Zoonotic Diseases Practice Questions

Q: Which of the following diseases is transmitted by a mite vector?

Scrub typhus (caused by Orientia tsutsugamushi). **Explanation:** The correct answer is **Scrub typhus (Option D)**. This disease is caused by *Orientia tsutsugamushi* and is transmitted to humans through the bite of the larval stage (chigger) of **trombiculid mites**. The medical concept revolves around identifying specific arthropod vectors for Rickettsial diseases, a high-yield area for NEET-PG. **Analysis of Options:** * **Scrub Typhus (Correct):** Transmitted by **larval mites (chiggers)**. A characteristic clinical feature is the **eschar**—a painless, black, necrotic lesion at the site of the mite bite. * **Typhus fever/Endemic typhus (Option A):** Caused by *Rickettsia typhi*, this is transmitted by the **rat flea** (*Xenopsylla cheopis*). * **Epidemic typhus (Option B):** Caused by *Rickettsia prowazekii*, it is transmitted by the **human body louse** (*Pediculus humanus corporis*). It is known for occurring in crowded conditions like refugee camps. * **Rocky Mountain spotted fever (Option C):** Caused by *Rickettsia rickettsii*, it is transmitted by **hard ticks** (e.g., *Dermacentor* species). **High-Yield Clinical Pearls for NEET-PG:** 1. **Weil-Felix Reaction:** A heterophile agglutination test used for diagnosis. Scrub typhus shows a positive reaction with **OX-K** (negative for OX-19 and OX-2). 2. **Drug of Choice:** Doxycycline is the gold standard treatment for almost all Rickettsial infections, including Scrub typhus. 3. **Vector Mnemonic:** Remember **"Mite-y Scrub"** to link Mites with Scrub typhus. 4. **Reservoir:** For Scrub typhus, the mite acts as both the vector and the reservoir (via transovarial transmission).

Q: Epidemic typhus is transmitted by:

Louse. **Explanation:** **Epidemic typhus** is caused by the bacterium ***Rickettsia prowazekii***. The primary vector for this disease is the **human body louse** (*Pediculus humanus corporis*). Transmission occurs when the louse feeds on an infected human, the bacteria multiply in the louse's gut, and are then excreted in its feces. When the louse bites another human, the person scratches the site, inadvertently rubbing the infected feces into the bite wound or other abrasions. **Analysis of Options:** * **B. Louse (Correct):** Specifically the body louse. It is associated with crowded, unsanitary conditions (wars, famine, refugee camps), leading to "epidemic" outbreaks. * **A. Mite:** Mites (specifically chiggers) transmit **Scrub typhus**, caused by *Orientia tsutsugamushi*. * **C. Flea:** The rat flea (*Xenopsylla cheopis*) transmits **Endemic (Murine) typhus**, caused by *Rickettsia typhi*. * **D. Tick:** Ticks are vectors for the **Spotted Fever Group**, such as Rocky Mountain Spotted Fever (*R. rickettsii*) and Indian Tick Typhus (*R. conorii*). **High-Yield Clinical Pearls for NEET-PG:** * **Brill-Zinsser Disease:** This is a recrudescent (latent) form of epidemic typhus that occurs years after the primary infection, acting as a reservoir for *R. prowazekii*. * **Weil-Felix Test:** A classic heterophile agglutination test used for diagnosis. Epidemic typhus shows a positive reaction with **OX-19**. * **Drug of Choice:** Doxycycline is the gold standard treatment for all rickettsial infections. * **Mnemonic:** "Epidemic is Bad (Body louse)" vs. "Endemic is Mouse (Flea/Rat)."

Q: Ralimar, a 30-year-old male sewage worker, is brought to the hospital with hemoptysis and altered mental status. His relatives report a history of fever, headache, and severe myalgia for 5 days. On examination, he was found to be severely jaundiced and had petechiae on oral and conjunctival mucosa. Laboratory investigations showed features of liver and renal failure. What is the most likely causative organism of this condition?

