Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 571: What is the recommended treatment for non-specific urethritis?

A. Erythromycin
B. Sulfa drugs
C. Tetracycline (Correct Answer)
D. Ampicillin

Explanation: **Explanation:** **Non-specific urethritis (NSU)**, also known as Non-gonococcal urethritis (NGU), refers to inflammation of the urethra not caused by *Neisseria gonorrhoeae*. The most common causative organism is ***Chlamydia trachomatis*** (serotypes D-K), followed by *Ureaplasma urealyticum* and *Mycoplasma genitalium* [1]. **1. Why Tetracycline is Correct:** Tetracyclines (specifically **Doxycycline**) are the traditional drugs of choice for NSU because they are highly effective against intracellular organisms like *Chlamydia* and *Mycoplasma*. They inhibit bacterial protein synthesis by binding to the 30S ribosomal subunit. In clinical practice and standard textbooks (like Harrison’s), a 7-day course of Doxycycline is a first-line recommendation. **2. Why the Other Options are Incorrect:** * **Erythromycin (A):** While it can be used as an alternative (especially in pregnancy where tetracyclines are contraindicated), it is generally less tolerated due to gastrointestinal side effects and is not the primary drug of choice compared to tetracyclines or azithromycin. * **Sulfa drugs (B):** These inhibit folic acid synthesis. While effective against some bacteria, they have poor activity against *Chlamydia* and *Mycoplasma*, making them ineffective for NSU. * **Ampicillin (D):** This is a beta-lactam antibiotic that targets the cell wall. Since *Chlamydia* is an intracellular pathogen and *Mycoplasma* lacks a cell wall, ampicillin is completely ineffective. **Clinical Pearls for NEET-PG:** * **First-line treatment (Current CDC guidelines):** Doxycycline (100 mg BID for 7 days) is now preferred over a single dose of Azithromycin due to increasing resistance in *Mycoplasma genitalium*. * **Co-infection:** Patients with Gonorrhea are often empirically treated for NSU (Chlamydia) simultaneously. * **Diagnosis:** NSU is diagnosed when urethritis is present (discharge/dysuria) but Gram stain fails to show Gram-negative intracellular diplococci [1].

Question 572: What is another name for dengue fever?

A. Break-bone fever (Correct Answer)
B. Chikungunya
C. Yellow fever
D. Kyasanur Forest disease

Explanation: **Explanation:** **Dengue fever** is caused by the Dengue virus (DENV 1-4), a single-stranded RNA virus of the *Flaviviridae* family, transmitted primarily by the **Aedes aegypti** mosquito. It is colloquially known as **"Break-bone fever"** (Option A) because of the characteristic severe myalgia, arthralgia, and deep bone pain that patients experience during the febrile phase. **Analysis of Incorrect Options:** * **Chikungunya (Option B):** While it also causes severe joint pain (the name means "to become contorted"), it is caused by a *Togavirus*. It is clinically distinguished from Dengue by more prominent, persistent arthritis and the absence of plasma leakage. * **Yellow Fever (Option C):** Also a *Flavivirus* transmitted by Aedes mosquitoes, but it is characterized by jaundice ("Yellow"), councilman bodies in the liver, and is not associated with the "break-bone" moniker. * **Kyasanur Forest Disease (Option D):** Known as "Monkey Fever," this is a tick-borne viral hemorrhagic fever endemic to Karnataka, India. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Aedes aegypti* (Day biter; breeds in artificial collections of clean water). * **Pathogenesis:** Secondary infection with a different serotype increases the risk of **Dengue Hemorrhagic Fever (DHF)** due to **Antibody-Dependent Enhancement (ADE)**. * **Diagnosis:** NS1 Antigen (Day 1-5); IgM/IgG ELISA (after Day 5). * **Hematology:** Characterized by leucopenia and thrombocytopenia. The hallmark of DHF is **plasma leakage** (rising hematocrit, pleural effusion, or ascites) [1]. * **Tourniquet Test:** A positive test (≥10 petechiae/square inch) indicates capillary fragility [1].

Question 573: All of the following are true regarding progressive multifocal leukoencephalopathy except?

A. It is the only manifestation of JC virus infection.
B. It is a late manifestation of AIDS.
C. Cerebellar involvement is unknown. (Correct Answer)
D. None of the above.

