Infectious Diseases — MCQs
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Splenic rupture is most common in infection with which Plasmodium species?
A 44-year-old man with a prior renal transplant presents with cough and shortness of breath on exertion. He denies sputum production and has no prior respiratory or cardiac illnesses. On physical examination, he appears dyspneic, respirations 24/min, pulse 110/min, and oxygen saturation 88%. His lungs are clear on auscultation and heart sounds are normal. Chest X-ray shows bilateral diffuse perihilar infiltrates. Bronchoscopy and bronchial brushings show clusters of cysts that stain with methenamine silver. Which of the following is the most appropriate next step in management?
What is the true treatment regarding hepatic amoebiasis?
Purpura fulminans is a characteristic feature of which condition?
XDR-TB is resistant to which of the following drug regimens?
Koplik spots are seen in which of the following conditions?
The reserve transcriptase sequence in HIV is best described as?
What is the most common gastrointestinal manifestation in HIV infection?
Which of the following is not related to kala azar?
Which of the following statements is true regarding viral hepatitis?
Infectious Diseases Indian Medical PG Practice Questions and MCQs
Question 551: Splenic rupture is most common in infection with which Plasmodium species?
- A. P. vivax
- B. P. ovale
- C. P. malariae
- D. P. falciparum (Correct Answer)
Explanation: Splenic rupture is a rare but life-threatening complication of malaria. While it can occur with any species, it is most commonly associated with **Plasmodium falciparum** [1]. **1. Why P. falciparum is the correct answer:** The underlying pathophysiology involves massive sequestration of parasitized red blood cells (pRBCs) within the splenic microvasculature. *P. falciparum* causes high levels of parasitemia and significant splenic congestion, leading to rapid organ enlargement (splenomegaly) [1]. The combination of acute inflammatory response, subcapsular hematoma formation, and increased intra-abdominal pressure (often due to minor trauma or even coughing) leads to the rupture of the tense splenic capsule. **2. Why other options are incorrect:** * **P. vivax:** While *P. vivax* is the second most common cause of splenic rupture and often cited in case reports due to its chronicity, statistically, *P. falciparum* remains the leading cause in endemic regions due to its higher severity and parasite load. * **P. ovale and P. malariae:** These species generally result in lower levels of parasitemia and less aggressive splenic involvement, making spontaneous or traumatic rupture extremely rare compared to *falciparum* [1]. **Clinical Pearls for NEET-PG:** * **Classic Presentation:** A patient with malaria presenting with sudden onset left upper quadrant pain, referred pain to the left shoulder (**Kehr’s sign**), and signs of hypovolemic shock. * **Management:** Hemodynamically stable patients may be managed conservatively; unstable patients require urgent splenectomy. * **Hyperreactive Malarial Splenomegaly (HMS):** Formerly known as Tropical Splenomegaly Syndrome, this is an exaggerated immune response to chronic malaria, characterized by massive splenomegaly and high IgM levels, but it is distinct from acute rupture.
Question 552: A 44-year-old man with a prior renal transplant presents with cough and shortness of breath on exertion. He denies sputum production and has no prior respiratory or cardiac illnesses. On physical examination, he appears dyspneic, respirations 24/min, pulse 110/min, and oxygen saturation 88%. His lungs are clear on auscultation and heart sounds are normal. Chest X-ray shows bilateral diffuse perihilar infiltrates. Bronchoscopy and bronchial brushings show clusters of cysts that stain with methenamine silver. Which of the following is the most appropriate next step in management?
