Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 21: What is the most common manifestation of congenital toxoplasmosis?

A. Hydrocephalus
B. Chorioretinitis (Correct Answer)
C. Calcification
D. Convulsions

Explanation: **Explanation:** Congenital Toxoplasmosis is caused by the transplacental transmission of *Toxoplasma gondii*. While many neonates are asymptomatic at birth, **Chorioretinitis** is the most common clinical manifestation overall. It occurs in approximately 75-80% of affected children, often presenting as blurred vision or strabismus later in life, even if the child appeared normal at birth. **Analysis of Options:** * **B. Chorioretinitis (Correct):** It is the most frequent finding and is often bilateral. It represents the "late" manifestation of the infection and is part of the classic Sabin’s Triad. * **A. Hydrocephalus:** This is a classic feature (part of the triad) but is less common than chorioretinitis. It typically results from obstructive aqueductal stenosis. * **C. Calcification:** Specifically **intracranial diffuse calcifications**. While highly characteristic of Toxoplasmosis (distinguishing it from the periventricular calcifications of CMV), they occur in only about 50-60% of symptomatic cases. * **D. Convulsions:** These are a secondary neurological complication resulting from intracranial damage/calcifications but are not the primary or most common diagnostic sign. **High-Yield Pearls for NEET-PG:** 1. **Sabin’s Triad:** Chorioretinitis, Hydrocephalus, and Intracranial Calcifications. 2. **Calcification Pattern:** Diffuse/Scattered (Toxoplasmosis) vs. Periventricular (CMV). 3. **Transmission Risk:** The risk of transmission increases with gestational age (highest in the 3rd trimester), but the **severity** of fetal damage is highest if infected in the 1st trimester. 4. **Treatment:** Spiramycin (to prevent transmission) or Pyrimethamine + Sulfadiazine + Folinic acid (for fetal/neonatal infection).

Question 22: Use of aspirin in children with viral disease is associated with which of the following?

A. Metabolic acidosis
B. Reye's syndrome (Correct Answer)
C. Renal tubular acidosis
D. Fixed drug eruption

Explanation: **Explanation:** The correct answer is **B. Reye's syndrome**. **Why it is correct:** Reye's syndrome is a rare but life-threatening condition characterized by **acute encephalopathy** and **fatty degeneration of the liver**. It is strongly associated with the administration of **aspirin (salicylates)** to children or adolescents during a viral illness, most commonly **Influenza B** or **Varicella (Chickenpox)**. The underlying pathophysiology involves **mitochondrial dysfunction**, leading to impaired fatty acid oxidation and hyperammonemia. **Why other options are incorrect:** * **A. Metabolic acidosis:** While salicylate toxicity (aspirin overdose) causes a mixed respiratory alkalosis and metabolic acidosis, it is not the specific syndrome associated with pediatric viral infections. * **C. Renal tubular acidosis (RTA):** RTA is a group of disorders involving the kidneys' inability to maintain acid-base balance. It is not linked to aspirin use in viral prodromes. * **D. Fixed drug eruption:** This is a localized cutaneous drug reaction that recurs at the same site upon re-exposure to a drug (e.g., NSAIDs, sulfonamides), but it is not the classic association described here. **High-Yield Clinical Pearls for NEET-PG:** * **Biochemical Hallmarks:** Elevated serum ammonia, prolonged Prothrombin Time (PT/INR), and elevated AST/ALT with **normal bilirubin**. * **Liver Biopsy Findings:** Microvesicular steatosis (small fat droplets in hepatocytes) without significant inflammation. * **Management:** Supportive care, focusing on managing cerebral edema (Mannitol) and correcting hypoglycemia. * **Prevention:** Use **Acetaminophen (Paracetamol)** or Ibuprofen instead of aspirin in children with fever. *Exception:* Aspirin is still used in pediatrics for **Kawasaki disease** and **Rheumatic fever**.

Question 23: Parotitis and orchitis are common manifestations of which disease?

