Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 451: What is the drug of choice for cytomegalovirus retinitis in HIV patients?

A. Acyclovir
B. Ganciclovir (Correct Answer)
C. Ribavarin
D. Vidarabine

Explanation: **Explanation:** **Cytomegalovirus (CMV) Retinitis** is the most common opportunistic ocular infection in HIV patients, typically occurring when the CD4 count falls below **50 cells/mm³**. It is characterized by "pizza-pie" or "cheese and ketchup" fundoscopic appearances (hemorrhage with yellowish-white exudates). **Why Ganciclovir is the Correct Answer:** Ganciclovir is a nucleoside analogue that inhibits viral DNA polymerase [1]. It is the **drug of choice** for CMV retinitis because it has high efficacy against CMV compared to other antivirals as it allows preferential phosphorylation by protein kinases of cytomegalovirus [1]. It can be administered intravenously, orally (Valganciclovir), or via intravitreal implants [1]. Valganciclovir (the prodrug) is now often preferred for induction and maintenance therapy due to its excellent oral bioavailability. **Why Other Options are Incorrect:** * **Acyclovir:** Primarily used for Herpes Simplex Virus (HSV) and Varicella-Zoster Virus (VZV) [1]. It lacks significant activity against CMV because CMV does not produce the enzyme *thymidine kinase* required to activate Acyclovir [1]. * **Ribavirin:** Used mainly for Hepatitis C (in combination) and Respiratory Syncytial Virus (RSV). It is not effective against CMV. * **Vidarabine:** An older antiviral previously used for HSV keratitis; it is rarely used today due to systemic toxicity and the availability of superior agents like Ganciclovir. **High-Yield Clinical Pearls for NEET-PG:** 1. **Side Effects:** The major dose-limiting side effect of Ganciclovir is **bone marrow suppression** (neutropenia and thrombocytopenia). 2. **Alternative Drugs:** If Ganciclovir resistance occurs (UL97 mutation), **Foscarnet** or **Cidofovir** are used. Note that Foscarnet is highly nephrotoxic. 3. **Prevention:** The best long-term prevention for CMV retinitis is the restoration of the immune system via **Highly Active Antiretroviral Therapy (HAART)**.

Question 452: Which of the following conditions is characterized by a double rise of temperature within a 24-hour period?

A. Kala Azar (Correct Answer)
B. Malaria
C. Tuberculosis
D. Hodgkin's lymphoma

Explanation: The correct answer is **Kala Azar (Visceral Leishmaniasis)**. **Why Kala Azar is correct:** Kala Azar is classically associated with a **"double peak" of fever** (bimodal fever) within a single 24-hour period [1]. This occurs due to the rapid multiplication of *Leishmania donovani* within the reticuloendothelial system. While not present in every case, it is a highly characteristic clinical sign often tested in exams. **Analysis of Incorrect Options:** * **Malaria:** Characterized by periodic paroxysms (chills, fever, and sweating). Depending on the species, the fever occurs every 48 hours (*P. vivax/falciparum* - Tertian) or 72 hours (*P. malariae* - Quartan), but not twice daily. * **Tuberculosis:** Typically presents with an **evening rise of temperature** (low-grade fever) accompanied by night sweats [1]. * **Hodgkin’s Lymphoma:** Classically associated with **Pel-Ebstein fever**, where bouts of high fever alternate with afebrile periods lasting days to weeks [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Kala Azar Triad:** Massive splenomegaly (often crossing the midline), hepatomegaly, and pancytopenia [1]. * **Skin Changes:** The name "Kala Azar" (Black Fever) comes from the hyperpigmentation of the skin (especially on the forehead and hands) seen in Indian patients. * **Diagnosis:** The gold standard is a splenic aspirate (highest yield), but bone marrow aspiration is safer [1]. Look for **LD bodies** (Amastigote form) in macrophages. * **Drug of Choice:** Liposomal Amphotericin B is currently the preferred treatment.

