Infectious Diseases Practice Questions

Q: A 24-year-old patient complains of diarrhea, vomiting, and abdominal pain aggravated on ingestion of food for 1 week. Stool microscopy reveals findings suggestive of parasitic infection. What is the appropriate treatment for this condition?

Ivermectin. ***Ivermectin*** - The combination of **diarrhea, vomiting, and abdominal pain** with stool microscopy showing **rhabditiform larvae** is pathognomonic of **Strongyloides stercoralis** infection. - **Ivermectin** is the **first-line treatment** for strongyloidiasis, with excellent efficacy against both intestinal and disseminated forms. *Tinidazole* - Primarily effective against **anaerobic bacteria** and **protozoa** like **Giardia** and **Entamoeba histolytica**. - Not effective against **helminths** like Strongyloides, which require antiparasitic agents with different mechanisms. *Praziquantel* - Specifically used for **trematode** (flukes) and **cestode** (tapeworm) infections like **Schistosoma** and **Taenia**. - Has **no activity** against **nematodes** like Strongyloides stercoralis, making it inappropriate for this case. *Niclofolan* - An **anthelmintic** primarily used for **liver flukes** and other **trematode infections** in veterinary medicine. - **Rarely used** in human medicine and **ineffective** against Strongyloides, which is a nematode parasite.

Q: What is the diagnostic test for group A streptococcal pharyngitis?

Bacitracin sensitivity. **Explanation:** The diagnosis of Group A Streptococcal (GAS) pharyngitis relies on identifying *Streptococcus pyogenes*. In the microbiology laboratory, **Bacitracin sensitivity** is the classic biochemical test used to differentiate GAS from other beta-hemolytic streptococci. * **Bacitracin Sensitivity (Correct):** *Streptococcus pyogenes* (Group A) is uniquely sensitive to low concentrations of bacitracin (0.04 units), showing a zone of inhibition around the disc. In contrast, Group B streptococci (*S. agalactiae*) are resistant. * **Bile Solubility Test (Incorrect):** This test is used to identify *Streptococcus pneumoniae*. *S. pneumoniae* possesses autolytic enzymes that are activated by bile salts, leading to the lysis of the colony. * **Catalase Test (Incorrect):** This is the primary test to differentiate *Staphylococci* (Catalase positive) from *Streptococci* (Catalase negative). All members of the *Streptococcus* genus are catalase-negative. * **Optochin Sensitivity (Incorrect):** This test differentiates *Streptococcus pneumoniae* (Optochin sensitive) from Viridans group streptococci (Optochin resistant). **High-Yield Clinical Pearls for NEET-PG:** * **PYR Test:** The Pyrrolidonyl Arylamidase (PYR) test is now considered more specific than Bacitracin for identifying GAS (GAS is PYR positive). * **ASO Titer:** Antistreptolysin O titers are used to diagnose **post-streptococcal sequelae** (like Rheumatic Fever), not acute pharyngitis. * **Centor Criteria:** Used clinically to estimate the probability of GAS pharyngitis (Fever, Tonsillar exudates, Tender anterior cervical lymphadenopathy, and Absence of cough). * **Complications:** Remember that while antibiotics prevent Rheumatic Fever, they do **not** prevent Post-Streptococcal Glomerulonephritis (PSGN).

Q: Hemorrhagic rashes are typically seen in which of the following conditions?