- A. amphotericin B
- B. cephalosporins
- C. trimethoprim-sulfamethoxazole (Correct Answer)
- D. aminoglycosides
Explanation: ### Explanation **Diagnosis: Pneumocystis jirovecii Pneumonia (PJP)** The patient presents with the classic triad of **PJP**: dyspnea, non-productive cough, and fever in an immunocompromised host (renal transplant recipient). Key diagnostic clues include: 1. **Clinical Dissociation:** Significant hypoxia (88% saturation) and tachypnea despite clear lungs on ausculation. 2. **Radiology:** Bilateral diffuse perihilar (interstitial) infiltrates [1]. 3. **Microscopy:** Silver-staining (Gomori Methenamine Silver - GMS) cysts in bronchial brushings are pathognomonic for *P. jirovecii* [1]. #### Why Trimethoprim-Sulfamethoxazole (TMP-SMX) is Correct? TMP-SMX is the **first-line treatment** and prophylaxis for PJP [1]. It inhibits folate synthesis in the organism. In severe cases (PaO₂ < 70 mmHg or A-a gradient > 35 mmHg), adjunctive corticosteroids should be added to prevent clinical worsening due to inflammatory response to dying organisms [1]. #### Why Other Options are Incorrect: * **A. Amphotericin B:** Used for systemic fungal infections like Cryptococcosis or Mucormycosis. Although *P. jirovecii* is classified as a fungus, it lacks ergosterol in its cell membrane, making it resistant to most antifungals. * **B. Cephalosporins:** These are β-lactam antibiotics targeting bacterial cell walls. They are ineffective against *P. jirovecii*, which lacks a typical bacterial peptidoglycan layer. * **D. Aminoglycosides:** These inhibit bacterial protein synthesis (30S subunit) and are used for Gram-negative infections; they have no activity against PJP. #### NEET-PG High-Yield Pearls: * **Stains for PJP:** Gomori Methenamine Silver (GMS) - shows crushed ping-pong ball appearance; Toluidine blue; Immunofluorescence (most sensitive) [1]. * **Lab Marker:** Elevated **Serum LDH** is highly sensitive (though non-specific) for PJP. * **Drug of Choice for Sulfa-allergic patients:** Clindamycin + Primaquine or Pentamidine. * **Prophylaxis:** Indicated in HIV patients with CD4 count < 200 cells/µL or transplant patients on immunosuppressants [2].
Question 553: What is the true treatment regarding hepatic amoebiasis?
- A. More common in females
- B. Multiple lesions
- C. Mostly treated conservatively (Correct Answer)
- D. Jaundice is common
Explanation: **Explanation:** Amoebic Liver Abscess (ALA), caused by *Entamoeba histolytica*, is the most common extra-intestinal manifestation of amoebiasis. **Why Option C is Correct:** The cornerstone of management for ALA is **medical therapy**. Over 90-95% of patients respond remarkably well to tissue amoebicides, primarily **Nitroimidazoles** (Metronidazole or Tinidazole), followed by a luminal amoebicide (e.g., Paromomycin or Diloxanide furoate) to eradicate the intestinal cyst stage. Surgical or percutaneous intervention is rarely needed, reserved only for large abscesses (>10 cm), imminent rupture, or lack of clinical response after 48-72 hours of antibiotics [2]. **Why Other Options are Incorrect:** * **Option A:** ALA is significantly **more common in males** (ratio approx. 7:1 to 10:1), likely due to the protective effect of menstrual blood loss (reducing iron availability for the parasite) and higher alcohol consumption in men. * **Option B:** ALA typically presents as a **solitary lesion**, most commonly located in the **superior-posterior aspect of the right lobe** of the liver (due to the portal blood flow patterns). * **Option D:** **Jaundice is uncommon** in ALA. If present, it usually signifies a very large abscess compressing the biliary tree or a secondary bacterial infection. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Description:** The aspirated pus is famously described as **"Anchovy sauce"** appearance (odorless, reddish-brown) [1]. * **Diagnosis:** Serology (IHA/ELISA) is highly sensitive; Ultrasound is the initial imaging of choice. * **Complication:** The most common serious complication is rupture into the pleural space or peritoneum. * **Key Difference:** Unlike pyogenic abscesses, amoebic abscesses are usually "cold" (less likely to have high-grade fever/toxic appearance) and rarely contain organisms in the pus (they reside in the abscess wall).
Question 554: Purpura fulminans is a characteristic feature of which condition?
- A. Scarlet fever
- B. Pseudomonas infection
- C. Acute meningococcemia (Correct Answer)
- D. Staphylococcal disease
Explanation: **Explanation:** **Purpura fulminans** is a life-threatening hematological emergency characterized by skin necrosis, disseminated intravascular coagulation (DIC), and multi-organ failure. **Why Acute Meningococcemia is correct:** Acute meningococcemia (caused by *Neisseria meningitidis*) is the most common cause of infectious purpura fulminans. The pathogenesis involves severe endothelial injury triggered by bacterial endotoxins (LOS), leading to the consumption of Protein C, Protein S, and Antithrombin III. This results in a prothrombotic state with microvascular thrombosis, followed by secondary fibrinolysis and hemorrhage, manifesting as rapidly spreading ecchymotic skin lesions and peripheral gangrene. **Why other options are incorrect:** * **Scarlet Fever:** Caused by Group A Streptococcus; it typically presents with a "sandpaper" rash, strawberry tongue, and Pastia’s lines [1], not necrotic purpura. * **Pseudomonas infection:** Classically associated with **Ecthyma gangrenosum**, which presents as painless, necrotic ulcers with an erythematous halo, usually in immunocompromised patients. * **Staphylococcal disease:** Often presents with bullous impetigo or Staphylococcal Scalded Skin Syndrome (SSSS), where the cleavage is superficial (stratum granulosum), unlike the deep dermal necrosis seen in purpura fulminans. **NEET-PG High-Yield Pearls:** * **Waterhouse-Friderichsen Syndrome:** The association of acute meningococcemia with bilateral adrenal hemorrhage and circulatory collapse. * **Treatment:** Immediate administration of IV Ceftriaxone (or Penicillin G if sensitive). Protein C concentrate may be used in severe cases of purpura fulminans. * **Non-infectious causes:** Inherited deficiency of Protein C or S can also cause purpura fulminans in neonates.
