Infectious Diseases Practice Questions

Q: A patient presented with fever for 8 days and difficulty in breathing for two days. On examination, a red painless rash was found on the left side of the chest. What is the appropriate treatment?

Doxycycline. ### Explanation The clinical presentation of prolonged fever (8 days), respiratory distress, and a **red painless rash** (specifically an **eschar**) is highly suggestive of **Scrub Typhus**, a rickettsial infection caused by *Orientia tsutsugamushi* [1]. **1. Why Doxycycline is Correct:** The "red painless rash" described is the classic **Eschar**—the hallmark of Scrub Typhus. It represents the site of a larval mite (chigger) bite, characterized by a necrotic center with a surrounding erythematous halo [1]. Scrub Typhus often presents with complications like **ARDS (Acute Respiratory Distress Syndrome)**, explaining the patient's difficulty in breathing. **Doxycycline** is the drug of choice for rickettsial diseases, acting by inhibiting bacterial protein synthesis. **2. Why Other Options are Incorrect:** * **Oseltamivir:** Used for Influenza. While flu causes fever and respiratory symptoms, it does not present with an eschar. * **Streptomycin:** An aminoglycoside used for Tuberculosis or Plague. It is not effective against intracellular rickettsial organisms. * **Ceftriaxone:** A third-generation cephalosporin used for bacterial pneumonia or meningitis. Rickettsial organisms are inherently resistant to beta-lactams. **3. NEET-PG High-Yield Pearls:** * **Vector:** Larval stage of Trombiculid mite (**Chigger**) [1]. * **Diagnosis:** **Weil-Felix test** (Heterophile antibody test) is a classic screening tool (OX-K positive), but **IgM ELISA** is now the gold standard. * **Common Complications:** ARDS, Meningoencephalitis, and Multi-Organ Dysfunction Syndrome (MODS). * **Alternative Treatment:** Azithromycin is preferred in pregnancy or for doxycycline-resistant strains [1].

Q: Which of the following parasites can cause duodenal stricture?

Strongyloides stercoralis. **Explanation:** **Strongyloides stercoralis** is the correct answer because of its unique ability to cause chronic, transmural inflammation in the upper gastrointestinal tract. Unlike most helminths, *Strongyloides* can undergo an **autoinfection cycle**, leading to a high worm burden (hyperinfection) [1]. The larvae penetrate the duodenal and jejunal mucosa, triggering an intense inflammatory response, eosinophilic infiltration, and subsequent fibrosis. Over time, this chronic inflammation leads to **cicatrization and duodenal strictures**, which may present clinically as gastric outlet obstruction. **Analysis of Incorrect Options:** * **Ascaris lumbricoides:** While it is the most common cause of intestinal obstruction (due to a physical bolus of worms), it typically affects the ileum and causes **mechanical** rather than structural/fibrotic strictures. * **Clonorchis sinensis:** This is a liver fluke. It primarily inhabits the **biliary tree**, leading to cholangitis, biliary strictures, and cholangiocarcinoma, but it does not cause duodenal strictures. * **Ankylostoma duodenale:** Hookworms attach to the duodenal mucosa to suck blood, leading to **iron deficiency anemia**. They do not invade the wall deeply enough to cause transmural fibrosis or stricture formation [2]. **NEET-PG Clinical Pearls:** * **Drug of Choice:** Ivermectin is the preferred treatment for Strongyloidiasis (Albendazole is an alternative) [1]. * **Hyperinfection Syndrome:** Often triggered by **corticosteroid therapy**, which enhances the transformation of rhabditiform larvae into invasive filariform larvae [1]. * **Diagnosis:** Look for **rhabditiform larvae** in the stool (not eggs) or use the **Entero-test (String test)** [1]. * **Larva Currens:** A pathognomonic, rapidly moving serpiginous cutaneous eruption associated with *Strongyloides* [1].

Q: Painless oral ulcers are associated with which of the following conditions?

