Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 511: Tuberculosis lymphadenitis of the cervical lymph nodes is also called:

A. Pott's disease
B. Lupus vulgaris
C. Scrofula (Correct Answer)
D. Ghon's focus

Explanation: **Explanation:** **Tuberculous Lymphadenitis (Scrofula)** The correct answer is **Scrofula**. This term specifically refers to tuberculosis of the cervical lymph nodes. It is the most common form of extrapulmonary tuberculosis [1]. In adults, it is primarily caused by *Mycobacterium tuberculosis*, whereas in children, it can also be caused by atypical mycobacteria (e.g., *M. scrofulaceum*). Clinically, it presents as "cold abscesses"—painless, firm, or matted swellings that may eventually develop into discharging sinuses [1]. **Analysis of Incorrect Options:** * **A. Pott’s Disease:** This refers to tuberculosis of the **spine**, typically involving the intervertebral discs and adjacent vertebrae, often leading to kyphosis (gibbus deformity) [2]. * **B. Lupus Vulgaris:** This is a progressive form of **cutaneous (skin) tuberculosis** characterized by "apple-jelly" nodules on diascopy, most commonly occurring on the face and neck. * **C. Ghon’s Focus:** This is a **primary pulmonary lesion** consisting of a small area of granulomatous inflammation (usually subpleural) in the mid or lower lobes of the lung [3]. **High-Yield Clinical Pearls for NEET-PG:** * **Most common site:** The **jugulodigastric** node is the most frequently involved cervical node. * **Diagnosis:** Fine Needle Aspiration Cytology (FNAC) is the initial investigation of choice, showing caseating granulomas. * **Histopathology:** Characterized by Langhans giant cells and central caseous necrosis [3]. * **Paradoxical Upgrading Reaction:** During ATT, lymph nodes may temporarily enlarge or new ones may appear; this is an immune response, not treatment failure [1].

Question 512: In HIV infection, prophylaxis for Pneumocystis jiroveci pneumonia may be stopped if the CD4 count persists above 200 cells/mm for what duration?

A. 1 month
B. 2 months
C. 3 months (Correct Answer)
D. 6 months

Explanation: **Explanation:** The primary goal of opportunistic infection (OI) prophylaxis in HIV patients is to prevent disease during periods of severe immunosuppression. For *Pneumocystis jiroveci* pneumonia (PCP), the risk of infection significantly decreases once the immune system recovers following the initiation of Highly Active Antiretroviral Therapy (HAART) [1]. **1. Why 3 months is correct:** According to standard clinical guidelines (CDC/WHO), PCP prophylaxis (usually with Trimethoprim-Sulfamethoxazole) can be safely discontinued if the **CD4+ T-cell count increases to >200 cells/mm³ for at least 3 consecutive months**. This duration is required to ensure that the immune recovery is stable and robust enough to handle potential exposure to the fungus without pharmacological support. **2. Why other options are incorrect:** * **1 and 2 months (Options A & B):** These durations are considered too short to confirm sustained immune reconstitution. Discontinuing prophylaxis prematurely increases the risk of "rebound" infections if the CD4 count fluctuates [2]. * **6 months (Option D):** While waiting 6 months is safe, it is not the minimum standard required. Guidelines aim to reduce pill burden and potential drug toxicities as soon as it is clinically safe to do so, which is established at the 3-month mark. **High-Yield Clinical Pearls for NEET-PG:** * **Indication for starting PCP prophylaxis:** CD4 count <200 cells/mm³ or presence of oropharyngeal candidiasis. * **Drug of Choice:** Trimethoprim-Sulfamethoxazole (Co-trimoxazole) [1]. * **Alternative if allergic:** Dapsone or Atovaquone [1]. * **Toxoplasmosis Prophylaxis:** Also discontinued when CD4 >200 cells/mm³ for >3 months. * **MAC Prophylaxis:** Discontinued when CD4 >100 cells/mm³ for >3 months.

Question 513: What is the most common fungal infection in febrile neutropenia?