Question 555: XDR-TB is resistant to which of the following drug regimens?
- A. Isoniazid, Rifampicin, Pyrazinamide, Ethambutol
- B. Isoniazid, Rifampicin, Kanamycin, Pyrazinamide
- C. Isoniazid, Rifampicin, Kanamycin, Ofloxacin (Correct Answer)
- D. Isoniazid, Rifampicin, Ethambutol, Ethionamide
Explanation: XDR-TB is resistant to which of the following drug regimens? **Explanation** Extensively Drug-Resistant Tuberculosis (XDR-TB) is a severe form of drug-resistant TB defined by specific resistance patterns to both first-line and second-line antitubercular drugs (ATDs) [1]. **1. Why Option C is Correct:** According to the WHO definition, XDR-TB is defined as TB that is resistant to: * **Isoniazid (H) and Rifampicin (R):** This baseline resistance defines Multidrug-Resistant TB (MDR-TB). * **Any Fluoroquinolone:** Such as Ofloxacin, Levofloxacin, or Moxifloxacin. * **At least one Second-line Injectable Drug:** Such as Kanamycin, Amikacin, or Capreomycin. Option C accurately reflects this combination (MDR + Fluoroquinolone + Injectable). **2. Analysis of Incorrect Options:** * **Option A:** This represents the standard first-line regimen (HRZE). Resistance to these defines "Poly-drug resistance" but not XDR. * **Option B:** While it includes resistance to H, R, and Kanamycin, it lacks resistance to a Fluoroquinolone, which is a mandatory criterion for XDR-TB. * **Option D:** Ethionamide is a second-line drug, but resistance to it (without an injectable or fluoroquinolone) does not meet the XDR criteria. **3. High-Yield Clinical Pearls for NEET-PG:** * **MDR-TB:** Resistance to at least Isoniazid and Rifampicin. * **Pre-XDR TB:** MDR-TB plus resistance to *either* a fluoroquinolone *or* a second-line injectable (but not both). * **New WHO Definition (2021 Update):** XDR-TB is now defined as MDR-TB plus resistance to any fluoroquinolone AND at least one additional Group A drug (Bedaquiline or Linezolid). *Note: For exam purposes, the classic definition (Option C) remains high-yield unless the "New WHO criteria" are specifically mentioned.* * **Treatment:** Bedaquiline-containing regimens (like BPaLM) are currently the preferred approach for resistant strains [1].
Question 556: Koplik spots are seen in which of the following conditions?
- A. Measles (Correct Answer)
- B. Mumps
- C. Rubella
- D. Diphtheria
Explanation: **Explanation:** **Koplik spots** are the pathognomonic enanthem of **Measles (Rubeola)**. They are small, bluish-white spots on an erythematous base, typically found on the buccal mucosa opposite the lower second molars [1]. They appear during the **prodromal phase**, approximately 48 hours before the characteristic maculopapular rash develops, and disappear as the rash spreads [1]. **Analysis of Options:** * **A. Measles (Correct):** Caused by the Rubeola virus. Koplik spots are a hallmark clinical finding that allows for early diagnosis before the skin rash appears [1]. * **B. Mumps:** Characterized by painful parotid gland swelling (parotitis). It does not present with an enanthem like Koplik spots. * **C. Rubella (German Measles):** While it presents with a rash, its characteristic oral finding is **Forchheimer spots** (small, red petechiae on the soft palate), not Koplik spots. * **D. Diphtheria:** Characterized by a thick, gray, adherent **pseudomembrane** over the tonsils and pharynx, which bleeds upon attempts to remove it. **High-Yield Clinical Pearls for NEET-PG:** * **The 3 C’s of Measles:** Cough, Coryza, and Conjunctivitis (seen in the prodromal stage). * **Rash Progression:** The Measles rash is maculopapular, starts behind the ears (retro-auricular), and spreads cephalocaudally (head to toe) [1]. * **Vitamin A:** Supplementation is recommended in all children with measles to reduce morbidity and mortality (especially from pneumonia and blindness) [1]. * **SSPE (Subacute Sclerosing Panencephalitis):** A rare, fatal, late neurological complication of measles occurring years after the initial infection [1].
