Infectious Diseases — MCQs

A 6-year-old boy develops symptoms of cough, fever, and malaise followed by a generalized maculopapular rash that has spread from the head downward. A clinical diagnosis of measles is made. A few days after the onset of the rash he is drowsy, lethargic, and complaining of headache. Lumbar puncture, electroencephalogram (EEG), and computerized tomography (CT) of the brain exclude other etiologies and confirm the diagnosis of encephalitis. Which of the following is the most likely delayed neurologic complication of measles virus encephalitis?

Q617Medium

What is the most likely diagnosis in a patient from Mauritania whose foot developed these abnormalities over several years?

Q618Medium

The differential diagnosis of botulism includes all of the following except?

Q619Medium

Which of the following is an initial presentation of HIV infection?

Q620Medium

A lung biopsy of an HIV-positive patient shows intra-nuclear basophilic inclusion bodies with a perinuclear halo. The patient's CD4 count was less than 100 at the time of diagnosis. What is the probable cause?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 611: What is the drug of choice for the treatment of Taenia solium and Taenia saginata infestation?

A. Metronidazole
B. Albendazole
C. Niclosamide (Correct Answer)
D. Diloxanide furoate

Explanation: ### Explanation **Correct Answer: C. Niclosamide** **Medical Concept:** Niclosamide is the drug of choice for intestinal tapeworm infections caused by *Taenia solium* (pork tapeworm) and *Taenia saginata* (beef tapeworm). It acts by inhibiting oxidative phosphorylation and stimulating ATPase activity in the mitochondria of the parasite, leading to the death of the scolex and proximal segments. Upon contact, the tapeworm is killed, and the segments are partially digested, making them easier to expel. *Note:* While Praziquantel is also highly effective and often preferred in modern clinical practice due to its availability, Niclosamide remains a classic "textbook" drug of choice for localized intestinal infestation. **Analysis of Incorrect Options:** * **A. Metronidazole:** This is an antiprotozoal and antibacterial agent. It is the drug of choice for amoebiasis, giardiasis, and trichomoniasis, but it has no activity against helminths like *Taenia*. * **B. Albendazole:** While Albendazole is the drug of choice for **Neurocysticercosis** (the larval form of *T. solium* in the CNS) and Hydatid disease, it is generally considered a second-line agent for simple intestinal taeniasis compared to Niclosamide or Praziquantel. * **D. Diloxanide furoate:** This is a luminal amoebicide used primarily for asymptomatic cyst passers of *Entamoeba histolytica*. It is ineffective against tapeworms. **High-Yield Clinical Pearls for NEET-PG:** * **Neurocysticercosis (NCC):** The drug of choice is **Albendazole** (plus corticosteroids to reduce inflammation). * **Hymenolepis nana:** Unlike other tapeworms, the drug of choice for *H. nana* is **Praziquantel**. * **Precaution with Niclosamide:** When treating *T. solium*, a laxative is often administered 1–2 hours after Niclosamide to ensure dead segments are expelled quickly, preventing the theoretical risk of cysticercosis via internal autoinfection (due to the release of viable eggs from digested segments).

Question 612: Which of the following diseases presents with pea-soup stools?

A. Cholera
B. Botulism
C. Typhoid (Correct Answer)
D. Polio

Explanation: **Explanation:** **Typhoid fever** (Enteric fever), caused by *Salmonella Typhi*, typically presents in the second week of illness with gastrointestinal symptoms [1]. The characteristic **"pea-soup stool"** refers to the thin, greenish-yellow, liquid consistency of the diarrhea, which occurs due to inflammation and ulceration of the Peyer’s patches in the terminal ileum [1], [2]. **Analysis of Options:** * **Cholera:** Presents with **"rice-water stools"** (profuse, non-bloody, watery diarrhea with flecks of mucus) [3]. It is caused by *Vibrio cholerae* toxin, leading to massive secretory diarrhea without significant mucosal inflammation [3]. * **Botulism:** Caused by *Clostridium botulinum* toxin, it typically presents with **descending paralysis** and autonomic dysfunction. Constipation is more common than diarrhea. * **Polio:** An enterovirus infection that primarily affects the anterior horn cells of the spinal cord. While it spreads via the feto-oral route, its hallmark is **asymmetric flaccid paralysis**, not a specific stool consistency. **Clinical Pearls for NEET-PG:** * **Step-ladder pyrexia:** The classic fever pattern seen in the first week of Typhoid. * **Faget’s Sign:** Relative bradycardia (pulse rate is lower than expected for the degree of fever), a high-yield diagnostic clue for Typhoid. * **Rose Spots:** Faint, salmon-colored macules on the trunk seen in the second week. * **Investigation of Choice:** * 1st week: Blood culture (most sensitive) * 2nd week: Widal test (serology) * 3rd week: Stool culture * 4th week: Urine culture * *Mnemonic: **BASU** (Blood, Agglutination/Widal, Stool, Urine)*

