Zoonotic Diseases Practice Questions

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

Q fever. The correct answer is **Q fever (Option D)**. ### **Explanation** While most Rickettsial diseases are transmitted via arthropod vectors (ticks, mites, lice, or fleas), **Q fever**, caused by *Coxiella burnetii*, is a notable exception. 1. **Why Q fever is the correct answer:** *Coxiella burnetii* is primarily transmitted to humans via **inhalation of infected aerosols** or dust contaminated by birth products (placenta), feces, or urine of infected livestock (sheep, goats, cattle). It is highly infectious due to its ability to form spore-like structures that survive harsh environmental conditions. No arthropod vector is required for human transmission. 2. **Why other options are incorrect:** * **Scrub typhus (*Orientia tsutsugamushi*):** Transmitted by the bite of larval mites (**Chiggers**). * **Epidemic typhus (*Rickettsia prowazekii*):** Transmitted by the **Human body louse**. * **Rocky Mountain Spotted Fever (*Rickettsia rickettsii*):** Transmitted by **Ticks** (e.g., *Dermacentor* species). ### **High-Yield Clinical Pearls for NEET-PG** * **Weil-Felix Test:** This heterophile agglutination test is **negative** in Q fever but positive in most other Rickettsial infections. * **Culture Negativity:** *Coxiella burnetii* is a common cause of **Culture-Negative Endocarditis**. * **Occupational Hazard:** Q fever is most common among veterinarians, farmers, and abattoir workers. * **Diagnosis:** Serology (IFA) is the gold standard. Look for "Doughnut granulomas" on liver biopsy in acute cases. * **Treatment:** Doxycycline is the drug of choice for most Rickettsial diseases, including Q fever.

Q: A 35-year-old man presents with sudden onset of fever, headache, myalgia, conjunctivitis, and skin bleeds. He recently visited a forest with a large monkey population. What is the likely vector for the suspected disease?

Ticks. **Explanation:** The clinical presentation of fever, headache, myalgia, conjunctivitis, and hemorrhagic manifestations (skin bleeds) following exposure to a forest with monkeys strongly suggests **Kyasanur Forest Disease (KFD)**, also known as "Monkey Fever." **1. Why Ticks are correct:** KFD is caused by the Kyasanur Forest Disease Virus (KFDV), a member of the *Flaviviridae* family. The primary vector is the hard tick, specifically ***Haemaphysalis spinigera***. The disease is endemic to the Western Ghats of India (Karnataka). Monkeys (Langurs and Bonnet macaques) act as amplifying hosts; their death often serves as a sentinel event signaling an outbreak. Humans are accidental "dead-end" hosts, usually infected via tick bites while visiting forested areas. **2. Why other options are incorrect:** * **Mosquitoes:** While they transmit other viral hemorrhagic fevers like Dengue and Yellow Fever, they are not the vectors for KFD. Dengue lacks the specific association with monkey deaths in forest settings. * **Fleas:** These are vectors for *Yersinia pestis* (Plague) and Murine typhus, which present differently (e.g., painful buboes). * **Mites:** Specifically, the Trombiculid mite (chigger) transmits Scrub Typhus, characterized by an eschar and a different clinical course. **3. NEET-PG High-Yield Pearls:** * **Sentinel Animals:** Sudden deaths of monkeys in the forest are the first sign of a KFD outbreak. * **Diagnosis:** PCR is used in the early phase (viremic stage); ELISA for IgM antibodies is used later. * **Prevention:** A **formalin-inactivated vaccine** is available for individuals in endemic areas. * **Seasonality:** Most cases occur during the dry months (January–June) when tick activity is high.

Q: In pneumonic plague, how does human-to-human transmission occur?

Respiratory droplets. **Explanation:** **Pneumonic plague** is the most severe and highly infectious form of plague caused by the Gram-negative coccobacillus *Yersinia pestis*. 1. **Why Respiratory Droplets is Correct:** In pneumonic plague, the bacteria infect the lungs, leading to severe pneumonia. When an infected individual coughs or sneezes, they expel **respiratory droplets** containing high concentrations of *Y. pestis*. Inhalation of these droplets by another human leads to **primary pneumonic plague**. This is the only form of plague that can be transmitted directly from human to human without an insect vector. 2. **Why Other Options are Incorrect:** * **Rat flea bite (Option A):** This is the primary mode of transmission for **Bubonic plague**. The flea (*Xenopsylla cheopis*) bites an infected rodent and then transmits the bacteria to humans. * **Rat bite (Option B):** While direct contact with infected animal tissues can cause plague, a simple rat bite is not the standard epidemiological route for pneumonic transmission. * **Discharge from wounds (Option C):** Direct contact with pus from buboes (suppurative lymph nodes) can transmit the infection through skin breaks, but this results in bubonic plague, not the rapid human-to-human spread characteristic of the pneumonic form. **High-Yield Clinical Pearls for NEET-PG:** * **Safety/Bioterrorism:** *Y. pestis* is classified as a **Category A Biothreat agent** due to its potential for aerosol dissemination. * **Morphology:** Shows characteristic **"Safety-pin appearance"** (bipolar staining) with Wayson or Giemsa stains. * **Virulence Factor:** The **F1 antigen** (capsular polysaccharide) is highly specific and used for diagnosis. * **Treatment:** Aminoglycosides (Streptomycin/Gentamicin) are the drugs of choice; Doxycycline is an alternative.

