Infectious Diseases Practice Questions

Q: Which of the following is NOT a causative agent of lymphatic filariasis?

Loa loa. Explanation: Lymphatic filariasis (Elephantiasis) is caused by thread-like filarial nematodes that occupy the lymphatic system, leading to lymphoedema and hydrocele. **Why Loa loa is the correct answer:** *Loa loa* is the causative agent of **Loiasis**, also known as "African Eye Worm." Unlike the agents of lymphatic filariasis, *Loa loa* resides in the **subcutaneous tissues** and is transmitted by the *Chrysops* (deer fly) [1]. It is clinically characterized by transient localized angioedema known as **Calabar swellings** and the visible migration of the adult worm across the subconjunctiva of the eye [1]. It does not cause lymphatic obstruction. **Why the other options are incorrect:** * **Wuchereria bancrofti:** The most common cause, responsible for approximately 90% of lymphatic filariasis cases worldwide. It is transmitted by *Culex*, *Anopheles*, and *Aedes* mosquitoes. * **Brugia malayi:** A major cause of lymphatic filariasis in South and Southeast Asia (including parts of India like Kerala). * **Brugia timori:** A localized cause of lymphatic filariasis restricted to the Timor islands of Indonesia. **High-Yield NEET-PG Pearls:** 1. **Vector Check:** *W. bancrofti* is primarily transmitted by the **Culex quinquefasciatus** mosquito in urban India. 2. **Diagnosis:** The gold standard is the identification of microfilariae in a **peripheral blood smear** collected at night (**Nocturnal Periodicity**, typically 10 PM – 2 AM). 3. **Drug of Choice:** **Diethylcarbamazine (DEC)** is the mainstay of treatment. However, it is contraindicated in patients with heavy *Loa loa* or *Onchocerca* co-infection due to the risk of encephalopathy or severe Mazzotti reaction [1]. 4. **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity response to *W. bancrofti* or *B. malayi* antigens, characterized by nocturnal cough, wheezing, and high peripheral eosinophilia [1].

Q: A 29-year-old male is suspected of having viral encephalitis. Which of the following is the most likely result from CSF analysis?

Raised protein, raised lymphocytes, normal glucose. ### Explanation The hallmark of viral infections of the Central Nervous System (CNS), including meningitis and encephalitis, is **lymphocytic pleocytosis** with relatively preserved biochemical parameters compared to bacterial infections [1]. **Why Option A is correct:** In viral encephalitis, the inflammatory response leads to an influx of white blood cells, predominantly **lymphocytes**. The inflammation also causes a breakdown of the blood-brain barrier, resulting in **mildly to moderately raised protein** levels. Crucially, viruses do not consume glucose for metabolism; therefore, the **CSF glucose remains normal** (typically >60% of blood glucose) [1]. **Why the other options are incorrect:** * **Option B:** Encephalitis typically triggers an immune response [2]; a "normal lymphocyte" count is rare unless the patient is severely immunocompromised or in the very early hyperacute phase. * **Option C & D:** **Raised glucose** in CSF is not a diagnostic feature of any CNS infection. High CSF glucose usually reflects systemic hyperglycemia (as CSF glucose levels follow blood glucose levels). --- ### High-Yield Clinical Pearls for NEET-PG: 1. **The "Rule of Two":** In viral CNS infections, look for **Normal Glucose** and **Lymphocytic Predominance**. 2. **Bacterial vs. Viral:** Bacterial meningitis shows **low glucose** (hypoglycorrhachia) and **neutrophilic** predominance. 3. **HSV Encephalitis:** If the question mentions **hemorrhagic** CSF or involvement of the **temporal lobes** on MRI, think Herpes Simplex Virus (HSV-1) [2]. This is the most common cause of sporadic fatal encephalitis. 4. **Xanthochromia:** If the CSF is yellowish, it indicates old blood (Subarachnoid Hemorrhage), not typical viral encephalitis. 5. **TB Meningitis:** Characterized by very high protein, very low glucose, and lymphocytic pleocytosis (often confused with viral, but glucose is the differentiator).

Q: Which of the following is not a cause of rash?

