Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 251: What is the most common ophthalmic lesion in AIDS?

A. Hard exudates
B. Cotton wool spots (Correct Answer)
C. Angioid streaks
D. Microaneurysms

Explanation: **Explanation:** **Cotton wool spots (CWS)** are the most common ophthalmic manifestation in patients with AIDS, occurring in approximately 25–50% of cases [1]. They are the hallmark of **HIV Microangiopathy**. * **Mechanism:** HIV causes immune complex deposition and direct endothelial damage in the retinal vasculature. This leads to precapillary arteriolar occlusion, resulting in focal ischemia of the nerve fiber layer. This ischemia causes axoplasmic stasis and the accumulation of "cytoid bodies," which appear clinically as fluffy, white, "cotton-like" lesions with indistinct margins. * **Clinical Significance:** Unlike CMV retinitis, CWS are non-infectious, asymptomatic, do not cause vision loss, and often resolve spontaneously. **Analysis of Incorrect Options:** * **Hard exudates (A):** These are lipid deposits resulting from chronic vascular leakage, typically seen in Diabetic Retinopathy or Hypertensive Retinopathy, not primarily in HIV. * **Angioid streaks (B):** These represent breaks in Bruch’s membrane. They are associated with systemic conditions like Pseudoxanthoma elasticum, Paget’s disease, and Sickle cell anemia (Mnemonic: **PEPSI**). * **Microaneurysms (D):** These are the earliest clinical sign of Diabetic Retinopathy, caused by pericyte loss and capillary wall weakening. **High-Yield Clinical Pearls for NEET-PG:** * **Most common opportunistic ocular infection in AIDS:** CMV Retinitis (characterized by "Pizza-pie" or "Crushed tomato and cheese" appearance). * **CMV Retinitis vs. CWS:** CMV retinitis follows a vascular pattern, involves full-thickness retinal necrosis, and causes permanent vision loss, whereas CWS are superficial and transient. * **CD4 Count Correlation:** CMV retinitis typically occurs when CD4 counts drop below **50 cells/mm³**, whereas HIV microangiopathy (CWS) can occur at higher counts [1].

Question 252: Which of the following antiretroviral drugs is a non-nucleoside reverse transcriptase inhibitor?

A. Zidovudine
B. Efavirenz (Correct Answer)
C. Saquinavir
D. Stavudine

Explanation: ### Explanation The correct answer is **Efavirenz (Option B)**. **Mechanism of Action:** Antiretroviral therapy (ART) is classified based on the stage of the HIV life cycle the drugs inhibit. **Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs)** like Efavirenz work by binding directly and non-competitively to the HIV-1 reverse transcriptase enzyme at a site distinct from the active site (allosteric site). This induces a conformational change that inhibits the enzyme's ability to convert viral RNA into DNA. **Analysis of Incorrect Options:** * **Zidovudine (Option A) and Stavudine (Option D):** These are **Nucleoside Reverse Transcriptase Inhibitors (NRTIs)**. Unlike NNRTIs, NRTIs are structural analogs of native nucleosides. They compete for the active site and act as "chain terminators" during DNA synthesis because they lack a 3'-OH group. * **Saquinavir (Option C):** This is a **Protease Inhibitor (PI)**. It prevents the cleavage of gag-pol polyproteins into functional viral proteins, resulting in the production of immature, non-infectious virions. **High-Yield Clinical Pearls for NEET-PG:** 1. **Efavirenz Side Effects:** Known for CNS side effects (vivid dreams, insomnia, dizziness) and is traditionally avoided in the first trimester of pregnancy due to potential neural tube defects (though recent WHO guidelines have updated its safety profile). 2. **Nevirapine:** Another common NNRTI; it is notorious for causing Stevens-Johnson Syndrome (SJS) and hepatotoxicity. 3. **Zidovudine (AZT):** The primary side effect is bone marrow suppression (anemia/neutropenia). It is also used for the prevention of mother-to-child transmission (MTCT). 4. **Current Standard:** The preferred first-line regimen in India (NACO guidelines) has shifted toward **TLD** (Tenofovir + Lamivudine + Dolutegravir), where Dolutegravir is an Integrase Strand Transfer Inhibitor (INSTI).

Question 253: Which viral infections are associated with hemolysis?

