Infectious Diseases Practice Questions

Q: A 2-year-old boy presents in late summer with a 2-day history of painful, ulcerative lesions of the mouth and a 1-day history of fever up to 103°F. He refuses to eat. On examination, he is irritable with a temperature of 102°F and has numerous erythematous, ulcerative lesions on the buccal mucosa and tongue. What is the most likely diagnosis?

Herpetic gingivostomatitis. **Explanation:** **Herpetic Gingivostomatitis** is the most common manifestation of primary **Herpes Simplex Virus type 1 (HSV-1)** infection in children, typically occurring between ages 6 months and 5 years. **Why it is the correct answer:** The clinical presentation is classic: high-grade fever, irritability, and painful ulcerative lesions. Key diagnostic features include the involvement of the **buccal mucosa, tongue, and gingiva** (which often becomes friable and bleeds). The refusal to eat (odynophagia) due to pain is a hallmark sign. Unlike herpangina, which is seasonal, HSV can occur year-round, though it often presents with more severe systemic symptoms and anterior oral involvement. **Why the other options are incorrect:** * **Herpangina:** Caused by Coxsackievirus A. While it also presents with fever and ulcers, the lesions are typically localized to the **posterior pharynx** (soft palate, tonsillar pillars, and uvula), sparing the buccal mucosa and gingiva. * **Aphthous stomatitis:** These are "canker sores." They are usually recurrent, not associated with high-grade fever or systemic toxicity, and typically present as solitary or few ulcers rather than diffuse stomatitis. * **Candidal gingivostomatitis:** Oral thrush presents as white, curd-like plaques that can be scraped off, leaving an erythematous base. It is usually painless and rarely causes high fever unless associated with systemic immunodeficiency. **NEET-PG High-Yield Pearls:** * **Tzanck Smear:** Shows **multinucleated giant cells** and Cowdry type A inclusion bodies (diagnostic for HSV/VZV). * **Treatment:** Supportive care (hydration) is primary; oral **Acyclovir** is effective if started within 72 hours of onset. * **Complication:** Watch for **Dehydration** (most common) and **Herpetic Whitlow** (autoinoculation of the finger).

Q: Perinatal transmission of Hepatitis B is maximum when infection in the mother occurs in which period?

3rd trimester. **Explanation:** The risk of vertical transmission of Hepatitis B Virus (HBV) is directly proportional to the gestational age at which maternal infection occurs. **Why the 3rd Trimester is Correct:** The rate of transmission is highest (approximately **60–90%**) if the mother acquires acute Hepatitis B during the **third trimester** or the immediate postpartum period. This is primarily because the majority of perinatal transmission occurs during labor and delivery (peripartum) through contact with maternal blood and vaginal secretions. If the mother is acutely infected close to the time of delivery, her viral load is at its peak, and there is insufficient time for maternal antibodies to develop and provide passive protection to the fetus. **Analysis of Incorrect Options:** * **1st Trimester:** The risk of transmission is lowest here (approx. **10%**). While the virus can cross the placenta, it is less common early in pregnancy. * **2nd Trimester:** The risk is intermediate (approx. **25–30%**). * **Lactation:** Although HBV is present in breast milk, breastfeeding does not pose an additional risk of transmission to the infant, especially if the infant has received the HBV vaccine and Hepatitis B Immune Globulin (HBIG). **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Route:** In endemic areas, the most common route of HBV transmission is **vertical (perinatal)**. * **Chronic Carrier State:** The younger the age of acquisition, the higher the risk of chronicity. Infants infected perinatally have a **90% risk** of becoming chronic carriers. * **HBeAg Status:** Transmission risk is highest (90%) if the mother is **HBeAg positive** (indicating high replication) and lower (10–20%) if she is HBeAg negative. * **Management:** To prevent transmission, the newborn must receive both the **HBV vaccine** and **HBIG** within 12 hours of birth.

Q: All are complications of diphtheria, except?