Explanation: **Explanation:** Progressive Multifocal Leukoencephalopathy (PML) is a demyelinating disease of the Central Nervous System caused by the reactivation of the **JC virus (John Cunningham virus)**, a polyomavirus [1]. **Why Option C is the correct answer (False statement):** The statement "Cerebellar involvement is unknown" is incorrect. While PML primarily affects the subcortical white matter of the cerebral hemispheres (parieto-occipital regions), it frequently involves the **cerebellum and brainstem**. In fact, ataxia and coordination deficits are common clinical presentations when the disease affects the cerebellar peduncles or the cerebellum itself. **Analysis of other options:** * **Option A (True):** JC virus is a ubiquitous virus that remains latent in the kidneys and lymphoid tissue of healthy individuals. PML is the **only clinically significant disease** caused by JC virus reactivation, occurring almost exclusively in the setting of profound cell-mediated immunodeficiency [1]. * **Option B (True):** PML is a classic opportunistic infection and an **AIDS-defining illness** [1]. It typically occurs as a late manifestation when CD4+ T-cell counts drop significantly, usually **below 100 cells/μL**. **High-Yield Clinical Pearls for NEET-PG:** * **Pathogenesis:** Selective destruction of **oligodendrocytes** (the myelin-producing cells of the CNS) [1]. * **MRI Findings:** Characterized by **multifocal, non-enhancing, T2/FLAIR hyperintense lesions** in the white matter without mass effect [1]. * **Diagnosis:** Gold standard is PCR for JC virus DNA in the **CSF**. Brain biopsy shows characteristic enlarged oligodendrocyte nuclei with viral inclusions. * **Drug Association:** Apart from HIV, PML is associated with **Natalizumab** (used in Multiple Sclerosis) and Rituximab.

Question 574: Regarding hepatobiliary disease, which of the following statements is true?

A. Hepatitis B is the most common viral cause of cirrhosis worldwide. (Correct Answer)
B. Fewer than 5% of patients with chronic hepatitis C will develop cirrhosis.
C. In India, hepatitis B is transmitted primarily by the feco-oral route.
D. Hepatitis C is a more frequent cause for fulminant hepatitis than hepatitis B infection.

Explanation: ### Explanation **1. Why Option A is Correct:** Hepatitis B virus (HBV) remains the leading viral cause of cirrhosis and hepatocellular carcinoma (HCC) globally. Despite the availability of vaccines, the high prevalence of chronic HBV infection—particularly in Asia and Sub-Saharan Africa—contributes significantly to the global burden of end-stage liver disease. **2. Why the Other Options are Incorrect:** * **Option B:** This is incorrect because the progression rate is much higher. Approximately **20–30%** of patients with chronic Hepatitis C (HCV) will develop cirrhosis over a period of 20–30 years. * **Option C:** In India, the primary route of Hepatitis B transmission is **horizontal** (during early childhood through minor trauma or shared household items) and **vertical** (perinatal). The feco-oral route is characteristic of Hepatitis A and E [1]. * **Option D:** Hepatitis B is a much more common cause of **fulminant hepatic failure** (FHF) than Hepatitis C. In fact, acute HCV infection rarely presents as fulminant hepatitis; HBV (often with HDV co-infection) and HEV (especially in pregnancy) are the leading viral causes of FHF. **3. High-Yield Clinical Pearls for NEET-PG:** * **Hepatitis E:** The most common cause of acute sporadic viral hepatitis in India and the leading cause of FHF in pregnant women. * **Hepatitis B:** The risk of chronicity is inversely proportional to age (90% in neonates vs. <5% in adults). * **Hepatitis C:** Known as the "silent killer" because ~80% of acute infections become chronic, often remaining asymptomatic until cirrhosis develops. * **Ground-glass hepatocytes:** Histological hallmark of chronic Hepatitis B (due to HBsAg accumulation).

Question 575: A 35-year-old man presents with loss of appetite, nausea, vomiting, and fatigue. Laboratory examination confirms the diagnosis of hepatitis B, and the man becomes icteric 2 weeks later. This patient is particularly vulnerable to the development of which of the following disorders?

