Infectious Diseases Practice Questions

Q: A patient is found to be positive for HBs Ag on routine laboratory evaluation. Other serological tests for hepatitis are unremarkable. He is clinically asymptomatic and liver enzymes are within the normal range. Which of the following best describes his diagnosis?

Inactive HBV carrier. The patient is an **Inactive HBV carrier**. This diagnosis is established based on the presence of HBsAg for >6 months (implied by the asymptomatic, routine finding) combined with normal liver enzymes (ALT/AST) and the absence of clinical symptoms, indicating a state of host-virus equilibrium where no active necroinflammation is occurring in the liver [1]. **Why Option A is correct:** An inactive carrier state is characterized by: 1. **HBsAg positivity.** [1] 2. **HBeAg negativity** and Anti-HBe positivity (usually). 3. **Normal ALT levels**, reflecting the absence of ongoing liver injury [1]. 4. Low HBV DNA levels (typically 1000 U/L). Serologically, IgM anti-HBc would be positive [1]. * **C. Chronic Hepatitis B:** While an inactive carrier is a subset of chronic infection, "Chronic Hepatitis B" as a clinical diagnosis usually implies **active** disease with elevated liver enzymes and evidence of liver damage (necroinflammation or fibrosis). * **D. Active HBV carrier:** This term is often used for patients with "HBeAg-positive chronic hepatitis" or "HBeAg-negative chronic hepatitis," where HBV DNA is high and ALT is elevated, indicating active viral replication and liver damage. **NEET-PG High-Yield Pearls:** * **HBsAg:** First marker to appear in blood; its persistence >6 months defines chronic infection [1]. * **Window Period:** The interval when HBsAg becomes negative but Anti-HBs has not yet appeared. **IgM anti-HBc** is the only diagnostic marker during this phase [1]. * **HBeAg:** Indicates high infectivity and active viral replication. * **Anti-HBs:** Indicates immunity (either via recovery or vaccination) [1].

Q: A 45-year-old female is diagnosed with pneumococcal meningitis. While awaiting culture sensitivity results, what is the best empirical treatment to start?

Vancomycin + ceftriaxone. **Explanation:** The empirical treatment of bacterial meningitis must cover the most likely pathogens (*Streptococcus pneumoniae*, *Neisseria meningitidis*) and account for increasing patterns of drug resistance. **Why Option D is Correct:** * **Ceftriaxone (3rd Gen Cephalosporin):** This is the backbone of therapy due to its excellent CSF penetration and broad-spectrum activity against common meningeal pathogens. * **Vancomycin:** Due to the rising prevalence of **Penicillin-resistant *Streptococcus pneumoniae* (PRSP)** and emerging resistance to cephalosporins, Vancomycin is added empirically. It ensures coverage against highly resistant strains until specific sensitivities are available. **Why Other Options are Incorrect:** * **A. Penicillin G:** While historically the drug of choice, it is no longer used empirically due to widespread high-level resistance in *S. pneumoniae*. * **B. Doxycycline:** This is a bacteriostatic drug with poor CSF penetration; it is not indicated for acute bacterial meningitis. * **C. Streptomycin:** This aminoglycoside has negligible CSF penetration and is primarily used for Tuberculosis or Plague, not for acute pyogenic meningitis. **High-Yield Clinical Pearls for NEET-PG:** 1. **Steroid Adjunct:** Dexamethasone should be administered **before or with the first dose** of antibiotics to reduce neurological complications (like hearing loss) caused by the inflammatory response to bacterial lysis. 2. **Age-Specific Coverage:** In patients >50 years or those who are immunocompromised, **Ampicillin** must be added to the regimen to cover *Listeria monocytogenes*. 3. **Prophylaxis:** Rifampicin is the drug of choice for chemoprophylaxis in close contacts of *N. meningitidis* or *H. influenzae* meningitis.

Q: A 30-year-old male presented to the hospital with complaints of seizures. An MRI of the brain was performed, as shown. What is the most probable diagnosis and its management, respectively?