Primary syphilis. ### Explanation **Correct Answer: B. Primary syphilis** **1. Why Primary Syphilis is Correct:** Primary syphilis is characterized by the **chancre**, which typically appears at the site of inoculation (including the lips, tongue, or oral mucosa). The hallmark of a syphilitic chancre is that it is a **painless**, indurated, and clean-based ulcer. It is often accompanied by painless regional lymphadenopathy. This lack of pain is a critical diagnostic differentiator in clinical practice and exams. **2. Why Other Options are Incorrect:** * **A & D (Secondary and Primary Herpes):** Infections caused by Herpes Simplex Virus (HSV-1 or HSV-2) are characteristically **painful**. Primary herpes often presents as acute gingivostomatitis with multiple painful vesicles and ulcers, while secondary (recurrent) herpes presents as painful "cold sores" or fever blisters. * **C (Tuberculosis):** Oral TB ulcers are rare but typically **very painful**. they often present as irregular, ragged ulcers on the dorsum of the tongue, usually secondary to pulmonary TB. **3. NEET-PG High-Yield Clinical Pearls:** * **Syphilis Rule of Thumb:** Primary (Chancre) and Secondary (Condyloma lata) lesions are generally **painless** but highly infectious. * **Painful vs. Painless Ulcers (Genital/Oral):** * **Painless:** Syphilis, Lymphogranuloma venereum (initial lesion), Donovanosis (Granuloma inguinale - usually painless but beefy red). * **Painful:** Herpes (HSV), Chancroid (*Haemophilus ducreyi* — "You *do cry* because it's painful"), Behçet’s disease, and Aphthous stomatitis. * **Diagnosis:** The gold standard for primary syphilis is **Darkfield Microscopy** (showing motile *Treponema pallidum*), as serological tests (VDRL/RPR) may still be negative in the early stages.

Q: A patient with cholera experiencing diarrhea presents with a weak thready pulse, clammy skin, hypotension, and central nervous system symptoms. This clinical presentation typically occurs when the fluid loss is approximately what percentage of body weight?

>10%. ### Explanation In Cholera, the severity of dehydration is directly proportional to the volume of fluid lost, which is categorized into mild, moderate, and severe stages based on the percentage of body weight lost. **1. Why >10% is Correct:** Loss of **>10% of body weight** indicates **Severe Dehydration**. At this stage, the intravascular volume is critically depleted, leading to **hypovolemic shock**. Clinical hallmarks include: * **Hemodynamic instability:** Hypotension and a weak, thready, or absent radial pulse [1]. * **Peripheral vasoconstriction:** Cold, clammy skin and cyanosis. * **Neurological impairment:** Altered sensorium, lethargy, or coma due to decreased cerebral perfusion [1]. * **Other signs:** Anuria and deeply sunken eyes. **2. Why other options are incorrect:** * **2% (Mild Dehydration):** Fluid loss is minimal. The patient is thirsty but hemodynamically stable with moist mucous membranes. * **5% (Mild to Moderate Dehydration):** Characterized by increased thirst, dry mouth, and slightly decreased skin turgor, but blood pressure remains normal. * **7% (Moderate Dehydration):** Presents with a rapid pulse, loss of skin elasticity (skin pinch goes back slowly), and irritability. However, the patient is not yet in frank shock or showing CNS depression. ### NEET-PG High-Yield Pearls: * **Gold Standard Treatment:** For severe dehydration (>10%), the immediate treatment is **aggressive IV resuscitation** with **Ringer’s Lactate** (preferred over Normal Saline as it better addresses metabolic acidosis). * **Drug of Choice:** While rehydration is primary, **Azithromycin** is currently the preferred antibiotic for cholera (single dose), though Doxycycline is also used. * **Stool Characteristics:** "Rice-water stools" with a fishy odor; non-bloody and non-mucoid [1]. * **Electrolyte Profile:** Hypokalemia and Hyperchloremic metabolic acidosis are common.

Q: Which of the following is FALSE regarding lymphoma in patients with Acquired Immunodeficiency Syndrome (AIDS)?