A. Hepatitis B
B. Hepatitis C
C. CMV (Correct Answer)
D. Hepatitis A

Explanation: The correct answer is **CMV (Cytomegalovirus)**. **1. Why CMV is Correct:** Cytomegalovirus (CMV) is a well-documented cause of **Autoimmune Hemolytic Anemia (AIHA)**, typically mediated by warm-reactive IgG antibodies or, less commonly, cold agglutinins [1]. The underlying mechanism involves molecular mimicry or virus-induced alteration of red blood cell (RBC) surface antigens, leading to a loss of self-tolerance and subsequent destruction of RBCs by the splenic macrophages [1]. Hemolysis is a recognized complication in both immunocompetent patients (mononucleosis-like syndrome) and immunocompromised individuals [1]. **2. Analysis of Incorrect Options:** * **Hepatitis A, B, and C:** While these hepatotropic viruses primarily cause liver inflammation and can occasionally be associated with hematological issues (like aplastic anemia in rare cases of Hepatitis A or B, or cryoglobulinemia in Hepatitis C), they are **not** classically associated with direct hemolysis. Hepatitis A may rarely trigger hemolysis in patients with pre-existing G6PD deficiency due to oxidative stress, but CMV is the established primary viral cause of AIHA among the choices provided. **3. NEET-PG High-Yield Pearls:** * **Viral triggers for AIHA:** The two most common viral triggers are **EBV (Epstein-Barr Virus)** and **CMV** [1], [2]. * **EBV vs. CMV:** EBV is classically associated with **Cold Agglutinin Disease** (IgM mediated) [2], whereas CMV is more frequently associated with **Warm AIHA** (IgG mediated) [1]. * **Other infections:** *Mycoplasma pneumoniae* is the most common bacterial cause of cold-type hemolysis (anti-I antibodies) [2]. * **Clinical Hint:** If a patient presents with fever, lymphadenopathy, splenomegaly, and a sudden drop in hemoglobin with a positive Coombs test, suspect CMV or EBV [1].

Question 254: Most common central nervous system (CNS) manifestation of HIV infection is:

A. Seizures
B. Dementia (Correct Answer)
C. Focal neurologic deficits
D. Stroke

Explanation: The most common central nervous system (CNS) manifestation of HIV infection is **HIV-Associated Dementia (HAD)**, also known as AIDS Dementia Complex [1]. **1. Why Dementia is Correct:** HIV is a neurotropic virus that crosses the blood-brain barrier early in the course of infection, primarily via infected macrophages and monocytes (the "Trojan Horse" hypothesis). It resides in the microglial cells. HAD typically occurs in the late stages of the disease when CD4 counts drop below 200 cells/mm³. It is characterized by a subcortical dementia pattern involving cognitive decline, behavioral changes, and motor dysfunction (e.g., slowed movements). **2. Why Other Options are Incorrect:** * **Seizures:** While common in HIV patients, they are usually secondary to opportunistic infections (like Toxoplasmosis [1] or Cryptococcosis) or space-occupying lesions, rather than the primary effect of the virus itself. * **Focal Neurologic Deficits:** These are typically seen in secondary complications such as Progressive Multifocal Leukoencephalopathy (PML) or CNS Lymphoma [1], but they are not the most frequent overall manifestation. * **Stroke:** HIV patients have an increased risk of stroke due to chronic inflammation and vasculopathy, but it remains less common than cognitive impairment. **NEET-PG High-Yield Pearls:** * **Most common opportunistic infection of the CNS in HIV:** Cerebral Toxoplasmosis [1]. * **Most common fungal infection of the CNS in HIV:** Cryptococcal Meningitis. * **Most common cause of a space-occupying lesion in HIV:** Cerebral Toxoplasmosis (followed by Primary CNS Lymphoma) [1]. * **Imaging finding in HAD:** Diffuse cerebral atrophy with ventricular enlargement and symmetric white matter T2 hyperintensities on MRI.

Question 255: An 80-year-old female patient complains of a 3-day history of a painful rash extending over the right half of her forehead and down to her right eyelid. There are weeping vesicular lesions on physical examination. Which of the following is the most likely diagnosis?

