Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 111: What caused the maximum damage to Napoleon's army during his march to Moscow?

A. Typhus (Correct Answer)
B. Plague
C. Diarrhea
D. Typhoid

Explanation: **Explanation:** The correct answer is **Typhus** (specifically Epidemic Typhus). Napoleon’s 1812 Russian campaign is a classic historical example of how infectious diseases can alter the course of history. **1. Why Typhus is Correct:** Epidemic Typhus is caused by **_Rickettsia prowazekii_** and is transmitted by the **human body louse** (*Pediculus humanus corporis*). During the march to Moscow, the Grande Armée faced severe overcrowding, lack of hygiene, and cold weather—conditions that favored louse infestation. It is estimated that Napoleon lost more soldiers to Typhus (over 100,000) than to actual combat with the Russian army. **2. Why the other options are incorrect:** * **Plague:** Caused by *Yersinia pestis*, it was a major historical killer (e.g., Black Death), but it was not the primary driver of mortality in the 1812 campaign. * **Diarrhea/Dysentery:** While present due to poor sanitation, these were secondary to the massive Typhus outbreaks. * **Typhoid:** Caused by *Salmonella typhi*, it is water-borne. While it plagued many 19th-century armies, the specific "Great Killer" of the Russian campaign was the louse-borne Typhus. **NEET-PG High-Yield Pearls:** * **Vector:** Body louse (Typhus) vs. Rat flea (Plague) vs. Tick (Rocky Mountain Spotted Fever). * **Weil-Felix Test:** A classic (though non-specific) diagnostic test for Rickettsial infections. Epidemic Typhus shows a positive reaction with **OX-19**. * **Brill-Zinsser Disease:** A recrudescent (latent) form of Epidemic Typhus occurring years after the primary attack. * **Drug of Choice:** Doxycycline is the gold standard for all Rickettsial diseases.

Question 112: What is the quarantine period for yellow fever?

A. 1 day
B. 2 days
C. 6 days (Correct Answer)
D. 10 days

Explanation: **Explanation:** The correct answer is **6 days**. In public health and international health regulations, the quarantine period for a disease is traditionally defined as the **maximum incubation period** of that specific infection. For Yellow Fever, the incubation period typically ranges from 3 to 6 days. Therefore, to ensure that an individual arriving from an endemic zone is not carrying the virus, they must be quarantined for the maximum duration of 6 days from the date of last possible exposure. **Analysis of Options:** * **A & B (1-2 days):** These are incorrect as they are shorter than the minimum incubation period; symptoms would likely not have manifested yet. * **C (6 days):** This is the **correct** answer, representing the maximum incubation period as per WHO International Health Regulations (IHR). * **D (10 days):** While the Yellow Fever vaccine becomes legally valid and provides immunity **10 days** after administration, this is not the quarantine period. **High-Yield Clinical Pearls for NEET-PG:** * **Vaccine Validity:** The Yellow Fever vaccine (17D strain) is valid for **life** (as per WHO 2016 update), but for international travel certificates, it becomes valid **10 days after vaccination**. * **Vector:** Primarily *Aedes aegypti* (Urban cycle) and *Haemagogus* (Jungle cycle). * **India Status:** India is "Yellow Fever receptive" (has the vector but not the virus). Hence, strict quarantine rules apply to travelers from the African and South American endemic belts. * **Contraindication:** The vaccine is a live attenuated vaccine and is contraindicated in infants <6 months, pregnant women, and immunocompromised individuals.

Question 113: What is true about poliomyelitis?

A. Paralytic poliomyelitis is the most common form.
B. It causes spastic paralysis.
C. Increased muscular activity leads to increased paralysis. (Correct Answer)
D. The oral polio vaccine is given only to children under 3 years of age.

