Infectious Diseases Practice Questions

Q: Which of the following is the most common cause of sporadic viral encephalitis in adults?

Herpes virus. **Explanation:** **1. Why Herpes Virus is Correct:** Herpes Simplex Virus-1 (HSV-1) is the most common cause of **sporadic, non-epidemic fatal viral encephalitis** in adults worldwide [1]. The underlying medical concept involves the virus remaining latent in the trigeminal ganglia; upon reactivation, it spreads retrograde to the **temporal and frontal lobes** [1]. This predilection for the temporal lobes leads to characteristic clinical features like complex partial seizures, olfactory hallucinations, and behavioral changes [1]. **2. Why the Other Options are Incorrect:** * **Enteroviruses:** While these are the most common cause of viral **meningitis**, they are a less frequent cause of encephalitis in adults compared to HSV. * **Epstein-Barr Virus (EBV):** EBV typically causes Infectious Mononucleosis. While it can cause neurological complications (like meningitis or encephalitis), it usually occurs in the context of primary infection or in immunocompromised states, making it far less common than HSV-1. * **HIV:** HIV can cause "HIV Encephalopathy" (Dementia Complex) or opportunistic infections (like CMV or Toxoplasmosis), but it is not the leading cause of acute sporadic viral encephalitis in the general adult population [1]. **3. Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** PCR of the CSF for HSV DNA (highly sensitive and specific). * **Imaging:** MRI is the modality of choice, showing hyperintensity in the **temporal lobes** and insular cortex [1]. * **EEG Finding:** Periodic Lateralized Epileptiform Discharges (**PLEDs**). * **Treatment:** Immediate IV **Acyclovir** (10 mg/kg every 8 hours) should be started empirically if encephalitis is suspected, as delay significantly increases mortality.

Q: What is the transmission rate of the Hepatitis C virus?

5%. The transmission rate of Hepatitis C Virus (HCV) is a high-yield topic for NEET-PG, particularly regarding occupational exposure and vertical transmission. [1] **Explanation of the Correct Answer (A):** The risk of HCV transmission following a single percutaneous exposure (e.g., a needle-stick injury) from an HCV-positive source is approximately **3% to 5%** (average 1.8% in some literature, but 5% is the standard textbook value for exams). [1] Unlike Hepatitis B, HCV is not highly efficient at transmitting through mucous membranes or intact skin. [2] In the context of vertical transmission (mother-to-child), the rate is also approximately **5%**, though this increases significantly if the mother is co-infected with HIV. **Analysis of Incorrect Options:** * **B (10%):** This overestimates the risk for a single exposure. While chronic infection occurs in about 75–85% of those infected, the initial transmission rate remains lower. * **C (25%) & D (50%):** These values are far too high for HCV. For comparison, the transmission rate of Hepatitis B (HBV) in a non-immune individual after a needle-stick injury from an HBeAg-positive source can be as high as **30%**. [2] **High-Yield Clinical Pearls for NEET-PG:** * **Rule of 3s (Needle-stick risk):** HIV ≈ 0.3%, HCV ≈ 3%, HBV ≈ 30% (in non-immunized). * **Sexual Transmission:** HCV is rarely transmitted sexually among monogamous heterosexual couples; however, the risk increases with multiple partners or MSM (men who have sex with men). * **Post-Exposure Prophylaxis (PEP):** Unlike HBV and HIV, there is **no effective PEP** (immunoglobulin or vaccine) for HCV. [1] Management involves monitoring HCV RNA and treating with Direct-Acting Antivirals (DAAs) only if chronic infection is established. * **Screening:** Anti-HCV antibody is the screening test of choice; HCV RNA is used to confirm active infection. [1]

Q: Brain abscess in an immunodeficient person is typically caused by which of the following microorganisms?

Cryptococcus. ### Explanation **Correct Option: A (Cryptococcus)** In immunocompromised individuals (especially those with HIV/AIDS, transplant recipients, or those on chronic steroids), the spectrum of CNS infections shifts from pyogenic bacteria to opportunistic pathogens. **Cryptococcus neoformans** is the most common fungal cause of CNS involvement in this population. While it typically presents as meningitis, it can also manifest as "Cryptococcomas" (fungal abscesses) or gelatinous pseudocysts within the brain parenchyma. The organism's thick polysaccharide capsule allows it to evade the host's weakened immune system, leading to granulomatous inflammation and abscess formation. **Analysis of Incorrect Options:** * **B. Staphylococcus:** *Staphylococcus aureus* is a leading cause of brain abscesses in **immunocompetent** individuals, often spreading hematogenously (e.g., from endocarditis) or via direct trauma/surgery. * **C. Pneumococcus:** *Streptococcus pneumoniae* is the most common cause of community-acquired bacterial meningitis but is a **rare** cause of focal brain abscesses. * **D. E. coli:** While *E. coli* can cause neonatal meningitis or brain abscesses following neurosurgical procedures, it is not the "typical" or most characteristic organism associated specifically with the immunodeficient state in general adult populations. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of brain abscess (Overall):** *Streptococcus viridans* (often anaerobic/mixed). * **Toxoplasmosis:** The most common cause of **multiple** ring-enhancing lesions in HIV patients (often a key differential for Cryptococcus) [1]. * **Diagnostic Clue:** For Cryptococcus, look for "Soap bubble appearance" on MRI (basal ganglia) and positive **India Ink** or **CrAg** (Cryptococcal Antigen) test. * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole maintenance.