Meningococcal infection. Explanation: The correct answer is **Meningococcal infection**. This condition, caused by *Neisseria meningitidis*, is a classic cause of a rapidly progressing hemorrhagic rash. **1. Why Meningococcal infection is correct:** The hallmark of meningococcemia is a **petechial or purpuric rash**. The underlying mechanism is **disseminated intravascular coagulation (DIC)** and perivascular inflammation (vasculitis). Bacterial endotoxins trigger widespread endothelial damage, leading to capillary leak and microvascular thrombosis. This manifests clinically as non-blanching petechiae that can coalesce into large ecchymoses known as **purpura fulminans**. **2. Why the other options are incorrect:** * **Malaria:** While severe *P. falciparum* can cause DIC and bleeding manifestations in late stages, it typically presents with fever, chills, and anemia. A hemorrhagic rash is not a primary diagnostic feature. * **Enteric Fever (Typhoid):** This is associated with **"Rose Spots"**—faint, salmon-colored, blanching macules usually found on the trunk. They are not hemorrhagic. * **Pneumonia:** Typical bacterial pneumonia (e.g., *S. pneumoniae*) presents with cough, fever, and pleuritic chest pain. Skin rashes are not a standard feature unless associated with specific pathogens like *Mycoplasma* (Erythema Multiforme). **Clinical Pearls for NEET-PG:** * **Waterhouse-Friderichsen Syndrome:** Adrenal hemorrhage secondary to severe meningococcemia, leading to acute adrenal insufficiency and shock. * **Glass Test:** A simple bedside test where a glass tumbler is pressed against the rash; if the spots do not fade (non-blanching), it suggests a medical emergency like meningococcal sepsis. * **Other Hemorrhagic Fevers:** Always consider Dengue (thrombocytopenia) and Rickettsial diseases (Rocky Mountain Spotted Fever) in the differential diagnosis of petechial rashes [1].

Q: An 18-year-old college student presents with a sore throat, fever, fatigue, and loss of appetite. Examination reveals pharyngitis with cervical lymphadenopathy. Blood tests show lymphocytosis and the presence of heterophile antibodies. Which of the following best describes the virus responsible for this illness?

Double-stranded, enveloped DNA virus. ### Explanation **Diagnosis: Infectious Mononucleosis (IM)** The clinical triad of fever, pharyngitis, and lymphadenopathy in a young adult, combined with **heterophile antibodies** (Monospot test positive) and lymphocytosis (atypical lymphocytes), is pathognomonic for Infectious Mononucleosis caused by the **Epstein-Barr Virus (EBV)** [1]. **1. Why Option A is Correct:** EBV is a member of the *Herpesviridae* family (specifically Human Gammaherpesvirus 4). All Herpesviruses share a specific structure: they are **double-stranded, linear DNA viruses** surrounded by an icosahedral capsid and a lipid **envelope** derived from the host nuclear membrane. **2. Why the Other Options are Incorrect:** * **Option B:** Nonenveloped DS-DNA viruses include Adenovirus and Papillomavirus. While Adenovirus causes pharyngitis, it does not typically produce heterophile antibodies or significant lymphocytosis. * **Option C:** This describes viruses like Influenza, HIV, or Paramyxoviruses (Mumps/Measles). While they cause systemic symptoms, their genomic structure does not match EBV [2]. * **Option D:** This describes Parvovirus B19 (the only medically significant SS-DNA virus), which causes Erythema Infectiosum (Slapped-cheek rash), not IM [3]. **Clinical Pearls for NEET-PG:** * **Atypical Lymphocytes:** These are actually **CD8+ T-cells** reacting against infected B-cells (Downey cells) [1]. * **Receptor:** EBV enters B-cells via the **CD21** receptor (also known as CR2). * **The "Ampicillin Rash":** If a patient with IM is mistakenly treated for strep throat with Ampicillin or Amoxicillin, they often develop a characteristic maculopapular rash [4]. * **Complications:** Splenic rupture (avoid contact sports) and associations with malignancies like Burkitt Lymphoma and Nasopharyngeal Carcinoma [1].

Q: A patient is being investigated for chronic diarrhoea. Small intestinal mucosal biopsy shows PAS positive foamy macrophages. What is the probable diagnosis?