A. Impetigo
B. Adult chickenpox
C. Herpes zoster (Correct Answer)
D. Coxsackie A virus

Explanation: The clinical presentation of a **painful, unilateral, vesicular rash** that follows a specific dermatomal distribution is classic for **Herpes Zoster (Shingles)** [1]. In this patient, the involvement of the forehead and eyelid indicates the **ophthalmic division of the Trigeminal nerve (CN V1)**, a condition known as Herpes Zoster Ophthalmicus. **Why Herpes Zoster is correct:** Herpes Zoster results from the reactivation of the latent Varicella-Zoster Virus (VZV) within the sensory ganglia (usually the dorsal root or cranial nerve ganglia) [2]. It is characterized by a prodrome of pain or paresthesia, followed by a dermatomal eruption of vesicles on an erythematous base [1]. It strictly respects the midline, which is the hallmark of this diagnosis. **Why other options are incorrect:** * **Impetigo:** Typically presents as "honey-colored" crusts, usually caused by *S. aureus* or *S. pyogenes*. It is not restricted to a single dermatome and is generally itchy rather than severely painful. * **Adult Chickenpox:** This is the primary infection of VZV. It presents with a generalized, pruritic, "dewdrop on a rose petal" rash in various stages of evolution, rather than a localized dermatomal pattern [2]. * **Coxsackie A Virus:** Most commonly causes Hand-Foot-and-Mouth disease or Herpangina. It presents with oral ulcers and vesicular rashes on the palms and soles, not a unilateral facial dermatomal distribution. **NEET-PG High-Yield Pearls:** * **Hutchinson’s Sign:** Vesicles on the tip, side, or root of the nose indicate involvement of the nasociliary branch of CN V1, predicting a high risk of ocular complications (keratitis/uveitis). * **Post-Herpetic Neuralgia (PHN):** The most common complication, defined as pain persisting >90 days after the rash heals [1]. * **Treatment:** Oral Acyclovir, Valacyclovir, or Famciclovir (ideally started within 72 hours) [3]. * **Ramsay Hunt Syndrome:** Zoster involving the geniculate ganglion (CN VII), presenting with facial palsy and vesicles in the external auditory canal.

Question 256: A patient with AIDS presents with an acute episode of diarrhea. Stool examination reveals an oval structure, 8 to 9 micrometers in diameter, which is acid-fast and fluoresces blue under ultraviolet light. What is the drug of choice for this patient?

A. Trimethoprim-sulfamethoxazole (Correct Answer)
B. Nitazoxanide
C. Primaquine
D. Niclosamide

Explanation: ### Explanation The clinical presentation and laboratory findings are diagnostic of **Cyclospora cayetanensis**. In patients with AIDS, *Cyclospora* causes chronic, watery diarrhea [1]. The key diagnostic features provided are: 1. **Size:** 8–10 μm (larger than *Cryptosporidium* at 4–5 μm). 2. **Staining:** Acid-fast (variable) [1]. 3. **Autofluorescence:** Under UV light (330–365 nm), *Cyclospora* oocysts fluoresce **blue/white**, which is a pathognomonic feature used to differentiate it from other coccidian parasites. **1. Why Trimethoprim-sulfamethoxazole (TMP-SMX) is correct:** TMP-SMX is the **drug of choice** for Cyclosporiasis [1]. While most protozoal infections are treated with metronidazole or nitazoxanide, *Cyclospora* (and *Cystoisospora*) are unique in their exquisite sensitivity to sulfonamides. In HIV patients, higher doses and long-term suppressive therapy may be required to prevent recurrence. **2. Why the other options are incorrect:** * **B. Nitazoxanide:** This is the drug of choice for *Cryptosporidium parvum* in immunocompetent patients. While it has broad activity, it is less effective than TMP-SMX for *Cyclospora*. * **C. Primaquine:** Used primarily for the radical cure of *Plasmodium vivax* malaria and as an alternative for *Pneumocystis jirovecii* pneumonia; it has no role in treating intestinal coccidia. * **D. Niclosamide:** This is an anthelmintic used for tapeworm infections (e.g., *Taenia saginata*); it is ineffective against protozoa. ### NEET-PG High-Yield Pearls: * **Size Comparison:** *Cryptosporidium* (4–5 μm) < *Cyclospora* (8–10 μm) < *Cystoisospora* (25–30 μm). * **Autofluorescence:** Only *Cyclospora* and *Cystoisospora* fluoresce under UV light; *Cryptosporidium* does not. * **Modified Acid-Fast Stain:** All three (the "Coccidia" trio) are acid-fast, but *Cyclospora* stains variably (some oocysts look like "ghosts") [1]. * **Treatment Exception:** Remember that for most intestinal parasites, we avoid antibiotics, but for **Cyclospora** and **Cystoisospora**, **TMP-SMX** (Co-trimoxazole) is the gold standard [1].