Hepatic failure. **Explanation:** Diphtheria is caused by *Corynebacterium diphtheriae*, which produces a potent **exotoxin** that inhibits protein synthesis (via ADP-ribosylation of Elongation Factor-2). While the bacteria remain localized to the upper respiratory tract (forming a pseudomembrane), the toxin spreads hematogenously, primarily affecting the heart, nervous system, and kidneys. **Why Hepatic Failure is the correct answer:** Hepatic failure is **not** a recognized complication of diphtheria. The toxin specifically targets tissues with high concentrations of receptors for the toxin, such as cardiac and neural tissues. While systemic toxemia can cause general malaise, the liver is not a primary target organ for the diphtheria toxin. **Analysis of other options:** * **Myocarditis (Option A):** This is the most common and most serious complication, occurring in about 10–25% of patients. It typically appears in the second week and is a leading cause of death. * **Ocular muscle palsy (Option B):** Neurological complications are common. **Cranial nerve palsies** (especially involving the soft palate, ciliary muscles causing blurring of vision, and extraocular muscles) typically occur in the 3rd to 5th week. * **Cerebellar ataxia (Option C):** While less common than peripheral neuropathy or palatal palsy, post-diphtheritic neurological involvement can rarely manifest as ataxia or encephalopathy due to the neurotoxic effects of the exotoxin. **NEET-PG High-Yield Pearls:** * **Most common cause of death:** Myocarditis. * **First sign of neurological involvement:** Palatal palsy (nasal twang/regurgitation). * **Treatment Priority:** Administer **Diphtheria Antitoxin (DAT)** immediately based on clinical suspicion; do not wait for culture results. * **Antibiotic of choice:** Erythromycin or Penicillin G (used to stop toxin production and prevent spread, but does not neutralize circulating toxin).

Q: What is the recommended single dose of Albendazole for a 10-year-old child being treated for roundworm infestation?

400 mg. **Explanation:** The correct answer is **400 mg (Option B)**. Albendazole is a broad-spectrum anthelmintic agent that works by inhibiting tubulin polymerization, leading to the metabolic disruption and death of the helminth. According to the World Health Organization (WHO) and the National Deworming Day (NDD) guidelines in India, the dosing for Albendazole in soil-transmitted helminth (STH) infections like *Ascaris lumbricoides* (roundworm) is age-dependent: * **Children aged 12–24 months:** 200 mg (half tablet) as a single dose. * **Children aged >24 months (2 years) to adults:** 400 mg (single tablet) as a single dose. Since the child in the question is 10 years old, the standard adult dose of 400 mg is indicated. **Analysis of Incorrect Options:** * **Option A (200 mg):** This is the recommended dose for children between 12 and 24 months of age. * **Options C and D (1 g and 2 g):** These doses are excessively high for a single treatment of roundworm and carry a significant risk of toxicity without added therapeutic benefit. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Binds to β-tubulin, inhibiting microtubule synthesis. * **Drug of Choice (DOC):** Albendazole is the DOC for Ascariasis, Hookworm, Enterobiasis (Pinworm), and Neurocysticercosis. * **Neurocysticercosis Dosing:** Unlike the single dose for worms, treatment for neurocysticercosis requires 15 mg/kg/day (max 800 mg) for 8–30 days, often co-administered with steroids to prevent inflammatory reactions. * **Contraindication:** Albendazole is generally avoided in the first trimester of pregnancy (teratogenic potential).

Q: A 12-year-old boy presents with fever, sore throat, and cervical lymph node enlargement. A throat swab is positive for group A beta-hemolytic streptococci, and he is started on penicillin. However, his symptoms worsen despite treatment. What is the next best step?

Perform a blood monospot test and CBC. **Explanation:** The clinical presentation of fever, sore throat, and cervical lymphadenopathy is classic for both **Streptococcal Pharyngitis** and **Infectious Mononucleosis (IM)** caused by the Epstein-Barr Virus (EBV). The key diagnostic challenge here is that approximately **30% of patients with IM are co-colonized with Group A Streptococcus (GAS)**. The failure to improve on penicillin, combined with worsening symptoms, strongly suggests that the primary underlying pathology is IM rather than a simple bacterial infection. Therefore, the next best step is to confirm the diagnosis of IM using a **Monospot test** (to detect heterophile antibodies) and a **CBC** (to look for absolute lymphocytosis and atypical lymphocytes/Downey cells). **Analysis of Options:** * **Option A:** Switching to another antibiotic like Azithromycin is incorrect because the lack of response to Penicillin (the gold standard for GAS) suggests a non-bacterial etiology. * **Option C:** IgE levels are markers for allergic reactions, not IM. EBV-specific serology involves IgM/IgG against Viral Capsid Antigen (VCA), not IgE. * **Option D:** While IM is suspected, Acyclovir is not routinely recommended as it does not provide clinical benefit. Prednisolone is reserved only for complications like airway obstruction or severe thrombocytopenia. **High-Yield Pearls for NEET-PG:** 1. **The "Ampicillin Rash":** If a patient with IM is mistakenly treated with Ampicillin or Amoxicillin, 70–90% develop a characteristic maculopapular rash. 2. **Atypical Lymphocytes:** These are T-cells (CD8+) reacting against EBV-infected B-cells. 3. **Splenomegaly:** Patients must be advised to avoid contact sports for 3–4 weeks to prevent splenic rupture. 4. **Diagnosis:** Monospot test is the screening test of choice in adolescents; EBV-specific antibodies are preferred in children <4 years (who often have negative Monospot results).