Whipple disease. **Explanation:** The presence of **PAS-positive foamy macrophages** in the lamina propria of the small intestine is the classic histopathological hallmark of **Whipple disease** [1]. This multisystemic illness is caused by the gram-positive bacterium *Tropheryma whipplei*. The PAS (Periodic Acid-Schiff) stain highlights the glycoprotein-rich cell walls of the partially digested bacteria within the lysosomes of macrophages. **Why the other options are incorrect:** * **Chronic amoebiasis:** Typically involves the colon (large intestine), not the small intestine [2]. Histology would show flask-shaped ulcers and trophozoites of *Entamoeba histolytica*, often containing ingested RBCs (erythrophagocytosis). * **Chronic giardiasis:** *Giardia lamblia* is an intraluminal parasite that attaches to the brush border. Diagnosis is made by identifying pear-shaped trophozoites in stool or duodenal aspirates; it does not cause PAS-positive macrophage infiltration. * **Intestinal sarcoidosis:** This is characterized by **non-caseating granulomas**, not foamy macrophages. While sarcoidosis can affect the GI tract, it is extremely rare compared to other manifestations. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Triad:** Diarrhea/Malabsorption, Weight loss, and Migratory large-joint Arthralgia [1]. * **Rule Out:** Always differentiate from *Mycobacterium avium-intracellulare* (MAI) infection in HIV patients, which also shows PAS-positive macrophages. However, MAI is **Acid-Fast Bacillus (AFB) positive**, whereas *T. whipplei* is **AFB negative**. * **Treatment:** Long-term antibiotics are required (usually Ceftriaxone followed by oral Trimethoprim-sulfamethoxazole for 1 year). * **Electron Microscopy:** Shows characteristic "trilaminar" cell wall organisms.

Q: Which of the following is not affected in leprosy?

Uterus. **Explanation:** The correct answer is **A. Uterus**. The underlying medical concept in Leprosy (Hansen’s disease), caused by *Mycobacterium leprae*, is its predilection for **cooler areas of the body**. *M. leprae* grows best at temperatures between 27°C and 33°C. Internal organs with high core body temperatures, such as the **uterus**, ovaries, lungs, and gastrointestinal tract, are characteristically spared. **Why the other options are incorrect:** * **Nerves (C):** Leprosy is primarily a disease of the peripheral nervous system [1]. The bacteria invade Schwann cells, leading to nerve thickening and sensory/motor loss [1]. This is a hallmark of the disease. * **Testes (B):** Unlike the uterus, the testes are located extra-abdominally in the scrotum, where the temperature is significantly lower than the core body temperature. This makes them a frequent site for systemic involvement, often leading to orchitis, atrophy, and infertility [1]. * **Eye (D):** The anterior segment of the eye is exposed to the environment and is cooler than the core body. Leprosy frequently affects the eyes through direct invasion or secondary to CN VII (facial nerve) palsy, leading to lagophthalmos, keratitis, and iridocyclitis [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Organs Spared in Leprosy:** Uterus, Ovaries, Lungs, CNS, Pancreas, and Spleen. * **Most Common Nerve Involved:** Ulnar nerve. * **Earliest Sensation Lost:** Temperature (followed by touch, then pain). * **Cardinal Signs:** Hypopigmented patches with loss of sensation, thickened peripheral nerves [1], and positive skin smears for acid-fast bacilli.

Q: Jarisch-Herxheimer reaction is seen in syphilis with treatment by which of the following drugs?

