Infectious Diseases Practice Questions

Q: Which of the following is true about Lyme disease?

Mood disorder is a chronic neurological manifestation.. **Explanation:** Lyme disease, caused by the spirochete **Borrelia burgdorferi**, progresses through three distinct stages [1]. Understanding the chronicity of symptoms is key to answering this question. **1. Why Option C is Correct:** Chronic neurological manifestations (Stage 3 or Late Disseminated Disease) occur months to years after the initial infection. These include **Lyme encephalopathy**, which typically presents as subtle cognitive impairments (memory loss, word-finding difficulties) and **mood disorders** (depression, irritability). Other late features include chronic axonal polyneuropathy. **2. Why the Other Options are Incorrect:** * **Option A:** Arthritis is a **late manifestation** (Stage 3), typically presenting as intermittent or persistent swelling in large joints, most commonly the knee. * **Option B:** Conduction block (specifically **AV block**) is a classic feature of early disseminated disease (Stage 2). It is the most common cardiac manifestation and can range from first-degree to complete heart block. * **Option C:** The causative organism is **Borrelia burgdorferi** (transmitted by *Ixodes* ticks) [1]. *Borrelia recurrentis* is the agent responsible for louse-borne Relapsing Fever. **High-Yield Clinical Pearls for NEET-PG:** * **Stage 1 (Early Localized):** Pathognomonic **Erythema Chronicum Migrans** (Bull’s eye rash) [1]. * **Stage 2 (Early Disseminated):** Multiple secondary annular lesions, **Bilateral Bell’s Palsy** (highly suggestive), and AV conduction blocks. * **Treatment:** **Doxycycline** is the drug of choice for early stages. For neurological (except isolated Bell's palsy) or severe cardiac involvement, **IV Ceftriaxone** is preferred. * **Vector:** *Ixodes* ticks [1].

Q: Oral hairy leukoplakia is seen in which of the following conditions?

AIDS. **Oral Hairy Leukoplakia (OHL)** is a white, corrugated (hair-like) lesion typically found on the lateral borders of the tongue. It is caused by the opportunistic reactivation of the **Epstein-Barr Virus (EBV)** in the setting of profound secondary immunodeficiency. 1. **Why AIDS is correct:** OHL is one of the most specific clinical indicators of **HIV infection** [1]. It occurs when the CD4+ T-cell count drops (usually below 200-300 cells/mm³). Unlike other white lesions, OHL is non-adherent and cannot be scraped off. 2. **Why other options are incorrect:** * **Hepatitis B:** This is a systemic viral infection affecting the liver; it does not typically present with opportunistic oral mucosal lesions like OHL. * **Smoker’s Keratitis (Leukoplakia):** While smoking causes oral leukoplakia, these are precancerous lesions related to chemical irritation, not viral reactivation. They are generally flat and can occur anywhere in the mouth. * **Candidiasis (Oral Thrush):** This is a fungal infection [1]. The key clinical distinction is that Candidal plaques **can be scraped off**, leaving an erythematous (bloody) base, whereas OHL cannot. **High-Yield Clinical Pearls for NEET-PG:** * **Etiology:** EBV (Human Herpesvirus 4). * **Pathology:** Characterized by acanthosis, hyperkeratosis, and "ballooning cells" in the upper stratum spinosum. * **Significance:** Its presence in an undiagnosed patient is a strong indication to screen for HIV. * **Treatment:** Usually not required as it is asymptomatic, but it responds to HAART (Highly Active Antiretroviral Therapy) as the immune system recovers.

Q: A truck driver presented with a history of fever for four weeks and a dry cough. He also reports a weight loss of approximately 10 kg. X-ray shows bilateral reticulonodular infiltrates. What is the most likely diagnosis?

Pneumocystis pneumonia. The clinical presentation points toward an opportunistic infection in an immunocompromised host [1]. The patient’s occupation (truck driver) is a classic social high-yield marker in exams for high-risk behavior and potential HIV/AIDS [2]. **1. Why Pneumocystis pneumonia (PCP) is correct:** PCP, caused by *Pneumocystis jirovecii*, typically presents subacutely with a triad of **fever, dry cough, and progressive dyspnea**. Significant weight loss suggests underlying HIV [2]. Radiologically, PCP characteristically presents with **bilateral, symmetrical perihilar reticulonodular infiltrates** or "ground-glass" opacities [1]. The dry nature of the cough is a hallmark, as the organism does not cause alveolar exudate like typical bacteria. **2. Why the other options are incorrect:** * **Tuberculosis:** While common in HIV and causing weight loss, TB usually presents with a productive cough, hemoptysis, and focal findings (like upper lobe cavities or miliary patterns) rather than diffuse, symmetrical reticulonodular infiltrates [1]. * **Pneumococcal pneumonia:** This is an acute bacterial infection presenting with high-grade fever, productive "rusty" sputum, and **lobar consolidation** on X-ray, rather than a four-week chronic course with reticular patterns [4]. * **Interstitial Lung Disease (ILD):** While ILD shows reticulonodular patterns, it is a chronic, non-infectious inflammatory/fibrotic process [3]. It would not typically present with a four-week history of fever and rapid 10 kg weight loss. **Clinical Pearls for NEET-PG:** * **Investigation of choice:** Induced sputum or Bronchoalveolar Lavage (BAL) with **Gomori Methenamine Silver (GMS)** stain showing "crushed ping-pong ball" cysts [1]. * **Blood marker:** Elevated **Serum LDH** is highly sensitive for PCP in HIV patients. * **Treatment:** High-dose **TMP-SMX** is the drug of choice [1]. Add steroids if $PaO_2 35$ mmHg.

