Infectious Diseases Practice Questions

Q: All of the following are seen in Legionnaire's disease except?

Unilateral pneumonitis. Legionnaire’s disease, caused by *Legionella pneumophila*, is a multisystem illness characterized by atypical pneumonia. The correct answer is **Unilateral pneumonitis** because the radiological hallmark of Legionnaire’s disease is typically **patchy, rapidly progressive, and often bilateral infiltrates**, rather than localized unilateral involvement. **Why Option D is correct:** While the disease may start as a focal infiltrate, it characteristically progresses to involve multiple lobes or both lungs [1]. Pleural effusions are also common. Therefore, "unilateral pneumonitis" is the least characteristic feature among the choices. **Why other options are incorrect:** * **Fever (A):** High-grade fever (often >40°C) is a classic feature. A key diagnostic clue is **Faget’s sign** (relative bradycardia), where the heart rate does not increase proportionally with the fever. * **Mental Confusion (B):** Neurological symptoms, particularly headache and confusion/encephalopathy, are common extrapulmonary manifestations that distinguish Legionella from other bacterial pneumonias [1]. * **Diarrhoea (C):** Gastrointestinal symptoms are highly characteristic. Watery, non-bloody diarrhea often precedes the respiratory symptoms. **High-Yield Clinical Pearls for NEET-PG:** * **Hyponatremia:** This is the most characteristic laboratory finding in Legionnaire’s disease (due to SIADH or renal loss). * **Diagnosis:** The **Urinary Antigen Test** is the most common rapid diagnostic tool (detects Serogroup 1). * **Culture:** Requires **BCYE (Buffered Charcoal Yeast Extract) agar** supplemented with L-cysteine and iron. * **Treatment:** Macrolides (Azithromycin) or Respiratory Fluoroquinolones (Levofloxacin) are the drugs of choice. Beta-lactams are ineffective as the organism is intracellular.

Q: What is the diagnostic test for Zollinger-Ellison syndrome?

Secretin test. Zollinger-Ellison Syndrome (ZES) is caused by a gastrin-secreting tumor (gastrinoma), leading to hypergastrinemia and severe peptic ulcer disease [1]. **Why Secretin Test is the Correct Answer:** The **Secretin Stimulation Test** is the most sensitive and specific provocative test for ZES. Under normal physiological conditions, secretin inhibits gastrin release from G-cells. However, in gastrinoma cells, secretin paradoxically stimulates the release of gastrin. A positive test is defined as an increase in serum gastrin levels of **>200 pg/mL** above the baseline after secretin injection. **Analysis of Incorrect Options:** * **Standard Test Meal:** In ZES, gastrin levels do not significantly increase after a meal because the secretion is autonomous. This test is more useful in diagnosing G-cell hyperplasia, where gastrin levels rise by >50%. * **ACTH Infusion:** This is used to evaluate adrenal function (e.g., Addison’s disease or Cushing’s syndrome [2]) and has no role in diagnosing gastrinomas. * **Calcium Infusion:** While calcium can stimulate gastrin release from a gastrinoma, it is less sensitive and more hazardous (due to hypercalcemia) than the secretin test. It is reserved for cases where ZES is strongly suspected but the secretin test is negative. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Most gastrinomas are found in the **"Gastrinoma Triangle"** (bounded by the cystic duct, junction of the 2nd and 3rd parts of the duodenum, and the neck of the pancreas). * **Association:** Approximately 25% of ZES cases are associated with **Multiple Endocrine Neoplasia type 1 (MEN1)**. * **Initial Screening:** The first step in diagnosis is measuring **Fasting Serum Gastrin (FSG)** levels (usually >1000 pg/mL) while the patient is off Proton Pump Inhibitors (PPIs) [1]. * **Localization:** Somatostatin Receptor Scintigraphy (Octreotide scan) is the preferred imaging modality to locate the tumor [3].

Q: A patient presents with lower gastrointestinal bleeding. Sigmoidoscopy shows ulcers in the sigmoid. Biopsy from this area shows flask-shaped ulcers. Which of the following is the most appropriate treatment?