A. Diphtheria
B. Measles
C. Rubella
D. Mumps (Correct Answer)

Explanation: **Explanation:** **Mumps** is an acute viral infection caused by the **Rubulavirus** (Paramyxoviridae family). It is characterized by a predilection for glandular and nervous tissues. 1. **Why Mumps is correct:** * **Parotitis:** The most common clinical manifestation (95% of symptomatic cases), typically presenting as painful, usually bilateral swelling of the parotid glands. * **Orchitis:** The most common complication in post-pubertal males (occurring in up to 30-40% of cases). It is usually unilateral and can lead to testicular atrophy, though permanent infertility is rare. 2. **Why other options are incorrect:** * **Diphtheria:** Caused by *Corynebacterium diphtheriae*, it presents with a "bull-neck" appearance due to cervical lymphadenopathy and a greyish pseudomembrane in the pharynx. It does not cause parotitis or orchitis. * **Measles (Rubeola):** Characterized by the 3 C’s (Cough, Coryza, Conjunctivitis), Koplik spots, and a maculopapular rash. Common complications include pneumonia and SSPE. * **Rubella (German Measles):** Presents with a milder rash and significant **post-auricular and suboccipital lymphadenopathy**, not parotid swelling. **High-Yield Clinical Pearls for NEET-PG:** * **Most common complication in children:** Aseptic meningitis. * **Most common cause of acquired sensorineural deafness** in children is Mumps (usually unilateral). * **Pancreatitis** is another classic glandular manifestation of Mumps. * **Diagnosis:** Clinical diagnosis is standard; elevated **Serum Amylase** is a key laboratory finding due to parotid involvement. * **Prevention:** Live attenuated vaccine (Jeryl Lynn strain) as part of the MMR vaccine.

Question 24: What is the most common cause of diarrhea in children?

A. Vibrio cholera
B. E. coli
C. Rotavirus (Correct Answer)
D. Pneumococcus

Explanation: **Explanation:** **Rotavirus** is the most common cause of severe, dehydrating diarrhea in children worldwide, particularly in those under 5 years of age. It primarily affects the mature enterocytes at the tips of the intestinal villi, leading to malabsorption and osmotic diarrhea. In India, despite the introduction of the Rotavirus vaccine in the Universal Immunization Programme (UIP), it remains a leading cause of pediatric morbidity. **Analysis of Options:** * **Vibrio cholerae (Option A):** While it causes severe "rice-water" stools and rapid dehydration, it occurs more in epidemic patterns rather than being the most common cause of routine pediatric diarrhea. * **E. coli (Option B):** Enterotoxigenic *E. coli* (ETEC) is a frequent cause of "traveler’s diarrhea" and is common in developing countries, but globally, viral etiologies (specifically Rotavirus) outnumber bacterial causes in the pediatric age group. * **Pneumococcus (Option D):** *Streptococcus pneumoniae* is a leading cause of pneumonia, meningitis, and otitis media in children, but it is not a primary gastrointestinal pathogen. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Rotavirus produces the **NSP4 enterotoxin**, which induces secretory diarrhea by increasing intracellular calcium. * **Seasonality:** In temperate climates, it peaks in winter; in India, it is seen year-round with a peak in the cooler months (October–February). * **Diagnosis:** The gold standard for rapid detection is **ELISA** or Latex Agglutination for Rotavirus antigen in stools. * **Vaccination:** Two main vaccines are used—**Rotarix** (Monovalent, 2 doses) and **RotaTeq/Rotavac** (Pentavalent/Multivalent, 3 doses). In the National Schedule, Rotavac is given at 6, 10, and 14 weeks.

Question 25: An 8-year-old child presents with acute lymphadenopathy and fever, and laboratory findings show 20% lymphocytosis. What is the most likely diagnosis?

