Infectious Diseases Practice Questions

Q: The clinical spectrum of Hansen's disease is best characterized by what?

Peripheral neuritis. **Explanation:** Hansen’s disease (Leprosy), caused by *Mycobacterium leprae*, is primarily a disease of the **peripheral nerves** and skin [1]. The hallmark of its clinical spectrum is **peripheral neuritis**. *M. leprae* has a unique tropism for Schwann cells; the resulting nerve damage is caused by both direct bacterial invasion and the host’s cell-mediated immune response. This leads to characteristic sensory loss, motor weakness, and autonomic dysfunction, which are the primary causes of the deformities and disabilities associated with the disease [2]. **Analysis of Options:** * **A. Immunologic anergy:** While this occurs in the **Lepromatous (LL)** pole of the spectrum (specific anergy to *M. leprae* antigens), it does not characterize the *entire* spectrum. Tuberculoid (TT) patients exhibit a strong delayed-type hypersensitivity response [1]. * **B. Chronic pneumonitis:** Unlike *M. tuberculosis*, *M. leprae* is obligately intracellular and prefers cooler temperatures (30-33°C). It does not typically involve the lungs. * **D. Bacilli in lesions that digest tissues:** *M. leprae* does not produce exotoxins or lytic enzymes that "digest" tissue. Tissue destruction is secondary to trauma (due to anesthesia) or immune-mediated inflammation [2]. **High-Yield NEET-PG Pearls:** * **Cardinal Signs:** Hypopigmented patches with loss of sensation, thickened peripheral nerves, and positive skin smears [1]. * **Nerve Involvement:** The **Ulnar nerve** is the most commonly involved nerve in Leprosy. * **Ridley-Jopling Classification:** A five-group spectrum (TT, BT, BB, BL, LL) based on the host's immunological status [1]. * **First Sign:** The earliest clinical sign of Leprosy is often a **loss of temperature sensation** (cold before hot).

Q: Which of the following antiviral drugs is NOT used in the management of chickenpox?

Nevirapine. ### Explanation **Correct Answer: D. Nevirapine** **1. Why Nevirapine is the Correct Answer:** Nevirapine is a **Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI)** used exclusively in the treatment of **HIV-1 infection** [2]. It works by binding directly to the reverse transcriptase enzyme of the Human Immunodeficiency Virus. It has no inhibitory activity against DNA viruses like the Varicella-Zoster Virus (VZV), which causes chickenpox. **2. Why the Other Options are Incorrect:** * **A. Acyclovir:** This is the drug of choice for treating chickenpox, especially in adolescents, adults, and immunocompromised patients [1]. It is a nucleoside analog that inhibits viral DNA polymerase [2]. * **B. Famciclovir:** This is a prodrug of penciclovir [2]. It has a longer half-life than acyclovir and is effective against VZV [1]. It is frequently used for herpes zoster but is also an acceptable alternative for varicella. * **C. Valacyclovir:** This is the L-valyl ester prodrug of acyclovir [2]. It has superior oral bioavailability compared to acyclovir and is commonly used in the management of VZV infections to reduce the severity and duration of symptoms [1]. **3. Clinical Pearls for NEET-PG:** * **Drug of Choice:** Oral Acyclovir is the standard for healthy patients >12 years old; **IV Acyclovir** is mandatory for disseminated disease or varicella pneumonia [1]. * **Mechanism of Action:** Acyclovir requires initial phosphorylation by **viral thymidine kinase** to become active (Acyclovir monophosphate) [2]. * **Contraindication:** Aspirin should be avoided in children with chickenpox due to the risk of **Reye’s Syndrome**. * **Post-exposure Prophylaxis:** Varicella-Zoster Immunoglobulin (VZIG) is indicated for exposed susceptible individuals at high risk (e.g., pregnant women, neonates, immunocompromised).

Q: A patient presents with features of ataxia and a history of a painless penile ulcer approximately 3 years ago, followed by a maculopapular rash. He is currently on treatment. Which is the MOST sensitive test to monitor his response to treatment?