Explanation: **Explanation:** **Why Option C is Correct:** In poliomyelitis, the severity of paralysis is influenced by physical activity during the **pre-paralytic stage**. Increased muscular activity or trauma (like intramuscular injections) leads to increased vascularity in the corresponding segment of the spinal cord. This allows more viruses to reach the anterior horn cells, resulting in more extensive neuronal damage and severe paralysis. This phenomenon is known as **"Provocation Paralysis."** **Analysis of Incorrect Options:** * **Option A:** Inapparent (asymptomatic) infection is the most common form, occurring in over 91-95% of cases. Paralytic polio is the rarest form, occurring in less than 1% of infections. * **Option B:** Poliovirus specifically destroys the **Anterior Horn Cells** of the spinal cord (Lower Motor Neuron). Therefore, it causes **Flaccid Paralysis**, characterized by loss of muscle tone and absent deep tendon reflexes, not spastic paralysis. * **Option D:** Under the Universal Immunization Programme (UIP) and Pulse Polio Immunization (PPI), OPV is administered to children up to **5 years of age**. **High-Yield Clinical Pearls for NEET-PG:** * **Agent:** RNA Enterovirus (Poliovirus Type 1 is most commonly associated with paralytic outbreaks). * **Transmission:** Fecal-oral route is the most common in developing countries. * **Clinical Sign:** "Tripod Sign" (child sits with hands behind for support due to spinal rigidity). * **Vaccine:** **Sabin (OPV)** is a live attenuated vaccine (induces local IgA immunity); **Salk (IPV)** is an inactivated vaccine (induces humoral IgG immunity). * **Eradication:** India was declared Polio-free by the WHO on March 27, 2014.

Question 114: Which of the following diseases are transmitted from animals to humans (zoonosis)?

A. Rabies, Plague, Measles
B. Japanese encephalitis, HIV, Plague
C. Rabies, Japanese encephalitis, HIV
D. Rabies, Plague, HIV (Correct Answer)

Explanation: ### Explanation **Concept Overview** A **zoonosis** is defined by the WHO as any disease or infection that is naturally transmissible from vertebrate animals to humans. These can be bacterial, viral, or parasitic and are transmitted through direct contact, food, water, or the environment. **Why Option D is Correct** * **Rabies:** A classic viral zoonosis transmitted primarily through the saliva of infected animals (dogs, bats, monkeys) via bites or scratches. * **Plague:** A bacterial zoonosis caused by *Yersinia pestis*. It is naturally maintained in wild rodent populations and transmitted to humans via the bite of an infected rat flea (*Xenopsylla cheopis*). * **HIV:** While now primarily a human-to-human infection, HIV is classified as a **zooanthroponosis**. It originated from Cross-species transmission (SIV) from non-human primates (chimpanzees and sooty mangabeys) to humans in West/Central Africa. **Analysis of Incorrect Options** * **Measles (Options A):** Measles is an **anthroponosis**. Humans are the only natural reservoir for the measles virus; it does not have an animal host. * **Japanese Encephalitis (Options B & C):** JE is technically an **obligate zoonosis** (maintained in a cycle between pigs/ardeid birds and *Culex* mosquitoes). However, in the context of standard NEET-PG classification, if a choice includes Measles (a strict human disease), it is eliminated. The inclusion of HIV in the correct option reflects recent trends in recognizing its simian origins. **NEET-PG High-Yield Pearls** * **Most Common Zoonosis in India:** Brucellosis is often cited as a major underreported zoonotic threat. * **Dead-end Hosts:** Humans are "dead-end hosts" for **Rabies** and **Japanese Encephalitis** because they do not typically transmit the infection back to the vector or other animals. * **Emerging Zoonoses:** 75% of emerging infectious diseases (e.g., Ebola, Nipah, COVID-19) are zoonotic in origin. * **Plague Vector:** Remember the "Index of Fleas"—a Rat Flea Index >1 is a warning sign for a potential plague outbreak.

Question 115: A healthcare worker sustains a needle-prick injury from a patient with HIV. What is the immediate management or treatment required?