Question 453: Kala azar is which of the following types of leishmaniasis?

A. Mucocutaneous leishmaniasis
B. Cutaneous leishmaniasis
C. Oriental sore
D. Visceral leishmaniasis (Correct Answer)

Explanation: **Explanation:** **Kala-azar**, also known as "Black Fever," is the most severe form of leishmaniasis caused by the protozoan parasite *Leishmania donovani* complex (primarily *L. donovani* and *L. infantum*) [1]. It is classified as **Visceral Leishmaniasis (Option D)** because the parasites migrate to the internal (visceral) organs, specifically the reticuloendothelial system, including the liver, spleen, and bone marrow [1]. **Analysis of Options:** * **Visceral Leishmaniasis (Correct):** Characterized by systemic involvement. The hallmark clinical triad includes prolonged irregular fever, massive splenomegaly (often "huge" or "dragging" sensation), and significant weight loss/anemia [1]. * **Cutaneous Leishmaniasis (B):** This form is limited to the skin, causing ulcers at the site of the sandfly bite [2]. It is typically caused by *L. tropica* or *L. major*. * **Oriental Sore (C):** This is simply a synonym for Old World Cutaneous Leishmaniasis [2]. * **Mucocutaneous Leishmaniasis (A):** Primarily seen in the New World (caused by *L. braziliensis*), this form involves the destruction of the mucous membranes of the nose, mouth, and throat [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Transmitted by the bite of the female **Phlebotomus sandfly** [1]. * **Infective Stage:** Promastigote; **Diagnostic Stage:** Amastigote (LD bodies) [1]. * **Gold Standard Diagnosis:** Bone marrow or splenic aspirate showing **LD bodies** (Amastigotes in macrophages) [1]. * **Drug of Choice:** **Liposomal Amphotericin B** is currently the preferred treatment. * **Post-Kala-azar Dermal Leishmaniasis (PKDL):** A sequel where skin lesions appear after the apparent cure of visceral leishmaniasis; it acts as an important reservoir for the disease [2].

Question 454: Seizures may be the presenting feature in all of the following, except?

A. Cryptococcus meningitis
B. Toxoplasmosis
C. CMV
D. Entamoeba histolytica (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Entamoeba histolytica**. **Medical Concept:** Seizures in the context of infectious diseases typically occur when a pathogen causes direct parenchymal involvement (encephalitis), space-occupying lesions (abscesses/granulomas), or significant meningeal inflammation. While *Entamoeba histolytica* is a common cause of intestinal amoebiasis and liver abscesses, it **rarely** involves the Central Nervous System (CNS). Even in the rare event of an amoebic brain abscess, it is almost never the *presenting* feature; it usually occurs as a terminal complication of disseminated disease in a severely debilitated patient. **Analysis of Options:** * **A. Cryptococcus meningitis:** This is the most common fungal infection of the CNS in immunocompromised patients (especially HIV/AIDS). It causes increased intracranial pressure and meningeal irritation, which frequently presents with seizures. * **B. Toxoplasmosis:** *Toxoplasma gondii* typically causes "ring-enhancing lesions" in the basal ganglia and corticomedullary junction. These focal lesions are highly epileptogenic, making seizures a classic presenting symptom. * **C. CMV (Cytomegalovirus):** In neonates (congenital) or immunocompromised adults, CMV can cause encephalitis or ventriculitis. The resulting cortical inflammation is a well-documented trigger for seizure activity. **NEET-PG High-Yield Pearls:** * **Most common cause of seizures in HIV patients:** Neurotoxoplasmosis (focal) or Cryptococcal meningitis (generalized). * **Most common cause of sporadic viral encephalitis:** Herpes Simplex Virus (HSV-1), which characteristically involves the temporal lobes and presents with complex partial seizures. * **Neurocysticercosis:** The most common cause of adult-onset seizures in developing countries like India. * **Amoebic CNS involvement:** While *E. histolytica* is rare, **Primary Amoebic Meningoencephalitis (PAM)** caused by *Naegleria fowleri* is a rapid, fatal CNS infection where seizures are common. [1]

Question 455: Kernig's sign is seen in which of the following conditions?

