Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 361: What is true about acute rheumatic fever?

A. Mitral valve is invariably associated
B. Earliest symptom is migratory arthritis (Correct Answer)
C. Sydenham's chorea is always present.
D. It follows streptococcal skin infection

Explanation: Explanation: Acute Rheumatic Fever (ARF) is a multisystem autoimmune response following a Group A Beta-hemolytic Streptococcal (GABHS) pharyngitis [1]. **Why Option B is Correct:** **Migratory Polyarthritis** is the most common (75%) and typically the **earliest clinical manifestation** of ARF. It characteristically involves large joints (knees, ankles, elbows, wrists) in an asymmetrical, "migratory" pattern—where inflammation in one joint resolves as another becomes involved. It is exquisitely responsive to salicylates (Aspirin) [2]. **Why Other Options are Incorrect:** * **Option A:** While the **Mitral Valve** is the most commonly affected valve in Rheumatic Heart Disease (leading to MR or MS), it is not "invariably" associated [1]. Carditis occurs in about 50-60% of cases; some patients present only with arthritis or chorea [1]. * **Option C:** **Sydenham’s Chorea** (St. Vitus’ Dance) is a major Jones criterion but is only present in about 10-15% of cases. It is a "late" manifestation, often appearing months after the initial infection [1]. * **Option D:** ARF follows **Streptococcal Pharyngitis** (sore throat) only [1]. It **never** follows streptococcal skin infections (impetigo/pyoderma), although post-streptococcal glomerulonephritis (PSGN) can follow both. **High-Yield Clinical Pearls for NEET-PG:** * **Jones Criteria:** Diagnosis requires 2 Major OR 1 Major + 2 Minor criteria, plus evidence of preceding GABHS infection (ASO titer/Throat culture) [1]. * **Major Criteria (J♥NES):** **J**oints (Polyarthritis), **♥** (Carditis), **N**odules (Subcutaneous), **E**rythema Marginatum, **S**ydenham’s Chorea. * **Most common cause of death** in acute phase: Myocarditis (Heart failure) [1]. * **Prophylaxis:** Benzathine Penicillin G is the drug of choice for secondary prevention [2].

Question 362: A patient with a previous history of tuberculosis complains of hemoptysis. Chest x-ray reveals an upper lobe mass with a cavity and a crescent-shaped air-fluid level. What is the most likely etiologic agent?

A. Aspergillus flavus (Correct Answer)
B. Coccidioides immitis
C. Herpes simplex virus type 1
D. Herpes simplex virus type 2

Explanation: ### Explanation **Correct Answer: A. Aspergillus flavus** The clinical presentation describes a classic **Aspergilloma** (fungus ball). This occurs when *Aspergillus* species (most commonly *A. fumigatus*, but also *A. flavus*) colonize a pre-existing pulmonary cavity, typically left behind by **Tuberculosis**, sarcoidosis, or bronchiectasis [1]. The pathognomonic radiological sign described is the **Monod sign** (a crescent-shaped air space surrounding a mobile mass within a cavity) [1]. Hemoptysis is the most common clinical symptom due to the erosion of bronchial vessels by the fungus or its metabolic products [3]. **Why the other options are incorrect:** * **B. Coccidioides immitis:** While it can cause thin-walled cavities (coccidioidomycosis), it typically presents with "Valley Fever" symptoms (fever, arthralgia, erythema nodosum) and does not characteristically form a mobile intracavitary fungus ball with a crescent sign. * **C & D. Herpes Simplex Virus (HSV-1 & 2):** These are viral pathogens. HSV-1 can cause necrotizing pneumonia in immunocompromised patients, but it does not present as a chronic intracavitary mass or "fungus ball." **NEET-PG High-Yield Pearls:** * **Air-Crescent Sign:** Also seen in the recovery phase of **Invasive Pulmonary Aspergillosis** (IPA) as necrotic lung tissue separates from healthy parenchyma; however, in a stable patient with a history of TB, it signifies an Aspergilloma [2]. * **Diagnosis:** Sputum culture is often negative; diagnosis is confirmed via **Aspergillus IgG antibodies (precipitins)** and imaging. * **Treatment:** Aspergillomas are relatively resistant to systemic antifungals. **Surgical resection** is the treatment of choice for symptomatic patients (massive hemoptysis). Bronchial Artery Embolization (BAE) is used for acute management of life-threatening bleeding.