Question 557: The reserve transcriptase sequence in HIV is best described as?
- A. RNA-DNA-RNA (Correct Answer)
- B. DNA-RNA
- C. DNA-RNA-DNA
- D. RNA-DNA
Explanation: ### Explanation The correct sequence for HIV reverse transcription is **RNA-DNA-RNA** [1]. This describes the flow of genetic information from the viral entry to the production of new viral progeny. **1. Why RNA-DNA-RNA is correct:** HIV is a retrovirus with a single-stranded positive-sense RNA genome. The process follows these steps: * **RNA → DNA:** Upon entering the host cell, the viral enzyme **Reverse Transcriptase (RT)** converts the viral RNA into a complementary DNA (cDNA) strand, which then becomes double-stranded DNA [2]. * **DNA → RNA:** This viral DNA integrates into the host genome (as a provirus) using the enzyme **Integrase** [1]. The host’s cellular machinery then transcribes this integrated DNA back into multiple copies of genomic viral RNA and messenger RNA (mRNA) to assemble new virions [1]. **2. Why other options are incorrect:** * **DNA-RNA / DNA-RNA-DNA:** These are incorrect because the HIV lifecycle begins with an RNA genome, not DNA. * **RNA-DNA:** This is an incomplete description. While reverse transcription ends at DNA, the ultimate goal of the viral lifecycle is to produce new RNA genomes for the next generation of viruses. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Reverse Transcriptase (RT):** It possesses three activities: RNA-dependent DNA polymerase, DNA-dependent DNA polymerase, and **RNase H** (which degrades the original RNA template) [2]. * **Error-Prone Nature:** RT lacks 3' to 5' proofreading activity, leading to high mutation rates and the rapid development of drug resistance. * **Drug Targets:** * **NRTIs** (e.g., Zidovudine, Tenofovir): Act as chain terminators. * **NNRTIs** (e.g., Efavirenz, Nevirapine): Bind directly to the enzyme to inhibit its action. * **Integration:** The transition from DNA back to RNA occurs in the host nucleus via **Host RNA Polymerase II**.
Question 558: What is the most common gastrointestinal manifestation in HIV infection?
- A. Amebiasis
- B. Cryptosporidiosis (Correct Answer)
- C. Giardiasis
- D. Hookworm infestation
Explanation: **Explanation:** Gastrointestinal (GI) complications are among the most frequent clinical manifestations of HIV/AIDS. **Cryptosporidiosis**, caused by the protozoan *Cryptosporidium parvum*, is the most common cause of chronic diarrhea in HIV-infected individuals, particularly when CD4 counts fall below 100 cells/mm³ [1]. It typically presents as profuse, watery, non-bloody diarrhea, which can lead to severe dehydration and malabsorption in immunocompromised patients [1]. **Analysis of Options:** * **Amebiasis (*Entamoeba histolytica*):** While common in the general population in developing countries, it is not specifically the most common GI manifestation linked to the HIV disease process itself. * **Giardiasis (*Giardia lamblia*):** This is a frequent cause of diarrhea globally, but it does not show the same increased prevalence or severity in HIV patients as opportunistic infections like Cryptosporidiosis. * **Hookworm infestation:** This is a soil-transmitted helminth infection. While prevalent in tropical regions, it is not an opportunistic infection associated with HIV progression. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** Cryptosporidiosis is diagnosed using **Modified Acid-Fast staining** (Kinyoun stain), which reveals bright red oocysts [1]. * **CD4 Correlation:** Chronic, life-threatening diarrhea due to *Cryptosporidium* usually occurs when **CD4 <100 cells/mm³** [1]. * **Other GI Pathogens in HIV:** * **Microsporidia:** Another common cause of chronic diarrhea (CD4 <50) [1]. * **CMV Colitis:** Most common cause of *bloody* diarrhea in AIDS (CD4 <50). * **MAC (Mycobacterium avium complex):** Causes systemic illness with diarrhea and malabsorption (CD4 <50) [1]. * **Treatment:** The primary management is **HAART** (Highly Active Antiretroviral Therapy) to restore immune function; Nitazoxanide has limited efficacy in advanced AIDS [1].
Question 559: Which of the following is not related to kala azar?