Q: Which of the following conditions is NOT diagnosed by the Weil-Felix reaction?

Q fever. ### Explanation The **Weil-Felix reaction** is a heterophile agglutination test used for the presumptive diagnosis of Rickettsial diseases. It relies on the principle of **cross-reactivity**, where antibodies produced against Rickettsial antigens cross-react with the somatic ‘O’ antigens of certain strains of *Proteus vulgaris* (OX-19, OX-2) and *Proteus mirabilis* (OX-K). **Why Q Fever is the Correct Answer:** Q fever is caused by ***Coxiella burnetii***. Unlike other Rickettsial organisms, *Coxiella* does not share common antigens with *Proteus* strains. Therefore, the Weil-Felix reaction is **negative** in Q fever. Diagnosis is typically confirmed via Serology (IFA) or PCR. **Analysis of Other Options:** * **Epidemic Typhus (*R. prowazekii*):** Shows a strongly positive reaction with **OX-19**. * **Endemic Typhus (*R. typhi*):** Also shows a strongly positive reaction with **OX-19**. * **Scrub Typhus (*Orientia tsutsugamushi*):** Characteristically reacts only with **OX-K**. **High-Yield Clinical Pearls for NEET-PG:** * **Memory Aid for Weil-Felix:** * **OX-19 & OX-2:** Positive in Typhus group and Spotted Fever group. * **OX-K:** Positive in Scrub Typhus (K for "K"arbuncle/Eschar, though not etiologically related). * **Negative Weil-Felix:** Q fever, Rickettsialpox, and Trench fever. * **Gold Standard:** The Indirect Fluorescent Antibody (IFA) test is the gold standard for Rickettsial diagnosis, as Weil-Felix lacks sensitivity and specificity. * **Q Fever Fact:** It is the only Rickettsial disease that **does not present with a rash** and does not require an arthropod vector for transmission (usually inhalation of contaminated aerosols).

Q: Which of the following viral infections is NOT typically transmitted from human to human?

Japanese B encephalitis. ### Explanation The correct answer is **Japanese B encephalitis (JEV)**. **1. Why Japanese B Encephalitis is the correct answer:** Japanese Encephalitis is a **zoonotic viral infection** caused by a Flavivirus. It follows a complex transmission cycle involving **Culex mosquitoes** (primarily *Culex tritaeniorhynchus*) as the vector, and **pigs or water birds** as the natural reservoirs/amplifying hosts. Humans are considered **"dead-end hosts"** because the level of viremia in human blood is typically insufficient to infect a biting mosquito. Therefore, direct human-to-human transmission does not occur. **2. Why the other options are incorrect:** * **SARS (Severe Acute Respiratory Syndrome):** Caused by a coronavirus, it is highly contagious and spreads primarily through respiratory droplets and direct contact between humans. * **Bird’s Flu (Avian Influenza, e.g., H5N1):** While primarily a disease of birds, limited and non-sustained human-to-human transmission has been documented, especially among close family contacts. * **Poliomyelitis:** This is an exclusively human pathogen. It is transmitted via the **fecal-oral route** (and occasionally respiratory droplets) from one person to another. **3. NEET-PG High-Yield Pearls:** * **Vector for JEV:** *Culex tritaeniorhynchus* (breeds in stagnant water/rice fields). * **Amplifying Host:** Pigs (they develop high-level viremia without getting sick). * **Dead-end Hosts:** Humans and Horses. * **Vaccine:** Live attenuated (SA-14-14-2) and Inactivated (Jenvac) vaccines are available. * **Other "Dead-end" infections:** Rabies, West Nile Virus, and Hydatid disease (Echinococcosis).

Q: The typhus group of fevers are transmitted by which of the following vectors?