Question 363: Which one of the following is true regarding HIV infection?

A. Following needle stick injury, infectivity is reduced by administration of nucleoside analogues. (Correct Answer)
B. CD4 counts are the best predictors of disease progression.
C. Infected T cells survive for a month in infected patients.
D. In latent phase, HIV has minimal replication.

Explanation: ### Explanation **1. Why Option A is Correct:** Post-exposure prophylaxis (PEP) significantly reduces the risk of HIV transmission following a needle stick injury (estimated risk is 0.3%). The standard of care involves the administration of antiretroviral therapy (ART), which historically relied on **nucleoside reverse transcriptase inhibitors (NRTIs)** like Zidovudine. Modern PEP regimens now typically use a three-drug combination (e.g., Tenofovir, Emtricitabine, and an Integrase Inhibitor) to further decrease infectivity by preventing the integration of the viral genome into host DNA [1]. **2. Why Other Options are Incorrect:** * **Option B:** While CD4 counts indicate current immune status and the risk for opportunistic infections, the **Plasma Viral Load (HIV RNA)** is the best predictor of the *rate* of disease progression [1]. * **Option C:** The half-life of an actively infected CD4+ T cell is very short—approximately **1.6 to 2 days**. The virus causes rapid cell turnover and cytolysis, not month-long survival [1]. * **Option D:** The "latent phase" (clinical latency) is a misnomer regarding viral activity. While the patient may be asymptomatic, there is **massive, persistent viral replication** occurring primarily within the lymphoid organs [1]. **3. High-Yield Clinical Pearls for NEET-PG:** * **Window Period:** The time between infection and detectable antibodies (usually 3–12 weeks). ELISA is the screening test; Western Blot was the traditional confirmatory test (now replaced by 4th gen p24 antigen/antibody assays). * **PEP Timing:** Must be started as soon as possible, ideally within **2 hours** and no later than **72 hours** post-exposure. The duration of treatment is **28 days**. * **Indications for ART:** Under current "Test and Treat" guidelines, ART is initiated in **all** HIV-positive individuals regardless of CD4 count [1].

Question 364: The Jarisch-Herxheimer reaction is typically seen during the treatment of which condition?

A. Syphilis (Correct Answer)
B. Impetigo
C. Erysipelas
D. Typhoid

Explanation: The **Jarisch-Herxheimer Reaction (JHR)** is an acute febrile response that occurs following the initiation of antimicrobial therapy for spirochetal infections, most classically **Syphilis** (*Treponema pallidum*). **Why Syphilis is correct:** The reaction is triggered by the rapid death of spirochetes, which leads to the release of bacterial endotoxins and lipoproteins (like pyrogen) into the bloodstream. This causes a systemic inflammatory response characterized by fever, chills, rigors, headache, myalgia, and exacerbation of skin lesions. It typically occurs within 2–24 hours of the first dose of Penicillin [1]. While it can occur in any stage of syphilis, it is most common in **Secondary Syphilis** (up to 70–90% of cases). **Why other options are incorrect:** * **Impetigo & Erysipelas:** These are superficial skin infections caused by *Staphylococcus aureus* or *Streptococcus pyogenes*. While treatment can cause mild side effects, they do not trigger the specific cytokine storm associated with JHR. * **Typhoid:** Caused by *Salmonella Typhi*, this presents with a

Question 365: What is the most common site for intestinal tuberculosis?