Q: CSF glucose levels are typically normal in which type of meningitis?

Viral. ### Explanation The diagnosis of meningitis relies heavily on CSF analysis. The core concept behind CSF glucose levels is that **bacteria, fungi, and malignant cells consume glucose** for metabolism or growth, whereas viruses do not. [1] **1. Why Viral Meningitis is Correct:** In viral (aseptic) meningitis, the virus does not utilize glucose for replication. Therefore, the CSF glucose level remains **normal** (typically >60% of simultaneous plasma glucose or >40 mg/dL) [4]. This is a hallmark finding that differentiates it from most other forms of meningitis. **2. Why the Other Options are Incorrect:** * **Pyogenic (Bacterial) Meningitis:** Bacteria consume glucose for energy, and there is impaired glucose transport across the blood-brain barrier. This leads to **markedly low** glucose levels (hypoglycorrhachia), often <40 mg/dL [3]. * **Tubercular Meningitis:** *Mycobacterium tuberculosis* causes a chronic inflammatory process that significantly **lowers** CSF glucose levels, usually accompanied by high protein and lymphocytic pleocytosis [2]. * **Carcinomatous Meningitis:** Malignant cells in the subarachnoid space have high metabolic requirements and utilize glucose rapidly, leading to **decreased** CSF glucose levels. **3. High-Yield NEET-PG Clinical Pearls:** * **Normal CSF Glucose:** 40–70 mg/dL (or 2/3rd of blood glucose). Always compare CSF glucose with a simultaneous blood glucose sample. * **Viral Exception:** Mumps and Herpes Simplex (HSV) can occasionally cause low CSF glucose, though it remains typically normal in most viral etiologies. * **The "Rule of 2s" for Bacterial Meningitis:** Look for **low** glucose ( 100), and **high** neutrophils (>1000) [3]. * **Viral CSF Profile:** Normal glucose, mildly elevated protein, and **lymphocytic** pleocytosis [4].

Q: Regarding tetanus, which of the following is NOT a true statement?

Coagulopathy. **Explanation:** Tetanus is caused by the neurotoxin **tetanospasmin**, produced by *Clostridium tetani*. The toxin acts by blocking the release of inhibitory neurotransmitters (GABA and glycine) from Renshaw cells in the spinal cord, leading to unchecked excitatory nerve impulses [1]. **Why Coagulopathy is the correct answer:** Coagulopathy is **not** a feature of tetanus. The pathology of tetanus is strictly neurological and neuromuscular. While severe cases may involve autonomic dysfunction (labile blood pressure, tachycardia, hyperpyrexia), the toxin does not interfere with the coagulation cascade or platelet function. **Analysis of incorrect options:** * **Trismus (Lockjaw):** This is the most common presenting symptom. It results from the masseter muscle spasm, preventing the patient from opening their mouth [1]. * **Generalized Rigidity:** The hallmark of generalized tetanus. It involves "board-like" abdominal rigidity and **opisthotonus** (arch-like hyperextension of the body). * **Respiratory Failure:** This is the leading cause of death in tetanus. It occurs due to laryngospasm, spasms of the chest wall/diaphragm, or as a complication of autonomic instability and secondary pneumonia. **High-Yield Clinical Pearls for NEET-PG:** * **Risus Sardonicus:** An abnormal, sustained spasm of the facial muscles that appears to produce grinning. * **Incubation Period:** Usually 3–21 days; a shorter incubation period correlates with increased severity and higher mortality. * **Diagnosis:** Purely **clinical**. Wound cultures are positive in only 30% of cases. * **Management:** Neutralization of unbound toxin with **Human Tetanus Immune Globulin (HTIG)**, wound debridement, and **Metronidazole** (preferred over Penicillin G as the latter is a GABA antagonist).

Q: In AIDS, lymphadenopathy is most often due to which of the following?