A. Aspergillus niger
B. Candida (Correct Answer)
C. Mucormycosis
D. Aspergillus fumigatus

Explanation: **Explanation:** In patients with febrile neutropenia, fungal infections typically emerge as secondary infections after 4–7 days of persistent fever despite broad-spectrum antibiotic therapy [1]. **Why Candida is the correct answer:** **Candida species** are the most common cause of fungal infections in neutropenic patients. The primary reason is the disruption of mucosal barriers (mucositis) caused by chemotherapy, which allows commensal *Candida* from the gastrointestinal or genitourinary tract to enter the bloodstream [1]. Among the species, *Candida albicans* remains the most frequent isolate, though non-albicans species (like *C. tropicalis*) are increasing in prevalence [1]. **Analysis of Incorrect Options:** * **Aspergillus fumigatus (Option D):** This is the most common **mould** (filamentous fungus) and the second most common fungal infection overall. It typically presents as Invasive Pulmonary Aspergillosis (IPA) and is more common in patients with prolonged, profound neutropenia (>10–15 days) [2]. * **Aspergillus niger (Option A):** While a member of the Aspergillus family, it is a less common cause of invasive disease compared to *A. fumigatus* and is more frequently associated with otomycosis. * **Mucormycosis (Option C):** This is an aggressive, angioinvasive infection seen in neutropenic patients and diabetics, but it is significantly rarer than both *Candida* and *Aspergillus*. **High-Yield Clinical Pearls for NEET-PG:** * **First-line Fungal Prophylaxis:** Fluconazole or Posaconazole (depending on the risk profile). * **Empiric Treatment:** If fever persists >4 days, start Echinocandins (e.g., Caspofungin) or Liposomal Amphotericin B [1]. * **Diagnostic Marker:** Beta-D-Glucan assay is used for *Candida* and *Aspergillus*, while Galactomannan is specific for *Aspergillus* [2]. * **Imaging:** The "Halo Sign" on CT chest is highly suggestive of early Invasive Aspergillosis [2].

Question 514: Subacute sclerosing panencephalitis is associated with which virus?

A. Mumps
B. Measles (Correct Answer)
C. Exanthema subitum
D. Erythema infectiosum

Explanation: **Explanation:** **Subacute Sclerosing Panencephalitis (SSPE)**, also known as Dawson disease, is a rare, progressive, and fatal neurodegenerative condition caused by a **persistent, aberrant infection of the Measles virus** (Rubeola) [1]. 1. **Why Measles is Correct:** SSPE occurs due to a mutated measles virus that lacks the 'M' (matrix) protein, preventing the virus from budding. Instead, it spreads directly from cell to cell via syncytia formation, evading the immune system. It typically manifests 7–10 years after an initial measles infection, especially in children infected before the age of two [1]. 2. **Why Incorrect Options are Wrong:** * **Mumps:** Primarily causes parotitis and orchitis; its neurological complication is typically acute aseptic meningitis, not a chronic panencephalitis. * **Exanthema Subitum (Roseola Infantum):** Caused by HHV-6. While it can cause febrile seizures, it is not associated with SSPE. * **Erythema Infectiosum (Fifth Disease):** Caused by Parvovirus B19. It is associated with aplastic crisis and hydrops fetalis, not chronic CNS degeneration. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Stages:** Characterized by behavioral changes (Stage 1), **myoclonic jerks** (Stage 2), and eventual vegetative state/decorticate rigidity. * **EEG Finding:** Pathognomonic **periodic, high-voltage slow-wave complexes** (Radermecker complexes). * **CSF Analysis:** Shows significantly **elevated anti-measles antibody titers** (intrathecal synthesis) and oligoclonal bands [2]. * **Diagnosis:** Brain biopsy shows **Cowdry type A** intranuclear inclusion bodies in neurons and glial cells. * **Prevention:** The most effective strategy is universal vaccination with the **MMR vaccine** [1].

Question 515: Which of the following is NOT a manifestation of Giardiasis?