A. Infectious mononucleosis (Correct Answer)
B. Acute lymphoblastic leukemia (ALL)
C. Pulmonary tuberculosis (Koch's)
D. Alpha-hemolytic streptococcal infection

Explanation: ### Explanation **Correct Answer: A. Infectious mononucleosis** **Why it is correct:** Infectious mononucleosis (IM), most commonly caused by the **Epstein-Barr Virus (EBV)**, typically presents with the classic triad of **fever, pharyngitis, and lymphadenopathy** (usually posterior cervical). The hallmark laboratory finding is **lymphocytosis** (absolute lymphocyte count >4,500/µL or >50% of total WBCs) with at least **10% atypical lymphocytes** (Downey cells). In this clinical scenario, the combination of acute fever, lymphadenopathy, and significant lymphocytosis (20% or more) strongly points toward a viral etiology like IM. **Why the other options are incorrect:** * **B. Acute lymphoblastic leukemia (ALL):** While ALL presents with lymphadenopathy and fever, the lymphocytosis usually consists of **lymphoblasts** (immature cells) rather than mature atypical lymphocytes. Patients also typically exhibit "bicytopenia" or "pancytopenia" (anemia and thrombocytopenia), which are absent here. * **C. Pulmonary tuberculosis:** TB presents with chronic (not acute) lymphadenopathy, usually involving the hilar or paratracheal nodes. The fever is typically low-grade with evening rises, and the blood picture usually shows monocytosis or a normal differential, not significant lymphocytosis. * **D. Alpha-hemolytic streptococcal infection:** This typically causes localized dental infections or subacute bacterial endocarditis. While Group A Beta-hemolytic Strep causes pharyngitis, it results in **neutrophilic leukocytosis**, not lymphocytosis. **High-Yield NEET-PG Pearls:** * **Atypical Lymphocytes:** These are actually **CD8+ T-cells** reacting against EBV-infected B-cells. * **Diagnostic Test:** The **Monospot test** (Heterophile antibody test) is the initial screening test of choice. * **Clinical Caution:** Administration of **Ampicillin or Amoxicillin** in a patient with IM often results in a characteristic maculopapular rash. * **Complication:** Splenic rupture is a rare but serious complication; patients should avoid contact sports for 3–4 weeks.

Question 26: Which of the following is NOT a contraindication to DPT vaccination?

A. Local reaction to a previous DPT dose (Correct Answer)
B. High fever following a previous DPT dose
C. Infantile spasms
D. Seizures after a previous DPT dose

Explanation: The DPT (Diphtheria, Pertussis, and Tetanus) vaccine, specifically the whole-cell pertussis component, is highly reactogenic. Distinguishing between minor side effects and absolute contraindications is a high-yield topic for NEET-PG. ### **Explanation of the Correct Answer** **Option A (Local reaction)** is the correct answer because minor local reactions (redness, swelling, or pain at the injection site) are considered **common side effects**, not contraindications. These reactions do not increase the risk of serious adverse events in subsequent doses. Vaccination should proceed as scheduled. ### **Analysis of Incorrect Options (Contraindications)** The following are considered absolute or relative contraindications/precautions due to the risk of neurological complications associated with the pertussis component: * **Option B (High fever >105°F/40.5°C):** A history of high fever within 48 hours of a previous dose is a precaution. It indicates a severe systemic response that may predispose the child to febrile seizures. * **Option C (Infantile Spasms):** Any progressive or unstable neurological disorder (e.g., uncontrolled epilepsy, infantile spasms, or progressive encephalopathy) is a contraindication until the condition is stabilized. * **Option D (Seizures):** Seizures occurring within 3 days of a previous DPT dose are a major precaution. In such cases, the pertussis component is usually dropped, and **DT (Diphtheria-Tetanus)** is administered instead. ### **NEET-PG High-Yield Pearls** * **Absolute Contraindication:** Encephalopathy (e.g., coma, prolonged seizures) within 7 days of a previous pertussis vaccine that is not attributable to another cause. * **Switching Vaccines:** If a child reacts poorly to DTwP (whole-cell), **DTaP (acellular)** is a safer alternative as it has fewer side effects, though it is more expensive. * **False Contraindications:** Mild respiratory infections, malnutrition, or a family history of seizures are **NOT** contraindications to DPT.