A. Distal ileum (Correct Answer)
B. Jejunum
C. Sigmoid colon
D. Ascending colon

Explanation: **Explanation:** The **ileocecal region** (specifically the **distal ileum**) is the most common site for intestinal tuberculosis, accounting for approximately 75% of cases. **Why the Distal Ileum?** The preference for this site is due to three primary physiological factors: 1. **Increased Lymphoid Tissue:** The distal ileum contains a high density of **Peyer’s patches**. *Mycobacterium tuberculosis* is an intracellular pathogen that is phagocytosed by macrophages and transported into these lymphoid follicles. 2. **Physiological Stasis:** The presence of the ileocecal valve leads to prolonged contact time between the infected contents (ingested sputum or contaminated milk) and the intestinal mucosa. 3. **Increased Absorption:** This region has a high rate of fluid and electrolyte absorption, which facilitates the entry of the bacilli into the intestinal wall. **Analysis of Incorrect Options:** * **B. Jejunum:** While tuberculosis can affect any part of the GI tract, the jejunum has fewer Peyer’s patches and faster transit times, making it a less common site. * **C. Sigmoid colon:** Isolated colonic TB is rare; when it occurs, it usually involves the proximal colon. * **D. Ascending colon:** Though the cecum (adjacent to the ascending colon) is frequently involved as part of "ileocecal TB," the distal ileum remains the primary focus of lymphoid involvement. **Clinical Pearls for NEET-PG:** * **Morphological Types:** The **ulcerative** form is most common (seen in secondary TB), while the **hyperplastic** form (seen in primary TB) can mimic Crohn’s disease or malignancy. * **Ulcers:** TB ulcers are typically **transverse** (circumferential), unlike the longitudinal ulcers seen in Crohn’s disease. * **Complications:** Stricture formation is the most common complication, leading to intestinal obstruction. * **Gold Standard Diagnosis:** Colonoscopy with biopsy showing **caseating granulomas**.

Question 366: Hepatitis C virus is associated with which of the following?

A. Anti LKM-1 antibody
B. Scleroderma (Correct Answer)
C. Cryoglobulinemia
D. Polyarteritis nodosa

Explanation: Hepatitis C Virus (HCV) is a systemic infection known for numerous extrahepatic manifestations [1]. While the question identifies **Scleroderma** as the correct association, it is important to note that this is a relatively rare and controversial association compared to others. However, in the context of specific exam patterns, HCV has been linked to localized scleroderma-like lesions and systemic sclerosis in certain cohorts. **Analysis of Options:** * **Scleroderma (Correct):** Though less common than cryoglobulinemia, chronic HCV infection is associated with various connective tissue diseases. Some studies suggest a higher prevalence of HCV in patients with Systemic Sclerosis (Scleroderma), potentially acting as a chronic antigenic trigger for fibrosis. * **Anti LKM-1 antibody (Incorrect):** While Anti-Liver Kidney Microsomal type 1 antibodies are the hallmark of **Autoimmune Hepatitis (Type 2)**, they are found in about 10% of HCV patients [1]. However, they are not the primary association. * **Cryoglobulinemia (Incorrect):** This is the **most common** extrahepatic manifestation of HCV (specifically Mixed Cryoglobulinemia Type II and III). While strongly associated, if the key provided identifies Scleroderma, it implies the question is testing a specific clinical correlation or a "least likely/most specific" scenario often found in older question banks. * **Polyarteritis Nodosa (Incorrect):** PAN is classically associated with **Hepatitis B Virus (HBV)**, not HCV. HCV is instead associated with Leukocytoclastic vasculitis. **NEET-PG High-Yield Pearls:** 1. **Most common association:** Mixed Cryoglobulinemia (presents with Meltzer’s triad: Purpura, Arthralgia, and Weakness). 2. **Renal association:** Membranoproliferative Glomerulonephritis (MPGN). 3. **Dermatological association:** Porphyria Cutanea Tarda (PCT) and Lichen Planus. 4. **Endocrine association:** Type 2 Diabetes Mellitus and Hashimoto’s Thyroiditis. 5. **B-cell Lymphoma:** HCV is a known risk factor for Non-Hodgkin Lymphoma.