A. Malaise
B. Diarrhea
C. Steatorrhea
D. Gastrointestinal bleeding (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Gastrointestinal bleeding**. *Giardia duodenalis* (also known as *G. lamblia*) is a flagellated protozoan that colonizes the upper small intestine (duodenum and jejunum). Unlike invasive pathogens like *Entamoeba histolytica* or *Shigella*, *Giardia* is **non-invasive**. It attaches to the intestinal villi via a ventral sucking disc, causing villous atrophy and malabsorption without penetrating the mucosa or causing ulceration. Therefore, it does **not** cause inflammatory diarrhea, mucosal friability, or gastrointestinal bleeding. **Analysis of Options:** * **Malaise (A):** This is a common constitutional symptom of chronic giardiasis, often accompanied by fatigue and weight loss due to nutrient malabsorption. * **Diarrhea (B):** This is the hallmark symptom. It typically begins as watery diarrhea but can transition into chronic, greasy stools. * **Steatorrhea (C):** *Giardia* interferes with the action of lipase and deconjugates bile salts, leading to fat malabsorption. This results in foul-smelling, bulky, frothy stools that float (steatorrhea). **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** 1–3 weeks (longer than bacterial/viral causes). * **Diagnosis:** Stool microscopy (cysts or pear-shaped trophozoites with "owl-eye" appearance). **String Test** (Entero-test) can be used if stool exams are negative. * **Drug of Choice:** Tinidazole (single dose) or Metronidazole. * **Association:** Common in patients with **IgA deficiency** (Common Variable Immunodeficiency). * **Key Distinction:** *Giardia* = Malabsorption/Non-bloody; *E. histolytica* = Invasive/Bloody (Dysentery).

Question 516: Multidrug Resistance Tuberculosis (MDR-TB) should be considered in patients with which of the following findings?

A. Contact with a known case of MDR TB
B. Clinical deterioration
C. Sputum smear positive at 5 months of treatment
D. All of the above (Correct Answer)

Explanation: **Explanation:** Multidrug-resistant tuberculosis (MDR-TB) is defined as resistance to at least **Isoniazid (H) and Rifampicin (R)**. Identifying patients at high risk for MDR-TB is crucial for initiating appropriate second-line treatment and preventing further transmission. **Why "All of the Above" is correct:** * **Contact with a known case of MDR-TB (Option A):** This is the strongest epidemiological risk factor. Primary resistance occurs when a person is directly infected with a strain that is already resistant. * **Clinical deterioration (Option B):** If a patient’s symptoms (fever, cough, weight loss) worsen despite being on standard First-Line Treatment (FLT), it indicates that the drugs are likely ineffective against the infecting strain. * **Sputum smear positive at 5 months (Option C):** Under the National TB Elimination Program (NTEP) guidelines, a patient who remains sputum smear or culture positive at the end of 5 months or more of treatment is defined as a **"Treatment Failure."** Failure to convert to negative is a hallmark indicator of drug resistance [1]. **Clinical Pearls for NEET-PG:** * **Diagnosis:** The investigation of choice for rapid screening of MDR-TB is **CBNAAT (GeneXpert)**, which detects Rifampicin resistance (a surrogate marker for MDR-TB). * **Extensively Drug-Resistant TB (XDR-TB):** Defined as MDR-TB plus resistance to any **Fluoroquinolone** and at least one **Group A drug** (Bedaquiline or Linezolid) as per the updated WHO definition. * **Universal Drug Susceptibility Testing (UDST):** Current guidelines mandate that every diagnosed TB patient should be screened for drug resistance at the time of diagnosis.

Question 517: In AIDS patients with a CD4 count >75 lymphocytes/mm ³, cotton wool spots on eye examination suggest infection by which of the following organisms?