Intravenous metronidazole. **Explanation:** The clinical presentation of lower gastrointestinal bleeding combined with the pathognomonic finding of **flask-shaped ulcers** on biopsy is diagnostic of **Amoebic Colitis**, caused by *Entamoeba histolytica* [1]. 1. **Why Option B is correct:** *Entamoeba histolytica* trophozoites invade the intestinal mucosa, causing lateral spread in the submucosa, which creates the classic "flask-shaped" appearance. **Metronidazole** (or Tinidazole) is the drug of choice for invasive amoebiasis as it is a potent tissue amoebicide. In cases of severe colitis or systemic symptoms, intravenous administration is preferred to ensure rapid therapeutic levels. 2. **Why the other options are incorrect:** * **Option A (Ceftriaxone):** This is a third-generation cephalosporin used for bacterial infections like Enteric fever or Shigellosis. It has no activity against protozoa like *E. histolytica*. * **Options C & D (Steroids/Sulphasalazine):** These are used to treat Inflammatory Bowel Disease (IBD), specifically Ulcerative Colitis [2]. While IBD also presents with bloody diarrhea and ulcers, the biopsy would show crypt abscesses rather than flask-shaped ulcers. Importantly, giving steroids in a case of amoebiasis can lead to toxic megacolon or perforation. **Clinical Pearls for NEET-PG:** * **Pathology:** The "flask shape" occurs because the organism cannot easily penetrate the muscularis propria, leading to lateral expansion in the submucosa. * **Diagnosis:** Stool microscopy may show trophozoites with ingested RBCs (erythrophagocytosis) [1]. * **Treatment Protocol:** Always follow a tissue amoebicide (Metronidazole) with a **luminal amoebicide** (e.g., Diloxanide furoate or Paromomycin) to eradicate the cyst stage and prevent relapse/transmission. * **Complication:** The most common extra-intestinal manifestation is an Amoebic Liver Abscess (anchovy sauce pus) [1].

Q: Which of the following is NOT a characteristic feature of cerebral malaria?

Bloody cerebrospinal fluid. **Explanation:** Cerebral malaria is a severe neurological complication of *Plasmodium falciparum* infection, characterized by unarousable coma (Glasgow Coma Scale <11) in the absence of other identifiable causes [2]. **Why "Bloody Cerebrospinal Fluid" is the correct answer:** In cerebral malaria, the cerebrospinal fluid (CSF) is typically **clear and colorless**. While there may be a mild increase in opening pressure and a slight elevation in protein levels (<100 mg/dL), the CSF cell count is usually normal (pleocytosis is rare). The presence of bloody or xanthochromic CSF suggests an alternative diagnosis, such as subarachnoid hemorrhage or a traumatic tap, and is **not** a feature of malaria [1]. **Analysis of Incorrect Options:** * **Retinal Hemorrhages:** This is a key diagnostic and prognostic marker. "Malarial retinopathy" (including retinal whitening, vessel changes, and hemorrhages) is highly specific for cerebral malaria and correlates with the severity of brain sequestration. * **Extensor Plantar Reflex:** Upper motor neuron signs are common. Patients often exhibit decerebrate or decorticate posturing, hyperreflexia, and a positive Babinski sign (extensor plantar response) due to diffuse encephalopathy. * **Absent Abdominal Reflex:** This is a classic clinical finding in cerebral malaria, reflecting the involvement of the corticospinal tracts. **High-Yield NEET-PG Pearls:** * **Pathogenesis:** Sequestration of parasitized RBCs in cerebral microvasculature (cytoadherence via PfEMP-1) [3]. * **Drug of Choice:** Intravenous **Artesunate** is the gold standard (preferred over Quinine). * **Hypoglycemia:** Always check blood glucose, as both the disease and Quinine treatment can cause severe hypoglycemia [2]. * **Mortality:** Even with treatment, mortality remains 15–20%.

Q: What is the least common cause of sporadic encephalitis?

