Infectious Diseases — MCQs

A 35-year-old HIV-positive man presents with a 6-month history of progressive memory loss and incontinence. He is currently on zidovudine and a protease inhibitor. Examination reveals deficits in cognitive and fine motor control functions. His CD4 cell count is 25/mm 3. MRI studies show moderate brain atrophy with no focal lesions. Lumbar puncture shows no cerebrospinal fluid abnormalities. What is the most likely diagnosis?

Q325Easy

Which variant of immunoblastic lymphoma is primarily seen in HIV patients?

Q326Medium

Acalculous cholecystitis can be seen in all the following conditions except?

Q327Easy

Which of the following is NOT involved in leprosy?

Q328Easy

In which of the following conditions is the pneumococcal vaccine indicated?

Q329Medium

A 35-year-old man presents with an 18 kg weight loss over the preceding 4 months. He reports no dieting, but experiences abdominal pain, nausea, and diarrhea. He also has a chronic cough. Sputum studies reveal Pneumocystis carinii, and esophagogastroduodenoscopy with biopsy shows Candida and Herpes in the esophagus. Which group of viruses is the causative agent of this patient's underlying disease?

Q330Medium

In the serological testing for HIV infection, an early positive ELISA is primarily due to the detection of which of the following?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 321: Ablett classification is used for grading which of the following conditions?

A. Hidradenitis suppurativa
B. Tetanus (Correct Answer)
C. Pyogenic abscess
D. Pyogenic granuloma

Explanation: **Explanation:** The **Ablett Classification** is the standard clinical tool used to grade the severity of **Tetanus**. It categorizes the disease based on the presence and intensity of symptoms such as trismus (lockjaw), muscle spasms, and autonomic dysfunction. * **Grade I (Mild):** Mild trismus, general spasticity, no respiratory distress, and no spasms. * **Grade II (Moderate):** Moderate trismus, rigid muscles, and brief, mild spasms. * **Grade III (Severe):** Severe trismus, generalized rigidity, and frequent, prolonged spasms with respiratory distress. * **Grade IV (Very Severe):** All features of Grade III plus severe **autonomic instability** (hypertension, tachycardia, or arrhythmia). **Why other options are incorrect:** * **Hidradenitis suppurativa:** Graded using the **Hurley Staging System** (Stage I-III). * **Pyogenic abscess:** These are typically described by anatomical location or etiology rather than a specific eponymized grading system like Ablett. * **Pyogenic granuloma:** This is a benign vascular tumor of the skin or mucous membranes; it does not have a formal severity classification system used in clinical practice. **NEET-PG High-Yield Pearls:** * **Tetanus Toxin:** *Tetanospasmin* acts by blocking the release of inhibitory neurotransmitters (**GABA and Glycine**) from Renshaw cells in the spinal cord. * **First Sign:** Trismus (lockjaw) is the most common presenting symptom. * **Risus Sardonicus:** A characteristic "sneering" facial expression due to facial muscle spasms. * **Management:** The priority is maintaining the airway, administering Metronidazole (preferred over Penicillin), and giving Human Tetanus Immunoglobulin (HTIG).

Question 322: What is the most common chronic viral illness?

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

Explanation: **Explanation:** The correct answer is **Hepatitis C (HCV)**. The question asks for the most common **chronic** viral illness, referring to the rate of chronicity following an acute infection. **1. Why Hepatitis C is correct:** Hepatitis C is notorious for its high propensity to persist in the body [1]. Approximately **75%–85%** of individuals infected with HCV fail to clear the virus and progress to chronic infection [1]. This high rate of chronicity occurs because the virus frequently undergoes genetic mutations (due to lack of proofreading by its RNA polymerase), allowing it to evade the host's immune response. **2. Why the other options are incorrect:** * **Hepatitis A:** This is an enterically transmitted virus (fecal-oral route) that causes only acute hepatitis. It **never** causes chronic infection. * **Hepatitis B (HBV):** While HBV is a major cause of chronic liver disease globally, the risk of chronicity depends on the age of acquisition. In adults, only **5%–10%** of cases become chronic [1]. Although the absolute number of people with chronic HBV is high, the *rate* of chronicity per infection is significantly lower than HCV [1]. * **Hepatitis D (HDV):** HDV is a defective virus that requires the presence of HBsAg to replicate. While it can cause severe chronic disease (especially in superinfections), it is far less common than HCV in the general population. **High-Yield NEET-PG Pearls:** * **Highest Chronicity Rate:** Hepatitis C (~80%). * **Most Common Cause of Post-Transfusion Hepatitis:** Hepatitis C (historically, before screening). * **Age and HBV Chronicity:** In neonates, HBV chronicity is **90%**, whereas in adults, it is **<10%** [1]. * **HCV Screening:** The first-line test is Anti-HCV antibodies; the confirmatory test is HCV-RNA (PCR) [1]. * **Treatment:** HCV is now considered "curable" with Direct-Acting Antivirals (DAAs) like Sofosbuvir.