A. Berry aneurysm
B. Coronary artery aneurysm
C. Dissecting aneurysm
D. Polyarteritis nodosa (Correct Answer)

Explanation: ### Explanation **Correct Option: D. Polyarteritis Nodosa (PAN)** The patient presents with acute Hepatitis B virus (HBV) infection [2]. There is a strong, well-documented clinical association between **Hepatitis B and Polyarteritis Nodosa (PAN)**. * **Pathophysiology:** PAN is a systemic necrotizing vasculitis of medium-sized and small arteries [1]. In the context of HBV, it is thought to be mediated by the deposition of **immune complexes** (HBsAg-Ab complexes) in the vessel walls, leading to inflammation and fibrinoid necrosis. * **Clinical Presentation:** PAN typically presents with "beaded" microaneurysms (often in renal or mesenteric arteries), hypertension, mononeuritis multiplex, and skin lesions (livedo reticularis) [1]. --- ### Why the other options are incorrect: * **A. Berry Aneurysm:** These are saccular aneurysms of the Circle of Willis, primarily associated with **Autosomal Dominant Polycystic Kidney Disease (ADPKD)**, Ehlers-Danlos syndrome, and coarctation of the aorta. * **B. Coronary Artery Aneurysm:** This is the classic complication of **Kawasaki Disease**, a vasculitis seen predominantly in children, not typically associated with HBV. * **C. Dissecting Aneurysm:** Most commonly associated with **chronic hypertension** or connective tissue disorders like **Marfan Syndrome**. It involves a tear in the tunica intima rather than an immune-mediated vasculitis. --- ### NEET-PG High-Yield Pearls: 1. **The "HBV-PAN" Link:** Approximately 10–30% of patients with PAN are HBsAg positive. 2. **Vessel Sparing:** PAN characteristically **spares the pulmonary arteries** (unlike Granulomatosis with Polyangiitis). 3. **Diagnosis:** The "gold standard" for PAN is a biopsy showing necrotizing inflammation or **angiography** showing multiple small aneurysms ("string of pearls" appearance). 4. **Treatment:** Management of HBV-associated PAN often requires a combination of corticosteroids, plasma exchange, and antiviral therapy.

Question 576: An 18-year-old male patient presents with urethral discharge that has not resolved after treatment with IM ceftriaxone, and urethral culture shows no growth. Which of the following is the most likely etiologic agent causing this infection?

A. Ceftriaxone-resistant Neisseria gonorrhoeae
B. Chlamydia psittaci
C. Chlamydia trachomatis (Correct Answer)
D. Herpes simplex virus

Explanation: The clinical presentation describes a classic case of **Non-Gonococcal Urethritis (NGU)** or persistent urethritis following treatment for gonorrhea [1]. **1. Why Chlamydia trachomatis is correct:** The patient was treated with IM Ceftriaxone, which is highly effective against *Neisseria gonorrhoeae* but ineffective against *Chlamydia trachomatis* [1]. *C. trachomatis* is an obligate intracellular organism; therefore, it **does not grow on standard urethral cultures** (which typically use Thayer-Martin or Chocolate agar for Gonococcus). Co-infection with both organisms is extremely common (up to 30-50% of cases), which is why syndromic management guidelines recommend treating both simultaneously. **2. Analysis of Incorrect Options:** * **A. Ceftriaxone-resistant N. gonorrhoeae:** While resistance is emerging globally, it is still rare. More importantly, if it were *N. gonorrhoeae*, the culture would typically show growth (Gram-negative diplococci), which is not the case here. * **B. Chlamydia psittaci:** This species causes Psittacosis (a type of atypical pneumonia) transmitted via birds; it is not a cause of sexually transmitted urethritis. * **C. Herpes simplex virus:** While HSV can cause urethritis, it is usually associated with significant pain, dysuria, and visible vesicular or ulcerative lesions, rather than isolated discharge [1]. **3. NEET-PG High-Yield Pearls:** * **Drug of Choice for Chlamydia:** Doxycycline (100 mg BID for 7 days) is now preferred over single-dose Azithromycin due to superior efficacy in NGU. * **Culture Media:** *N. gonorrhoeae* requires **Thayer-Martin Medium** (Mueller-Hinton agar with vancomycin, colistin, and nystatin). * **Incubation Period:** Gonorrhea has a short incubation (2–7 days), while Chlamydia is longer (7–21 days) [1]. * **Most common cause of NGU:** *Chlamydia trachomatis* (Serotypes D-K). The second most common cause is *Mycoplasma genitalium*.