Less responsive to treatment. The landscape of HIV-associated lymphomas has evolved significantly with the advent of **Combined Antiretroviral Therapy (cART)**. **Why Option D is the Correct (False) Statement:** Historically, AIDS-related lymphomas (ARL) had a dismal prognosis. However, in the modern cART era, the statement that they are "less responsive to treatment" is no longer accurate. When treated with standard chemo-immunotherapy (like R-CHOP or dose-adjusted EPOCH-R) alongside cART, HIV-positive patients achieve **remission rates and overall survival outcomes comparable to HIV-negative patients**. Therefore, HIV status alone is no longer a primary predictor of poor treatment response. **Analysis of Incorrect Options:** * **Option A & B:** ARL is characterized by its atypical distribution. While it can involve lymph nodes (**Intranodal**), a hallmark of AIDS-related B-cell lymphomas is the high frequency of **Extranodal involvement** (seen in up to 80% of cases), commonly affecting the CNS, GI tract, liver, and bone marrow [1]. * **Option C:** These lymphomas are characteristically **Highly Aggressive** [2]. The most common subtypes are Diffuse Large B-cell Lymphoma (DLBCL) and Burkitt Lymphoma, both of which exhibit rapid clinical progression and high-grade histological features [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Primary CNS Lymphoma:** Strongly associated with **EBV infection** (detected via CSF PCR) and typically occurs at CD4 counts ** 200 cells/µL**) compared to other ARLs. * **HHV-8:** Associated with Primary Effusion Lymphoma (PEL) and Kaposi Sarcoma. * **Key Management:** The most critical step in improving survival is the **concomitant administration of cART** with chemotherapy.

Q: Which of the following is NOT a treatment for neurocysticercosis?

Ivermectin. Neurocysticercosis (NCC), caused by the larval stage of *Taenia solium*, requires a multi-modal treatment approach depending on the stage and location of the cysts [1]. **Why Ivermectin is the correct answer:** Ivermectin is a broad-spectrum antiparasitic agent primarily used for Strongyloidiasis, Onchocerciasis, and Scabies [4]. It does **not** have a proven clinical role in the treatment of neurocysticercosis. The standard cysticidal drugs are Albendazole and Praziquantel [2]. **Analysis of other options:** * **Albendazole (Option A):** The drug of choice for NCC. It has better CNS penetration than Praziquantel and is more effective at killing viable cysts [2]. * **Praziquantel (Option B):** An alternative or adjunct cysticidal agent [1]. In cases of multiple parenchymal cysts, combination therapy (Albendazole + Praziquantel) is now often recommended to increase the rate of cyst clearance. * **Surgery (Option D):** Indicated in specific complications such as intraventricular cysts (endoscopic removal), hydrocephalus (VP shunt), or subarachnostroid NCC with mass effect. **High-Yield Clinical Pearls for NEET-PG:** 1. **Steroids First:** Always administer corticosteroids (e.g., Dexamethasone) *before* or concurrently with cysticidal drugs to prevent neurological worsening due to the inflammatory response to dying larvae. 2. **Seizure Control:** Anti-epileptic drugs (AEDs) are the first line of management for patients presenting with seizures [3]. 3. **Contraindication:** Cysticidal drugs are generally **avoided** in Cysticercal Encephalitis (diffuse brain edema) and Ocular Cysticercosis (risk of irreversible blindness due to inflammation). 4. **Calcified Cysts:** These are dead larvae; they do not require antiparasitic treatment, only symptomatic management for seizures.

Q: What is common in adult parvovirus infection?

Arthropathy. **Explanation:** Parvovirus B19, a small single-stranded DNA virus, exhibits a distinct clinical spectrum based on the host's age and hematological status. **Why Arthropathy is the correct answer:** In **adults** (especially women), the most common clinical presentation of Parvovirus B19 infection is **arthropathy**. It typically presents as a symmetrical inflammatory polyarthritis affecting the small joints of the hands, wrists, knees, and feet. Unlike rheumatoid arthritis, it is usually self-limiting and does not cause joint destruction. The pathogenesis is immune-mediated (Type III hypersensitivity), involving the deposition of immune complexes in the joints. **Analysis of Incorrect Options:** * **A & B. Bone Marrow/Pure Red Cell Aplasia (PRCA):** While the virus infects erythroid progenitor cells via the P-antigen, aplastic crises occur primarily in patients with **pre-existing high red cell turnover** (e.g., Sickle Cell Anemia, Hereditary Spherocytosis). Chronic PRCA is typically seen in **immunocompromised** individuals. * **C. Erythema Infectiosum (Fifth Disease):** This is the classic presentation in **children**, characterized by the "slapped-cheek" rash followed by a reticular "lace-like" body rash. It is less common in adults. **High-Yield Clinical Pearls for NEET-PG:** * **Receptor:** P-antigen (Globoside) on erythroblasts. * **Pregnancy:** Infection can lead to **Hydrops Fetalis** due to severe fetal anemia and high-output cardiac failure (not congenital malformations). * **Diagnosis:** IgM antibodies (acute) or PCR (especially in immunocompromised/aplastic crisis where antibody response is poor). * **Key Association:** Parvovirus B19 is the smallest DNA virus and is non-enveloped.

