Infectious Diseases Practice Questions

Q: The endotoxin of which of the following Gram-negative bacteria does not play a significant role in the pathogenesis of the natural disease?

Vibrio cholerae. **Explanation:** The pathogenesis of bacterial diseases generally involves either **endotoxins** (Lipopolysaccharide/LPS found in the outer membrane of Gram-negative bacteria) or **exotoxins** (secreted proteins). **Why Vibrio cholerae is the correct answer:** While *Vibrio cholerae* is a Gram-negative bacterium and possesses endotoxin (LPS) in its cell wall, this endotoxin plays **no significant role** in the clinical manifestation of Cholera. The natural disease is caused almost entirely by the **Cholera Toxin (Choleragen)**, a potent **exotoxin** [1]. This A-B type toxin increases intracellular cAMP, leading to the massive secretion of water and electrolytes into the intestinal lumen, resulting in "rice-water" stools [1]. **Analysis of Incorrect Options:** * **Escherichia coli & Klebsiella spp.:** These are classic Enterobacteriaceae. In conditions like neonatal sepsis, UTI, or pneumonia caused by these organisms, the release of **LPS (Endotoxin)** into the bloodstream triggers the release of cytokines (TNF-α, IL-1), leading to septic shock and systemic inflammatory response syndrome (SIRS). * **Pseudomonas aeruginosa:** This organism utilizes a combination of virulence factors. While it produces Exotoxin A, its **endotoxin** is a major contributor to the pathogenesis of Pseudomonas-induced septicemia and shock. **NEET-PG High-Yield Pearls:** * **Endotoxin (LPS):** The toxic component is **Lipid A**. It is heat-stable and encoded by chromosomal genes. * **Vibrio cholerae:** The toxin is encoded by a bacteriophage (**CTXφ**). Stool dark-field microscopy shows the typical ‘shooting star’ motility of V. cholerae [1]. * **Key Distinction:** Endotoxins typically cause fever and shock; Exotoxins (like Cholera toxin) usually have specific pharmacological actions without necessarily causing fever.

Q: Which of the following types of hepatitis is associated with an immune-mediated vasculitis characterized by p-ANCA antibodies?

Hepatitis B. **Explanation:** The correct answer is **Hepatitis B**. This association is a classic high-yield concept in medical pathology and clinical medicine. **1. Why Hepatitis B is correct:** Hepatitis B virus (HBV) is strongly associated with **Polyarteritis Nodosa (PAN)**, a systemic necrotizing vasculitis of medium and small-sized arteries. PAN is an immune-complex mediated disease where HBsAg-anti-HBs complexes deposit in vessel walls, leading to inflammation [1]. While PAN is classically "pauci-immune" (meaning ANCA is usually negative), a specific subset of patients—particularly those with microscopic polyangiitis or certain variants of PAN—can demonstrate **p-ANCA (perinuclear Anti-Neutrophil Cytoplasmic Antibodies)** positivity. Approximately 10–30% of patients with PAN are chronic carriers of HBV. **2. Why other options are incorrect:** * **Hepatitis A:** This is an acute, self-limiting infection transmitted via the fecal-oral route [2]. It is not associated with chronic immune-complex mediated vasculitides. * **Hepatitis C:** HCV is most famously associated with **Mixed Cryoglobulinemia** (Type II and III), which presents with the triad of purpura, arthralgia, and weakness. While it causes vasculitis, it is not typically associated with p-ANCA. * **Hepatitis D:** HDV requires the presence of HBV to replicate. While it increases the severity of liver disease, the specific association with p-ANCA vasculitis is primarily attributed to the underlying HBV infection. **Clinical Pearls for NEET-PG:** * **PAN Presentation:** Look for "string of beads" appearance on angiography, hypertension (renal artery involvement), and mononeuritis multiplex. * **HCV vs. HBV:** If the question mentions **Cryoglobulins**, think **HCV**. If it mentions **PAN or p-ANCA**, think **HBV** [1]. * **Rule of Thumb:** PAN characteristically **spares the lungs**, unlike other ANCA-associated vasculitides like Granulomatosis with Polyangiitis (GPA).

Q: Which of the following is NOT a feature of arthritis in acute rheumatic fever?