Question 613: All are useful for the management of severe Clostridium difficile infection except?

A. Intravenous Metronidazole
B. Neomycin enema (Correct Answer)
C. Fecal transplant
D. Tigecycline

Explanation: The management of severe and fulminant Clostridioides difficile infection (CDI) requires targeted antimicrobial therapy and, in refractory cases, innovative interventions. [1] ### Why Neomycin enema is the correct answer: Neomycin is an aminoglycoside that is poorly absorbed from the gut. [2] However, it is primarily effective against aerobic gram-negative bacilli and has no activity against anaerobes like C. difficile. [2] Furthermore, broad-spectrum antibiotics like Neomycin can worsen CDI by further disrupting the normal intestinal flora, which is the underlying pathophysiology of the disease. Therefore, it has no role in management. ### Explanation of other options: * Intravenous Metronidazole: In fulminant CDI (characterized by hypotension, shock, ileus, or megacolon), IV Metronidazole is used in combination with high-dose oral (or rectal) Vancomycin. It is a mainstay for severe cases where oral drug delivery may be compromised. [1] * Fecal Transplant (FMT): FMT is highly effective for recurrent CDI and is increasingly recommended for severe/fulminant cases that do not respond to standard antibiotic therapy. It restores healthy gut microbiota to suppress C. difficile overgrowth. * Tigecycline: This is a glycylcycline antibiotic with potent activity against anaerobes. It is considered a "rescue therapy" or salvage option in severe, refractory CDI when standard treatments fail. [1] ### Clinical Pearls for NEET-PG: * Drug of Choice (DOC): Oral Fidaxomicin or oral Vancomycin are now preferred over Metronidazole for the first episode of CDI (IDSA guidelines). [1] * Fulminant CDI Criteria: Hypotension, shock, ileus, or toxic megacolon. * Treatment of Fulminant CDI: Oral Vancomycin (500 mg QID) + IV Metronidazole + Vancomycin enemas (if ileus is present). * Bezlotoxumab: A monoclonal antibody against C. difficile toxin B, used to prevent recurrence.

Question 614: Which of the following is the most common site for syphilitic aneurysm?

A. Descending aorta
B. Ascending aorta (Correct Answer)
C. Internal carotid artery
D. External carotid artery

Explanation: Syphilitic (luetic) aneurysm is a manifestation of **Tertiary Syphilis**, occurring years after the initial infection [2]. The underlying pathology is **obliterative endarteritis** of the **vasa vasorum** (the small blood vessels supplying the walls of large arteries). This leads to ischemic destruction of the tunica media, loss of elastic tissue, and subsequent weakening of the vessel wall, resulting in a "tree-bark" appearance and aneurysmal dilatation. **Why the Ascending Aorta is correct:** The **ascending aorta** is the most common site because it has the highest concentration of vasa vasorum, which are the primary targets of *Treponema pallidum*. The infection typically involves the aortic root and the ascending portion, often leading to aortic regurgitation due to dilation of the aortic ring [3]. **Why other options are incorrect:** * **Descending aorta:** While syphilis can affect the arch and descending aorta, it is significantly less common than ascending involvement. In contrast, **atherosclerotic aneurysms** most commonly involve the abdominal aorta (below the renal arteries) [1]. * **Internal/External carotid arteries:** These are rarely involved in syphilitic vasculitis. Syphilis primarily targets the elastic arteries (aorta) rather than muscular arteries like the carotids. **High-Yield Clinical Pearls for NEET-PG:** * **"Tree-barking" appearance:** A classic gross pathological finding of the aortic intima in syphilis due to scarring. * **Aortic Regurgitation:** The most common valvular complication of syphilitic aortitis [3]. * **Coronary Ostial Stenosis:** Syphilitic aortitis can narrow the openings of the coronary arteries, leading to angina. * **Diagnosis:** Screening with VDRL/RPR; confirmation with FTA-ABS or TPHA. * **Treatment:** Intramuscular Benzathine Penicillin G is the drug of choice.

