Infectious Diseases Practice Questions

Q: Which of the following is NOT typically seen in Dengue fever?

Hepato-splenomegaly. ### Explanation In Dengue fever, the hallmark clinical features are related to capillary leak and bone marrow suppression. While **Hepatomegaly** (enlargement of the liver) is a common finding and a recognized "warning sign" in Dengue Hemorrhagic Fever (DHF), **Splenomegaly is rare**. The presence of significant hepato-splenomegaly should prompt a clinician to consider alternative diagnoses such as Malaria, Enteric fever, or Kala-azar. **Analysis of Options:** * **A. Hemorrhagic tendencies:** These are common due to thrombocytopenia and vascular dysfunction. Manifestations include petechiae, ecchymosis, and mucosal bleeding (e.g., epistaxis) [1]. * **B. High grade fever:** Dengue typically presents with a sudden-onset, high-grade fever (often "saddleback" or biphasic) accompanied by retro-orbital pain and severe myalgia ("break-bone fever") [1]. * **C. Circulatory problems:** Plasma leakage due to increased capillary permeability can lead to hemoconcentration, pleural effusion, ascites, and in severe cases, Dengue Shock Syndrome (DSS) [1]. * **D. Hepato-splenomegaly:** As noted, while the liver is often tender and enlarged, the spleen is typically not involved. **Clinical Pearls for NEET-PG:** * **Vector:** *Aedes aegypti* (Day biter; breeds in clean stagnant water). * **Warning Signs:** Abdominal pain, persistent vomiting, mucosal bleed, lethargy, and **Hepatomegaly >2 cm**. * **Lab Findings:** Leukopenia (early sign), Thrombocytopenia, and rising Hematocrit (indicates plasma leak). * **Tourniquet Test:** Positive if >10–20 petechiae per square inch; used as a screening tool for capillary fragility [1]. * **NS1 Antigen:** Best for early diagnosis (Days 1–5). IgM/IgG ELISA is used after Day 5.

Q: A 20-year-old male presents with fever, fatigue, posterior cervical lymphadenopathy, palatal petechiae, and splenomegaly. Peripheral smear shows atypical lymphocytes and the heterophile antibody is positive. What is the likely diagnosis?

Infectious mononucleosis. ### Explanation **Correct Answer: C. Infectious Mononucleosis (IM)** **Reasoning:** The clinical triad of **fever, pharyngitis, and lymphadenopathy** (classically posterior cervical) is hallmark for Infectious Mononucleosis, caused by the **Epstein-Barr Virus (EBV)** [2]. * **Palatal petechiae** and **splenomegaly** are highly specific physical findings [3]. * The laboratory diagnosis is confirmed by the presence of **atypical lymphocytes** (Downey cells)—which are actually activated T-cells—and a **positive Heterophile antibody test** (Monospot test), which detects IgM antibodies that agglutinate sheep or horse red blood cells [1]. **Why Incorrect Options are Wrong:** * **A & B (Acute/Lymphocytic Leukemia):** While leukemia can present with lymphadenopathy and splenomegaly, the presence of a positive heterophile antibody is pathognomonic for IM. Furthermore, leukemia would typically show "blasts" on a smear rather than reactive atypical lymphocytes, along with cytopenias (anemia/thrombocytopenia). * **D (Chronic Myeloid Leukemia):** CML typically presents in older adults with massive splenomegaly and a "leukemoid" blood picture (predominance of neutrophils, myelocytes, and metamyelocytes) with a low LAP score [3], not fever and pharyngitis in a young adult. **High-Yield Clinical Pearls for NEET-PG:** 1. **The "Ampicillin Rash":** If a patient with IM is mistakenly treated with Ampicillin or Amoxicillin for suspected strep throat, they often develop a characteristic maculopapular rash. 2. **Splenic Rupture:** This is a rare but life-threatening complication; patients must avoid contact sports for 3–4 weeks. 3. **Diagnosis:** Monospot test may be false-negative in the first week of illness or in children <4 years old. 4. **Atypical Lymphocytes:** These are **CD8+ T-cells** reacting against EBV-infected B-cells [1].

Q: A 29-year-old man presents with fever, myalgia, headache, nausea, and a rash on his wrists, ankles, and body after a hiking trip where he experienced numerous insect bites. Examination reveals a blood pressure of 90/60 mmHg, pulse of 100/min, and respirations of 20/min. He has multiple macules, some with hemorrhagic centers consistent with petechiae. A clinical diagnosis of Rocky Mountain Spotted Fever (RMSF) is made. What is the most common central nervous system (CNS) presentation in this condition?