Shigella. The correct answer is **Shigella**. In clinical medicine, Shigella is primarily characterized by bacillary dysentery (fever, abdominal cramps, and mucoid/bloody stools). It is an invasive intestinal pathogen but does not typically cause a systemic cutaneous rash. **Why the other options are incorrect:** * **Salmonella (S. Typhi):** Causes **"Rose Spots."** These are 2–4 mm, blanching, erythematous maculopapules typically found on the upper abdomen and chest during the second week of Enteric Fever. * **Meningococci (N. meningitidis):** Classically causes a **petechial or purpuric rash**. In severe cases (Meningococcemia), it can lead to *Purpura Fulminans* due to disseminated intravascular coagulation (DIC). * **Staphylococcus (S. aureus):** Associated with various rashes, most notably the diffuse erythematous "sunburn-like" rash of **Toxic Shock Syndrome (TSS)**, which later undergoes desquamation. It also causes localized infections like impetigo and scalded skin syndrome. **NEET-PG High-Yield Pearls:** 1. **Rose Spots:** Pathognomonic for Enteric fever (Salmonella), seen in only ~25% of cases. 2. **Waterhouse-Friderichsen Syndrome:** Adrenal hemorrhage associated with fulminant Meningococcemia. 3. **Palmar/Sole Rash:** If a question mentions a rash involving palms and soles, think of **Syphilis (Secondary)**, **Rocky Mountain Spotted Fever**, or **Coxsackievirus (Hand-Foot-Mouth disease)**. 4. **Shigella Complication:** While it lacks a rash, remember its association with **HUS (Hemolytic Uremic Syndrome)** and **Reactive Arthritis** (HLA-B27).

Q: What is the outpatient treatment for community-acquired pneumonia?

Azithromycin. The treatment of Community-Acquired Pneumonia (CAP) is guided by the likely causative organisms, most commonly *Streptococcus pneumoniae*, *Haemophilus influenzae*, and atypical pathogens like *Mycoplasma pneumoniae* [3]. **1. Why Azithromycin is correct:** In previously healthy outpatients with no risk factors for drug-resistant *S. pneumoniae*, **Macrolides** (Azithromycin or Clarithromycin) or **Doxycycline** are the first-line empirical treatments. Azithromycin is preferred due to its excellent coverage against atypical pathogens and its convenient once-daily dosing [3]. In regions with high macrolide resistance or for patients with comorbidities, a respiratory fluoroquinolone (e.g., Levofloxacin) or a combination of a Beta-lactam plus a Macrolide is indicated. **2. Why the other options are incorrect:** * **Cefotaxime:** This is a third-generation cephalosporin administered parenterally (IV/IM). It is used for inpatient management of CAP, not for routine outpatient treatment. * **Ampicillin:** While active against some gram-positive organisms, it is inactivated by beta-lactamase-producing strains of *H. influenzae* and has no activity against atypical pathogens, making it poor monotherapy for CAP [3]. * **Gentamicin:** This aminoglycoside is primarily active against aerobic gram-negative bacilli. It has poor lung penetration and no activity against *S. pneumoniae* or atypicals, making it inappropriate for CAP. **High-Yield Clinical Pearls for NEET-PG:** * **CURB-65 Score:** Used to decide the site of care (Outpatient vs. Inpatient) [2]. A score of 0-1 suggests outpatient treatment. * **Atypical Pneumonia:** Characterized by a subacute onset and "walking pneumonia" symptoms; Macrolides are the drug of choice [3]. * **Drug of Choice for MRSA Pneumonia:** Linezolid or Vancomycin [1]. * **Drug of Choice for *Legionella*:** Azithromycin or Levofloxacin.

Q: A nurse is evaluating a client who is HIV positive and prescribed IV Pentamidine for Pneumocystis jirovecii pneumonia. Which of the following assessments after administration is most important to relay to the physician?