Question 577: What is true about tuberculosis in HIV patients?

A. Sputum positivity
B. INH prophylaxis prevents the development of TB
C. Lack characteristic features of TB (Correct Answer)
D. Highly positive PPD reaction

Explanation: **Explanation:** The presentation of Tuberculosis (TB) in HIV-infected individuals is heavily dependent on the patient's immune status (CD4 count) [1]. **1. Why Option C is Correct:** In patients with advanced HIV (low CD4 counts), the immune system fails to mount a robust inflammatory response. This leads to a **lack of characteristic features** such as cavitary lesions on chest X-rays (which require intact cell-mediated immunity) and typical granuloma formation. Instead, these patients often present with atypical findings like lower lobe infiltrates, intrathoracic lymphadenopathy, or even normal chest X-rays despite active disease [1]. Extrapulmonary and disseminated TB are also significantly more common. **2. Why the other options are incorrect:** * **Option A (Sputum Positivity):** HIV patients often have **lower sputum positivity** rates (paucibacillary disease) because the lack of cavitation reduces the bacterial load expelled into the airways. * **Option B (INH Prophylaxis):** While Isoniazid Preventive Therapy (IPT) significantly reduces the risk of *reactivating* latent TB, it does not provide absolute prevention against new infections or the eventual development of TB if the underlying immunosuppression is not managed with ART. * **Option D (Highly positive PPD):** HIV patients often exhibit **anergy** (a false-negative skin test) because the T-cell response required for a positive PPD/Mantoux test is deficient [2]. A reaction of ≥5 mm is considered positive in HIV, but many remain non-reactive despite infection. **Clinical Pearls for NEET-PG:** * **Most common opportunistic infection** in HIV patients in India: Tuberculosis [1]. * **TB-IRIS:** Paradoxical worsening of TB symptoms after starting ART due to immune recovery. * **Diagnosis:** WHO recommends **NAAT (CBNAAT/GeneXpert)** as the initial diagnostic test for all HIV-positive TB suspects due to low smear sensitivity.

Question 578: What is the drug of choice for Madura mycosis?

A. Imipenem
B. Dapsone
C. Itraconazole (Correct Answer)
D. Amikacin

Explanation: **Explanation:** Madura mycosis, or **Mycetoma**, is a chronic granulomatous infection of the subcutaneous tissue characterized by a triad of localized swelling, underlying bone destruction, and the formation of sinus tracts that discharge grains [2]. It is classified into two types based on the causative agent: **Eumycetoma** (fungal) and **Actinomycetoma** (bacterial) [2]. 1. **Why Itraconazole is correct:** The term "Madura mycosis" specifically refers to **Eumycetoma** (caused by fungi like *Madurella mycetomatis*). For fungal mycetoma, medical management is challenging and often requires long-term antifungal therapy. **Itraconazole** is currently considered the drug of choice due to its superior efficacy and safety profile compared to older antifungals like Ketoconazole [2], [1]. 2. **Why other options are incorrect:** * **Dapsone & Amikacin:** These are components of the **Welsh Regime**, which is the gold standard treatment for **Actinomycetoma** (bacterial origin). They are ineffective against the fungal agents of Madura mycosis. * **Imipenem:** This is a broad-spectrum carbapenem antibiotic used for severe bacterial infections (including some Nocardia species in actinomycetoma) but has no role in treating fungal infections. **High-Yield Clinical Pearls for NEET-PG:** * **The "Dot-in-Circle" Sign:** A characteristic MRI finding in mycetoma where small grains appear as dark spots within high-intensity inflammatory circles. * **Grains:** The color of the discharged grains can hint at the etiology (e.g., **Black grains** are pathognomonic for Eumycetoma; **Yellow/White grains** are common in Actinomycetoma) [2]. * **Treatment Duration:** Eumycetoma often requires treatment for 6–12 months and may still necessitate surgical excision (debridement or amputation) due to poor drug penetration into the fibrotic lesion [2].

Question 579: Which of the following is not typically associated with hepatitis C infection?