- A. Pancytopenia
- B. Oral miltefosine
- C. Hyperpigmentation
- D. Tropical splenomegaly syndrome (Correct Answer)
Explanation: The correct answer is **D. Tropical splenomegaly syndrome**, as it is a distinct clinical entity unrelated to Visceral Leishmaniasis (Kala-azar). **1. Why Tropical Splenomegaly Syndrome (TSS) is the correct answer:** TSS, also known as **Hyper-reactive Malarial Splenomegaly (HMS)**, is an abnormal immunological response to chronic or repeated **Malaria** infections (usually *P. falciparum*). It is characterized by massive splenomegaly, high titers of anti-malarial antibodies, and elevated serum IgM. It is not caused by *Leishmania donovani*. **2. Analysis of incorrect options (Features of Kala-azar):** * **Pancytopenia:** Kala-azar causes bone marrow suppression and splenic sequestration, leading to anemia, leucopenia, and thrombocytopenia. [2] * **Oral Miltefosine:** This is the first effective **oral** treatment for Visceral Leishmaniasis. It is highly effective but contraindicated in pregnancy due to teratogenicity. * **Hyperpigmentation:** The name "Kala-azar" literally translates to "Black Fever." It refers to the characteristic dusky hyperpigmentation of the skin (especially on the forehead, hands, and abdomen) seen in Indian patients. **Clinical Pearls for NEET-PG:** * **Vector:** Sandfly (*Phlebotomus argentipes*). [1] * **Gold Standard Diagnosis:** Demonstration of **LD bodies** (Amastigotes) in splenic aspirate (highest sensitivity) or bone marrow biopsy. [2] * **Drug of Choice:** **Liposomal Amphotericin B** is currently the preferred treatment due to high cure rates and low resistance. * **PKDL:** Post-Kala-azar Dermal Leishmaniasis occurs in 5-10% of cases in India after the apparent cure of systemic disease, acting as a reservoir for infection.
Question 560: Which of the following statements is true regarding viral hepatitis?
- A. Raised transaminase levels correlate well with the extent of hepatic injury.
- B. Transaminase levels show variable elevation during the prodromal phase. (Correct Answer)
- C. Hepatitis A virus (HAV) infection is diagnosed by estimating IgG antibodies.
- D. Elevation of transaminases is specific for liver injury.
Explanation: ### Explanation **Correct Option: B. Transaminase levels show variable elevation during the prodromal phase.** In viral hepatitis, the prodromal phase (pre-icteric phase) is characterized by non-specific symptoms like malaise, anorexia, and nausea. During this period, serum transaminases (AST and ALT) begin to rise, typically reaching their peak just before or at the onset of clinical jaundice [1]. The degree of elevation is variable but often exceeds 500–1000 U/L in acute cases [1]. **Why the other options are incorrect:** * **A. Raised transaminase levels correlate well with the extent of hepatic injury:** This is a common misconception. Transaminase levels reflect **acute hepatocyte membrane damage** but do not correlate with the severity of liver necrosis or the ultimate prognosis. A patient with fulminant hepatic failure may actually show "falling" transaminase levels due to the exhaustion of viable hepatocytes (the "crashing" liver) [3]. * **C. HAV infection is diagnosed by IgG antibodies:** Acute Hepatitis A is diagnosed by detecting **IgM anti-HAV** [2]. IgG anti-HAV appears later and persists for life, indicating past infection or immunity (post-vaccination), not acute disease [2]. * **D. Elevation of transaminases is specific for liver injury:** AST and ALT are not exclusively specific to the liver. AST is found in cardiac muscle, skeletal muscle, and RBCs (elevation seen in myocardial infarction or hemolysis). While ALT is more specific to the liver, it can also be elevated in severe muscle trauma. **High-Yield Clinical Pearls for NEET-PG:** * **De Ritis Ratio (AST/ALT):** In most viral hepatitis, **ALT > AST**. However, in **Alcoholic Hepatitis**, the ratio is typically **> 2:1**. * **Bilirubin:** In acute hepatitis, jaundice usually appears when serum bilirubin exceeds **2.5–3.0 mg/dL**. * **Prothrombin Time (PT):** This is the best indicator of liver **synthetic function** and the most important prognostic marker in acute viral hepatitis. A prolonged PT suggests progression to fulminant hepatic failure.
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Principles of Antimicrobial Therapy
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Fever of Unknown Origin
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HIV/AIDS and Related Infections
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Viral Infections (Hepatitis, Herpes, etc.)
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Sepsis and Septic Shock
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Infection in Immunocompromised Hosts
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Emerging and Re-emerging Infections
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Antimicrobial Resistance
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