A. Cytomegalovirus (CMV) (Correct Answer)
B. Toxoplasma gondii
C. Cryptococcus neoformans
D. Acanthamoeba

Explanation: In AIDS patients with a CD4 count >75 lymphocytes/mm3, cotton wool spots on eye examination suggest infection by which of the following organisms? [1] **Explanation:** **1. Why Cytomegalovirus (CMV) is Correct:** In patients with HIV/AIDS, **Cytomegalovirus (CMV) Retinitis** is the most common opportunistic ocular infection. It typically occurs when the CD4 count falls below **50–100 cells/mm3**. Cotton wool spots (CWS) represent microinfarcts of the retinal nerve fiber layer. While CWS can be a non-specific finding of HIV retinopathy, in the context of advanced immunosuppression, they are often the earliest clinical sign of CMV retinitis [1]. As the disease progresses, it manifests as the classic "pizza-pie" or "cheese and ketchup" appearance (hemorrhage with white exudates). **2. Why the Other Options are Incorrect:** * **Toxoplasma gondii:** Ocular toxoplasmosis typically presents as focal necrotizing retinochoroiditis with significant vitreous inflammation ("headlight in the fog" appearance), rather than isolated cotton wool spots. [1] * **Cryptococcus neoformans:** This primarily causes fungal meningitis. Ocular involvement is usually secondary to increased intracranial pressure (papilledema) or direct optic nerve involvement, rather than retinal cotton wool spots. [1] * **Acanthamoeba:** This is associated with keratitis (corneal infection), particularly in contact lens users. It presents with severe pain and a characteristic ring-shaped corneal infiltrate, not retinal pathology. **3. Clinical Pearls for NEET-PG:** * **HIV Retinopathy:** The most common eye finding in HIV; characterized by benign, transient cotton wool spots that do not require specific treatment. [1] * **CMV Retinitis Treatment:** Valganciclovir (oral), Ganciclovir (IV), or Foscarnet. * **Immune Reconstitution Inflammatory Syndrome (IRIS):** Starting ART in patients with CMV can lead to "Immune Recovery Uveitis." * **CD4 Thresholds:** * <200: Pneumocystis jirovecii * <100: Toxoplasmosis, Cryptococcosis * <50: CMV, Mycobacterium avium complex (MAC)

Question 518: Which of the following is NOT a recognized infectious cause of eosinophilia?

A. Malaria (Correct Answer)
B. Ascaris lumbricoides
C. Filariasis
D. Strongyloidiasis

Explanation: **Explanation:** The key to answering this question lies in understanding the host immune response to different types of pathogens. **Eosinophilia** is a hallmark of **helminthic (parasitic worm)** infections, particularly during the tissue-invasive phase of their life cycle [1]. **1. Why Malaria is the Correct Answer:** Malaria is caused by *Plasmodium* species, which are **protozoa**, not helminths. Protozoal infections (like Malaria, Amoebiasis, and Giardiasis) characteristically do **not** cause eosinophilia. Malaria typically presents with anemia, thrombocytopenia, and atypical lymphocytosis, but an elevated eosinophil count should prompt a search for a co-infection. **2. Why the other options are incorrect:** * **Ascaris lumbricoides:** Causes eosinophilia during the **Loeffler’s syndrome** phase, where larvae migrate through the lungs [1]. * **Filariasis:** Caused by *Wuchereria bancrofti*, it is a classic cause of tropical pulmonary eosinophilia (TPE), characterized by extreme elevations in eosinophil counts and IgE [2]. * **Strongyloidiasis:** This helminth can persist for decades in the host via autoinfection; it is a well-known cause of fluctuating or persistent eosinophilia [1]. **High-Yield Clinical Pearls for NEET-PG:** * **NAACP mnemonic** for causes of eosinophilia: **N**eoplasm, **A**llergy/Asthma, **A**ddison’s disease, **C**onnective tissue disorders, and **P**arasites (Helminths). * **Protozoa vs. Helminths:** Remember that protozoa (Malaria, Leishmaniasis, Trypanosomiasis) generally cause **leukopenia or normal counts**, whereas helminths (especially those with a tissue phase) cause **eosinophilia**. * **Exception:** Ectoparasites like Scabies can sometimes cause mild eosinophilia due to allergic sensitization.

Question 519: What is the treatment of choice for tropical splenomegaly?

A. Chloroquine for 6 months
B. Mefloquine for 3 months
C. Proguanil (Correct Answer)
D. Pyrimethamine + sulphadoxine for 1 month