Leptospira. **Explanation:** The clinical presentation describes a classic case of **Weil’s Disease**, the severe icteric form of **Leptospirosis**. **Why Leptospira is correct:** The patient’s occupation as a **sewage worker** is a high-yield diagnostic clue, as *Leptospira interrogans* is transmitted through water contaminated by the urine of infected rodents (rats). The progression from a flu-like illness (fever, headache, severe myalgia) to a triad of **jaundice, renal failure, and hemorrhage** (hemoptysis and petechiae) is pathognomonic for Weil’s disease. A key distinguishing feature often seen in these patients is **conjunctival suffusion** (redness without exudate). **Why other options are incorrect:** * **Plague (*Yersinia pestis*):** While it can cause hemoptysis (Pneumonic plague), it typically presents with painful lymphadenopathy (buboes) and lacks the specific hepatic-renal failure pattern seen here. * **Yersinia (*Y. enterocolitica*):** Primarily causes enterocolitis or pseudoappendicitis; it does not present with this severe systemic hemorrhagic-icteric profile. * **Rickettsial fever:** While it causes fever, headache, and rashes, it rarely presents with severe jaundice and hepatic failure as the primary manifestation compared to Leptospirosis. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Microscopic Agglutination Test (MAT). * **Culture Media:** EMJH medium or Fletcher’s medium. * **Morphology:** Tightly coiled spirochetes with "hooked ends" (umbrella handle/question mark shape). * **Treatment:** Doxycycline (mild cases) or IV Penicillin G (severe cases). * **Biphasic Nature:** Leptospiremic phase (first week) followed by the Immune phase (second week).

Q: Weil-Felix reaction is positive with OXK antigen in which condition?

Scrub typhus. The **Weil-Felix reaction** is a heterophile agglutination test used for the presumptive diagnosis of Rickettsial diseases. It relies on the cross-reactivity between antibodies produced during a Rickettsial infection and the somatic (O) antigens of certain strains of *Proteus vulgaris* (OX19, OX2) and *Proteus mirabilis* (OXK). ### **Explanation of Options** * **Scrub Typhus (Correct):** Caused by *Orientia tsutsugamushi*, this condition is unique because it is the only Rickettsial infection that reacts exclusively with the **OXK** antigen. It shows no reaction with OX19 or OX2. * **Epidemic Typhus:** Caused by *Rickettsia prowazekii*, it typically shows a strongly positive reaction with **OX19** and a weak/negative reaction with OX2 and OXK. * **Endemic (Murine) Typhus:** Caused by *Rickettsia typhi*, it follows the same pattern as Epidemic typhus, reacting strongly with **OX19**. * **Trench Fever:** Caused by *Bartonella quintana*. This organism does not belong to the Rickettsia genus and is **Weil-Felix negative**. ### **High-Yield NEET-PG Pearls** * **The "K" Rule:** Remember **K** for **K**rub (Scrub) Typhus. * **Rocky Mountain Spotted Fever (RMSF):** Shows a positive reaction with both **OX19 and OX2**. * **Q Fever:** Caused by *Coxiella burnetii*; it is characteristically **Weil-Felix negative**. * **Rickettsialpox:** Caused by *Rickettsia akari*; it is also **Weil-Felix negative**. * **Vector for Scrub Typhus:** Larval stage (chigger) of trombiculid mites. Look for the characteristic **eschar** (black necrotic scab) at the bite site in clinical vignettes.

Q: Which is the common feature of spirillary rat bite fever?