Non specific enlargement of lymph node. In patients with HIV/AIDS, lymphadenopathy is a frequent clinical finding. The most common cause is **Persistent Generalized Lymphadenopathy (PGL)**, which histologically manifests as **non-specific follicular hyperplasia** (non-specific enlargement) [1]. This occurs due to the chronic immune activation and B-cell proliferation in response to the HIV virus itself, rather than a secondary opportunistic infection or malignancy [1]. PGL is defined as enlarged nodes (>1 cm) at two or more extra-inguinal sites persisting for more than 3 months without an obvious cause [1]. **Analysis of Incorrect Options:** * **A. Tuberculosis:** While TB is the most common *opportunistic infection* causing lymphadenopathy in AIDS patients (especially in India), it is statistically less frequent than the non-specific reactive changes caused by HIV itself [1]. * **B. Lymphoma:** HIV patients have a significantly higher risk of Non-Hodgkin Lymphoma (NHL), but it represents a small percentage of total lymphadenopathy cases compared to reactive hyperplasia [1]. * **D. Kaposi’s Sarcoma:** This is an AIDS-defining illness caused by HHV-8. While it can involve lymph nodes, it typically presents with characteristic cutaneous lesions and is far less common than non-specific enlargement [1]. **NEET-PG High-Yield Pearls:** * **PGL Definition:** Nodes >1cm, ≥2 extra-inguinal sites, >3 months duration [1]. * **Biopsy Indication:** In AIDS, a lymph node biopsy is indicated if there are constitutional symptoms (fever, weight loss), rapid enlargement of nodes, or asymmetrical/fixed nodes to rule out TB or Lymphoma [1]. * **Most common site for PGL:** Cervical, axillary, and posterior occipital nodes. * **Histology of PGL:** Early stage shows exuberant follicular hyperplasia; late stage shows follicular involution/depletion.

Question 1

Secondary infections in HIV infected patients are classified under which category?

Accepted Answer

Category IV

Answer

Category I

Answer

Category II

Answer

Category III

Question 2

Which of the following is the most common cause of sporadic viral encephalitis in adults?

Accepted Answer

Herpes virus

Answer

Enteroviruses

Answer

Ebstein-Barr virus

Answer

HIV

Question 3

What is the transmission rate of the Hepatitis C virus?

Accepted Answer

5%

Answer

10%

Answer

25%

Answer

50%

Question 4

Brain abscess in an immunodeficient person is typically caused by which of the following microorganisms?

Accepted Answer

Cryptococcus

Answer

Staphylococcus

Answer

Pneumococcus

Answer

E. coli

Question 5

CSF glucose levels are typically normal in which type of meningitis?

Accepted Answer

Viral

Answer

Pyogenic

Answer

Tubercular

Answer

Carcinomatous

Question 6

A 60-year-old alcoholic smoker abruptly develops high fever, shakes, a severe headache, and muscle pain. He initially has a dry, insignificant cough, but over the next few days he develops marked shortness of breath requiring assisted ventilation. Chest x-ray demonstrates homogeneous radiographic shadowing that initially involves the left lower lobe but continues to spread until both lungs are extensively involved. Culture of bronchoalveolar lavage fluid on buffered charcoal yeast extract (BCYE) demonstrates a coccobacillary pathogen. Which of the following is the most likely causative organism?

Accepted Answer

Legionella pneumophila

Answer

Listeria monocytogenes

Answer

Streptococcus pneumoniae

Answer

Staphylococcus aureus

Question 7

A 32-year-old woman acutely develops high fever, hypotension, and rash. This is followed by vomiting, diarrhea, confusion, and abdominal pain. In the hospital, evidence of multiorgan failure develops. Desquamation of the skin occurs 1 week after the acute illness. The illness started 3 days after the onset of menstruation. Which of the following is the most likely diagnosis?

Accepted Answer

Staphylococcus aureus toxic shock syndrome (TSS)

Answer

Streptococcal infection (scarlet fever)

Answer

Clostridial infection

Answer

Rocky Mountain Spotted Fever (RMSF)

Question 8

A 24-year-old woman presents with fever, chills, and rigors. On physical examination, her temperature is 39.4°C, blood pressure 100/60 mm Hg, pulse 110/min, and oxygen saturation 95%. There is a 3/6 pansystolic murmur at the right sternal border, which increases with inspiration. Her arms show multiple tattoos and needle marks from injection drug use. Blood cultures are positive for S. aureus, and she is started on appropriate antibiotics. Her renal function is mildly impaired, and her urinalysis is positive for protein with red blood cell casts on microscopy. Which of the following mechanisms is the most likely explanation for her renal abnormalities?

Accepted Answer

High level of circulating immune complexes

Answer

Septic emboli

Answer

Cardiac failure with prerenal azotemia

Answer

Fungal disease

Question 9

Regarding tetanus, which of the following is NOT a true statement?

Accepted Answer

Coagulopathy

Answer

Trismus

Answer

Generalized rigidity

Answer

Respiratory failure

Question 10

In AIDS, lymphadenopathy is most often due to which of the following?

Accepted Answer

Non specific enlargement of lymph node

Answer

Tuberculosis

Answer

Lymphoma

Answer

Kaposi's sarcoma

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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