CSF pleocytosis. ### Explanation The patient’s clinical history (painless penile ulcer followed by a rash) indicates a progression from primary to secondary syphilis [1]. The current presentation of **ataxia** suggests **Neurosyphilis** (specifically Tabes Dorsalis). **Why CSF Pleocytosis is the Correct Answer:** In neurosyphilis, monitoring treatment success relies on objective markers of inflammation. **CSF pleocytosis (elevated WBC count)** is the **most sensitive indicator** of active CNS infection and the first parameter to normalize following effective therapy. A decreasing white cell count in the CSF confirms a positive response to treatment. If the cell count does not decrease after 6 months or is not normal by 2 years, re-treatment is indicated. **Analysis of Incorrect Options:** * **VDRL/RPR (Options A & B):** These are non-treponemal tests used for screening and monitoring systemic (non-CNS) syphilis [2]. While CSF-VDRL is highly specific for diagnosing neurosyphilis, it is less sensitive than pleocytosis for monitoring the *immediate* response to treatment, as titers may decline slowly. * **TPI (Option C):** The Treponema Pallidum Immobilization (TPI) test is a specific treponemal test. Treponemal tests (like TPI, FTA-ABS, and TPHA) usually remain positive for life ("immunological memory") and are therefore **useless** for monitoring treatment response or detecting reinfection. **NEET-PG High-Yield Pearls:** * **Diagnosis of Neurosyphilis:** CSF-VDRL is the "Gold Standard" for diagnosis due to its high specificity, but it lacks sensitivity. * **Order of Normalization:** Following successful treatment of neurosyphilis, CSF pleocytosis resolves first, followed by CSF protein levels, and finally CSF-VDRL titers. * **Drug of Choice:** Aqueous Crystalline Penicillin G (18–24 million units per day) for 10–14 days is the treatment of choice for neurosyphilis.

Q: Which of the following is the most common symptom of tetanus?

Trismus. **Explanation:** **Trismus (Lockjaw)** is the most common and typically the earliest presenting symptom of generalized tetanus [1]. It is caused by the masseter muscle's hypersensitivity to the tetanus toxin (tetanospasmin), which blocks the release of inhibitory neurotransmitters (GABA and glycine) in the spinal cord and brainstem [1]. This leads to sustained muscular contraction. In over 50–75% of cases, trismus is the hallmark initial sign that leads patients to seek medical attention. **Analysis of Incorrect Options:** * **Risus sardonicus:** While a characteristic sign of tetanus, it refers to the "sardonic smile" caused by the contraction of the facial muscles (frontalis and orbicularis oris). It usually occurs *after* or alongside trismus, but is not as universally the first or most common symptom. * **Hyperreflexia:** This is a clinical finding in tetanus due to the loss of upper motor neuron inhibition [1], but it is a non-specific sign and not the primary presenting complaint. * **Tonic-clonic convulsions:** Tetanus causes "tetanic spasms" (generalized muscle contractions), which are distinct from true epileptic tonic-clonic seizures. These spasms are triggered by external stimuli (noise, light) and occur in more advanced stages of the disease. **Clinical Pearls for NEET-PG:** * **Pathophysiology:** Tetanospasmin travels via **retrograde axonal transport** to the CNS [1]. * **Cephalic Tetanus:** A rare form involving cranial nerves (most commonly **CN VII**); it can occasionally present with flaccid paralysis instead of spasm. * **Neonatal Tetanus:** Usually occurs due to umbilical cord infection; the first sign is typically the **inability to suckle**. * **Management:** The priority is neutralizing unbound toxin with **Human Tetanus Immunoglobulin (HTIG)** and wound debridement. Metronidazole is the preferred antibiotic.

Q: All of the following statements about miliary tuberculosis are true except?