Question 323: Which of the following is NOT a major feature of AIDS?

A. Fever lasting longer than 1 month
B. Diarrhea lasting longer than 1 month
C. Loss of more than 10% of body weight
D. Cough lasting longer than 1 month (Correct Answer)

Explanation: This question is based on the **WHO Case Definition for AIDS Surveillance**, which categorizes clinical signs into Major and Minor criteria. [1] ### **Explanation of the Correct Answer** **D. Cough lasting longer than 1 month** is the correct answer because it is classified as a **Minor Sign**, not a major feature. [1] While respiratory infections (like *Pneumocystis jirovecii* or Tuberculosis) are common in AIDS patients, a chronic cough is considered a non-specific symptom that requires further investigation but does not carry the same diagnostic weight as the major signs in the surveillance definition. [1] ### **Analysis of Incorrect Options (Major Signs)** The WHO clinical criteria for AIDS in adults require at least **two major signs** associated with at least **one minor sign**. The major signs include: * **A. Fever lasting >1 month:** Persistent or intermittent pyrexia is a hallmark of advanced HIV/AIDS. [1] * **B. Diarrhea lasting >1 month:** Chronic diarrhea (often due to Cryptosporidium or CMV) is a primary indicator of the wasting syndrome. [1] * **C. Weight loss >10% of body weight:** Also known as "Slim Disease," involuntary profound weight loss is a cardinal major feature. [1] ### **Clinical Pearls for NEET-PG** * **Minor Signs of AIDS:** Persistent cough (>1 month), generalized pruritic dermatitis, recurrent herpes zoster, oropharyngeal candidiasis, and generalized lymphadenopathy. [1] * **The "Slim Disease":** In Africa, AIDS was historically referred to as Slim Disease due to the triad of fever, diarrhea, and massive weight loss. [1] * **Exception:** The presence of **Generalized Kaposi Sarcoma** or **Cryptococcal Meningitis** is sufficient by itself for the diagnosis of AIDS under these criteria. * **CD4 Count:** Remember that regardless of clinical signs, a **CD4 count <200 cells/mm³** is the laboratory definition of AIDS.

Question 324: A 35-year-old HIV-positive man presents with a 6-month history of progressive memory loss and incontinence. He is currently on zidovudine and a protease inhibitor. Examination reveals deficits in cognitive and fine motor control functions. His CD4 cell count is 25/mm 3. MRI studies show moderate brain atrophy with no focal lesions. Lumbar puncture shows no cerebrospinal fluid abnormalities. What is the most likely diagnosis?

A. CMV encephalitis
B. Cryptococcal meningoencephalitis
C. HIV encephalitis (Correct Answer)
D. HIV myelopathy

Explanation: The clinical presentation of progressive cognitive decline, memory loss, and motor dysfunction (fine motor deficits) in an advanced HIV patient (CD4 < 50/mm³) is characteristic of **HIV-Associated Dementia (HAD)**, also known as **HIV Encephalitis**. [1] **Why HIV Encephalitis is correct:** The diagnosis is supported by the triad of cognitive, motor, and behavioral symptoms. Key diagnostic markers in this case include: * **MRI findings:** Symmetrical cortical atrophy and ventricular enlargement without focal mass lesions or enhancement. * **CSF analysis:** Typically unremarkable or showing mild protein elevation, helping rule out opportunistic infections. * **Pathophysiology:** It is caused by direct HIV infection of microglia and macrophages, leading to multinucleated giant cell formation. [1] **Why other options are incorrect:** * **CMV Encephalitis:** Usually presents acutely with delirium and cranial nerve palsies. MRI typically shows periventricular enhancement, which is absent here. [1] * **Cryptococcal Meningoencephalitis:** Presents with signs of increased intracranial pressure (headache, vomiting, papilledema). CSF analysis would show positive India ink staining or Cryptococcal Antigen (CrAg). * **HIV Myelopathy (Vacuolar Myelopathy):** Primarily affects the spinal cord, presenting with spastic paraparesis and loss of vibratory/position sense. While it causes incontinence, it does not explain the cognitive/memory deficits. **NEET-PG High-Yield Pearls:** * **Most common cause of dementia in HIV:** HIV Encephalitis. * **Pathological hallmark:** Multinucleated giant cells (formed by fusion of HIV-infected macrophages). * **MRI vs. PML:** HIV Encephalitis shows **symmetrical** periventricular white matter changes without mass effect; Progressive Multifocal Leukoencephalopathy (PML) shows **asymmetrical** subcortical white matter lesions. * **Treatment:** Optimization of ART (Antiretroviral Therapy) with drugs having high CNS penetration (e.g., Zidovudine, Abacavir).

