Infectious Diseases Practice Questions

Q: What is true about acute rheumatic fever?

Earliest symptom is migratory arthritis. 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].

Q: 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?

Aspergillus flavus. ### 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.

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

Syphilis. 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

Q: What is the most common site for intestinal tuberculosis?

Distal ileum. **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**.

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

Collagenase. ### 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."

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

Stool. **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."

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

Non-suppurative, painless lymphadenopathy. **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].

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

Hepatitis A. 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.

Question 1

What is true about acute rheumatic fever?

Accepted Answer

Earliest symptom is migratory arthritis

Answer

Mitral valve is invariably associated

Answer

Sydenham's chorea is always present.

Answer

It follows streptococcal skin infection

Question 2

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?

Accepted Answer

Aspergillus flavus

Answer

Coccidioides immitis

Answer

Herpes simplex virus type 1

Answer

Herpes simplex virus type 2

Question 3

Which one of the following is true regarding HIV infection?

Accepted Answer

Following needle stick injury, infectivity is reduced by administration of nucleoside analogues.

Answer

CD4 counts are the best predictors of disease progression.

Answer

Infected T cells survive for a month in infected patients.

Answer

In latent phase, HIV has minimal replication.

Question 4

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

Accepted Answer

Syphilis

Answer

Impetigo

Answer

Erysipelas

Answer

Typhoid

Question 5

What is the most common site for intestinal tuberculosis?

Accepted Answer

Distal ileum

Answer

Jejunum

Answer

Sigmoid colon

Answer

Ascending colon

Question 6

Hepatitis C virus is associated with which of the following?

Accepted Answer

Scleroderma

Answer

Anti LKM-1 antibody

Answer

Cryoglobulinemia

Answer

Polyarteritis nodosa

Question 7

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

Accepted Answer

Collagenase

Answer

Streptodornase

Answer

Streptokinase

Answer

Altepase

Question 8

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

Accepted Answer

Stool

Answer

Milk

Answer

Sweat

Answer

Lymph

Question 9

Which of the following statements is FALSE regarding Infectious mononucleosis?

Accepted Answer

Non-suppurative, painless lymphadenopathy

Answer

Maculopapular rash or petechial rash

Answer

Lymphocytosis is usually demonstrable, with >10% atypical lymphocytes

Answer

Transient bilateral upper lid edema

Question 10

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

Accepted Answer

Hepatitis A

Answer

Rabies

Answer

Hepatitis B

Answer

Tetanus

Infectious Diseases — MCQs

Infectious Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?