Mantoux test is always positive. Explanation: Miliary tuberculosis (TB) is a life-threatening form of TB resulting from the **hematogenous dissemination** of *Mycobacterium tuberculosis* [1]. **Why Option D is the Correct Answer (The "Except" Statement):** The Mantoux (Tuberculin Skin Test) is **not** always positive in miliary TB. In fact, it is negative in approximately **30–50%** of cases. This occurs due to **anergy**, where the body’s cell-mediated immune response is overwhelmed by the high bacterial load or suppressed by severe systemic illness, malnutrition, or concurrent viral infections (like HIV). **Analysis of Other Options:** * **Option A & B:** Miliary TB can occur during **primary infection** (common in children) or as a result of **secondary reactivation** of a latent focus (common in adults/elderly) [1]. Both represent a failure of the immune system to contain the bacilli locally. * **Option C:** Sputum microscopy is **usually negative** because miliary TB involves interstitial seeding rather than cavitary lesions that communicate with the airways. Diagnosis often requires biopsy (liver/bone marrow) or high-resolution CT (HRCT). **NEET-PG High-Yield Pearls:** * **Chest X-ray:** Classically shows 1–2 mm "millet seed" sized spots distributed uniformly throughout both lung fields [1]. * **Fundoscopy:** The presence of **choroid tubercles** is a pathognomonic clinical sign of miliary TB [1]. * **Common Lab Finding:** Hyponatremia (often due to SIADH or adrenal involvement). * **Gold Standard for Diagnosis:** While CXR is the initial tool, **transbronchial lung biopsy** or bone marrow biopsy has a higher diagnostic yield.

Q: A patient is diagnosed with HIV and Tuberculosis. What is the recommended order for starting Anti-Tuberculosis Therapy (ATT) and combination Antiretroviral Therapy (cART)?

Start ATT first. **Explanation:** In patients co-infected with HIV and Tuberculosis (TB), the standard of care is to **start Anti-Tuberculosis Therapy (ATT) first**, followed by combination Antiretroviral Therapy (cART). **Why ATT is started first:** The primary goal is to reduce the mycobacterial load and stabilize the patient before introducing antiretrovirals. Starting cART too early or simultaneously increases the risk of **Immune Reconstitution Inflammatory Syndrome (IRIS)**. IRIS occurs when the recovering immune system mounts an exaggerated inflammatory response against TB antigens, leading to clinical worsening. Furthermore, starting both together complicates the management of drug-drug interactions (especially with Rifampicin) and overlapping toxicities (like hepatotoxicity). **Analysis of Incorrect Options:** * **B & C:** Starting cART first or simultaneously significantly raises the risk of paradoxical IRIS and increases the pill burden, which may lead to poor adherence and severe adverse drug reactions. * **D:** Treating HIV alone while ignoring active TB is fatal. TB is a leading cause of mortality in HIV patients; uncontrolled TB accelerates HIV progression by increasing viral replication. **Clinical Pearls for NEET-PG:** * **Timing:** cART should generally be started **within 2 weeks** if the CD4 count is **<50 cells/mm³** and within **8 weeks** for others. * **Exception:** In **TB Meningitis**, cART should be delayed (usually 6–8 weeks) regardless of CD4 count to prevent life-threatening intracranial IRIS. * **Drug Interaction:** Rifampicin is a potent enzyme inducer. When used with cART, **Efavirenz** is often preferred, or the dose of **Dolutegravir** must be increased to twice daily.

Q: Which of the following can be used as a diagnostic modality for herpes labialis?

PCR assay. ### Explanation **Correct Answer: D. PCR assay** **1. Why PCR assay is the correct answer:** Polymerase Chain Reaction (PCR) is currently the **gold standard** and the most sensitive diagnostic modality for detecting Herpes Simplex Virus (HSV-1 and HSV-2). In cases of herpes labialis, PCR can detect viral DNA even when the viral load is low or during the crusting stage of the lesion. It is significantly more sensitive than viral culture and provides rapid results, making it the preferred choice in modern clinical practice. **2. Analysis of Incorrect Options:** * **A. Tzanck smear:** While historically popular, it is a non-specific test. It identifies **multinucleated giant cells** and Cowdry Type A inclusion bodies, which are seen in both HSV and Varicella-Zoster Virus (VZV). It cannot differentiate between the two, nor can it identify the specific HSV strain. * **B. Culture:** Viral culture was previously the gold standard. However, it has a high false-negative rate because the virus is labile and requires viable cells. Its sensitivity decreases rapidly as the lesion begins to heal. * **C. Gram stain:** This is used for identifying **bacteria** based on their cell wall properties. It has no utility in diagnosing viral infections like Herpes. **3. Clinical Pearls for NEET-PG:** * **Most common site:** The vermilion border of the lip is the most frequent site for herpes labialis (HSV-1) [1]. * **Histopathology:** Look for "Acantholysis" and "Margination of chromatin" in Tzanck smears. * **Treatment of choice:** Oral Acyclovir or Valacyclovir. * **Recurrence:** HSV remains latent in the **Trigeminal ganglion** for orofacial herpes and the **Sacral ganglion** for genital herpes [1]. * **Encephalitis:** HSV-1 is the most common cause of sporadic fatal encephalitis; here, **CSF PCR** is the diagnostic investigation of choice.