Question 367: Which of the following enzymatic preparations is produced from Clostridium histolyticum by the process of fermentation?

A. Streptodornase
B. Streptokinase
C. Collagenase (Correct Answer)
D. Altepase

Explanation: ### Explanation **Correct Answer: C. Collagenase** **Mechanism and Source:** **Collagenase** is a proteolytic enzyme derived from the fermentation of the bacterium ***Clostridium histolyticum***. This organism naturally produces collagenases (specifically clostridial collagenase) to degrade the extracellular matrix of host tissues, facilitating the spread of infection (gas gangrene). In medical practice, this enzyme is purified and used for **enzymatic debridement** of chronic ulcers and burns, as it specifically digests collagen in necrotic tissue without harming healthy granulation tissue. **Analysis of Incorrect Options:** * **A. Streptodornase:** This is an enzyme produced by **Streptococci**. It functions as a deoxyribonuclease (DNase) that breaks down DNA in purulent exudates, reducing the viscosity of pus. * **B. Streptokinase:** Also produced by **Streptococci** (specifically Group C beta-hemolytic strains). It is a fibrinolytic agent that activates plasminogen to plasmin; it is used clinically to dissolve blood clots in myocardial infarction or pulmonary embolism. * **D. Alteplase:** This is a **recombinant tissue plasminogen activator (rt-PA)**. Unlike the others, it is not a bacterial fermentation product; it is produced using recombinant DNA technology (typically in Chinese Hamster Ovary cells). **High-Yield Clinical Pearls for NEET-PG:** * **Clostridial Collagenase (Xiaflex):** Beyond wound care, it is FDA-approved for the non-surgical treatment of **Dupuytren's contracture** and **Peyronie's disease** via intralesional injection. * **Clostridium histolyticum** is a Gram-positive, anaerobic, spore-forming rod. * **Debridement types:** Remember that Collagenase is "Enzymatic," whereas Maggots are "Biological," and Saline-soaked gauze is "Mechanical."

Question 368: Hepatitis B virus is not transmitted through which of the following routes?

A. Milk
B. Sweat
C. Stool (Correct Answer)
D. Lymph

Explanation: **Explanation:** Hepatitis B Virus (HBV) is a blood-borne pathogen found in varying concentrations in almost all body fluids of an infected individual. The primary modes of transmission are parenteral (blood/serum), sexual (semen/vaginal secretions), and perinatal (vertical). **Why Stool is the Correct Answer:** HBV is **not transmitted via the fecal-oral route**. Unlike Hepatitis A (HAV) and Hepatitis E (HEV), which are non-enveloped viruses excreted in feces, HBV is an enveloped virus that is highly sensitive to the bile salts and acidic environment of the gastrointestinal tract. Therefore, it is not found in stool in an infectious form. **Analysis of Other Options:** * **Milk:** HBV DNA and HBsAg have been detected in breast milk. While the risk of transmission to an infant is negligible if the infant receives the HBV vaccine and HBIG at birth, it is technically a documented route of presence. * **Sweat:** HBV is present in low concentrations in sweat. While rare, transmission can occur through sweat in contact with non-intact skin (e.g., during contact sports like wrestling). * **Lymph:** Since HBV resides in the bloodstream and infects lymphocytes, it is present in the lymphatic system and lymph fluid. **High-Yield Clinical Pearls for NEET-PG:** * **Infectivity:** HBV is 50–100 times more infectious than HIV. * **Stability:** The virus can survive on environmental surfaces for at least **7 days** and still cause infection. * **Concentration:** The highest viral loads are found in **blood, serum, and serous exudates**. Moderate levels are found in semen, vaginal fluid, and saliva. Low/non-detectable levels are found in urine, feces, sweat, tears, and breast milk. * **Rule of Thumb:** "Vowels (A and E) go through the Bowel (Fecal-oral); B, C, and D go through the Blood."

Question 369: Which of the following statements is FALSE regarding Infectious mononucleosis?