Question 257: A 15-year-old female with HIV infection on antiretroviral therapy presents with nausea, vomiting, and flank pain. Urine microscopy showed rectangular plate and needle-shaped crystals. Serum creatinine was raised. What is the likely cause?

A. Indinavir (Correct Answer)
B. Ritonavir
C. Nevirapine
D. Zidovudine

Explanation: ### Explanation The clinical presentation of nausea, vomiting, flank pain, and acute kidney injury (raised creatinine) in an HIV-positive patient points toward **nephrolithiasis and obstructive uropathy** [1]. **1. Why Indinavir is the Correct Answer:** Indinavir is a Protease Inhibitor (PI) known for its poor solubility at physiological urinary pH. Approximately 20% of the drug is excreted unchanged in the urine. This leads to the formation of **Indinavir crystals**, which are characteristically described as **rectangular plates, fans, or needle-shaped crystals**. These crystals can cause crystalluria, nephrolithiasis (kidney stones), and "sludge" formation, leading to obstructive uropathy and interstitial nephritis. **2. Why the Other Options are Incorrect:** * **Ritonavir (B):** While also a Protease Inhibitor, it is primarily used in low doses as a "booster" for other PIs. It is not typically associated with crystalluria or nephrolithiasis. * **Nevirapine (C):** An NNRTI primarily associated with hepatotoxicity and severe dermatological reactions like Stevens-Johnson Syndrome (SJS), not renal stones. * **Zidovudine (D):** An NRTI whose hallmark side effects are bone marrow suppression (anemia, neutropenia) and myopathy. It does not cause crystal-induced kidney injury. **3. High-Yield Clinical Pearls for NEET-PG:** * **Management:** Indinavir-induced stones are **radiolucent** (not seen on X-ray). Treatment involves vigorous hydration (at least 1.5–2 liters/day) and temporary discontinuation of the drug. * **Other Drugs causing Crystalluria:** Acyclovir (needle-shaped), Sulfonamides (rosette/wheat-sheaf), and Methotrexate. * **Tenofovir (TDF):** Another high-yield HIV drug causing renal issues, but it presents as **Fanconi Syndrome** (proximal tubule dysfunction) rather than stones.

Question 258: What is true about amoebic liver abscess?

A. The male to female ratio is greater than 10:1. (Correct Answer)
B. It is not predisposed by alcohol consumption.
C. It is more common in patients with diabetes.
D. Entamoeba histolytica is isolated in more than 50% of cases from blood culture.

Explanation: **Amoebic Liver Abscess (ALA)** is the most common extra-intestinal manifestation of infection by *Entamoeba histolytica*. [1] ### **Explanation of Options** * **Option A (Correct):** ALA shows a striking male preponderance, with a **male-to-female ratio often exceeding 10:1**. While intestinal amoebiasis affects both sexes equally, ALA is significantly more common in adult men. This is hypothesized to be due to the protective effect of menstrual blood loss (reducing iron availability for the parasite) and the hormonal influence on the immune response. * **Option B (Incorrect):** **Alcohol consumption** is a well-known predisposing factor for ALA. Chronic alcohol intake can impair the liver's Kupffer cell function and alter the local immune environment, making the liver more susceptible to abscess formation. * **Option C (Incorrect):** Unlike pyogenic liver abscesses, which are strongly associated with **Diabetes Mellitus**, ALA does not show a significant clinical correlation with diabetes. * **Option D (Incorrect):** *E. histolytica* is a protozoan, not a bacterium; it is **never isolated from blood cultures**. Diagnosis is typically made via serology (ELISA for antibodies) and imaging (USG/CT). ### **High-Yield Clinical Pearls for NEET-PG** * **Location:** Most commonly involves the **Right Lobe** of the liver (due to the bulk of portal blood flow). * **Aspirate:** Classically described as **"Anchovy sauce"** appearance (odorless, reddish-brown, consisting of liquefied hepatocytes). [1] * **Microscopy:** Trophozoites are rarely found in the pus (only in <15% of cases) because they reside in the abscess wall, not the necrotic center. * **Treatment of Choice:** **Metronidazole** (or Tinidazole) followed by a luminal amoebicide (e.g., Diloxanide furoate or Paromomycin) to eradicate the intestinal colonization.