Question 1

The clinical spectrum of Hansen's disease is best characterized by what?

Accepted Answer

Peripheral neuritis

Answer

Immunologic anergy

Answer

Chronic pneumonitis

Answer

Bacilli in lesions that digest tissues

Question 2

Which of the following antiviral drugs is NOT used in the management of chickenpox?

Accepted Answer

Nevirapine

Answer

Acyclovir

Answer

Famciclovir

Answer

Valacyclovir

Question 3

A 22-year-old man with AIDS complains of persistent cough, night sweats, low-grade fever, and general malaise. A chest X-ray reveals an area of consolidation in the periphery of the left upper lobe, as well as hilar lymphadenopathy. Sputum cultures show acid-fast bacilli. Which of the following is the most likely diagnosis?

Accepted Answer

Tuberculosis

Answer

Bronchopneumonia

Answer

Pulmonary abscess

Answer

Sarcoidosis

Question 4

A patient presents with features of ataxia and a history of a painless penile ulcer approximately 3 years ago, followed by a maculopapular rash. He is currently on treatment. Which is the MOST sensitive test to monitor his response to treatment?

Accepted Answer

CSF pleocytosis

Answer

VDRL (Veneral Disease Research Laboratory)

Answer

RPR

Answer

TPI

Question 5

Which of the following is the most common symptom of tetanus?

Accepted Answer

Trismus

Answer

Risus sardonicus

Answer

Hyperreflexia

Answer

Tonic clonic convulsion

Question 6

All of the following statements about miliary tuberculosis are true except?

Accepted Answer

Mantoux test is always positive

Answer

May occur following primary infection

Answer

May occur following secondary reactivation

Answer

Sputum microscopy is usually negative

Question 7

A 62-year-old man with a history of mild intermittent bronchial asthma presents for a first visit after not seeing a doctor for over 10 years. He is sexually active with a single long-term partner and does not recall receiving any vaccines since childhood. Which of the following vaccines should be offered?

Accepted Answer

Pneumococcal, influenza, zoster, and tetanus-diphtheria-acellular pertussis (Tdap)

Answer

Pneumococcal, influenza, zoster, and tetanus-diphtheria (Td)

Answer

Pneumococcal, influenza, and human papillomavirus (HPV)

Answer

Pneumococcal, influenza, and tetanus-diphtheria-acellular pertussis (Tdap)

Question 8

A patient is diagnosed with HIV and Tuberculosis. What is the recommended order for starting Anti-Tuberculosis Therapy (ATT) and combination Antiretroviral Therapy (cART)?

Accepted Answer

Start ATT first

Answer

Start cART first

Answer

Start both simultaneously

Answer

Start cART only

Question 9

Which of the following can be used as a diagnostic modality for herpes labialis?

Accepted Answer

PCR assay

Answer

Tzanck smear

Answer

Culture

Answer

Gram stain under microscope

Question 10

A patient presents with lower gastrointestinal bleed. Sigmoidoscopy shows ulcers in the sigmoid colon. Biopsy from this area shows flask-shaped ulcers. Which of the following is the most appropriate treatment?

Accepted Answer

Intravenous metronidazole

Answer

Intravenous ceftriaxone

Answer

Intravenous steroids and sulphasalazine

Answer

Hydrocortisone enemas

Infectious Diseases — MCQs

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