Question 615: What drug is used for the chemoprophylaxis of leptospirosis?

A. Doxycycline (Correct Answer)
B. Ampicillin
C. Amoxicillin
D. Cefotaxime

Explanation: **Explanation:** Leptospirosis is a zoonotic infection caused by the spirochete *Leptospira interrogans*. Chemoprophylaxis is indicated for individuals with high-risk exposure, such as rescue workers in flood-prone areas or military personnel in endemic jungles. [1] **Why Doxycycline is correct:** **Doxycycline (200 mg orally once weekly)** is the drug of choice for the chemoprophylaxis of leptospirosis. It has been clinically proven to reduce the incidence of symptomatic disease in individuals exposed to contaminated water or soil. Its long half-life and broad-spectrum activity against spirochetes make it the gold standard for prevention. **Why the other options are incorrect:** * **Ampicillin and Amoxicillin:** While these are effective first-line treatments for **mild, symptomatic** leptospirosis (especially in pregnant women or children where tetracyclines are contraindicated), they are not used for routine weekly prophylaxis. * **Cefotaxime:** This is a third-generation cephalosporin used for the treatment of **severe, hospitalized cases** (Weil’s disease) as an alternative to intravenous Penicillin G. It is never used for prophylaxis due to its parenteral administration and risk of promoting antibiotic resistance. **High-Yield Clinical Pearls for NEET-PG:** * **Treatment of Choice (Mild):** Oral Doxycycline or Azithromycin. * **Treatment of Choice (Severe/Weil’s):** IV Penicillin G (Drug of Choice) or IV Ceftriaxone/Cefotaxime. * **Jarisch-Herxheimer Reaction:** Can occur following the initiation of antibiotic therapy in leptospirosis, similar to syphilis. * **Gold Standard Diagnosis:** Microscopic Agglutination Test (MAT). [1] * **Clinical Triad of Weil’s Disease:** Jaundice, Renal failure (azotemia), and Hemorrhage.

Question 616: A 6-year-old boy develops symptoms of cough, fever, and malaise followed by a generalized maculopapular rash that has spread from the head downward. A clinical diagnosis of measles is made. A few days after the onset of the rash he is drowsy, lethargic, and complaining of headache. Lumbar puncture, electroencephalogram (EEG), and computerized tomography (CT) of the brain exclude other etiologies and confirm the diagnosis of encephalitis. Which of the following is the most likely delayed neurologic complication of measles virus encephalitis?

A. Meningitis
B. Pure motor paralysis
C. Autonomic neuropathy
D. Mental retardation or epilepsy (Correct Answer)

Explanation: ### Explanation **Correct Option: D. Mental retardation or epilepsy** **Mechanism and Clinical Concept:** Measles virus is associated with several neurological complications. The scenario describes **Acute Disseminated Encephalomyelitis (ADEM)** or **Acute Measles Encephalitis**, which typically occurs within 1–2 weeks of the rash. This is an immune-mediated inflammatory process causing demyelination. Unlike the transient nature of the initial infection, the resulting neuronal damage in survivors is often permanent. Approximately **25% to 40%** of children who survive measles encephalitis suffer from long-term neurological sequelae, most commonly **mental retardation (intellectual disability), epilepsy (seizure disorders)**, deafness, or motor deficits. **Why Other Options are Incorrect:** * **A. Meningitis:** While meningeal irritation can occur during the acute phase, it is an acute inflammatory process, not a "delayed neurologic complication" or a permanent sequela like the brain parenchymal damage seen in encephalitis. * **B. Pure motor paralysis:** This is more characteristic of Poliovirus (anterior horn cell involvement) or Guillain-Barré Syndrome. Measles encephalitis causes global cerebral dysfunction rather than isolated motor pathway destruction. * **C. Autonomic neuropathy:** This is not a recognized complication of measles. Autonomic dysfunction is typically associated with conditions like Diabetes Mellitus, Amyloidosis, or Guillain-Barré Syndrome. **NEET-PG High-Yield Pearls:** 1. **Subacute Sclerosing Panencephalitis (SSPE):** A very late complication (7–10 years after infection) caused by a persistent mutant measles virus [1]. Key findings: **Periodic complexes on EEG** and high CSF antibody titers [1]. 2. **Vitamin A:** Supplementation reduces morbidity and mortality in children with acute measles. 3. **Koplik Spots:** Pathognomonic enanthem found on the buccal mucosa opposite the lower second molars during the prodromal stage [1]. 4. **Most common cause of death in Measles:** Pneumonia (Hecht’s Giant Cell Pneumonia) [1].