Lymphadenopathy. **Explanation:** Rat-bite fever (RBF) is caused by two distinct organisms: *Streptobacillus moniliformis* (streptobacillary RBF) and *Spirillum minus* (spirillary RBF, also known as **Sodoku**). **Why Lymphadenopathy is correct:** In **Spirillary RBF (*S. minus*)**, the initial bite wound typically heals but then reactivates, becoming indurated and occasionally ulcerating (chancre-like). A hallmark feature that distinguishes it from the streptobacillary form is **marked regional lymphadenopathy** (lymphangitis and lymphadenitis) accompanying the site of the bite. This reflects the lymphatic spread of the spirochete-like organism. **Analysis of Incorrect Options:** * **B. Endocarditis:** While a known complication of *Streptobacillus moniliformis*, it is extremely rare in *Spirillum minus* infections. * **C. Hepatosplenomegaly:** Though systemic involvement occurs, hepatosplenomegaly is not a "common" or defining diagnostic feature compared to the localized lymphatic involvement. * **D. Amegakaryocytic thrombocytopenia:** This is not a feature of RBF. While some systemic infections cause reactive thrombocytopenia, amegakaryocytic forms are typically related to bone marrow failure or specific viral triggers (e.g., CMV). **High-Yield Clinical Pearls for NEET-PG:** * **Sodoku (*S. minus*):** Characterized by a prolonged incubation (1–4 weeks), reactivation of the bite site, and **lymphadenopathy**. Arthritis is rare. * **Streptobacillary RBF:** Characterized by a short incubation (<7 days), rapid onset of fever, and **migratory polyarthritis** (50% of cases). The bite wound usually heals without reactivation. * **Diagnosis:** *S. minus* cannot be cultured on artificial media; it is diagnosed via **dark-field microscopy** of blood/exudate or animal inoculation. * **Treatment:** Penicillin G is the drug of choice for both forms.

Q: What is true about scrub typhus?

Transmitted by bite of chiggers (a type of mite). **Explanation:** Scrub typhus is a zoonotic rickettsial infection caused by **Orientia tsutsugamushi**. It is a high-yield topic for NEET-PG due to its prevalence in the "Tsutsugamushi Triangle." **Why Option B is Correct:** The infection is transmitted to humans through the bite of the larval stage of trombiculid mites, commonly known as **chiggers**. These mites serve as both the vector and the natural reservoir. **Analysis of Incorrect Options:** * **Option A:** An **eschar** (a painless, black, necrotic scab at the site of the bite) is a classic clinical hallmark of scrub typhus. While not present in all patients, its presence is highly suggestive of the diagnosis. * **Option C:** Scrub typhus is caused by *Orientia tsutsugamushi*. *Rickettsia typhi* is the causative agent of **Endemic (Murine) Typhus**, transmitted by rat fleas. * **Option D:** **Transovarial transmission** (from adult mite to egg) and transstadial transmission occur within the mite population, allowing the bacteria to persist in the environment without a vertebrate host. **NEET-PG High-Yield Pearls:** * **Weil-Felix Test:** Scrub typhus shows a positive reaction with **OX-K** (negative for OX-2 and OX-19). * **Drug of Choice:** **Doxycycline** is the gold standard treatment. Azithromycin is an alternative, especially in pregnancy. * **Habitat:** It is typically found in secondary vegetation growth (scrub) that follows the clearing of primary forests. * **Diagnosis:** Immunofluorescence assay (IFA) is the gold standard serological test.

Q: An 8-year-old girl presents with fever and bone pain localized to her right calf after being bitten in the leg by a neighbor's cat. X-ray reveals a lytic lesion of the right tibia. Bone culture results are pending. Which organism do you expect to be the cause of infection?