Sudden sweating and hunger.. **Explanation:** **Correct Option: C (Sudden Sweating and Hunger)** Pentamidine is a potent antiprotozoal agent used for *Pneumocystis jirovecii* pneumonia (PCP), but it is notorious for its metabolic side effects. It is directly toxic to the pancreatic islet cells. Initially, this causes an excessive release of insulin, leading to **severe hypoglycemia** [1]. Symptoms like sudden sweating, hunger, tremors, and confusion are classic signs of hypoglycemia and require immediate intervention to prevent seizures or coma [1]. Long-term use can eventually lead to islet cell destruction and secondary diabetes mellitus. **Analysis of Incorrect Options:** * **A (Blood pressure of 100/62 mm Hg):** While IV Pentamidine can cause hypotension if infused too rapidly, this specific reading is within a borderline normal range and is less acutely life-threatening than severe hypoglycemia. * **B (Redness and pain at the infusion site):** Pentamidine is an irritant and can cause local thrombophlebitis. While it requires nursing care (e.g., changing the site), it is not a systemic emergency. * **D (Unusual taste or dryness in the mouth):** A metallic taste (dysgeusia) is a common, benign side effect of Pentamidine and does not require urgent physician notification. **Clinical Pearls for NEET-PG:** 1. **Metabolic Profile:** Pentamidine causes a "double hit" on the pancreas—initial **hypoglycemia** (due to insulin leak) followed by potential **hyperglycemia/Diabetes** (due to B-cell cytolysis) [1]. 2. **Renal Impact:** Nephrotoxicity is common (up to 25% of patients); monitor serum creatinine closely. 3. **Cardiac Warning:** It can cause **QT prolongation** and Torsades de Pointes. 4. **PCP Prophylaxis:** While IV/IM is used for treatment, aerosolized Pentamidine is used for prophylaxis in patients who cannot tolerate Cotrimoxazole (TMP-SMX) [2].

Q: Which of the following is not a marker of the active replicative phase of chronic hepatitis B?

Anti-HBc. ### Explanation The correct answer is **C. Anti-HBc**. In Hepatitis B serology, markers are categorized based on whether they indicate active viral replication or the host's immune response [1]. **1. Why Anti-HBc is the correct answer:** **Anti-HBc (Antibody to Hepatitis B core antigen)** is a marker of **exposure**, not replication [1]. * **IgM anti-HBc** indicates acute infection (or a flare) [1]. * **IgG anti-HBc** indicates a past or chronic infection. Crucially, Anti-HBc persists for life regardless of whether the virus is actively replicating or has been cleared. Therefore, it cannot differentiate between the active replicative phase and the inactive carrier state. **2. Analysis of Incorrect Options (Markers of Replication):** * **HBV DNA (Option A):** This is the most sensitive and quantitative marker of viral load and active replication, often measured via PCR [1]. * **HBV DNA Polymerase (Option B):** This enzyme is required for viral synthesis; its presence directly correlates with active viral multiplication. * **AST and ALT (Option D):** While these are markers of hepatocellular injury, in the context of Chronic HBV, elevated transaminases typically signify the **Immune Clearance Phase**, where the host immune system attacks hepatocytes harboring replicating viruses. **3. High-Yield Clinical Pearls for NEET-PG:** * **HBeAg:** The classic serological marker for high infectivity and active replication. * **Window Period:** The interval where HBsAg and Anti-HBs are both negative; **IgM anti-HBc** is the only diagnostic marker during this time [1]. * **Inactive Carrier State:** Characterized by HBsAg (+), HBeAg (-), Anti-HBe (+), and low/undetectable HBV DNA with normal ALT [1]. * **Pre-core Mutant:** A scenario where the patient has high HBV DNA and active liver disease but is **HBeAg negative** (due to a mutation in the precore region) [1].

Q: A 21-year-old medical student suffered a needle stick injury. The patient has a history of illicit intravenous drugs abuse. One month later, the medical student develops jaundice. Which of the following findings would implicate hepatitis B as the etiology?