A. Pneumonia
B. Acute bacterial meningitis (Correct Answer)
C. Mental retardation
D. Cerebral palsy

Explanation: **Explanation:** **Kernig’s sign** is a classic clinical indicator of **meningeal irritation** [1]. It is elicited with the patient lying supine; the hip and knee are flexed to 90 degrees, and the examiner then attempts to passively extend the knee. The sign is positive if there is resistance or pain in the lower back/posterior thigh, preventing full extension [1]. This occurs because the maneuver stretches the inflamed spinal nerve roots and hypersensitive meninges. * **Acute Bacterial Meningitis (Correct):** This condition involves inflammation of the leptomeninges (arachnoid and pia mater) [1]. The resulting meningismus leads to protective spinal muscle spasms, making Kernig’s sign a hallmark physical finding, alongside Brudzinski’s sign and nuchal rigidity [1]. * **Pneumonia:** This is a localized infection of the lung parenchyma. While severe pneumonia can cause systemic illness, it does not involve the meninges and therefore does not produce Kernig’s sign. * **Mental Retardation & Cerebral Palsy:** These are neurodevelopmental/static encephalopathic conditions. While cerebral palsy may present with spasticity, it lacks the acute inflammatory process of the meninges required to trigger a positive Kernig’s sign. **Clinical Pearls for NEET-PG:** * **Brudzinski’s Sign:** Passive flexion of the neck leads to involuntary flexion of the hips and knees [1]. * **Sensitivity vs. Specificity:** Both Kernig’s and Brudzinski’s signs have **low sensitivity** (often absent in elderly or infants) but **high specificity** for meningitis. * **Jolt Accentuation Maneuver:** Asking the patient to turn their head horizontally 2-3 times per second; worsening of headache is the most sensitive clinical sign for meningitis.

Question 456: A patient presents with acute onset high-grade fever, chills, productive cough with rusty-colored sputum, and pleuritic chest pain. The chest X-ray is shown below. What is the most likely diagnosis?

A. Tuberculosis
B. Klebsiella pneumonia
C. Pneumocystis pneumonia
D. Pneumococcal Pneumonia (Correct Answer)

Explanation: ***Pneumococcal Pneumonia*** - **Lobar consolidation** on chest X-ray is the classic radiographic pattern for **Streptococcus pneumoniae** pneumonia. - Most common cause of **community-acquired pneumonia** in immunocompetent adults, presenting with homogeneous consolidation affecting an entire lobe. *Tuberculosis* - Typically presents with **upper lobe involvement** and **cavitation** on chest imaging, not lobar consolidation. - Associated with **night sweats**, **weight loss**, and **chronic cough** over weeks to months. *Klebsiella pneumonia* - Usually causes **upper lobe consolidation** with **bulging fissure sign** and potential **cavitation**. - More commonly seen in **alcoholics** and **diabetics**, with thick, bloody sputum production. *Pneumocystis pneumonia* - Characterized by **bilateral interstitial infiltrates** or **ground-glass opacities**, not lobar consolidation. - Occurs almost exclusively in **immunocompromised patients** (HIV, organ transplant recipients).

Question 457: What represents a medical emergency in an asplenic patient?