Q: All of the following are true regarding congenital syphilis EXCEPT?

Conductive hearing loss. **Explanation:** Congenital syphilis is caused by the transplacental transmission of *Treponema pallidum*. The manifestations are traditionally divided into **Early** (appearing before 2 years of age) and **Late** (appearing after 2 years). **Why Option C is the correct answer (The Exception):** Congenital syphilis is associated with **Sensorineural hearing loss**, not conductive hearing loss. This occurs due to eighth cranial nerve (vestibulocochlear) involvement or labyrinthitis. It typically presents in late childhood or adolescence and is a key component of the classic **Hutchinson’s Triad** (Interstitial keratitis, Sensorineural deafness, and Hutchinson’s teeth). **Analysis of Incorrect Options:** * **Option A (Rhinitis):** Also known as "snuffles," this is often the **earliest** clinical sign of congenital syphilis. It is characterized by a highly infectious mucopurulent or bloody nasal discharge. * **Option B (Notched incisors):** Known as **Hutchinson’s teeth**, these are permanent upper central incisors that are peg-shaped, widely spaced, and notched. This is a classic late manifestation. * **Option D (Linear scars):** Known as **Rhagades**, these are linear scars at the angles of the mouth, nose, or anus resulting from the healing of painful fissures (syphilitic rhagades) seen in the neonatal period. **High-Yield Clinical Pearls for NEET-PG:** * **Hutchinson’s Triad:** Interstitial keratitis, 8th nerve deafness, Hutchinson’s teeth. * **Bone Signs:** Wimberger’s sign (localized destruction of the medial proximal tibial metaphysis) and Parrot’s pseudoparalysis (due to painful osteochondritis). * **Mulberry Molars:** Pitting of the occlusal surfaces of the first molars. * **Saddle Nose:** Deformity caused by the destruction of the nasal septum. * **Treatment:** Penicillin G is the drug of choice for all stages.

Q: A child presents with fever for 2 days, altered sensorium, and purpuric rashes. His blood pressure is 90/60 mmHg. What is the treatment of choice?

IV Penicillin. ### Explanation **Correct Answer: C. IV Penicillin** The clinical triad of **fever, altered sensorium, and purpuric rashes** (petechiae or ecchymoses) is the classic presentation of **Meningococcemia** (caused by *Neisseria meningitidis*). The presence of purpura indicates a medical emergency, often progressing to Waterhouse-Friderichsen syndrome (adrenal hemorrhage and shock). **Why IV Penicillin?** Historically and for exam purposes, **IV Penicillin G** remains the treatment of choice for confirmed meningococcal disease due to its high efficacy and narrow spectrum. In empirical settings, third-generation cephalosporins (Ceftriaxone) are often used, but Penicillin is the definitive classic answer for *N. meningitidis*. It works by inhibiting bacterial cell wall synthesis. **Why the other options are incorrect:** * **A & B (IV Quinine / IV Artesunate):** These are treatments for severe/complicated **Malaria**. While cerebral malaria causes fever and altered sensorium, it does not typically present with a rapidly progressing purpuric rash. * **D (Chloroquine):** This is used for uncomplicated *P. vivax* malaria. It has no role in treating bacterial sepsis or meningococcemia. **Clinical Pearls for NEET-PG:** * **Drug of Choice for Chemoprophylaxis (Close Contacts):** Rifampicin (Adults/Children). Ciprofloxacin or Ceftriaxone are alternatives. * **Most Common Serogroup in India:** Historically Serogroup A; globally, Serogroups B and C are common. * **Characteristic Rash:** "Non-blanching" purpuric spots, often starting on the trunk and lower extremities. * **Initial Empirical Choice:** If the question asks for the *initial* empirical management before the organism is known, Ceftriaxone is preferred. However, for the specific entity of Meningococcemia, Penicillin is the gold standard.