Rhinovirus. The correct answer is **D. Rhinovirus**. **Medical Concept:** Sporadic encephalitis refers to isolated cases of brain inflammation occurring year-round, independent of seasonal outbreaks. While many viruses are neurotropic (capable of infecting nerve tissue), **Rhinovirus** is primarily restricted to the upper respiratory tract. It thrives at temperatures slightly below core body temperature (33–35°C) and lacks the typical mechanisms to cross the blood-brain barrier. While extremely rare case reports exist in immunocompromised individuals, it is not considered a standard or recognized cause of sporadic encephalitis in clinical practice. **Analysis of Options:** * **HSV (Option A):** Herpes Simplex Virus-1 is the **most common cause** of sporadic fatal encephalitis worldwide [1]. It typically involves the temporal lobes [1]. * **VZV (Option B):** Varicella-Zoster Virus is a significant cause of sporadic encephalitis, often occurring during primary infection (chickenpox) or reactivation (shingles), frequently associated with vasculopathy. * **Arboviruses (Option C):** While many arboviruses (like Japanese Encephalitis) are epidemic/seasonal, several can present sporadically depending on geographic location and vector prevalence. They are well-established neurotropic pathogens. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of sporadic encephalitis:** HSV-1. * **Most common cause of epidemic encephalitis in India:** Japanese Encephalitis (JE) virus. * **Gold Standard Diagnosis:** CSF PCR for viral DNA/RNA. * **Imaging Choice:** MRI is superior to CT; look for temporal lobe involvement in HSV [1]. * **Treatment:** Empiric Acyclovir should be started immediately if encephalitis is suspected.

Question 1

An HIV patient developed goiter. On examination, there was non-tender diffuse enlargement of the thyroid. All of the following can be causes of this condition, except:

Accepted Answer

Aspergillus

Answer

Toxoplasma

Answer

Cryptococcus

Answer

Pneumocystis

Question 2

All of the following are seen in Legionnaire's disease except?

Accepted Answer

Unilateral pneumonitis

Answer

Fever

Answer

Mental confusion

Answer

Diarrhoea

Question 3

What is an early manifestation of a patient infected with HIV virus?

Accepted Answer

Unexplained fear and weight loss

Answer

Elevation of p16

Answer

Kaposi's sarcoma

Answer

Hairy cell leukoplakia

Question 4

What is the diagnostic test for Zollinger-Ellison syndrome?

Accepted Answer

Secretin test

Answer

Standard test meal

Answer

ACTH infusion

Answer

Calcium infusion

Question 5

A patient presents with lower gastrointestinal bleeding. Sigmoidoscopy shows ulcers in the sigmoid. Biopsy from this area shows flask-shaped ulcers. Which of the following is the most appropriate treatment?

Accepted Answer

Intravenous metronidazole

Answer

Intravenous ceftriaxone

Answer

Intravenous steroids and sulphasalazine

Answer

Hydrocortisone enemas

Question 6

What is the recommended duration of treatment for multidrug-resistant tuberculosis (MDR-TB)?

Accepted Answer

16-24 months

Answer

8-12 months

Answer

12-16 months

Answer

2-3 years

Question 7

Which of the following is NOT a characteristic feature of cerebral malaria?

Accepted Answer

Bloody cerebrospinal fluid

Answer

Retinal hemorrhages

Answer

Extensor plantar reflex

Answer

Absent abdominal reflex

Question 8

Hemolysis is most severe with Plasmodium falciparum infection compared to other malarial parasites because of which of the following?

Accepted Answer

Ability of the parasite to infect red blood cells of all ages

Answer

Associated gram-negative bacteremia

Answer

Ability of the organism to infect selectively reticulocytes

Answer

Ability of the organism to escape immune recognition by the immune system

Question 9

What is the least common cause of sporadic encephalitis?

Accepted Answer

Rhinovirus

Answer

Herpes Simplex Virus (HSV)

Answer

Varicella-Zoster Virus (VZV)

Answer

Arbovirus

Question 10

A 31-year-old man with AIDS complains of difficulty in swallowing. Examination of his oral cavity demonstrates whitish membranes covering much of his tongue and palate. Endoscopy also reveals several whitish, ulcerated lesions in the esophagus. These pathologic findings are fundamentally caused by loss of which of the following immune cells?

Accepted Answer

Helper T lymphocytes

Answer

B lymphocytes

Answer

Killer T lymphocytes

Answer

Monocytes/macrophages

Infectious Diseases — MCQs

Infectious Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?