Mites, Human body louse, and Fleas. The **Typhus group of fevers** are rickettsial diseases characterized by fever, headache, and a characteristic rash. These are categorized based on their specific vectors and causative agents. ### **Explanation of the Correct Answer** The correct answer is **C (Mites, Human body louse, and Fleas)** because the typhus group traditionally includes: 1. **Epidemic Typhus:** Caused by *Rickettsia prowazekii* and transmitted by the **Human body louse** (*Pediculus humanus corporis*). 2. **Endemic (Murine) Typhus:** Caused by *Rickettsia typhi* and transmitted by **Rat fleas** (*Xenopsylla cheopis*). 3. **Scrub Typhus:** Caused by *Orientia tsutsugamushi* and transmitted by the bite of infected **larval mites (chiggers)**. ### **Why Other Options are Incorrect** * **Options A, B, and D** are incorrect because they include the **Sand fly**. Sand flies are the vectors for **Leishmaniasis (Kala-azar)** and **Sandfly fever (Pappataci fever)**, neither of which belong to the rickettsial typhus group. ### **High-Yield NEET-PG Clinical Pearls** * **Weil-Felix Test:** A heterophile agglutination test used for diagnosis (though being replaced by ELISA/IFA). * *Epidemic/Endemic Typhus:* OX-19 positive. * *Scrub Typhus:* OX-K positive. * **Drug of Choice:** **Doxycycline** is the gold standard treatment for all rickettsial infections, regardless of age. * **Scrub Typhus Hallmark:** Look for the **"Eschar"** (a black, necrotic scab at the site of the mite bite), which is a pathognomonic clinical sign. * **Brill-Zinsser Disease:** A recrudescent (latent) form of Epidemic Typhus that occurs years after the primary infection.

Q: Murine typhus is caused by which of the following pathogens?

Rickettsia typhi. **Explanation:** **Murine typhus** (also known as endemic typhus) is caused by **Rickettsia typhi**. It is primarily transmitted to humans via the **rat flea (*Xenopsylla cheopis*)**. The reservoir for this pathogen is the urban rat. Clinically, it presents with fever, headache, and a maculopapular rash that typically spreads from the trunk to the extremities (centrifugal spread). **Analysis of Options:** * **Rickettsia prowazekii (Option A):** Causes **Epidemic typhus**. It is transmitted by the **human body louse** (*Pediculus humanus corporis*). It is more severe than murine typhus and can recur years later as Brill-Zinsser disease. * **Rickettsia conori (Option B):** Causes **Boutonneuse fever** (Indian tick typhus/Mediterranean spotted fever). It is transmitted by the brown dog tick and is characterized by a pathognomonic black crust at the site of the bite called an **"eschar."** * **Coxiella burnetii (Option D):** Causes **Q fever**. Unlike other rickettsial diseases, it does not cause a rash, does not require an arthropod vector (transmitted via inhalation of aerosols), and is **Weil-Felix negative**. **High-Yield Clinical Pearls for NEET-PG:** * **Weil-Felix Test:** A heterophile agglutination test using *Proteus* antigens. *R. typhi* and *R. prowazekii* react with **OX-19**. * **Drug of Choice:** Doxycycline is the gold standard treatment for all rickettsial infections. * **Vector Mnemonic:** **E**pidemic = **L**ouse (EL), **E**ndemic (Murine) = **F**lea (EF).

Q: Q fever is caused by which Rickettsial Agent?

C. burnetii. **Explanation:** **Correct Answer: C. Coxiella burnetii** Q fever is caused by *Coxiella burnetii*. Although historically classified under the family Rickettsiaceae due to its obligate intracellular nature, it is genetically distinct. Unlike other rickettsial diseases, Q fever is unique because it **does not present with a rash** and does not require an arthropod vector for human transmission; it is primarily acquired through the inhalation of infected aerosols from livestock (cattle, sheep, goats). **Analysis of Incorrect Options:** * **A. R. prowazekii:** This agent causes **Epidemic Typhus**, which is transmitted by the human body louse. * **B. R. tsutsugamushi (Orientia tsutsugamushi):** This agent causes **Scrub Typhus**, transmitted by the bite of a larval mite (chigger). * **C. Rochalimaea quintana (Bartonella quintana):** This agent causes **Trench Fever**, also transmitted by the human body louse. **High-Yield Clinical Pearls for NEET-PG:** * **Weil-Felix Test:** Q fever is **Weil-Felix negative** (unlike most other rickettsial infections). * **Resistance:** *C. burnetii* is highly resistant to environmental stressors (heat, drying) due to its spore-like form. * **Diagnosis:** The gold standard is Serology (IFA). * **Clinical Presentation:** Often presents as an atypical pneumonia or hepatitis. In chronic cases, **culture-negative endocarditis** is a classic association. * **Drug of Choice:** Doxycycline.