Positive hepatitis B surface antigen. **Explanation:** The clinical presentation describes an acute onset of jaundice following a high-risk parenteral exposure (needle stick injury). To diagnose acute Hepatitis B Virus (HBV) infection, one must identify markers of active viral replication [1]. **Why Option A is Correct:** **Hepatitis B surface antigen (HBsAg)** is the first serological marker to appear in the blood after infection, often detectable 2 to 6 weeks before the onset of symptoms or jaundice [1]. Its presence indicates an active (acute or chronic) infection. In this scenario, one month post-exposure, HBsAg is the most reliable indicator that the student has contracted HBV [2]. **Why Other Options are Incorrect:** * **Option B (Anti-HBs):** This antibody indicates immunity, either from a successful vaccination or recovery from a past infection [2]. It does not signify an active, acute illness. * **Option C (Anti-HAV):** This indicates a past or present Hepatitis A infection [3]. HAV is transmitted via the fecal-oral route, not through needle stick injuries (parenteral). * **Option D (Anti-HBc):** While IgM anti-HBc is a marker of acute infection, "Anti-HBc" (Total) is non-specific as it remains positive for life after any natural infection [2]. Without specifying the IgM isotype, HBsAg is a more definitive marker for diagnosing the etiology of the current jaundice. **NEET-PG High-Yield Pearls:** 1. **Window Period:** The interval when HBsAg becomes negative but Anti-HBs has not yet appeared. During this time, **IgM Anti-HBc** is the only diagnostic marker of acute HBV [1]. 2. **HBeAg:** Indicates high viral replication and maximum infectivity. 3. **Post-Exposure Prophylaxis (PEP):** If a student is unvaccinated, PEP involves both the HBV vaccine and Hepatitis B Immune Globulin (HBIG), ideally within 24 hours.

Question 1

Which of the following is NOT a causative agent of lymphatic filariasis?

Accepted Answer

Loa loa

Answer

Brugia malayi

Answer

Brugia timori

Answer

Wuchereria bancrofti

Question 2

A 29-year-old male is suspected of having viral encephalitis. Which of the following is the most likely result from CSF analysis?

Accepted Answer

Raised protein, raised lymphocytes, normal glucose

Answer

Raised protein, normal lymphocytes, normal glucose

Answer

Raised protein, raised lymphocytes, raised glucose

Answer

Normal protein, raised lymphocytes, raised glucose

Question 3

What are the investigations in a clinically suspected case of tuberculosis?

Accepted Answer

Mantoux test (in children)

Answer

Sputum AFB

Answer

QuantiFERON TB Gold

Answer

Bactec

Question 4

Which of the following is not a cause of rash?

Accepted Answer

Shigella

Answer

Salmonella

Answer

Meningococci

Answer

Staphylococcus

Question 5

What is the outpatient treatment for community-acquired pneumonia?

Accepted Answer

Azithromycin

Answer

Cefotaxime

Answer

Ampicillin

Answer

Gentamicin

Question 6

A nurse is evaluating a client who is HIV positive and prescribed IV Pentamidine for Pneumocystis jirovecii pneumonia. Which of the following assessments after administration is most important to relay to the physician?

Accepted Answer

Sudden sweating and hunger.

Answer

Blood pressure of 100/62 mm Hg.

Answer

Redness and pain at the infusion site.

Answer

Unusual taste or dryness in the mouth.

Question 7

Which of the following is not a marker of the active replicative phase of chronic hepatitis B?

Accepted Answer

Anti-HBc

Answer

HBV DNA

Answer

HBV DNA polymerase

Answer

AST and ALT

Question 8

Which of the following organisms can cause acalculous cholecystitis?

Accepted Answer

Leptospirosis

Answer

Malaria

Answer

Staphylococcus

Answer

Nocardiosis

Question 9

Post-transplant cytomegalovirus infection may cause which of the following?

Accepted Answer

Gastrointestinal ulceration and hemorrhage

Answer

Pyelonephritis

Answer

Cholecystitis

Answer

Intraabdominal abscess

Question 10

A 21-year-old medical student suffered a needle stick injury. The patient has a history of illicit intravenous drugs abuse. One month later, the medical student develops jaundice. Which of the following findings would implicate hepatitis B as the etiology?

Accepted Answer

Positive hepatitis B surface antigen

Answer

Positive antihepatitis B surface antibody

Answer

Positive antihepatitis A antibody

Answer

Positive antihepatitis B-core antibody

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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