Question 259: Which of the following statements about acute hepatitis is true?

A. In Hepatitis C virus (HCV) infection, genotypes 2 and 3 are the most prevalent worldwide.
B. Anti-HCV antibodies are never present in 10% of cases. (Correct Answer)
C. Hepatitis E virus (HEV) is the commonest cause of acute hepatitis.
D. Hepatitis A virus (HAV) is more common in adults than in children.

Explanation: The correct answer is **Option B**. In approximately **10% of acute Hepatitis C (HCV) cases**, anti-HCV antibodies are never detectable during the acute phase of the illness. This occurs because the "window period" for antibody seroconversion can be prolonged (averaging 7–8 weeks) [1]. In these patients, the diagnosis must be confirmed by detecting **HCV RNA** using PCR, which is the earliest marker of infection [1]. **Analysis of Incorrect Options:** * **Option A:** Worldwide, **Genotype 1** is the most prevalent HCV genotype (approx. 46%), followed by Genotype 3 [1]. In India, Genotype 3 is the most common. * **Option C:** While HEV is a major cause of epidemics in developing countries, **Hepatitis A (HAV)** is globally the most common cause of acute viral hepatitis, especially in the pediatric population [2]. * **Option D:** HAV is significantly **more common in children** [2]. In endemic areas like India, most children are exposed early in life, often resulting in asymptomatic or mild infections, leading to lifelong immunity before reaching adulthood. **High-Yield Clinical Pearls for NEET-PG:** * **HCV Diagnosis:** HCV RNA is the gold standard for diagnosing acute infection; Anti-HCV indicates exposure but cannot distinguish between acute, chronic, or resolved infection [1]. * **HEV & Pregnancy:** HEV carries a high mortality rate (up to 20%) in pregnant women, particularly in the third trimester, due to fulminant hepatic failure. * **Hepatitis B:** The first serological marker to appear is **HBsAg**, while the first antibody to appear is **Anti-HBc (IgM)**.

Question 260: In chronic Hepatitis B (HBV) infection, the presence of HBeAg suggests which of the following?

A. Ongoing viral replication (Correct Answer)
B. Resolving infection
C. Development of cirrhosis
D. Development of Hepatoma

Explanation: **Explanation:** The **Hepatitis B e-antigen (HBeAg)** is a soluble protein derived from the precore region of the HBV genome [1]. It serves as a qualitative marker of **active viral replication** and high infectivity [1]. 1. **Why Option A is Correct:** HBeAg is secreted by hepatocytes only when the virus is actively replicating. Its presence in the serum correlates with high levels of HBV DNA and indicates that the patient is highly contagious [1]. The transition from HBeAg-positive to anti-HBe (seroconversion) usually signals a reduction in viral load and a transition to a lower replicative state [1]. 2. **Why Other Options are Incorrect:** * **Option B (Resolving infection):** Resolution is characterized by the disappearance of HBsAg and the appearance of **Anti-HBs** [1]. HBeAg persistence indicates chronicity, not resolution. * **Option C & D (Cirrhosis/Hepatoma):** While chronic HBV is a major risk factor for cirrhosis and Hepatocellular Carcinoma (HCC), HBeAg is a marker of replication, not a direct marker of structural liver damage or malignancy [1]. Notably, HCC can occur in "HBeAg-negative" patients if they have high viral DNA or have integrated the virus into their genome. **NEET-PG High-Yield Pearls:** * **Window Period:** The time between the disappearance of HBsAg and the appearance of Anti-HBs. The only marker present is **Anti-HBc IgM** [1]. * **Precore Mutant:** A condition where the patient has high HBV DNA and active liver disease but is **HBeAg negative** (due to a mutation in the precore region that prevents HBeAg secretion) [1]. * **Best indicator of HBV infectivity:** HBV DNA levels (quantitative) or HBeAg (qualitative) [1]. * **First marker to appear:** HBsAg [1].

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