Encephalitis. **Explanation:** **Rocky Mountain Spotted Fever (RMSF)**, caused by *Rickettsia rickettsii*, is a systemic vasculitis. The pathogen infects the vascular endothelial cells, leading to increased capillary permeability, microvascular leakage, and inflammatory responses across various organ systems, including the Central Nervous System (CNS) [2]. **1. Why Encephalitis is Correct:** CNS involvement is a hallmark of severe RMSF due to widespread microvascular injury in the brain. **Encephalitis** is the most common CNS manifestation, presenting as altered mental status, confusion, lethargy, or even coma. It occurs in approximately 25–35% of patients. Pathologically, this is characterized by "typhus nodules" (glial nodules) and perivascular mononuclear infiltration. [2] **2. Why Incorrect Options are Wrong:** * **A & C (Hemiplegia/Paraplegia):** While focal neurological deficits can occur due to localized vasculitis or stroke-like events, they are much less common than global cerebral dysfunction (encephalitis). * **B (Cranial nerve abnormalities):** These are rare complications (e.g., deafness or ocular palsies) and do not represent the primary or most frequent CNS presentation compared to the diffuse involvement seen in encephalitis. **3. Clinical Pearls for NEET-PG:** * **The Classic Triad:** Fever, headache, and a centripetal rash (starts on wrists/ankles and spreads to the trunk) [1]. * **The Rash:** Typically appears on day 3–5; it starts as maculopapular and often becomes **petechial** (a sign of severe microvascular damage). * **Treatment:** **Doxycycline** is the drug of choice for all ages, including children, as the benefit of treating this potentially fatal disease outweighs the risk of dental staining. * **Laboratory findings:** Look for hyponatremia and thrombocytopenia in the clinical vignette.

Q: Migratory necrolytic erythema is seen in which of the following conditions?

Glucagonoma syndrome. **Explanation:** **Migratory Necrolytic Erythema (MNE)** is a pathognomonic cutaneous marker for **Glucagonoma**, a rare alpha-cell tumor of the pancreas. The rash typically presents as pruritic, painful, erythematous plaques that progress to vesicles and bullae, eventually crusting and healing with hyperpigmentation. It most commonly affects the perineum, buttocks, and distal extremities. The underlying mechanism is thought to be related to hypoaminoacidemia, zinc deficiency, or the direct effect of excess glucagon causing inflammatory arachidonic acid release. **Analysis of Incorrect Options:** * **Peutz-Jeghers Syndrome:** Characterized by hamartomatous gastrointestinal polyps and **mucocutaneous hyperpigmentation** (melanotic macules) on the lips, buccal mucosa, and digits. * **Sarcoidosis:** Associated with various skin manifestations, most notably **Lupus Pernio** (violaceous plaques on the nose/cheeks) and **Erythema Nodosum** (painful pretibial nodules). * **Amyloidosis:** Classic skin findings include **"Pinch purpura"** (periorbital ecchymosis) and waxy, translucent papules or plaques due to amyloid deposition in the dermis. **High-Yield Clinical Pearls for NEET-PG:** * **Glucagonoma Syndrome (The 4 D's):** **D**ermatitis (MNE), **D**iabetes (mild), **D**epression, and **D**eep Vein Thrombosis (DVT). * **Laboratory findings:** Extremely high serum glucagon levels (>1000 pg/mL) and low serum amino acids. * **Treatment:** Somatostatin analogues (Octreotide) are used to control symptoms by inhibiting glucagon release before surgical resection.

Q: Which of the following is NOT seen in Mycoplasma pneumoniae infections?

Best treated by cefotaxime. **Explanation:** The correct answer is **C (Best treated by cefotaxime)** because *Mycoplasma pneumoniae* is a "cell wall-deficient" bacterium. Since it lacks a peptidoglycan cell wall, it is inherently resistant to beta-lactam antibiotics like cephalosporins (e.g., cefotaxime) and penicillins, which act by inhibiting cell wall synthesis. The drugs of choice are protein synthesis inhibitors such as **Macrolides** (Azithromycin), Tetracyclines (Doxycycline), or Fluoroquinolones. **Analysis of other options:** * **A. Diffuse infiltration of lungs:** Characteristically, *Mycoplasma* causes "Atypical Pneumonia." Clinical symptoms are often mild ("walking pneumonia"), but chest X-rays show disproportionately extensive interstitial or diffuse infiltrates, often described as a "patchy" or "ground-glass" appearance. * **B. Cannot be cultured routinely:** *Mycoplasma* is extremely fastidious, requires specialized media (e.g., PPLO agar/Eaton’s agar), and grows very slowly (2–3 weeks). Therefore, culture is not used for routine clinical diagnosis. * **D. Serology is useful in diagnosis:** Since culture is impractical, diagnosis relies on serology (detecting IgM antibodies) or PCR. Historically, the **Cold Agglutinin test** (IgM against I-antigen on RBCs) was used, though it is non-specific. **NEET-PG High-Yield Pearls:** * **Appearance on Culture:** "Fried egg" colonies. * **Extrapulmonary Manifestations:** Bullous myringitis (ear pain), Stevens-Johnson Syndrome, and autoimmune hemolytic anemia (due to cold agglutinins). * **Smallest free-living organism:** It contains both DNA and RNA but lacks a cell wall.

Q: All of the following features are seen in dengue hemorrhagic fever except?