Neurocysticercosis, Albendazole. ***Neurocysticercosis, Albendazole*** - Young adult with **seizures** and classic MRI findings including **ring enhancement** and potential **scolex sign** (pathognomonic for neurocysticercosis) strongly suggest this diagnosis. - **Albendazole** is the first-line antiparasitic treatment for viable cysticerci, often combined with **corticosteroids** to reduce inflammatory response. *Metastasis, Radiotherapy* - Typically occurs in **older patients** (>50 years) with a known **primary malignancy** and presents with **multiple lesions** at gray-white junction. - **Ring enhancement** pattern in metastasis usually shows **thicker, more irregular walls** compared to the thin, smooth walls seen in neurocysticercosis. *Brain abscess, Antibiotic therapy* - Usually presents with **fever**, **headache**, and **altered mental status** along with **restricted diffusion on DWI** (bright signal), which differentiates it from cystic lesions. - Risk factors include **immunocompromised state**, **dental infections**, or **cardiac abnormalities**, not typically seen in healthy young adults with isolated seizures. *Tuberculosis, Anti-tuberculosis therapy* - **Tuberculoma** typically shows **calcification** and **solid enhancement** rather than cystic appearance, often with surrounding **cerebral edema**. - Usually associated with **systemic TB symptoms** (fever, weight loss, night sweats) or **pulmonary TB** on chest imaging, which are absent in this case.

Q: Which of the following is NOT an AIDS-defining illness?

Oropharyngeal candidiasis. The classification of HIV progression into AIDS is based on the presence of specific opportunistic infections or malignancies, known as **AIDS-defining illnesses**, or a CD4 count below 200 cells/mm³. [1] **Why Oropharyngeal Candidiasis is the correct answer:** While **Oropharyngeal candidiasis (Oral Thrush)** is a very common opportunistic infection in HIV patients, it is **not** an AIDS-defining illness. [1] It typically occurs when CD4 counts drop below 500 cells/mm³ and serves as a clinical marker of disease progression. [1] In contrast, **Esophageal candidiasis** (involvement of the esophagus, trachea, or lungs) is considered an AIDS-defining condition. **Analysis of Incorrect Options:** * **CMV Retinitis:** This is a classic AIDS-defining illness, usually occurring when the CD4 count is extremely low (<50 cells/mm³). It is the most common cause of blindness in AIDS patients. * **Primary CNS Lymphoma:** This is a high-grade B-cell lymphoma associated with EBV infection in HIV patients. It is a definitive AIDS-defining malignancy. * **Kaposi’s Sarcoma:** Caused by HHV-8, this vascular tumor is one of the most common sentinel malignancies that define the transition to AIDS. **High-Yield Clinical Pearls for NEET-PG:** * **Most common AIDS-defining illness worldwide:** *Pneumocystis jirovecii* pneumonia (PCP). [1] * **Most common opportunistic infection in HIV (overall):** Oral Candidiasis (Thrush). [1] * **CD4 Thresholds:** * <200 cells/mm³: PCP, Esophageal Candidiasis. [1] * <100 cells/mm³: Toxoplasmosis, Cryptococcosis. * <50 cells/mm³: CMV Retinitis, Mycobacterium Avium Complex (MAC). * **Mnemonic:** Remember that "Oral" is not AIDS-defining, but "Esophageal" is.

Q: Which of the following has been strongly implicated as a causative agent for Kaposi's sarcoma?