Question 27: Which vaccines are not recommended for an 8-year-old unimmunized child?

A. Pertussis
B. Salk vaccine
C. BCG vaccine
D. All of the above (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. All of the above**, based on the age-specific recommendations for immunization in older children. 1. **Pertussis (Option A):** The whole-cell Pertussis vaccine (wP) is generally not recommended for children above **7 years of age** due to an increased risk of severe local and systemic reactions (fever, soreness). In older children and adults, the acellular form with reduced antigen content (**Tdap**) is preferred over the standard DTwP/DTaP. 2. **Salk vaccine (IPV) (Option B):** According to the National Immunization Schedule (NIS) and WHO guidelines, the primary focus for Polio vaccination is children under 5 years. In an unimmunized 8-year-old, the risk of Vaccine-Associated Paralytic Polio (VAPP) and the epidemiological shift make routine IPV less of a priority compared to the primary series in infancy, though some private guidelines (IAP) may offer it up to age 18 in specific catch-up scenarios. 3. **BCG vaccine (Option C):** BCG is most effective in preventing severe forms of childhood tuberculosis (miliary and meningeal TB). It is recommended at birth or up to **1 year of age** under the National Immunization Schedule. Beyond age 1, its protective efficacy diminishes significantly, and it is generally not recommended for an 8-year-old. **High-Yield Clinical Pearls for NEET-PG:** * **Age Cut-off for DTwP:** 7 years. Use Tdap for catch-up in older children. * **BCG Limit:** 1 year (National Schedule); however, some guidelines allow it up to 5 years if the child is Mantoux negative, but never routinely at age 8. * **Catch-up Immunization:** For a child >7 years, the standard catch-up includes Td (Tetanus-Diphtheria), Hepatitis B, and MMR. * **Live Vaccines:** Always contraindicated in pregnancy and severe immunocompromised states (except HIV with CD4 >15%).

Question 28: Koplik spots are pathognomonic of which disease?

A. Measles (Correct Answer)
B. Present on the buccal mucosa opposite the upper molars
C. Always present in the prodromal phase
D. All of the above

Explanation: **Explanation:** **Koplik spots** are considered the **pathognomonic** (diagnostic) sign of **Measles (Rubeola)**. They are small, irregular, bluish-white spots on an erythematous base, often described as "grains of salt on a red background." 1. **Why Option A is correct:** Koplik spots are unique to Measles. They appear during the **prodromal phase**, approximately 48 hours before the characteristic maculopapular rash develops. Their presence allows for a definitive clinical diagnosis even before the rash appears. 2. **Why Option B and C are incorrect (in the context of the question):** While Option B describes the correct location and Option C describes the correct timing, the question asks which **disease** they are pathognomonic of. Therefore, "Measles" is the specific answer required. (Note: In some MCQ formats, if the question asks "Which of the following is true regarding Koplik spots?", "All of the above" might be correct, but here the focus is the disease entity). **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Most commonly found on the buccal mucosa opposite the **lower second molars** (though they can spread). * **Timeline:** They appear 2 days before the rash and typically disappear within 1–2 days after the rash starts. * **Measles Triad (3 C's):** Cough, Coryza, and Conjunctivitis (seen in the prodromal phase). * **Rash Progression:** The Measles rash is cephalocaudal (starts behind the ears/hairline and spreads downwards) and fades with brownish discoloration and desquamation. * **Vitamin A:** Supplementation is recommended for all children with Measles to reduce morbidity and mortality.

Question 29: A 3-year-old child presents with symptoms of influenza. Aspirin is contraindicated in this patient due to the increased risk of which of the following conditions?