Explanation: **Explanation:** **Tropical Splenomegaly Syndrome (TSS)**, now more commonly referred to as **Hyperreactive Malarial Splenomegaly (HMS)**, is an aberrant immunological response to chronic or repeated malaria infections. It is characterized by massive splenomegaly, high titers of anti-malarial antibodies, and elevated serum IgM levels. **Why Proguanil is the Correct Choice:** The cornerstone of management for HMS is **long-term malaria chemoprophylaxis**. The goal is to eliminate the antigenic stimulus (Plasmodium parasites) that drives the hyper-immune response. **Proguanil** (daily) or **Chloroquine** (weekly) are the preferred agents [1]. Proguanil is frequently cited in standard textbooks (like Harrison’s) as the treatment of choice because it is well-tolerated for the prolonged duration (often lifelong or for several years) required to reduce spleen size and normalize hematological parameters. **Analysis of Incorrect Options:** * **Option A (Chloroquine for 6 months):** While Chloroquine is used, the duration of 6 months is often insufficient. Treatment usually needs to be continued for years or indefinitely in endemic areas to prevent relapse. * **Option B (Mefloquine for 3 months):** Mefloquine is generally reserved for prophylaxis in resistant areas or acute treatment; it is not the standard first-line agent for the long-term management of HMS [1]. * **Option D (Pyrimethamine + Sulphadoxine):** This combination is used for acute malaria treatment or intermittent preventive treatment in pregnancy (IPTp), but its side effect profile and resistance patterns make it unsuitable for the long-term daily/weekly prophylaxis required in HMS [1]. **Clinical Pearls for NEET-PG:** * **Diagnostic Criteria (Fakir and Crane):** Massive splenomegaly (>10cm), elevated IgM (>2 SD above local mean), and clinical response to long-term antimalarials. * **Pathophysiology:** Excessive production of B-lymphocytes and IgM leading to immune-complex deposition in the splenic sinusoids. * **Histology:** Hepatic sinusoidal lymphocytosis (Kupffer cell hyperplasia) is a characteristic finding. * **Complication:** If untreated, it can progress to splenic lymphoma or secondary infections.

Question 520: Which is a common central nervous system (CNS) lesion in HIV?

A. Cryptococcus
B. Toxoplasma
C. Lymphoma
D. All of the above (Correct Answer)

Explanation: **Explanation:** In patients with HIV/AIDS, the central nervous system (CNS) is a frequent site of opportunistic infections and malignancies, particularly when the CD4 count drops below 200 cells/mm³. [1] 1. **Toxoplasma gondii:** This is the **most common** cause of focal CNS lesions in HIV patients. It typically presents with fever, headache, and focal neurological deficits. On MRI, it classically shows multiple "ring-enhancing lesions" with a predilection for the basal ganglia. [1] 2. **Primary CNS Lymphoma (PCNSL):** This is the second most common cause of focal CNS lesions. It is strongly associated with the **Epstein-Barr Virus (EBV)**. Radiologically, it often presents as a large, solitary, weakly enhancing lesion, making it the primary differential diagnosis for Toxoplasmosis. [1] 3. **Cryptococcus neoformans:** This is the **most common cause of fungal meningitis** in HIV. While it primarily presents as meningitis (diffuse involvement), it can also form "cryptococcomas" (solid lesions) or "soap-bubble" lesions in the basal ganglia. **Why "All of the above" is correct:** All three entities are hallmark opportunistic conditions in advanced HIV. While their clinical presentations differ slightly, they are all frequently encountered CNS pathologies in this patient population. **High-Yield Clinical Pearls for NEET-PG:** * **Most common CNS mass lesion:** Toxoplasmosis. * **Most common fungal CNS infection:** Cryptococcosis (Diagnosed via India Ink or CrAg test). * **Toxoplasmosis vs. Lymphoma:** If a patient fails to respond to anti-toxoplasma therapy (Pyrimethamine + Sulfadiazine) within 2 weeks, a brain biopsy is indicated to rule out Lymphoma. [1] * **Thallium-201 SPECT:** Positive (increased uptake) in Lymphoma, negative in Toxoplasmosis.

Practice by Chapter

Principles of Antimicrobial Therapy

Practice Questions

Fever of Unknown Origin

Practice Questions

HIV/AIDS and Related Infections

Practice Questions

Tuberculosis and Mycobacterial Diseases

Practice Questions

Tropical and Parasitic Infections

Practice Questions

Viral Infections (Hepatitis, Herpes, etc.)

Practice Questions

Healthcare-Associated Infections

Practice Questions

Fungal Infections

Practice Questions

Sepsis and Septic Shock

Practice Questions

Infection in Immunocompromised Hosts

Practice Questions

Emerging and Re-emerging Infections

Practice Questions

Antimicrobial Resistance

Practice Questions

Vaccination Principles

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free