Q: Which of the following is not typically seen in Weil's disease?

Lung involvement. **Explanation:** **Leptospirosis** is a zoonotic infection caused by *Leptospira interrogans*. It typically presents in two phases: an initial anicteric phase and a more severe icteric phase known as **Weil’s Disease** [1]. **Why "Lung involvement" is the correct answer:** While pulmonary symptoms (like Pulmonary Hemorrhage Syndrome) can occur in severe leptospirosis, they are **not** part of the classic clinical triad that defines **Weil’s Disease**. Weil’s disease is specifically characterized by the triad of **Jaundice, Renal Failure, and Hemorrhage**. In the context of standard medical examinations like NEET-PG, lung involvement is considered a separate severe manifestation rather than a defining feature of the Weil’s triad. **Analysis of Incorrect Options:** * **A. Fever:** This is the most common presenting symptom of both the septicemic and immune phases of leptospirosis [1]. * **B. Jaundice:** A hallmark of Weil’s disease. Unlike viral hepatitis, the jaundice in Weil’s is often "orange-yellow" and occurs despite minimal hepatic necrosis. * **C. Renal failure:** Acute Kidney Injury (AKI) is a defining feature, typically presenting as non-oliguric hypokalemic renal failure due to tubular damage [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad of Weil’s:** Jaundice + Azotemia (Renal failure) + Hemorrhages (Purpura/Epistaxis). * **Conjunctival Suffusion:** Pathognomonic sign (redness of eyes without inflammatory exudate). * **Gold Standard Test:** Microscopic Agglutination Test (MAT) [1]. * **Drug of Choice:** Doxycycline (mild cases/prophylaxis) or IV Penicillin G (severe cases). * **Occupational Risk:** Farmers, sewage workers, and those exposed to rodent urine in water [1].

Q: A patient presents with headache, fever, and stiff neck. What is the most likely organism responsible?

Streptococcus Pneumoniae. ### Explanation The clinical triad of **headache, fever, and neck stiffness (nuchal rigidity)** is the classic presentation of **Acute Bacterial Meningitis** [1]. **Why Streptococcus pneumoniae is correct:** *Streptococcus pneumoniae* (Pneumococcus) is the **most common cause** of community-acquired bacterial meningitis in adults of all ages, as well as in children over the age of 2. It is often associated with concurrent infections like pneumonia, otitis media, or sinusitis. It carries the highest mortality and morbidity rates among the common causative agents [1]. **Analysis of Incorrect Options:** * **Staphylococcus aureus (A):** This is an uncommon cause of meningitis. It is typically seen in specific clinical contexts, such as post-neurosurgical procedures, head trauma, or secondary to infective endocarditis/bacteremia [2]. * **Listeria monocytogenes (B):** This is an important cause in specific "at-risk" populations: neonates, the elderly (>65 years), pregnant women, and immunocompromised individuals. It is not the most common cause in the general population. * **Streptococcus agalactiae (Group B Strep) (C):** This is the **most common cause of meningitis in neonates** (0–3 months), transmitted during birth from the maternal genital tract. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause overall:** *S. pneumoniae*. * **Most common cause in adolescents/young adults:** *Neisseria meningitidis* (often associated with a petechial rash). * **Empiric Treatment:** Ceftriaxone + Vancomycin [1]. Add **Ampicillin** if *Listeria* is suspected (extremes of age/immunocompromised). * **Dexamethasone:** Should be administered shortly before or with the first dose of antibiotics to reduce neurological complications (especially in Pneumococcal meningitis). * **CSF Findings in Bacterial Meningitis:** High opening pressure, high PMNs (neutrophils), low glucose (<40 mg/dL), and high protein [1].

Q: Tuberculous pleural effusion is characterized by all, except?