Question 325: Which variant of immunoblastic lymphoma is primarily seen in HIV patients?

A. Primary Effusion Lymphoma (Correct Answer)
B. Centroblastic Lymphoma
C. Anaplastic Lymphoma
D. Any of the Above

Explanation: **Explanation:** **Primary Effusion Lymphoma (PEL)** is a rare subtype of B-cell non-Hodgkin lymphoma that occurs almost exclusively in patients with advanced HIV/AIDS [2]. It is characterized by malignant effusions in body cavities (pleural, pericardial, or peritoneal) without a detectable solid tumor mass. **Why Option A is correct:** PEL is biologically unique because it is universally associated with **Human Herpesvirus 8 (HHV-8/KSHV)** infection. Morphologically, the cells exhibit a "null" phenotype (lacking surface B-cell markers like CD20 [1]) and show **immunoblastic** or plasmablastic features. Because of its strong association with HIV and its distinct immunoblastic morphology in fluid cytology, it is the classic variant linked to this patient population [2]. **Why other options are incorrect:** * **Option B (Centroblastic Lymphoma):** This is a morphologic variant of Diffuse Large B-Cell Lymphoma (DLBCL). While DLBCL is common in HIV, "centroblastic" refers to cells derived from germinal centers, whereas PEL is specifically the immunoblastic variant associated with body cavity effusions [1]. * **Option C (Anaplastic Lymphoma):** Anaplastic Large Cell Lymphoma (ALCL) is a T-cell lymphoma [1] characterized by CD30 expression and the t(2;5) translocation. It is not specifically categorized as an immunoblastic variant seen primarily in HIV. **High-Yield Clinical Pearls for NEET-PG:** * **Pathogen Association:** PEL is caused by **HHV-8** (KSHV); many cases are also co-infected with **EBV**. * **Clinical Presentation:** Presents as "liquid phase" lymphoma (effusions) in an immunocompromised host [2]. * **Immunophenotype:** Typically "null-cell" type (CD45 positive, but negative for CD19, CD20, and surface Immunoglobulins). CD138 (syndecan-1) is often positive, indicating plasmacytoid differentiation. * **Other HIV-associated Lymphomas:** Burkitt Lymphoma (starry-sky appearance) and Primary CNS Lymphoma (EBV-associated) [1].

Question 326: Acalculous cholecystitis can be seen in all the following conditions except?

A. Enteric fever
B. Dengue hemorrhagic fever
C. Leptospirosis
D. Malaria (Correct Answer)

Explanation: Acalculous cholecystitis (AC) refers to acute inflammation of the gallbladder in the absence of gallstones. It typically occurs in critically ill patients or as a complication of specific systemic infections [1]. **Why Malaria is the correct answer:** While Malaria (especially *P. falciparum*) can cause multi-organ dysfunction, including jaundice and hepatomegaly, **acalculous cholecystitis is not a recognized or typical complication of Malaria.** Jaundice in malaria is primarily pre-hepatic (hemolysis) or hepatocellular, rather than obstructive or related to gallbladder wall inflammation. **Analysis of incorrect options:** * **Enteric Fever (Typhoid):** The gallbladder is a primary site for *Salmonella typhi* colonization. It can cause acute acalculous cholecystitis during the illness or lead to a chronic carrier state. * **Dengue Hemorrhagic Fever (DHF):** Gallbladder wall thickening and acalculous cholecystitis are well-documented in DHF. It is often used as a marker of plasma leakage and disease severity. * **Leptospirosis:** This zoonosis can cause vasculitis and localized inflammation leading to acalculous cholecystitis, particularly in the pediatric population or severe cases (Weil’s disease). **High-Yield Clinical Pearls for NEET-PG:** 1. **Risk Factors for AC:** Major trauma, burns, prolonged fasting (TPN), post-cardiac surgery, and sepsis [1]. 2. **Pathogenesis:** Primarily involves gallbladder stasis and ischemia rather than stone obstruction. 3. **Imaging:** Ultrasound is the initial investigation of choice; look for gallbladder wall thickening (>4mm), pericholecystic fluid, and a positive **sonographic Murphy’s sign** in the absence of stones. 4. **Other Infectious Causes:** HIV (CMV/Cryptosporidium), Cholera, and Brucellosis.