A. Cat bite
B. Dog bite (Correct Answer)
C. Fish bite
D. Human bite

Explanation: **Explanation:** The correct answer is **Dog bite**. Asplenic or hyposplenic patients are at a significantly increased risk for **Overwhelming Post-Splenectomy Infection (OPSI)**, primarily caused by encapsulated organisms [1]. **Why Dog Bite is the Correct Answer:** Dog bites can transmit ***Capnocytophaga canimorsus***, a fastidious Gram-negative rod found in the normal oral flora of dogs (and occasionally cats). In immunocompetent individuals, it rarely causes severe disease. However, in asplenic patients, it can lead to fulminant sepsis, disseminated intravascular coagulation (DIC), and multi-organ failure within hours. Due to the high mortality rate (up to 30-60%), any dog bite in an asplenic patient is considered a medical emergency requiring immediate prophylactic antibiotics (typically Amoxicillin-Clavulanate). **Analysis of Incorrect Options:** * **Cat bite:** While cats also carry *Capnocytophaga*, they are more commonly associated with *Pasteurella multocida* and *Bartonella henselae*. While serious, the specific association with fatal septicemia in asplenic patients is classically linked to dog bites in medical examinations. * **Fish bite:** Associated with *Vibrio vulnificus* (especially in patients with chronic liver disease/hemochromatosis) or *Mycobacterium marinum*. * **Human bite:** Associated with *Eikenella corrodens* and anaerobic flora. While prone to infection, they do not carry the specific risk of OPSI seen with *Capnocytophaga*. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of OPSI:** *Streptococcus pneumoniae* (followed by *H. influenzae* and *N. meningitidis*). * **Prophylaxis:** Asplenic patients should receive the pneumococcal, meningococcal, and Hib vaccines. * **Peripheral Smear Findings:** Look for **Howell-Jolly bodies** (nuclear remnants), Pappenheimer bodies, and target cells. * **Emergency Management:** Asplenic patients with a fever should be taught to take "standby" antibiotics (like Levofloxacin or Amoxicillin-Clavulanate) immediately and seek hospital care.

Question 458: The oral lesion called mucous patches is usually multiple, grayish white plaques associated with what?

A. Pain
B. No pain (Correct Answer)
C. Itching
D. Burning sensation

Explanation: **Explanation:** The correct answer is **B. No pain**. **Mucous patches** are a classic clinical manifestation of **Secondary Syphilis**, caused by the spirochete *Treponema pallidum*. These lesions are highly infectious, slightly elevated, grayish-white, or "snail-track" erosions that appear on the oral mucosa, tongue, or tonsils [1]. A hallmark feature of syphilitic lesions (both the primary chancre and secondary mucous patches) is that they are characteristically **painless** [1]. This lack of pain is a crucial diagnostic differentiator from other ulcerative oral conditions. **Analysis of Incorrect Options:** * **A. Pain:** Unlike aphthous ulcers or herpetic stomatitis, which are exquisitely painful [2], syphilitic mucous patches do not cause significant discomfort. * **C. Itching:** Pruritus (itching) is rarely a feature of mucosal syphilis. While the secondary syphilis skin rash (maculopapular) is famously non-itchy [1], the mucosal lesions are also asymptomatic. * **D. Burning sensation:** This is typically associated with conditions like oral candidiasis (thrush) or lichen planus, rather than syphilis. **High-Yield Clinical Pearls for NEET-PG:** * **Secondary Syphilis** is known as the "Great Imitator." It typically presents with a generalized maculopapular rash (including palms and soles), generalized lymphadenopathy, and mucous patches [1]. * **Condyloma Lata:** These are moist, wart-like, painless papules found in intertriginous areas (like the anogenital region), also characteristic of secondary syphilis [1]. * **Diagnosis:** Screening is done via non-specific treponemal tests (**VDRL/RPR**), and confirmation is via specific tests (**FTA-ABS/TPHA**). * **Treatment:** The drug of choice for all stages of syphilis remains **Benzathine Penicillin G**.

Question 459: Which of the following pneumonias is caused by contaminated air conditioners?