Pasteurella multocida. **Explanation:** The clinical presentation of a localized bone lesion (osteomyelitis) following a cat bite is classic for **Pasteurella multocida**. **1. Why Pasteurella multocida is correct:** *Pasteurella multocida* is a small, Gram-negative coccobacillus that is part of the normal oral flora of cats (up to 90% carriage) and dogs. It is the most common organism isolated from infected animal bite wounds. Unlike other infections, *Pasteurella* is known for its **rapid progression** (often within 24 hours) and its propensity to cause deep-seated infections like **osteomyelitis** or septic arthritis, especially if the bite involves a puncture wound that reaches the periosteum. **2. Why the other options are incorrect:** * **Brucella melitensis:** Associated with the consumption of unpasteurized dairy products or contact with infected livestock (goats/sheep). It causes undulant fever and chronic osteoarticular complications (commonly sacroiliitis), but not acute cat-bite infections. * **Eikenella corrodens:** Part of the human oral flora. It is typically associated with **human bites** ("clenched fist injuries") or endocarditis, not feline bites. * **Francisella tularensis:** Causes Tularemia. While it can be transmitted by cats, it typically presents with an ulceroglandular syndrome (skin ulcer with painful regional lymphadenopathy) rather than direct pyogenic osteomyelitis at the bite site. **Clinical Pearls for NEET-PG:** * **Drug of Choice:** Amoxicillin-Clavulanate is the first-line treatment for animal bites. *Pasteurella* is notably resistant to Macrolides and first-generation Cephalosporins. * **Cat Scratch Disease:** Caused by *Bartonella henselae*; presents with subacute regional lymphadenopathy rather than acute osteomyelitis. * **Radiology:** In acute *Pasteurella* osteomyelitis, lytic lesions can appear more rapidly than in typical staphylococcal osteomyelitis.

Q: Which of the following is NOT transmitted by arthropods?

Q fever. **Explanation:** The correct answer is **Q fever**. While most rickettsial and related diseases are transmitted via arthropod vectors, Q fever is a notable exception. **1. Why Q Fever is the Correct Answer:** Q fever is caused by *Coxiella burnetii*. Unlike other rickettsial diseases, it is primarily a **zoonosis** transmitted to humans via **inhalation** of contaminated aerosols or dust from the birth products, feces, or urine of infected livestock (sheep, goats, cattle). It can also be transmitted through the consumption of unpasteurized milk. Although ticks can carry the organism in nature, they play a negligible role in human transmission. **2. Analysis of Incorrect Options:** * **Rickettsial pox:** Caused by *Rickettsia akari*, it is transmitted by the **mite** (*Liponyssoides sanguineus*). * **Rocky Mountain Spotted Fever (RMSF):** Caused by *Rickettsia rickettsii*, it is transmitted by **ticks** (e.g., *Dermacentor variabilis*). * **Relapsing fever:** This can be **Louse-borne** (Epidemic relapsing fever caused by *Borrelia recurrentis*) or **Tick-borne** (Endemic relapsing fever caused by *Borrelia duttoni*). **3. NEET-PG High-Yield Clinical Pearls:** * **Q Fever:** It is the most heat-resistant pathogen found in milk; hence, it is used as the indicator organism for the efficiency of **pasteurization**. * **Weil-Felix Test:** This is a classic diagnostic test for rickettsial diseases, but it is **negative** in Q fever. * **Occupational Hazard:** Q fever is common among veterinarians, abattoir workers, and farmers. * **Morphology:** *Coxiella burnetii* is an obligate intracellular organism that forms spore-like structures, allowing it to survive harsh environmental conditions.

Q: What is the most likely causative agent of community-acquired pneumonia in a person rearing sheep?