A. Polyarteritis nodosa (PAN) (Correct Answer)
B. Cryoglobulinemia
C. Porphyria cutanea tarda
D. Lichen planus

Explanation: The correct answer is **Polyarteritis nodosa (PAN)** because it is classically associated with **Hepatitis B virus (HBV)**, not Hepatitis C. Approximately 10–30% of PAN cases are linked to chronic HBV infection due to the deposition of immune complexes in small and medium-sized arteries. [1] **Analysis of Options:** * **Cryoglobulinemia (Option B):** This is the most common extrahepatic manifestation of Hepatitis C (HCV). Specifically, **Type II and III Mixed Cryoglobulinemia** occur because HCV triggers B-cell proliferation, leading to immune complexes that cause vasculitis, glomerulonephritis, and palpable purpura. [2] * **Porphyria cutanea tarda (Option C):** There is a strong epidemiological link between HCV and PCT. Chronic HCV infection can lead to an acquired deficiency of the enzyme *uroporphyrinogen decarboxylase*, resulting in skin fragility and blistering on sun-exposed areas. * **Lichen planus (Option D):** This mucocutaneous condition is frequently associated with HCV. Patients often present with the "6 Ps" (Planar, Purple, Polygonal, Pruritic, Papules, and Plaques) and Wickham striae. **NEET-PG High-Yield Pearls:** * **Hepatitis B associations:** Polyarteritis nodosa (PAN) and Membranous glomerulonephritis. [1] * **Hepatitis C associations:** Mixed Cryoglobulinemia, Porphyria Cutanea Tarda, Lichen Planus, and Membranoproliferative Glomerulonephritis (MPGN). [2] * **Key Distinction:** If a question mentions "Medium-vessel vasculitis + Hepatitis," think **HBV (PAN)**. If it mentions "Small-vessel vasculitis/Purpura + Hepatitis," think **HCV (Cryoglobulinemia)**.

Question 580: Which of the following is NOT a feature of Entamoeba histolytica?

A. Bloody diarrhea
B. Amoeboma in the right iliac fossa
C. Hepatomegaly
D. Cartwheel appearance on CT (Correct Answer)

Explanation: The correct answer is **D. Cartwheel appearance on CT**. ### **Explanation** The **Cartwheel appearance** on imaging (CT/Ultrasound) is a classic radiological sign of a **Hydatid cyst** (caused by *Echinococcus granulosus*), not *Entamoeba histolytica* [2], [3]. This appearance occurs due to the presence of multiple daughter cysts and internal septations within the mother cyst [3]. *Entamoeba histolytica* typically presents as an **Amoebic Liver Abscess (ALA)**. On CT, it appears as a well-defined, low-attenuation lesion, often with a peripheral enhancing rim, but it lacks the internal daughter cysts seen in Hydatid disease. ### **Why other options are features of E. histolytica:** * **A. Bloody diarrhea:** *E. histolytica* causes intestinal amoebiasis by invading the colonic mucosa, leading to characteristic **flask-shaped ulcers**. This results in "amoebic dysentery," characterized by blood and mucus in the stool [1]. * **B. Amoeboma in the right iliac fossa:** An amoeboma is a chronic inflammatory pseudotumor (granuloma) that forms in the colon, most commonly in the **cecum** or ascending colon [1]. It can present as a palpable mass in the right iliac fossa, mimicking carcinoma or appendicular mass [1]. * **C. Hepatomegaly:** Extra-intestinal amoebiasis most commonly affects the liver [1]. Patients with an Amoebic Liver Abscess typically present with fever, right upper quadrant pain, and **tender hepatomegaly**. ### **High-Yield NEET-PG Pearls:** * **Trophozoites:** The diagnostic stage in stool; they may contain **ingested RBCs** (erythrophagocytosis). * **Anchovy Sauce Pus:** The classic description of the aspirated material from an amoebic liver abscess (sterile, odorless, chocolate-brown) [1]. * **Treatment:** Metronidazole or Tinidazole (to kill trophozoites) followed by a luminal agent like Paromomycin or Diloxanide furoate (to clear cysts).

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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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Tuberculosis and Mycobacterial Diseases

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Tropical and Parasitic Infections

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Viral Infections (Hepatitis, Herpes, etc.)

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Healthcare-Associated Infections

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Fungal Infections

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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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Vaccination Principles

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