

Macrophages (immune cells)

Answer

Platelets (thrombocytes)

Question 8

Most common route of infection in pasteurella cellulitis -

Accepted Answer

Animal bites or scratches

Answer

Aerosols or dust

Answer

Contaminated tissue

Answer

Human to human

Question 9

In human infections, the morula form is seen in which of the following organisms?

Accepted Answer

Ehrlichia

Answer

Chlamydiae

Answer

Bartonella quintana

Answer

Mycoplasma hominis

Question 10

What is the causative agent of Izumi fever?

Accepted Answer

Yersinia pseudotuberculosis

Answer

Yersinia enterocolitica

Answer

Pseudomonas aeruginosa

Answer

Pasteurella multocida

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

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