Q: Which of the following is true about Bacillus anthracis?

It causes a zoonotic disease.. **Explanation:** *Bacillus anthracis* is a Gram-positive, spore-forming, non-motile aerobic rod. It primarily affects herbivores (cattle, sheep, goats) and is the causative agent of **Anthrax**. **1. Why Option A is Correct:** Anthrax is a classic **zoonotic disease**. Humans are accidental hosts who acquire the infection through contact with infected animals or contaminated animal products (hides, wool, hair). The spores enter the body via skin abrasions (Cutaneous), inhalation (Pulmonary), or ingestion (Gastrointestinal). **2. Why Other Options are Incorrect:** * **Option B:** Unlike many respiratory infections, **person-to-person transmission of anthrax does not occur**, even in the inhalational form. It is not considered contagious between humans. * **Option C:** While *B. anthracis* is indeed a major **bioterrorism agent** (Category A), the question asks for the "most true" or primary biological characteristic in many standard formats. However, in most medical contexts, both A and C are technically true. In the context of this specific question, its classification as a zoonosis is its fundamental epidemiological definition. * **Option D:** Antibiotics are the **mainstay of treatment**. Ciprofloxacin or Doxycycline are the drugs of choice. Early administration is critical, especially in inhalational anthrax. **NEET-PG High-Yield Pearls:** * **McFadyean’s Reaction:** Used for presumptive identification (polychrome methylene blue staining shows purple capsules around blue bacilli). * **Morphology:** "Bamboo stick" appearance and "Medusa head" colonies on agar. * **Virulence Factors:** Encoded on plasmids **pXO1** (Toxins: Edema factor, Lethal factor, Protective antigen) and **pXO2** (Polypeptide capsule made of D-glutamic acid). * **Occupational Hazard:** Often called "Woolsorter’s disease" (inhalational) or "Hide-porter’s disease" (cutaneous).

Question 1

Which of the following is NOT transmitted by arthropods?

Accepted Answer

Q fever

Answer

Scrub typhus

Answer

Epidemic typhus

Answer

Rocky Mountain Spotted Fever (RMSF)

Question 2

A 35-year-old man presents with sudden onset of fever, headache, myalgia, conjunctivitis, and skin bleeds. He recently visited a forest with a large monkey population. What is the likely vector for the suspected disease?

Accepted Answer

Ticks

Answer

Mosquito

Answer

Fleas

Answer

Mites

Question 3

In pneumonic plague, how does human-to-human transmission occur?

Accepted Answer

Respiratory droplets

Answer

Rat flea bite

Answer

Rat bite

Answer

Discharge from wounds

Question 4

Which of the following conditions is NOT diagnosed by the Weil-Felix reaction?

Accepted Answer

Q fever

Answer

Endemic typhus

Answer

Scrub typhus

Answer

Epidemic typhus

Question 5

Which of the following viral infections is NOT typically transmitted from human to human?

Accepted Answer

Japanese B encephalitis

Answer

SARS

Answer

Bird's flu

Answer

Poliomyelitis

Question 6

The typhus group of fevers are transmitted by which of the following vectors?

Accepted Answer

Mites, Human body louse, and Fleas

Answer

Mites, Human body louse, and Sand fly

Answer

Mites, Sand fly, and Fleas

Answer

Human body louse, Sand fly, and Fleas

Question 7

Murine typhus is caused by which of the following pathogens?

Accepted Answer

Rickettsia typhi

Answer

Rickettsia prowazekii

Answer

Rickettsia conori

Answer

Coxiella burnetii

Question 8

Q fever is caused by which Rickettsial Agent?

Accepted Answer

C. burnetii

Answer

R. prowazekii

Answer

R. tsutsugamushi

Answer

Rochalimaea quintana

Question 9

Which of the following is NOT true regarding scrub typhus?

Accepted Answer

It is caused by the bite of an adult mite on a vertebrate host.

Answer

It is caused by Rickettsia tsutsugamushi.

Answer

It is spread by mites.

Answer

Tetracycline is an effective treatment.

Question 10

Which of the following is true about Bacillus anthracis?

Accepted Answer

It causes a zoonotic disease.

Answer

It can be transmitted from person to person.

Answer

It is an agent used in bioterrorism.

Answer

Antibiotics have no role in its treatment.

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

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