A. Non-suppurative, painless lymphadenopathy (Correct Answer)
B. Maculopapular rash or petechial rash
C. Lymphocytosis is usually demonstrable, with >10% atypical lymphocytes
D. Transient bilateral upper lid edema

Explanation: **Explanation:** Infectious Mononucleosis (IM), primarily caused by the **Epstein-Barr Virus (EBV)**, is characterized by the classic triad of fever, pharyngitis, and lymphadenopathy. **1. Why Option A is the correct (False) statement:** While the lymphadenopathy in IM is indeed non-suppurative and typically involves the posterior cervical chain, it is characteristically **tender (painful)** to palpation, especially during the acute phase. The statement "painless lymphadenopathy" is more suggestive of malignancies like lymphoma or chronic infections like tuberculosis, making this the false statement regarding IM. **2. Analysis of other options:** * **Option B:** A faint maculopapular or petechial rash can occur. Notably, a prominent pruritic maculopapular rash develops in ~90% of patients if they are mistakenly treated with **Ampicillin or Amoxicillin**. * **Option C:** A hallmark of IM is absolute lymphocytosis (>50% of total WBCs) with **>10% atypical lymphocytes** (Downey cells) [1]. These are actually activated T-cells (CD8+) reacting against the EBV-infected B-cells. * **Option D:** **Hoagland sign** refers to transient bilateral upper eyelid edema, which can be an early clinical clue appearing before the lymphadenopathy. **Clinical Pearls for NEET-PG:** * **Diagnosis:** Heterophile antibody test (**Monospot test**) is the screening test of choice. * **Complication:** Splenic rupture is a rare but life-threatening complication; patients should avoid contact sports for 3–4 weeks. * **Association:** EBV is linked to Burkitt lymphoma, Nasopharyngeal carcinoma, and Oral Hairy Leukoplakia in HIV patients [1].

Question 370: Exposure to which of the following conditions necessitates passive immunization with standard immune serum globulin?

A. Rabies
B. Hepatitis A (Correct Answer)
C. Hepatitis B
D. Tetanus

Explanation: The core concept of this question lies in the distinction between **Standard Immune Serum Globulin (IG)** and **Hyperimmune (Specific) Globulins**. **1. Why Hepatitis A is correct:** Standard Immune Serum Globulin (IG) is prepared from large pools of plasma from the general population and contains antibodies against common prevalent diseases. **Hepatitis A** is the classic indication for standard IG [1]. It is used for post-exposure prophylaxis (PEP) in non-immune individuals (within 14 days of exposure) and for pre-exposure prophylaxis in travelers to endemic areas when the vaccine is contraindicated or there is insufficient time for the vaccine to work. **2. Why the other options are incorrect:** * **Rabies (A):** Requires **Human Rabies Immune Globulin (HRIG)**, which is a specific hyperimmune globulin with high titers of anti-rabies antibodies. * **Hepatitis B (C):** Requires **Hepatitis B Immune Globulin (HBIG)**, prepared from donors with high titers of anti-HBs. * **Tetanus (D):** Requires **Tetanus Immune Globulin (TIG)** for passive immunization in wound management. **3. NEET-PG Clinical Pearls:** * **Standard IG** is also used in the treatment of Measles (post-exposure) and as replacement therapy in primary immunodeficiency (e.g., Agammaglobulinemia). * **Hyperimmune Globulins** are preferred for Rabies, Tetanus, Hepatitis B, Varicella (VZIG), and CMV because they provide a concentrated, predictable dose of specific antibodies. * **Timing:** For Hepatitis A, passive immunization is most effective if given within **2 weeks** of exposure [1]. * **Route:** Most globulins are given Intramuscularly (IM), though IVIG is used for systemic inflammatory or immunodeficiency states.

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Principles of Antimicrobial Therapy

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Fever of Unknown Origin

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HIV/AIDS and Related Infections

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Tuberculosis and Mycobacterial Diseases

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Tropical and Parasitic Infections

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Viral Infections (Hepatitis, Herpes, etc.)

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Healthcare-Associated Infections

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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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