Coxiella burnetii. **Explanation:** The correct answer is **Coxiella burnetii**, the causative agent of **Q fever**. **Why Coxiella burnetii is correct:** Q fever is a classic zoonotic infection associated with exposure to livestock, particularly **sheep, goats, and cattle**. The bacteria are excreted in high concentrations in the placenta, birth fluids, urine, and feces of infected animals. Transmission to humans occurs via **inhalation of contaminated aerosols** or dust. Clinically, acute Q fever most commonly presents as a self-limiting febrile illness, but it is a well-known cause of **culture-negative endocarditis** and **atypical community-acquired pneumonia** (often showing "ground-glass" opacities on imaging). **Why the other options are incorrect:** * **Histoplasma capsulatum:** While it causes pneumonia, it is associated with exposure to **bird or bat droppings** (guano), often in caves or old buildings, rather than livestock. * **Streptococcus pneumoniae:** This is the most common cause of typical community-acquired pneumonia in the general population, but it lacks a specific epidemiological link to sheep rearing. * **Bacillus anthracis:** While associated with herbivores (Woolsorter’s disease), inhalation anthrax typically presents as a rapidly progressive, fatal **hemorrhagic mediastinitis** (widened mediastinum) rather than a standard community-acquired pneumonia. **NEET-PG High-Yield Pearls:** * **Organism:** *Coxiella burnetii* is an obligate intracellular Gram-negative bacterium (formerly Rickettsial). * **Diagnosis:** Serology is the gold standard (Indirect Immunofluorescence Assay). * **Chronic Q Fever:** Characterized by **Phase I antibodies** (IgG ≥ 1:800); Acute Q fever shows higher **Phase II antibodies**. * **Treatment:** Doxycycline is the drug of choice for acute cases. * **Key Association:** If a question mentions a "pregnant sheep" or "veterinarian/farmer" with pneumonia or hepatitis, think Q fever.

Question 1

Which of the following diseases is transmitted by a mite vector?

Accepted Answer

Scrub typhus (caused by Orientia tsutsugamushi)

Answer

Typhus fever (caused by Rickettsia typhi)

Answer

Epidemic typhus (caused by Rickettsia prowazekii)

Answer

Rocky Mountain spotted fever (caused by Rickettsia rickettsii)

Question 2

Epidemic typhus is transmitted by:

Accepted Answer

Louse

Answer

Mite

Answer

Flea

Answer

Tick

Question 3

Ralimar, a 30-year-old male sewage worker, is brought to the hospital with hemoptysis and altered mental status. His relatives report a history of fever, headache, and severe myalgia for 5 days. On examination, he was found to be severely jaundiced and had petechiae on oral and conjunctival mucosa. Laboratory investigations showed features of liver and renal failure. What is the most likely causative organism of this condition?

Accepted Answer

Leptospira

Answer

Plague

Answer

Yersinia

Answer

Rickettsial fever

Question 4

Weil-Felix reaction is positive with OXK antigen in which condition?

Accepted Answer

Scrub typhus

Answer

Trench fever

Answer

Endemic typhus

Answer

Epidemic typhus

Question 5

Which is the common feature of spirillary rat bite fever?

Accepted Answer

Lymphadenopathy

Answer

Endocarditis

Answer

Hepatosplenomegaly

Answer

Amegakaryocytic thrombocytopenia

Question 6

What is true about scrub typhus?

Accepted Answer

Transmitted by bite of chiggers (a type of mite)

Answer

No eschar

Answer

Caused by Rickettsia typhi

Answer

No transovarial transmission

Question 7

Which organism has a special predilection towards the placenta?

Accepted Answer

Brucella

Answer

Neisseria meningitides

Answer

Haemophilus influenzae

Answer

Moraxella catarrhalis

Question 8

An 8-year-old girl presents with fever and bone pain localized to her right calf after being bitten in the leg by a neighbor's cat. X-ray reveals a lytic lesion of the right tibia. Bone culture results are pending. Which organism do you expect to be the cause of infection?

Accepted Answer

Pasteurella multocida

Answer

Brucella melitensis

Answer

Eikenella corrodens

Answer

Francisella tularensis

Question 9

Which of the following is NOT transmitted by arthropods?

Accepted Answer

Q fever

Answer

Rickettsial pox

Answer

Rocky mountain spotted fever

Answer

Relapsing fever

Question 10

What is the most likely causative agent of community-acquired pneumonia in a person rearing sheep?

Accepted Answer

Coxiella burnetii

Answer

Histoplasma capsulatum

Answer

Streptococcus pneumoniae

Answer

Bacillus anthracis

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

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