Penicillins. The **Jarisch-Herxheimer Reaction (JHR)** is a transient clinical phenomenon classically seen following the initiation of antibiotic therapy for spirochetal infections, most notably **Syphilis** (*Treponema pallidum*). [1] **Why Penicillin is the correct answer:** The reaction occurs due to the rapid destruction of spirochetes by bactericidal antibiotics like **Penicillin**. As the bacteria die, they release large amounts of endotoxin-like lipoproteins (e.g., Treponemal lipopolysaccharides) into the bloodstream. This triggers a massive release of pro-inflammatory cytokines (TNF-α, IL-6, and IL-8), leading to symptoms like fever, chills, headache, myalgia, and exacerbation of skin lesions. It typically occurs within 2–12 hours of the first dose. **Analysis of Incorrect Options:** * **Tetracyclines:** While Tetracyclines can occasionally trigger JHR (as they are used in penicillin-allergic patients), Penicillin is the **prototypical** and most common trigger mentioned in medical literature and exams. [1] * **Co-trimoxazole & Sulfonamides:** These drugs are not used in the standard treatment of Syphilis and are not associated with the classic Jarisch-Herxheimer reaction. **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Association:** Secondary Syphilis (seen in ~70–90% of cases). * **Other Diseases:** JHR can also be seen in Lyme disease, Leptospirosis, and Relapsing fever (*Borrelia*). [1] * **Management:** It is a self-limiting condition. Management is **supportive** with NSAIDs and antipyretics. Treatment of syphilis should **not** be discontinued. * **Prevention in Pregnancy:** In pregnant women, JHR can trigger preterm labor or fetal distress; however, Penicillin is still administered under monitoring.

Question 1

A 24-year-old patient complains of diarrhea, vomiting, and abdominal pain aggravated on ingestion of food for 1 week. Stool microscopy reveals findings suggestive of parasitic infection. What is the appropriate treatment for this condition?

Accepted Answer

Ivermectin

Answer

Tinidazole

Answer

Praziquantel

Answer

Niclofolan

Question 2

What is the diagnostic test for group A streptococcal pharyngitis?

Accepted Answer

Bacitracin sensitivity

Answer

Bile solubility test

Answer

Catalase test

Answer

Optochin sensitivity

Question 3

Hemorrhagic rashes are typically seen in which of the following conditions?

Accepted Answer

Meningococcal infection

Answer

Malaria

Answer

Enteric fever

Answer

Pneumonia

Question 4

Which of the following does not fit the definition of Pyrexia of Unknown Origin (PUO)?

Accepted Answer

Undiagnosed after three days of appropriate inpatient investigation

Answer

Requires exclusion of immunosuppression

Answer

Temperature exceeding 38.3°C on several occasions

Answer

Fever persisting for more than three weeks

Question 5

What is true about acute rheumatic fever?

Accepted Answer

Caused by antecedent alpha-hemolytic streptococcus infection

Answer

Chorea

Answer

Erythema nodosum

Answer

Arthritis

Question 6

An 18-year-old college student presents with a sore throat, fever, fatigue, and loss of appetite. Examination reveals pharyngitis with cervical lymphadenopathy. Blood tests show lymphocytosis and the presence of heterophile antibodies. Which of the following best describes the virus responsible for this illness?

Accepted Answer

Double-stranded, enveloped DNA virus

Answer

Double-stranded, nonenveloped DNA virus

Answer

Single-stranded, enveloped RNA virus

Answer

Single-stranded, nonenveloped DNA virus

Question 7

What is the indication for prophylaxis in Pneumocystis jirovecii pneumonia?

Accepted Answer

CD4 count < 200 cells/µL

Answer

Tuberculosis

Answer

Viral load > 25,000 copies/mL

Answer

Oral candidiasis

Question 8

A patient is being investigated for chronic diarrhoea. Small intestinal mucosal biopsy shows PAS positive foamy macrophages. What is the probable diagnosis?

Accepted Answer

Whipple disease

Answer

Chronic amoebiasis

Answer

Chronic giardiasis

Answer

Intestinal sarcoidosis

Question 9

Which of the following is not affected in leprosy?

Accepted Answer

Uterus

Answer

Testes

Answer

Nerve

Answer

Eye

Question 10

Jarisch-Herxheimer reaction is seen in syphilis with treatment by which of the following drugs?

Accepted Answer

Penicillins

Answer

Tetracyclines

Answer

Co-trimoxazole

Answer

Sulfonamides

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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