Question 617: What is the most likely diagnosis in a patient from Mauritania whose foot developed these abnormalities over several years?

A. Actinomycetoma (Correct Answer)
B. Kaposi's sarcoma
C. Leishmaniasis
D. Malignant melanoma

Explanation: ***Actinomycetoma*** - Mauritania is located in the **mycetoma belt** of Africa, making actinomycetoma highly endemic in this region with characteristic **Madura foot** presentation. - The chronic progression over several years with **painless swelling**, **deformity**, and likely **draining sinuses** is pathognomonic for mycetoma. *Kaposi's sarcoma* - Presents as **purple-red nodules** or plaques, typically on skin and mucous membranes, not chronic foot deformity. - Associated with **HIV infection** or **HHV-8** and does not cause the characteristic draining sinuses seen in mycetoma. *Leishmaniasis* - **Cutaneous leishmaniasis** presents as **ulcerative lesions** that heal spontaneously, not chronic progressive foot deformity. - **Visceral leishmaniasis** affects internal organs with fever and hepatosplenomegaly, not localized foot abnormalities. *Malignant melanoma* - Appears as an **asymmetric pigmented lesion** with irregular borders and color variation, not chronic swelling. - Grows rapidly over months rather than the **slow progression over years** typical of mycetoma.

Question 618: The differential diagnosis of botulism includes all of the following except?

A. Myasthenia Gravis
B. Guillain Barre syndrome
C. Polio
D. Clostridial myonecrosis (Correct Answer)

Explanation: The correct answer is **Clostridial myonecrosis** (Gas Gangrene). While both botulism and myonecrosis are caused by *Clostridium* species, their clinical presentations are diametrically opposed. **1. Why Clostridial Myonecrosis is the correct answer:** Botulism is characterized by **afebrile, symmetric, descending flaccid paralysis** with prominent cranial nerve involvement (diplopia, dysphagia, ptosis) [1]. In contrast, **Clostridial myonecrosis** (caused by *C. perfringens*) is an acute, life-threatening soft tissue infection characterized by severe pain, crepitus, and systemic toxicity (fever, tachycardia). It does not present with neurologic paralysis, making it an unlikely differential for botulism. **2. Why other options are incorrect (Differentials for Botulism):** * **Myasthenia Gravis:** Presents with ptosis and diplopia. However, it is characterized by "fatigability" and typically spares the pupils, whereas botulism often involves fixed/dilated pupils [1]. * **Guillain-Barré Syndrome (GBS):** Specifically the **Miller Fisher variant** presents with the triad of ataxia, areflexia, and ophthalmoplegia. Unlike botulism (descending), classic GBS is an **ascending** paralysis. * **Polio:** Presents with acute flaccid paralysis. However, polio is usually **asymmetric**, associated with a prodromal febrile illness, and lacks the sensory or symmetric cranial nerve involvement seen in botulism. **Clinical Pearls for NEET-PG:** * **Botulism Triad:** 1. Afebrile 2. Symmetric descending flaccid paralysis 3. Clear sensorium [1]. * **The "Ds" of Botulism:** Diplopia, Dysarthria, Dysphonia, Dysphagia [1]. * **Key Distinction:** Botulism causes **pupillary involvement** (mydriasis), which helps distinguish it from Myasthenia Gravis [1]. * **Diagnosis:** Confirmed by identifying the toxin in serum, stool, or food (Mouse Bioassay is the gold standard).

Question 619: Which of the following is an initial presentation of HIV infection?