A. Prophylactic vaccination
B. Antiretroviral therapy (Correct Answer)
C. Vaccination and antiretroviral therapy
D. HIV testing

Explanation: ### Explanation **Correct Answer: B. Antiretroviral therapy** The immediate management of a needle-stick injury (NSI) involving a known HIV-positive source is the initiation of **Post-Exposure Prophylaxis (PEP)** using Antiretroviral Therapy (ART). The goal is to inhibit viral replication before the virus can establish a systemic infection. According to NACO guidelines, PEP should be started as soon as possible—ideally within **2 hours** and no later than **72 hours**—and continued for **28 days**. **Analysis of Incorrect Options:** * **A & C (Vaccination):** There is currently no effective prophylactic vaccine available for HIV. Vaccination is a standard protocol for Hepatitis B post-exposure, but not for HIV. * **D (HIV testing):** While baseline testing of the healthcare worker (HCW) is mandatory to establish their pre-exposure status, it is a diagnostic step, not a "treatment" or "management" to prevent infection. Treatment (ART) must not be delayed while waiting for test results. **High-Yield Clinical Pearls for NEET-PG:** * **The "Golden Period":** PEP is most effective if started within 2 hours of exposure. * **Standard PEP Regimen (NACO):** A 3-drug regimen is now preferred: **Tenofovir (300mg) + Lamivudine (300mg) + Dolutegravir (50mg)** once daily for 28 days. * **Immediate First Aid:** Wash the site with soap and water. **Do not scrub** or use antiseptics like bleach; **do not squeeze** the wound to induce bleeding. * **Risk of Transmission:** The average risk of HIV transmission after a percutaneous exposure to HIV-infected blood is approximately **0.3%**. (Compare this to Hepatitis B, which is 6–30%, and Hepatitis C, which is ~1.8%).

Question 116: Which of the following are measures taken in Guinea worm prophylaxis, EXCEPT?

A. Safe drinking water
B. Control of Cyclops
C. Health education
D. Mass treatment with Mebendazole (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Mass treatment with Mebendazole**. Guinea worm disease (*Dracunculiasis*) is unique because there is **no effective vaccine or specific curative medicine** available to prevent or treat the infection. While Mebendazole has been trialed to facilitate the easier extraction of the worm by reducing inflammation, it does not prevent infection or act as a mass prophylactic agent. **Why the other options are incorrect (Measures for Prophylaxis):** * **Safe drinking water:** This is the cornerstone of prevention. Since the disease is transmitted by drinking water containing infected *Cyclops* (water fleas), providing piped water, borehole wells, or using fine-mesh cloth filters (0.15mm) effectively interrupts transmission. * **Control of Cyclops:** Biological or chemical control of the intermediate host is vital. Chemical treatment of stagnant water sources with **Temephos (Abate)** kills *Cyclops* without making the water unsafe for human consumption. * **Health education:** Educating the community to prevent infected individuals from wading into drinking water sources (which triggers the release of larvae) is essential to break the life cycle. **High-Yield Clinical Pearls for NEET-PG:** * **Eradication Status:** India was declared Guinea worm-free by the WHO in **February 2000**. The last case in India was reported in July 1996 (Rajasthan). * **Agent:** *Dracunculus medinensis* (the "fiery serpent"). * **Intermediate Host:** *Cyclops* (also known as the "water flea"). * **Incubation Period:** Approximately **1 year** (8–14 months). * **Diagnosis:** Typically made clinically by observing the worm emerging from a painful skin ulcer, usually on the lower limbs.

Question 117: All of the following cause a false positive Mantoux test except?