HHV-8. The correct answer is **HHV-8 (Human Herpesvirus 8)**, also known as **Kaposi’s Sarcoma-associated Herpesvirus (KSHV)**. **Why HHV-8 is correct:** HHV-8 is a gamma-herpesvirus that is the primary and necessary etiological agent for all clinical forms of Kaposi’s Sarcoma (KS). It infects vascular endothelial cells, leading to their transformation into spindle cells. The virus carries oncogenes (like viral cyclin and v-FLIP) that promote cell proliferation and inhibit apoptosis. Beyond KS, HHV-8 is also strongly implicated in **Primary Effusion Lymphoma (PEL)** and **Multicentric Castleman Disease**. **Why the other options are incorrect:** * **HHV-7:** Primarily associated with **Pityriasis rosea** and some cases of Exanthema subitum (Roseola infantum). * **HHV-2:** Known as Herpes Simplex Virus-2 (HSV-2), it is the leading cause of **genital herpes** and neonatal herpes. * **HHV-6:** The primary causative agent of **Roseola infantum** (Sixth disease) in children. **High-Yield Clinical Pearls for NEET-PG:** 1. **Four Types of KS:** Classic (elderly Mediterranean men), Endemic (African), Iatrogenic (transplant-related), and Epidemic (AIDS-associated). 2. **Histology:** Look for "slit-like spaces" containing extravasated RBCs and spindle-shaped cells. 3. **Treatment:** For AIDS-related KS, the first step is often **HAART** (Highly Active Antiretroviral Therapy). For systemic disease, **Liposomal Doxorubicin** is the drug of choice. 4. **Marker:** HHV-8 LNA-1 (Latent Nuclear Antigen) staining is the gold standard for histological diagnosis.

Q: Which of the following is an AIDS-defining opportunistic illness?

Invasive carcinoma of the cervix. **Explanation:** The diagnosis of AIDS is made in an HIV-infected individual when the CD4+ T-cell count falls below 200 cells/mm³ or when they develop a specific **AIDS-defining illness** as categorized by the CDC. **1. Why Invasive Cervical Carcinoma is correct:** Invasive cervical carcinoma is one of the three malignancies classified as AIDS-defining (alongside Kaposi sarcoma and Non-Hodgkin lymphoma). It is caused by high-risk strains of **Human Papillomavirus (HPV)**. In HIV-positive patients, the lack of cell-mediated immunity allows HPV to persist and progress rapidly to malignancy, making it a hallmark of advanced immunosuppression. **2. Why other options are incorrect:** * **Oral Candidiasis (Thrush):** While very common in HIV patients, it is considered a "Category B" (Symptomatic, non-AIDS) condition. It usually occurs at CD4 counts between 200–500 cells/mm³. Only **Esophageal, Tracheal, or Bronchial Candidiasis** is AIDS-defining. * **Cyclosporiasis:** This causes diarrheal illness but is not on the official CDC AIDS-defining list. However, **Isosporiasis** (Cystoisospora) and **Cryptosporidiosis** (if lasting >1 month) are AIDS-defining. * **Herpes Zoster (Shingles):** This occurs frequently in HIV patients due to waning immunity but is not AIDS-defining. However, **chronic/disseminated Herpes Simplex (HSV)** ulcers (lasting >1 month) are AIDS-defining. **High-Yield NEET-PG Pearls:** * **Mnemonic for AIDS-defining Cancers:** "K-L-C" (Kaposi Sarcoma, Lymphoma [Burkitt’s/Immunoblastic/Primary CNS], and Cervical Carcinoma). * **CD4 Cut-offs:** * **<200:** Pneumocystis jirovecii pneumonia (PJP). * **<100:** Toxoplasmosis, Cryptococcosis. * **<50:** Mycobacterium avium complex (MAC), CMV Retinitis. * **Note:** Pulmonary Tuberculosis is AIDS-defining regardless of the CD4 count in an HIV-positive patient.

Q: Mulberry molars are characteristic features of which condition?