Increased mesothelial cells. Tuberculous pleural effusion (TPE) is a delayed hypersensitivity reaction to mycobacterial antigens entering the pleural space. Understanding its biochemical and cellular profile is crucial for NEET-PG. **Why "Increased mesothelial cells" is the correct answer (the exception):** In TPE, the pleural inflammation causes intense fibrin deposition and thickening of the visceral and parietal pleura. This layer of fibrin "coats" the pleural surfaces, preventing mesothelial cells from shedding into the fluid. Therefore, a **paucity of mesothelial cells (typically 60% of serum LDH:** TPE is an **exudative effusion**. According to Light’s Criteria, an exudate must have a pleural fluid LDH to serum LDH ratio > 0.6 (60%). * **Hemorrhagic fluid:** While TPE is classically straw-colored, it can be serosanguinous or hemorrhagic in about 10-15% of cases [1]. It does not exclude the diagnosis. * **Increased Adenosine Deaminase (ADA):** ADA is a marker of T-cell activation. Since TPE is a T-cell mediated response, ADA levels are typically high (usually **>40 U/L**). This is a highly sensitive screening test. **High-Yield Clinical Pearls for NEET-PG:** 1. **Cellular Profile:** Early TPE may show neutrophils, but it characteristically evolves into **lymphocytic predominance** (>50-70%). 2. **Gold Standard:** Pleural biopsy (showing granulomas) has a higher yield than fluid culture or AFB staining. [2] 3. **Interferon-gamma:** High levels in pleural fluid are also diagnostic of TPE. 4. **Glucose:** Usually low to normal, but if very low (<60 mg/dL), it suggests a high bacterial burden or chronicity.

Q: Which of the following is used for the prevention of Pneumocystis jiroveci infection in HIV positive patients?

Sulfamethoxazole + trimethoprim. **Explanation:** **Sulfamethoxazole + Trimethoprim (Co-trimoxazole)** is the drug of choice for both the **prophylaxis and treatment** of *Pneumocystis jirovecii* pneumonia (PCP) in HIV-positive patients. In immunocompromised individuals, particularly those with a CD4 count **<200 cells/mm³**, PCP is a major opportunistic infection. Co-trimoxazole works by inhibiting two consecutive steps in the bacterial/fungal folic acid synthesis pathway (synergistic sequential blockade), effectively preventing the replication of the organism. **Why other options are incorrect:** * **Azithromycin:** This is a macrolide used primarily for the prophylaxis of *Mycobacterium avium complex* (MAC) in HIV patients when CD4 counts drop below 50 cells/mm³. * **Acyclovir:** This is an antiviral agent used for infections caused by the Herpes Simplex Virus (HSV) and Varicella-Zoster Virus (VZV); it has no activity against fungi like *P. jirovecii*. * **Levofloxacin:** A fluoroquinolone used for bacterial respiratory infections and as a second-line agent for Tuberculosis, but it is ineffective against PCP. **High-Yield Clinical Pearls for NEET-PG:** * **Prophylaxis Threshold:** Start PCP prophylaxis in HIV patients if CD4 35$ mmHg, corticosteroids are added to reduce inflammation caused by dying organisms.

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: 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].

Question 1

Which of the following is true about Lyme disease?

Accepted Answer

Mood disorder is a chronic neurological manifestation.

Answer

Arthritis is an early manifestation.

Answer

Conduction block is not seen.

Answer

The causative organism is Borrelia recurrentis.

Question 2

Oral hairy leukoplakia is seen in which of the following conditions?

Accepted Answer

AIDS

Answer

Hepatitis B

Answer

Smoker's keratitis

Answer

Candidiasis

Question 3

A patient diagnosed with TB meningitis is started on antituberculosis treatment. Facial weakness persists despite treatment. The physician administers high-dose steroids, and within one week, the patient develops pain radiating down the back of the right leg and difficulty dorsiflexing the right foot. What is the most likely cause of these new symptoms?

Accepted Answer

Borrelia radiculopathy

Answer

Diabetic mononeuritis multiplex

Answer

Isoniazid neuropathy

Answer

Tuberculosis radiculopathy

Question 4

A truck driver presented with a history of fever for four weeks and a dry cough. He also reports a weight loss of approximately 10 kg. X-ray shows bilateral reticulonodular infiltrates. What is the most likely diagnosis?

Accepted Answer

Pneumocystis pneumonia

Answer

Tuberculosis

Answer

Pneumococcal pneumonia

Answer

Interstitial lung disease

Question 5

Which of the following is not typically seen in Weil's disease?

Accepted Answer

Lung involvement

Answer

Fever

Answer

Jaundice

Answer

Renal failure

Question 6

A patient presents with headache, fever, and stiff neck. What is the most likely organism responsible?

Accepted Answer

Streptococcus Pneumoniae

Answer

Staphylococcus Aureus

Answer

Listeria

Answer

Streptococcus Agalactiae

Question 7

Tuberculous pleural effusion is characterized by all, except?

Accepted Answer

Increased mesothelial cells

Answer

LDH > 60% of serum LDH

Answer

Hemorrhagic fluid

Answer

Increased adenosine deaminase

Question 8

Which of the following is used for the prevention of Pneumocystis jiroveci infection in HIV positive patients?

Accepted Answer

Sulfamethoxazole + trimethoprim

Answer

Azithromycin

Answer

Acyclovir

Answer

Levofloxacin

Question 9

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 10

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

Accepted Answer

Viral

Answer

Pyogenic

Answer

Tubercular

Answer

Carcinomatous

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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