Question 327: Which of the following is NOT involved in leprosy?

A. Central Nervous System (CNS) (Correct Answer)
B. Testis
C. Skin
D. Cornea

Explanation: **Explanation:** The correct answer is **A. Central Nervous System (CNS)**. **Why CNS is not involved:** *Mycobacterium leprae* has a unique predilection for cooler areas of the body. The organism thrives at temperatures between **30°C and 33°C**. The Central Nervous System (brain and spinal cord) is protected by the blood-brain barrier and maintains a core body temperature of approximately **37°C**, which is inhibitory to the growth and survival of *M. leprae*. Therefore, leprosy characteristically spares the CNS. **Why the other options are involved:** * **Skin (C):** This is the most common site of involvement [1]. Lesions range from hypopigmented patches in Tuberculoid leprosy to diffuse infiltration and nodules (lepromas) in Lepromatous leprosy. * **Testis (B):** The testes are located outside the body cavity to maintain a lower temperature, making them a prime target. Involvement can lead to orchitis, testicular atrophy, and subsequent sterility or gynecomastia [1]. * **Cornea (D):** The anterior segment of the eye is cooler than the posterior segment. Leprosy frequently affects the cornea (keratitis), iris, and ciliary body, potentially leading to blindness [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Target Tissues:** *M. leprae* primarily affects the skin, peripheral nerves (especially the ulnar, common peroneal, and posterior tibial), anterior chamber of the eye, upper respiratory tract mucosa, and testes [1]. * **Nerve Involvement:** It is the most common cause of peripheral neuropathy worldwide. * **Immune Response:** The clinical spectrum depends on the host’s **Cell-Mediated Immunity (CMI)**; strong CMI leads to Tuberculoid (TT), while weak CMI leads to Lepromatous (LL) leprosy [1]. * **Cardinal Signs:** Hypopigmented patches with loss of sensation, thickened peripheral nerves, and a positive slit-skin smear [1].

Question 328: In which of the following conditions is the pneumococcal vaccine indicated?

A. HIV infection (Correct Answer)
B. Patients who have undergone splenectomy
C. Sickle cell anemia
D. Corticosteroid therapy

Explanation: **Explanation:** The pneumococcal vaccine is indicated for individuals at increased risk of invasive pneumococcal disease (IPD). While all the options listed represent conditions where the vaccine is recommended, the question asks to identify the most appropriate indication based on standard clinical guidelines (like CDC/ACIP) often tested in NEET-PG. **1. Why HIV infection is the correct answer:** Patients with **HIV infection** are at a significantly higher risk (up to 100 times) of developing invasive pneumococcal disease compared to healthy individuals, regardless of their CD4 count [1]. Because HIV causes a progressive decline in both cellular and humoral immunity, vaccination is a priority. Current guidelines recommend a sequential dosing schedule (PCV15/PCV20 followed by PPSV23) for all HIV-positive adults. **2. Analysis of other options:** * **Splenectomy (B) & Sickle Cell Anemia (C):** These conditions cause **functional or anatomical asplenia**. While vaccination is mandatory for these patients (due to the risk of Overwhelming Post-Splenectomy Infection - OPSI), they are often categorized under "Asplenia" protocols. * **Corticosteroid therapy (D):** This falls under "Immunocompromised states." However, it usually refers to high-dose systemic steroids (≥20 mg/day of prednisone for ≥14 days). **Note on Question Structure:** In many competitive exams, if multiple options are technically correct, the "best" answer is often the one representing the highest risk group or the most classic board-style association. However, in standard clinical practice, **all four** are valid indications. **High-Yield Clinical Pearls for NEET-PG:** * **Types of Vaccines:** * **PCV13/15/20 (Conjugate):** Better mucosal immunity and T-cell response. * **PPSV23 (Polysaccharide):** Covers more serotypes but is T-cell independent (weaker memory). * **Splenectomy Timing:** Ideally, vaccinate **2 weeks before** elective surgery or **2 weeks after** emergency surgery. * **Target Organisms in Asplenia:** *S. pneumoniae* (most common), *H. influenzae*, and *N. meningitidis*.