A. HIV/AIDS (Correct Answer)
B. Prior BCG vaccine
C. Degraded tuberculin
D. Faulty technique of injection

Explanation: The Mantoux test (Tuberculin Skin Test) is a **Type IV Delayed-Type Hypersensitivity (DTH)** reaction. It relies on a functional cellular immune system (T-cells) to mount a response to the injected PPD (Purified Protein Derivative). ### **Why HIV/AIDS is the Correct Answer** In **HIV/AIDS**, there is a progressive depletion of CD4+ T-lymphocytes. Because the body lacks the immune cells necessary to mount a hypersensitivity reaction, an infected individual may show a negative result despite having Tuberculosis. This is known as **Anergy**. Therefore, HIV/AIDS causes a **False Negative** result, not a false positive. ### **Explanation of Other Options (Causes of False Positives)** * **Prior BCG Vaccination:** The BCG vaccine contains live attenuated *M. bovis*. The immune system develops memory against these antigens, which can cross-react with the PPD used in the Mantoux test, leading to a positive skin reaction in the absence of actual TB infection. * **Degraded Tuberculin:** If the PPD solution is contaminated or improperly stored, it can cause localized non-specific inflammation or irritation at the injection site, which may be misread as a positive induration. * **Faulty Technique:** Injecting the PPD too superficially or using an excessive volume can cause localized trauma or a "wheal" that mimics a positive induration. ### **High-Yield Clinical Pearls for NEET-PG** * **Reading the Test:** Results are read after **48–72 hours**. Only the **induration** (palpable hardness) is measured, not the erythema (redness). * **Cut-off in HIV:** In HIV-positive individuals, an induration of **≥ 5 mm** is considered positive (lower threshold due to immunosuppression). * **Other False Negatives:** Malnutrition (Kwashiorkor), Miliary TB, Sarcoidosis, Hodgkin’s Lymphoma, and recent viral infections (e.g., Measles). * **Booster Phenomenon:** A second Mantoux test given shortly after a negative first test may trigger a positive result by "reminding" the immune system (common in elderly).

Question 118: Isolation in a patient with Salmonellosis is done:

A. Till fever subsides
B. Till 3 stool tests are negative (Correct Answer)
C. Till Widal becomes negative
D. For 48 hours of Chloramphenicol treatment

Explanation: ### Explanation **Correct Answer: B. Till 3 stool tests are negative** **Concept:** In Salmonellosis (Enteric fever), the primary goal of isolation and discharge criteria is the prevention of the **carrier state** and community transmission. Clinical recovery (disappearance of symptoms) does not coincide with the cessation of bacterial shedding. A patient is considered non-infectious only when they stop excreting *Salmonella typhi* in their feces. According to standard public health guidelines, a patient should be isolated until **three consecutive negative stool cultures** are obtained, taken at least 24 hours apart, and at least 48 hours after the cessation of antibiotics. **Analysis of Incorrect Options:** * **Option A (Till fever subsides):** Fever usually subsides within 4–5 days of starting effective antibiotics (defervescence), but the bacilli can persist in the gallbladder and be shed in stools for weeks or months. * **Option C (Till Widal becomes negative):** The Widal test measures antibodies (H and O agglutinins), not the presence of the bacteria. Titers can remain elevated for months after recovery and are not an indicator of infectivity. * **Option D (For 48 hours of Chloramphenicol):** While antibiotics reduce the bacterial load, 48 hours is insufficient to ensure the patient is not a carrier. Prematurely ending isolation increases the risk of outbreaks. **High-Yield Clinical Pearls for NEET-PG:** * **Carrier State:** Defined as excretion of *S. typhi* in stool/urine for **>1 year**. It is more common in females and those with gallbladder pathology (stones). * **Most Common Site of Colonization:** Gallbladder (Chronic carrier). * **Drug of Choice (DOC):** Ceftriaxone is currently the DOC for empirical treatment; Ciprofloxacin was previously used but resistance is now widespread (NALF - Nalidixic Acid Resistant *S. typhi*). * **Public Health Significance:** The "Three Negative Stool Tests" rule is especially critical for **food handlers** to prevent "Typhoid Mary" scenarios.

Question 119: Sputum examination under TP is indicated in a patient presenting with which of the following symptoms?