A. Primary CNS lymphoma
B. Kaposi sarcoma
C. Bacterial pneumonia (Correct Answer)
D. Extrapulmonary tuberculosis

Explanation: **Explanation:** The correct answer is **Bacterial pneumonia**. While HIV is famously associated with rare opportunistic infections, **bacterial pneumonia** is actually one of the most common initial clinical presentations of HIV infection [1]. Unlike many AIDS-defining illnesses that require a severely low CD4 count, bacterial pneumonia (most commonly caused by *Streptococcus pneumoniae*) can occur at any stage of the disease, including relatively high CD4 counts (>500 cells/µL) [1]. It often serves as the "sentinel event" that leads to an HIV diagnosis. **Analysis of Incorrect Options:** * **Primary CNS Lymphoma (A):** This is an AIDS-defining malignancy strongly associated with EBV. It typically occurs in the advanced stages of immunosuppression, usually when the CD4 count falls below **50 cells/µL**. * **Kaposi Sarcoma (B):** Caused by HHV-8, this is a common AIDS-defining malignancy [2]. While it can occur at moderate CD4 counts, it is generally considered a manifestation of established AIDS rather than an initial presentation in the general HIV population. * **Extrapulmonary Tuberculosis (D):** While TB is the most common opportunistic infection in HIV patients in India, *pulmonary* TB occurs early, whereas *extrapulmonary* TB (e.g., lymph node, meningeal) typically signifies more advanced immunosuppression (CD4 <200-300 cells/µL) [2]. **High-Yield Pearls for NEET-PG:** * **Most common respiratory infection in HIV:** Bacterial pneumonia (specifically *S. pneumoniae*). * **Most common opportunistic infection (OI) in India:** Tuberculosis [2]. * **Most common fungal OI:** *Pneumocystis jirovecii* (PCP) – typically occurs when CD4 <200 cells/µL [1]. * **Initial presentation:** Recurrent bacterial infections or herpes zoster in a young patient should always prompt an HIV screening test [1].

Question 620: A lung biopsy of an HIV-positive patient shows intra-nuclear basophilic inclusion bodies with a perinuclear halo. The patient's CD4 count was less than 100 at the time of diagnosis. What is the probable cause?

A. Cytomegalovirus (CMV) (Correct Answer)
B. Mycobacterium avium complex (MAC)
C. Pneumocystis jirovecii pneumonia (PJP)
D. Tuberculosis (TB)

Explanation: ### Explanation The correct answer is **Cytomegalovirus (CMV)**. **1. Why CMV is correct:** The histopathological description of **"intra-nuclear basophilic inclusion bodies with a perinuclear halo"** is the classic description of **"Owl’s Eye" inclusions**. CMV is a double-stranded DNA virus (HHV-5) that causes systemic infections in immunocompromised patients, particularly those with HIV and a **CD4 count <50–100 cells/mm³** [1]. In the lungs, CMV pneumonitis presents with these characteristic large cells (cytomegaly) containing dark viral inclusions surrounded by a clear halo. **2. Why the other options are incorrect:** * **Mycobacterium avium complex (MAC):** Typically presents with acid-fast bacilli within macrophages. It usually causes systemic symptoms (fever, night sweats) and diarrhea rather than isolated pulmonary pathology in HIV. * **Pneumocystis jirovecii (PJP):** On histology, PJP shows a characteristic **"crushed ping-pong ball"** or "cup-and-saucer" appearance on Silver stain (GMS) [2]. It presents with a "foamy" alveolar exudate, not intranuclear inclusions. * **Tuberculosis (TB):** Characterized by **caseating granulomas** and Acid-Fast Bacilli (AFB) on Ziehl-Neelsen staining [2]. While common in HIV, it does not produce viral inclusion bodies. **3. NEET-PG High-Yield Pearls:** * **CMV Retinitis:** The most common clinical manifestation of CMV in HIV (presents as "pizza-pie" or "cheese and ketchup" fundus). * **CMV Esophagitis:** Characterized by **linear/longitudinal ulcers** (vs. HSV which causes punched-out/volcano ulcers). * **Drug of Choice:** **Ganciclovir** is the first-line treatment; Foscarnet is used for resistant cases. * **Biopsy Gold Standard:** Presence of Owl's eye inclusions is pathognomonic.

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Fever of Unknown Origin

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HIV/AIDS and Related Infections

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Viral Infections (Hepatitis, Herpes, etc.)

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Fungal Infections

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Sepsis and Septic Shock

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Infection in Immunocompromised Hosts

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Emerging and Re-emerging Infections

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Antimicrobial Resistance

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Vaccination Principles

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