Falling hematocrit value. In Dengue Hemorrhagic Fever (DHF), the hallmark pathophysiological change is **increased vascular permeability**, leading to plasma leakage. This results in **hemoconcentration**, which manifests as a **rising hematocrit (≥20% increase from baseline)**, not a falling one. A falling hematocrit is typically seen only after significant clinical hemorrhage or during the recovery phase (due to hemodilution). ### Analysis of Options: * **Option C (Correct):** Falling hematocrit is the "except" because DHF is characterized by plasma escaping the intravascular space, causing the blood to become more concentrated (rising hematocrit). * **Option A:** A **Positive Tourniquet Test** (≥10–20 petechiae per square inch) is a classic sign of capillary fragility and is one of the diagnostic criteria for DHF [1]. * **Option B:** **Thrombocytopenia** (platelet count <100,000 cells/mm³) is a mandatory WHO criterion for the diagnosis of DHF [1]. * **Option D:** Like Dengue Fever, DHF begins with an **acute onset of high-grade fever**, usually lasting 2–7 days [1]. ### NEET-PG High-Yield Pearls: * **WHO Criteria for DHF:** 1) Fever, 2) Hemorrhagic manifestations (e.g., positive tourniquet test), 3) Thrombocytopenia (<1 lac), and 4) Evidence of plasma leakage (rising hematocrit, pleural effusion, or ascites). * **Critical Phase:** Occurs around the time of **defervescence** (when fever drops). This is when the risk of Shock (Dengue Shock Syndrome) is highest [1]. * **Grading:** DHF is graded I to IV. Grades III and IV are classified as Dengue Shock Syndrome (DSS). * **Most sensitive indicator of plasma leakage:** A rising hematocrit.

Question 1

Which of the following is NOT typically seen in Dengue fever?

Accepted Answer

Hepato-splenomegaly

Answer

Hemorrhagic tendencies

Answer

High grade fever

Answer

Circulatory problems

Question 2

Which vaccine is contraindicated in patients with AIDS?

Accepted Answer

BCG

Answer

DPT

Answer

Rabies

Answer

Measles

Question 3

What constitutes a complicated urinary tract infection (UTI)?

Accepted Answer

A urinary tract infection that occurs in the presence of underlying structural, medical, or neurological disease.

Answer

A urinary tract infection in the absence of underlying renal or neurological disease.

Answer

More than three symptomatic urinary tract infections within 12 months, despite clinical therapy.

Answer

Recurrent urinary tract infections caused by a different pathogen at any time.

Question 4

A 20-year-old male presents with fever, fatigue, posterior cervical lymphadenopathy, palatal petechiae, and splenomegaly. Peripheral smear shows atypical lymphocytes and the heterophile antibody is positive. What is the likely diagnosis?

Accepted Answer

Infectious mononucleosis

Answer

Acute leukemia

Answer

Lymphocytic leukemia

Answer

Chronic myeloid leukemia

Question 5

A 29-year-old man presents with fever, myalgia, headache, nausea, and a rash on his wrists, ankles, and body after a hiking trip where he experienced numerous insect bites. Examination reveals a blood pressure of 90/60 mmHg, pulse of 100/min, and respirations of 20/min. He has multiple macules, some with hemorrhagic centers consistent with petechiae. A clinical diagnosis of Rocky Mountain Spotted Fever (RMSF) is made. What is the most common central nervous system (CNS) presentation in this condition?

Accepted Answer

Encephalitis

Answer

Hemiplegia

Answer

Cranial nerve abnormalities

Answer

Paraplegia

Question 6

A young female presents with myalgia, fever, headache, diarrhea, and an erythematous rash which first appeared in the groin. What is the most likely diagnosis?

Accepted Answer

Toxic shock syndrome

Answer

Toxic epidermal necrolysis

Answer

Staphylococcal scalded skin syndrome

Answer

Epidermolysis bullosa

Question 7

Migratory necrolytic erythema is seen in which of the following conditions?

Accepted Answer

Glucagonoma syndrome

Answer

Peutz-Jeghers syndrome

Answer

Sarcoidosis

Answer

Amyloidosis

Question 8

Which of the following is NOT seen in Mycoplasma pneumoniae infections?

Accepted Answer

Best treated by cefotaxime

Answer

Diffuse infiltration of lungs

Answer

Cannot be cultured routinely

Answer

Serology is useful in diagnosis

Question 9

A patient is found to be HIV positive on routine check-up. They have no symptoms and a CD4 count of 800 cells/mm³. What is the recommended management for this patient?

Accepted Answer

Tenofovir plus lamivudine plus efavirenz for lifelong treatment.

Answer

No treatment is required.

Answer

Zidovudine plus stavudine for 28 days.

Answer

Tenofovir plus zidovudine plus lamivudine for lifelong treatment.

Question 10

All of the following features are seen in dengue hemorrhagic fever except?

Accepted Answer

Falling hematocrit value

Answer

Positive tourniquet test

Answer

Platelet counts less than 1 lac

Answer

Acute onset of high fever

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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