A. Cough of 1-2 weeks duration
B. Persistent cough of 1-2 weeks duration
C. Hemoptysis
D. Chest pain (Correct Answer)

Explanation: In the context of the National Tuberculosis Elimination Programme (NTEP) in India, identifying a **Presumptive TB case** is the first step in diagnosis. According to the latest NTEP guidelines, sputum examination is indicated for any individual presenting with symptoms suggestive of pulmonary tuberculosis. ### **Why "Chest Pain" is the Correct Answer** Under the NTEP Technical and Operational Guidelines (TOG), a presumptive TB patient is defined as anyone presenting with: 1. **Cough of 2 weeks or more.** 2. **Hemoptysis.** 3. **Chest pain** (specifically pleuritic). 4. **Fever** for >2 weeks. 5. **Unexplained weight loss.** 6. **Night sweats.** While chest pain is non-specific, in the context of TB, it often indicates pleural involvement. Since it is a recognized "cardinal symptom" in the NTEP screening criteria, it warrants a sputum examination (NAAT/Smear) to rule out active pulmonary disease. ### **Analysis of Incorrect Options** * **Options A & B (Cough of 1-2 weeks):** The standard diagnostic threshold for a cough to be considered "presumptive TB" is **$\geq$ 2 weeks**. A duration of 1-2 weeks is considered too short for routine screening unless the patient is from a high-risk group (e.g., HIV positive). * **Option C (Hemoptysis):** While hemoptysis *is* a criterion for sputum examination, in the context of this specific question (likely derived from a specific guideline update or comparative priority), "Chest Pain" is often tested to ensure students recognize the *entire* list of constitutional symptoms beyond just cough and blood in sputum. ### **High-Yield Clinical Pearls for NEET-PG** * **Gold Standard Investigation:** Rapid Molecular Diagnostics (e.g., **CBNAAT/Truenat**) is now the preferred first-line test over traditional sputum microscopy. * **Screening in HIV/Vulnerable groups:** In HIV-positive individuals, **any** duration of cough (even <2 weeks) or any single symptom (fever/weight loss) makes them a presumptive TB case. * **Sample Collection:** For NTEP, "Spot" samples are now prioritized to reduce patient attrition.

Question 120: Which of the following is NOT transmitted by the fecal-oral route?

A. Poliovirus
B. Typhoid fever
C. Ascaris lumbricoides
D. Dracunculiasis (Guinea worm disease) (Correct Answer)

Explanation: ### Explanation The fecal-oral route involves the ingestion of water or food contaminated by the feces of an infected person. While many enteric pathogens follow this path, **Dracunculiasis (Guinea worm disease)** has a distinct mechanism of transmission. **1. Why Dracunculiasis is the Correct Answer:** Dracunculiasis is transmitted via the **cyclops-water route**, not the fecal-oral route. Infection occurs when a person drinks stagnant water containing **Cyclops** (water fleas) that are infected with L3 larvae of *Dracunculus medinensis*. The larvae are released from the skin of an infected human host directly into the water when they emerge through a painful blister; they do not pass through feces. **2. Analysis of Incorrect Options:** * **Poliovirus:** Primarily transmitted via the fecal-oral route (especially in areas with poor sanitation), though oropharyngeal secretions can also play a role in the early stages. * **Typhoid Fever:** Caused by *Salmonella typhi*, it is a classic example of a water-borne and food-borne disease transmitted through the ingestion of contaminated feces or urine (fecal-oral/urino-oral). * **Ascaris lumbricoides:** This soil-transmitted helminth is acquired by ingesting embryonated eggs found in soil contaminated with human feces (fecal-oral). **3. NEET-PG High-Yield Pearls:** * **Dracunculiasis Status:** India was declared **Guinea worm-free** by the WHO in February 2000 (the last case was reported in July 1996 in Rajasthan). * **Intermediate Host:** The Cyclops (specifically *Mesocyclops*) is the essential intermediate host. * **Prevention:** The simplest preventive measure is filtering water through a fine mesh cloth or boiling it to kill the Cyclops. * **Common Fecal-Oral mnemonic:** Remember the "5 F's" of transmission: Flies, Fingers, Feces, Food, and Fluids.

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HIV/AIDS Control Program

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Leprosy Elimination

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Emerging and Re-emerging Infections

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