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

Infectious mononucleosis. ### Explanation The clinical presentation of acute fever, lymphadenopathy, and significant lymphocytosis in a child is a classic triad for **Infectious Mononucleosis (IM)**, most commonly caused by the Epstein-Barr Virus (EBV). **Why Option A is Correct:** Infectious mononucleosis typically presents with the "mononucleosis triad": fever, pharyngitis, and lymphadenopathy (usually posterior cervical). A key hematological hallmark is **absolute lymphocytosis** (often >50% of the total WBC count) with at least **10% atypical lymphocytes** (Downey cells). These atypical cells are actually activated T-lymphocytes reacting against EBV-infected B-cells. **Why Other Options are Incorrect:** * **Option B (ALL):** While ALL presents with lymphadenopathy and fever, the "lymphocytosis" in leukemia consists of **lymphoblasts** (immature cells), not mature atypical lymphocytes. Furthermore, ALL is usually associated with cytopenias (anemia, thrombocytopenia), which are absent here. * **Option C (Pulmonary TB):** TB typically presents with chronic (not acute) lymphadenopathy, night sweats, and weight loss. While it causes lymphocytosis, it does not typically present with the acute febrile syndrome described. * **Option D (Alpha-hemolytic Strep):** Bacterial infections usually cause **neutrophilia** with a "left shift" (increased band cells), rather than lymphocytosis. **NEET-PG High-Yield Pearls:** * **Diagnostic Test:** The **Monospot test** (Heterophile antibody test) is the initial screening test of choice. * **Atypical Lymphocytes:** Also seen in CMV, Toxoplasmosis, and Viral Hepatitis, but EBV is the most common cause. * **Clinical Caution:** Avoid prescribing **Ampicillin or Amoxicillin** in suspected IM, as it frequently causes a characteristic maculopapular rash. * **Complication:** Splenic rupture is a rare but serious complication; patients should avoid contact sports for 3–4 weeks.

Question 1

A 2-year-old boy presents in late summer with a 2-day history of painful, ulcerative lesions of the mouth and a 1-day history of fever up to 103°F. He refuses to eat. On examination, he is irritable with a temperature of 102°F and has numerous erythematous, ulcerative lesions on the buccal mucosa and tongue. What is the most likely diagnosis?

Accepted Answer

Herpetic gingivostomatitis

Answer

Herpangina

Answer

Aphthous stomatitis

Answer

Candidal gingivostomatitis

Question 2

Perinatal transmission of Hepatitis B is maximum when infection in the mother occurs in which period?

Accepted Answer

3rd trimester

Answer

1st trimester

Answer

2nd trimester

Answer

Lactation

Question 3

A 3-year-old boy presents with a 1-day history of loose stools, fever, abdominal cramping, headache, and myalgia. He has no blood in the stool. A careful history reveals that he has several pet turtles. Which of the following is most likely the causative agent of his diarrhea?

Accepted Answer

Salmonella spp

Answer

Chlamydia psittaci

Answer

Entamoeba histolytica

Answer

Staphylococcus aureus

Question 4

All are complications of diphtheria, except?

Accepted Answer

Hepatic failure

Answer

Myocarditis

Answer

Ocular muscle palsy

Answer

Cerebellar ataxia

Question 5

A 5-year-old girl presents with a several-day history of localized swelling in the right side of her neck. There is no recent history of sore throat. Physical examination reveals a low-grade fever and one very tender, firm, slightly enlarged lymph node in the right cervical region. A CBC shows mild leukocytosis, and fine needle aspiration of the lymph node reveals scattered neutrophils. Which of the following is the most likely diagnosis?

Accepted Answer

Bacterial lymphadenitis

Answer

Granulomatous lymphadenitis

Answer

Necrotizing lymphadenitis

Answer

Toxoplasmic lymphadenitis

Question 6

What is the recommended single dose of Albendazole for a 10-year-old child being treated for roundworm infestation?

Accepted Answer

400 mg

Answer

200 mg

Answer

1 g

Answer

2 g

Question 7

A 12-year-old boy presents with fever, sore throat, and cervical lymph node enlargement. A throat swab is positive for group A beta-hemolytic streptococci, and he is started on penicillin. However, his symptoms worsen despite treatment. What is the next best step?

Accepted Answer

Perform a blood monospot test and CBC

Answer

Start azithromycin

Answer

Check IgE for infectious mononucleosis

Answer

Presume Epstein-Barr virus infection and start acyclovir and prednisolone

Question 8

All of the following are true regarding congenital syphilis EXCEPT?

Accepted Answer

Conductive hearing loss

Answer

Rhinitis is an early sign

Answer

Notched incisors

Answer

Linear scars at the angle of mouth

Question 9

A child presents with fever for 2 days, altered sensorium, and purpuric rashes. His blood pressure is 90/60 mmHg. What is the treatment of choice?

Accepted Answer

IV Penicillin

Answer

IV Quinine

Answer

IV Artesunate

Answer

Chloroquine

Question 10

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

Accepted Answer

Infectious mononucleosis

Answer

Acute lymphoblastic leukemia (ALL)

Answer

Pulmonary tuberculosis (Koch's)

Answer

Alpha-hemolytic Streptococcal infection

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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