Question 329: A 35-year-old man presents with an 18 kg weight loss over the preceding 4 months. He reports no dieting, but experiences abdominal pain, nausea, and diarrhea. He also has a chronic cough. Sputum studies reveal Pneumocystis carinii, and esophagogastroduodenoscopy with biopsy shows Candida and Herpes in the esophagus. Which group of viruses is the causative agent of this patient's underlying disease?

A. Caliciviridae
B. Coronaviridae
C. Flaviviridae
D. Retroviridae (Correct Answer)

Explanation: ### Explanation **Correct Option: D. Retroviridae** The clinical presentation describes a patient with profound weight loss (wasting syndrome) and multiple **AIDS-defining illnesses**. The presence of *Pneumocystis jirovecii* (formerly *P. carinii*) pneumonia, esophageal Candidiasis, and Herpes simplex esophagitis in a young patient is pathognomonic for advanced **Human Immunodeficiency Virus (HIV)** infection [1]. HIV is a member of the **Retroviridae** family (specifically the genus *Lentivirus*). These are enveloped, single-stranded RNA viruses that use the enzyme **reverse transcriptase** to convert their RNA genome into DNA, which then integrates into the host cell's genome (CD4+ T-cells) [3]. **Incorrect Options:** * **A. Caliciviridae:** This family includes the Norovirus, which is a leading cause of acute viral gastroenteritis (outbreaks in cruises/schools) but does not cause chronic immunosuppression or opportunistic infections. * **B. Coronaviridae:** This family includes SARS-CoV, MERS-CoV, and SARS-CoV-2. While they cause respiratory distress, they are not associated with the chronic opportunistic infections seen in this case. * **C. Flaviviridae:** This family includes viruses like Hepatitis C, Dengue, Yellow Fever, and Zika. While Hep C is chronic, it primarily affects the liver and does not typically present with *Pneumocystis* pneumonia. **High-Yield Clinical Pearls for NEET-PG:** * **AIDS Diagnosis:** Defined by a CD4 count <200 cells/mm³ or the presence of an AIDS-defining illness (e.g., Esophageal Candidiasis, PCP, Kaposi Sarcoma, CMV retinitis) [1]. * **Pneumocystis jirovecii:** The most common opportunistic infection in AIDS [3]. On silver stain (GMS), it shows "crushed ping-pong ball" appearance. Drug of choice: **TMP-SMX**. * **Esophagitis in HIV:** * *Candida:* White plaques (most common) [2]. * *HSV:* Small, deep "punched-out" ulcers. * *CMV:* Large, shallow linear ulcers. * **Screening & Confirmation:** Screening is done via ELISA (4th gen p24 antigen/antibody combo); confirmation is via Western Blot or HIV RNA PCR.

Question 330: In the serological testing for HIV infection, an early positive ELISA is primarily due to the detection of which of the following?

A. P24 antibody
B. Gp 120 antibody
C. Gp 120 antigen
D. P24 antigen (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. P24 antigen**. **1. Why P24 antigen is correct:** The p24 protein is a structural component of the HIV viral capsid [1]. During the early stages of infection (the "window period"), there is a massive burst of viral replication before the body has time to mount a measurable antibody response. The **p24 antigen** becomes detectable in the serum as early as **1 to 3 weeks** after exposure. Modern **4th generation ELISA kits** (the current gold standard for screening) are designed to detect both the p24 antigen and HIV-1/2 antibodies simultaneously. This significantly narrows the window period compared to older tests [1]. **2. Why the other options are incorrect:** * **A & B (p24 and gp120 antibodies):** Antibodies against HIV proteins (like p24, gp120, or gp41) typically take **3 to 12 weeks** to reach detectable levels (seroconversion) [1]. Therefore, they are not the "earliest" markers in a positive ELISA. * **C (gp120 antigen):** While gp120 is a major envelope glycoprotein, it is not the primary antigen targeted in standard diagnostic ELISA screening. The p24 antigen is produced in much higher quantities and is the established marker for early detection. **Clinical Pearls for NEET-PG:** * **Window Period:** The time between infection and the point when a test can detect the virus. 4th Gen ELISA reduces this to ~14 days. * **Order of appearance of markers:** HIV-RNA (by PCR) → p24 Antigen → HIV Antibodies. * **Confirmatory Test:** While ELISA is for screening, the **Western Blot** (detecting antibodies to p24, gp41, and gp120/160) was historically the confirmatory test [1], though it is now being replaced by HIV-1/HIV-2 antibody differentiation immunoassays. * **Best initial test for a neonate born to an HIV+ mother:** HIV-DNA PCR (because maternal IgG antibodies cross the placenta, making ELISA unreliable).

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Principles of Antimicrobial Therapy

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Fever of Unknown Origin

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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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