Joint deformities are common sequels. The arthritis of Acute Rheumatic Fever (ARF) is characteristically **non-deforming**. Even without treatment, the inflammation typically resolves within 1–5 weeks without leaving any residual joint damage or chronic sequelae. This distinguishes it from other inflammatory conditions like Rheumatoid Arthritis, which leads to joint erosion and permanent deformity. ### **Analysis of Options** * **A. Elevated ASO titer:** This is a diagnostic requirement [1]. According to the **Jones Criteria**, evidence of a preceding Group A Streptococcal (GAS) infection (e.g., elevated/rising Antistreptolysin O titer) is essential for diagnosis [1]. * **C. Dramatic response to aspirin:** The response to salicylates (Aspirin) or NSAIDs is so rapid and complete (usually within 48 hours) that if a patient does not respond, the diagnosis of ARF should be reconsidered. * **D. Involvement of large joints:** ARF typically presents as a **migratory polyarthritis** affecting large joints such as the knees, ankles, elbows, and wrists. Small joints are rarely involved. ### **High-Yield Clinical Pearls for NEET-PG** * **Jaccoud’s Arthropathy:** While ARF is non-deforming, a rare condition called Jaccoud’s arthropathy (painless loosening of ligaments) can occur after recurrent attacks, but it is functional rather than erosive. * **Jones Criteria (Revised):** Arthritis is a **Major Criterion**. In high-risk populations, even monoarthritis or polyarthralgia can be considered a major criterion. * **Inverse Relationship:** There is often an inverse relationship between the severity of arthritis and the severity of carditis; patients with severe arthritis often have milder carditis [1]. * **Treatment:** Aspirin remains the drug of choice for arthritis, while corticosteroids are reserved for severe carditis.

Q: Lady Windermere's syndrome is associated with which of the following organisms?

Non-tuberculous mycobacteria. **Explanation:** **Lady Windermere’s Syndrome** is a specific clinical presentation of pulmonary infection caused by **Non-Tuberculous Mycobacteria (NTM)**, most commonly *Mycobacterium avium complex* (MAC) [1]. The syndrome typically occurs in elderly, immunocompetent women who do not have pre-existing lung disease. The underlying pathophysiology is linked to **voluntary cough suppression**. Historically, it was observed in women who, for social reasons, refrained from coughing and expectorating. This leads to the stagnation of secretions in the dependent lobes (specifically the **right middle lobe** or the lingula), creating a nidus for NTM infection. Radiologically, it is characterized by bronchiectasis and tree-in-bud nodules. **Analysis of Incorrect Options:** * **A. Treponema pallidum:** The causative agent of Syphilis; it is associated with aortitis and neurosyphilis, not chronic pulmonary NTM infections. * **B. Listeria monocytogenes:** A gram-positive rod causing meningitis and sepsis, particularly in neonates, the elderly, and the immunocompromised. * **D. Chlamydia trachomatis:** A common cause of STIs and trachoma; it does not cause the chronic bronchiectatic pattern seen in this syndrome. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Patient Profile:** Elderly female, thin habitus, often associated with skeletal abnormalities like pectus excavatum or scoliosis. * **Commonest Organism:** *Mycobacterium avium-intracellulare* (MAC) [1]. * **Radiology Hallmark:** Bronchiectasis and nodules specifically involving the **Right Middle Lobe (RML)** or the **Lingula**. * **Treatment:** Long-term multi-drug therapy (typically Macrolides, Ethambutol, and Rifampin).

Q: Mild steatorrhea is caused by which of the following?

Giardia. **Explanation:** **Giardia lamblia** is the correct answer because it primarily infects the upper small intestine (duodenum and jejunum) [2]. The pathophysiology involves the trophozoites adhering to the intestinal mucosa via a ventral sucking disc [2]. This leads to the **blunting of villi** and the **malabsorption of fats**, resulting in characteristic foul-smelling, greasy, non-bloody stools known as **steatorrhea**. Unlike invasive pathogens, *Giardia* causes a functional deficiency of enzymes (like disaccharidases) and interferes with bile salt activity, further contributing to fat malabsorption. **Analysis of Incorrect Options:** * **Trichomonas vaginalis:** This is a flagellated protozoan that causes urogenital infections (vaginitis/urethritis), not intestinal disease. It is a common cause of "strawberry cervix." * **Entamoeba histolytica:** This organism causes amoebic dysentery [1]. It invades the colonic mucosa, leading to "flask-shaped ulcers" and bloody diarrhea (hematochezia), rather than malabsorptive steatorrhea [1]. * **Entamoeba coli:** This is considered a non-pathogenic commensal of the human colon. Its presence in stool indicates fecal-oral contamination but does not cause clinical disease or steatorrhea. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Tinidazole (single dose) or Metronidazole. * **Diagnosis:** Stool microscopy (cysts/trophozoites) or the **String Test (Entero-test)** if stool samples are negative. * **Risk Factors:** Common in travelers ("Traveler’s Diarrhea"), hikers (drinking unfiltered stream water), and individuals with **IgA deficiency** [2][3]. * **Morphology:** Trophozoites have a characteristic "falling leaf" motility and a "monkey face" appearance on staining.