A. Gastric bleeding
B. Thrombocytopenia
C. Fanconi syndrome
D. Reye's syndrome (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Reye's syndrome** **Mechanism and Rationale:** Reye’s syndrome is a rare but life-threatening condition characterized by **acute encephalopathy** and **fatty degeneration of the liver**. It is strongly associated with the use of **salicylates (Aspirin)** in children and adolescents during viral prodromes, most commonly **Influenza (Type B)** and **Varicella (Chickenpox)**. The underlying pathophysiology involves **mitochondrial dysfunction**, leading to impaired fatty acid oxidation. This results in hyperammonemia and cerebral edema. Clinically, it presents with protracted vomiting followed by altered mental status, seizures, and hepatomegaly without jaundice. **Analysis of Incorrect Options:** * **A. Gastric bleeding:** While aspirin causes gastric irritation and bleeding in adults due to COX-1 inhibition, it is not the primary reason for its absolute contraindication in pediatric viral infections. * **B. Thrombocytopenia:** Aspirin causes irreversible inhibition of platelet aggregation (anti-platelet effect), but it does not typically cause a decrease in the absolute platelet count (thrombocytopenia). * **C. Fanconi syndrome:** This is a disorder of proximal renal tubular function. While certain drugs (like expired tetracycline or cisplatin) can cause it, aspirin is not a recognized trigger. **High-Yield Clinical Pearls for NEET-PG:** * **Biochemical Hallmarks:** Elevated serum ammonia, prolonged Prothrombin Time (PT/INR), and elevated AST/ALT with **normal bilirubin**. * **Liver Biopsy Findings:** Microvesicular steatosis (small fat droplets in hepatocytes). * **Exceptions:** Aspirin is still used in children for specific conditions like **Kawasaki Disease** and **Juvenile Idiopathic Arthritis (JIA)**, under strict supervision. * **Drug of Choice:** Acetaminophen (Paracetamol) or Ibuprofen are the preferred antipyretics in children with viral fever.

Question 30: Which of the following is a characteristic feature of Henoch-Schönlein Purpura?

A. Blood in stool (Correct Answer)
B. Thrombocytopenia
C. Intracranial hemorrhage
D. Susceptibility to infection

Explanation: **Explanation:** **Henoch-Schönlein Purpura (HSP)**, now commonly termed IgA Vasculitis, is the most common systemic vasculitis in children. It is a small-vessel vasculitis characterized by the deposition of **IgA-dominant immune complexes**. **Why "Blood in stool" is correct:** Gastrointestinal involvement occurs in approximately 75% of patients. The vasculitis affects the splanchnic circulation, leading to mucosal edema and submucosal hemorrhage. This clinically manifests as colicky abdominal pain, vomiting, and **hematochezia (blood in stool)** or melena. A significant complication to remember for exams is **ileo-colic intussusception**, where the submucosal hemorrhage acts as a lead point. **Analysis of Incorrect Options:** * **B. Thrombocytopenia:** HSP is a **non-thrombocytopenic purpura**. In fact, the platelet count is typically normal or even elevated (as an acute phase reactant). This is a crucial diagnostic differentiator from Immune Thrombocytopenic Purpura (ITP). * **C. Intracranial hemorrhage:** While serious, this is an extremely rare complication of HSP. It is more commonly associated with severe thrombocytopenia (like ITP) or vascular malformations. * **D. Susceptibility to infection:** HSP is an immune-mediated reaction (often following a URI), not an immunodeficiency state. **NEET-PG High-Yield Pearls:** * **Classic Tetrad:** Palpable purpura (without thrombocytopenia), Arthritis/Arthralgia, Abdominal pain, and Renal involvement (Hematuria). * **Skin:** Purpura is typically distributed over dependent areas (buttocks and lower extremities). * **Renal:** HSP Nephritis is histologically identical to **IgA Nephropathy (Berger’s disease)**. * **Diagnosis:** Primarily clinical; Biopsy (if done) shows **Leukocytoclastic vasculitis** with IgA deposits on immunofluorescence.

Practice by Chapter

Vaccine-Preventable Diseases

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Immunization Schedule

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Common Childhood Infections

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Pediatric HIV

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Congenital Infections

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Fever in Infants and Children

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Meningitis and Encephalitis

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Respiratory Tract Infections

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Gastrointestinal Infections

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Parasitic Infections

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Tuberculosis in Children

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Opportunistic Infections

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