Congenital syphilis. **Explanation:** **Congenital Syphilis (Correct Answer):** Mulberry molars are a pathognomonic dental abnormality caused by the transplacental transmission of *Treponema pallidum*. The infection leads to inflammation of the tooth germ during the morphodifferentiation stage of development. This results in the permanent first molars having multiple, poorly developed rudimentary cusps and a narrowed occlusal surface, giving them a bumpy, "mulberry-like" appearance. **Analysis of Incorrect Options:** * **Severe Fluorosis:** Characterized by "mottling" of enamel, presenting as chalky white patches or brownish discoloration and pitting, but it does not produce the specific multi-cusped morphology of mulberry molars. * **Trauma at birth:** While trauma can cause localized enamel hypoplasia (Turner’s tooth), it typically affects a single tooth and does not result in the symmetrical, multi-cusped pattern seen in syphilis. * **Chronic suppurative abscess:** Localized infection (Turner’s hypoplasia) usually affects the permanent successor of a primary tooth (like a premolar) due to apical periodontitis of the deciduous tooth, rather than systemic developmental changes. **NEET-PG High-Yield Pearls:** * **Hutchinson’s Triad:** A classic triad of Congenital Syphilis consisting of: 1. **Hutchinson’s teeth:** Notched, peg-shaped permanent incisors. 2. **Interstitial keratitis:** Leading to corneal scarring. 3. **Sensorineural hearing loss:** Due to 8th cranial nerve involvement. * **Other Skeletal Signs:** Saddle nose deformity, Saber shins (anterior bowing of the tibia), and Clutton’s joints (painless symmetrical knee swelling). * **Early vs. Late:** Mulberry molars are considered a "stigmata" or late manifestation (appearing after age 2).

Question 1

A patient is found to be positive for HBs Ag on routine laboratory evaluation. Other serological tests for hepatitis are unremarkable. He is clinically asymptomatic and liver enzymes are within the normal range. Which of the following best describes his diagnosis?

Accepted Answer

Inactive HBV carrier

Answer

Acute Hepatitis B

Answer

Chronic Hepatitis B

Answer

Active HBV carrier

Question 2

A 45-year-old female is diagnosed with pneumococcal meningitis. While awaiting culture sensitivity results, what is the best empirical treatment to start?

Accepted Answer

Vancomycin + ceftriaxone

Answer

Penicillin G

Answer

Doxycycline

Answer

Streptomycin

Question 3

A 30-year-old male presented to the hospital with complaints of seizures. An MRI of the brain was performed, as shown. What is the most probable diagnosis and its management, respectively?

Accepted Answer

Neurocysticercosis, Albendazole

Answer

Metastasis, Radiotherapy

Answer

Brain abscess, Antibiotic therapy

Answer

Tuberculosis, Anti-tuberculosis therapy

Question 4

Antibiotic prophylaxis is not recommended in which of the following procedures?

Accepted Answer

Making of impressions

Answer

Dental extraction

Answer

Replantation of tooth

Answer

Gingivectomy

Question 5

Which of the following is NOT an AIDS-defining illness?

Accepted Answer

Oropharyngeal candidiasis

Answer

CMV retinitis

Answer

Primary CNS lymphoma

Answer

Kaposi's sarcoma

Question 6

What is the diagnosis in a patient who appears sick, has a bull neck, and is tachycardic?

Accepted Answer

Diphtheria

Answer

Epiglottitis

Answer

Infectious mononucleosis

Answer

Rheumatic fever

Question 7

Which of the following has been strongly implicated as a causative agent for Kaposi's sarcoma?

Accepted Answer

HHV-8

Answer

HHV-7

Answer

HHV-2

Answer

HHV-6

Question 8

Which of the following is an AIDS-defining opportunistic illness?

Accepted Answer

Invasive carcinoma of the cervix

Answer

Oral candidiasis (thrush)

Answer

Cyclosporiasis

Answer

Herpes zoster virus

Question 9

What represents a medical emergency in an asplenic patient?

Accepted Answer

Dog bite

Answer

Cat bite

Answer

Fish bite

Answer

Human bite

Question 10

Mulberry molars are characteristic features of which condition?

Accepted Answer

Congenital syphilis

Answer

Severe fluorosis

Answer

Trauma at the time of birth

Answer

Chronic suppurative abscess in overlying gingival tissue

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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