A. Pneumococci
B. Staphylococci
C. E. coli
D. Legionella (Correct Answer)

Explanation: **Explanation:** **Legionella pneumophila** is the correct answer because it is an aerobic, Gram-negative rod that thrives in aquatic environments. It colonizes man-made water systems such as **air conditioning cooling towers**, humidifiers, whirlpool spas, and showerheads [1]. Transmission occurs via the **inhalation of contaminated aerosols** (mists) produced by these systems. It does not spread person-to-person . **Analysis of Incorrect Options:** * **A. Pneumococci (*S. pneumoniae*):** The most common cause of community-acquired pneumonia (CAP). It is part of the normal nasopharyngeal flora and spreads via respiratory droplets, not environmental water systems. * **B. Staphylococci (*S. aureus*):** Typically causes post-viral pneumonia (e.g., after Influenza) or hematogenous spread (e.g., IV drug users) [1]. It is associated with skin flora and hospital environments. * **C. E. coli:** An enteric Gram-negative organism. It primarily causes pneumonia in neonates or via aspiration in debilitated/ICU patients; it is not associated with aerosolized water from AC units. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Look for "atypical pneumonia" features—high fever, **diarrhea** (GI symptoms), and **hyponatremia** (low sodium). * **Diagnosis:** The **Urinary Antigen Test** is the rapid test of choice. Culture requires **Buffered Charcoal Yeast Extract (BCYE) agar** supplemented with L-cysteine and iron. * **Treatment:** Macrolides (Azithromycin) or Fluoroquinolones (Levofloxacin). It is inherently resistant to Beta-lactams because it is an intracellular pathogen. * **Pontiac Fever:** A milder, flu-like illness caused by *Legionella* without pneumonia.

Question 460: Mulberry molars are characteristic features of which condition?

A. Severe fluorosis
B. Trauma at the time of birth
C. Congenital syphilis (Correct Answer)
D. Chronic suppurative abscess in overlying gingival tissue

Explanation: **Explanation:** **Congenital Syphilis (Correct Answer):** Mulberry molars are a pathognomonic dental abnormality caused by the transplacental transmission of *Treponema pallidum*. The infection leads to inflammation of the tooth germ during the morphodifferentiation stage of development. This results in the permanent first molars having multiple, poorly developed rudimentary cusps and a narrowed occlusal surface, giving them a bumpy, "mulberry-like" appearance. **Analysis of Incorrect Options:** * **Severe Fluorosis:** Characterized by "mottling" of enamel, presenting as chalky white patches or brownish discoloration and pitting, but it does not produce the specific multi-cusped morphology of mulberry molars. * **Trauma at birth:** While trauma can cause localized enamel hypoplasia (Turner’s tooth), it typically affects a single tooth and does not result in the symmetrical, multi-cusped pattern seen in syphilis. * **Chronic suppurative abscess:** Localized infection (Turner’s hypoplasia) usually affects the permanent successor of a primary tooth (like a premolar) due to apical periodontitis of the deciduous tooth, rather than systemic developmental changes. **NEET-PG High-Yield Pearls:** * **Hutchinson’s Triad:** A classic triad of Congenital Syphilis consisting of: 1. **Hutchinson’s teeth:** Notched, peg-shaped permanent incisors. 2. **Interstitial keratitis:** Leading to corneal scarring. 3. **Sensorineural hearing loss:** Due to 8th cranial nerve involvement. * **Other Skeletal Signs:** Saddle nose deformity, Saber shins (anterior bowing of the tibia), and Clutton’s joints (painless symmetrical knee swelling). * **Early vs. Late:** Mulberry molars are considered a "stigmata" or late manifestation (appearing after age 2).

Practice by Chapter

Principles of Antimicrobial Therapy

Practice Questions

Fever of Unknown Origin

Practice Questions

HIV/AIDS and Related Infections

Practice Questions

Tuberculosis and Mycobacterial Diseases

Practice Questions

Tropical and Parasitic Infections

Practice Questions

Viral Infections (Hepatitis, Herpes, etc.)

Practice Questions

Healthcare-Associated Infections

Practice Questions

Fungal Infections

Practice Questions

Sepsis and Septic Shock

Practice Questions

Infection in Immunocompromised Hosts

Practice Questions

Emerging and Re-emerging Infections

Practice Questions

Antimicrobial Resistance

Practice Questions

Vaccination Principles

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free