Question 1

A 70-year-old male presented with complaints of abdominal pain, nausea, headache, malaise, persistent fever for 2 weeks, and constipation. On examination, a characteristic rash was observed on the trunk and chest. His vital signs were BP 120/70 mm Hg and HR 65 bpm. Examination revealed hepatomegaly and splenomegaly. Blood culture was negative; however, a bone marrow culture showed a Gram-negative organism that ferments glucose with acid production, reduces nitrates, does not ferment lactose, and is motile by means of flagella. What is the drug of choice if the isolated organism is a multi-drug resistant variety?

Accepted Answer

Ceftriaxone

Answer

Ciprofloxacin

Answer

Moxifloxacin

Answer

Ceftazidime

Question 2

The endotoxin of which of the following Gram-negative bacteria does not play a significant role in the pathogenesis of the natural disease?

Accepted Answer

Vibrio cholerae

Answer

Escherichia coli

Answer

Klebsiella spp.

Answer

Pseudomonas aeruginosa

Question 3

Which of the following types of hepatitis is associated with an immune-mediated vasculitis characterized by p-ANCA antibodies?

Accepted Answer

Hepatitis B

Answer

Hepatitis A

Answer

Hepatitis C

Answer

Hepatitis D

Question 4

A patient who underwent renal transplantation 2 months ago presents with difficulty breathing. Chest X-ray shows bilateral diffuse interstitial pneumonia. What is the probable etiologic agent?

Accepted Answer

Cytomegalovirus (CMV)

Answer

Histoplasma capsulatum

Answer

Candida species

Answer

Pneumocystis jirovecii

Question 5

Which of the following is NOT a feature of arthritis in acute rheumatic fever?

Accepted Answer

Joint deformities are common sequels

Answer

Elevated ASO titer

Answer

Dramatic response to aspirin

Answer

Involvement of large joints

Question 6

Lady Windermere's syndrome is associated with which of the following organisms?

Accepted Answer

Non-tuberculous mycobacteria

Answer

Treponema pallidum

Answer

Listeria monocytogenes

Answer

Chlamydia trachomatis

Question 7

A 56-year-old man presents with intermittent fevers and malaise for the past 2 weeks, with no other localizing symptoms. Two months prior, he underwent valve replacement surgery for a bicuspid aortic valve, receiving a mechanical valve with an uncomplicated postoperative course. On examination, his temperature is 38°C, blood pressure is 124/80 mm Hg, pulse is 72/min, and head and neck are normal. Auscultation reveals a 3/6 systolic ejection murmur, a mechanical second heart sound, and a 2/6 early diastolic murmur. Lungs are clear and skin examination is normal. Three sets of blood cultures and an urgent echocardiogram are performed. Which of the following is the most likely causative organism?

Accepted Answer

Staphylococcus epidermidis

Answer

Staphylococcus aureus

Answer

Streptococcus viridans

Answer

Enterococci

Question 8

Mild steatorrhea is caused by which of the following?

Accepted Answer

Giardia

Answer

Trichomonas vaginalis

Answer

E. histolytica

Answer

Entamoeba coli

Question 9

A 38-year-old AIDS patient presents with a one-week history of fever and increasing headache. He also reports photophobia, nausea, and weakness. His past medical history is significant for Pneumocystis pneumonia, and his CD4 count is 89. Current medications include trimethoprim/sulfamethoxazole and indinavir. Cerebrospinal fluid (CSF) analysis reveals 4 WBCs, and budding encapsulated yeast forms grow on Sabouraud's agar. What is the accurate description of the morphology of the infectious form of the organism responsible for this patient's illness?

Accepted Answer

Encapsulated budding yeasts

Answer

Broad-based, budding yeasts

Answer

Budding yeasts in a pseudohyphae

Answer

Cylindrical arthroconidia

Question 10

Which of the following statements about HIV is incorrect?

Accepted Answer

The most common cause of seizures in HIV patients is Candida.

Answer

PML is caused by JC virus.

Answer

CNS lymphoma is the most common CNS tumor.

Answer

CMV is the most common cause of retinitis.

Infectious Diseases — MCQs

Infectious Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?