Q: What is the treatment of choice for Pneumocystis jirovecii pneumonia?

Trimethoprim/sulfamethoxazole. **Explanation:** **Pneumocystis jirovecii pneumonia (PCP)** is a life-threatening opportunistic fungal infection primarily seen in immunocompromised patients, particularly those with HIV/AIDS (typically when CD4 counts fall below 200 cells/mm³). **1. Why Trimethoprim/sulfamethoxazole (TMP-SMX) is the Correct Choice:** TMP-SMX (Co-trimoxazole) is the **first-line treatment and prophylaxis** for PCP [1]. It works by inhibiting two consecutive steps in the fungal folic acid synthesis pathway. For moderate-to-severe infections, it is administered intravenously; for mild cases, oral administration is sufficient. In patients with severe hypoxia (PaO₂ 35 mmHg), **adjunctive corticosteroids** must be added to reduce the inflammatory response triggered by dying organisms [1]. **2. Why Other Options are Incorrect:** * **B. Erythromycin:** A macrolide antibiotic used for atypical pneumonias (like *Legionella* or *Mycoplasma*). It has no activity against *P. jirovecii*. * **C. Ofloxacin:** A fluoroquinolone used for bacterial infections (UTIs, respiratory infections). It is ineffective against fungal pathogens. * **D. Tetracycline:** Primarily used for Rickettsial infections or *Chlamydia*. It does not cover *P. jirovecii*. **High-Yield Clinical Pearls for NEET-PG:** * **Radiology:** Classic "bat-wing" appearance or bilateral perihilar ground-glass opacities on CXR/HRCT [1]. * **Diagnosis:** Definitive diagnosis requires visualization of cysts via **Gomori Methenamine Silver (GMS)** stain or Giemsa stain from induced sputum or Bronchoalveolar Lavage (BAL) [1]. * **Alternative Treatment:** If the patient is allergic to sulfa drugs, the second-line treatment is **Primaquine plus Clindamycin** or **Pentamidine**. * **Marker:** Elevated **Serum Beta-D-Glucan** is a highly sensitive (though non-specific) marker for PCP.

Q: Opisthotonus is typically seen in which of the following conditions?

Tetanus. **Explanation:** **Opisthotonus** is a state of severe hyperextension and spasticity in which an individual's head, neck, and spinal column enter into a complete "bridging" or arching position. **1. Why Tetanus is Correct:** Tetanus is caused by the toxin **tetanospasmin** produced by *Clostridium tetani* [2]. This toxin travels retrograde to the CNS and inhibits the release of inhibitory neurotransmitters (**GABA and Glycine**) from Renshaw cells. The loss of inhibition leads to unchecked muscular spasms. Opisthotonus occurs because the extensor muscles of the back are more powerful than the flexors, causing the characteristic backward arching during a generalized spasm. **2. Why Other Options are Incorrect:** * **Anthrax:** Caused by *Bacillus anthracis*, it typically presents as cutaneous eschars, hemorrhagic mediastinitis (inhalation), or GI distress, but does not cause generalized muscle arching. * **Tetany:** Caused by hypocalcemia, it presents with carpopedal spasm (Trousseau’s sign) and facial twitching (Chvostek’s sign), but not the full-body opisthotonic posturing seen in tetanus [3]. * **Rabies:** Characterized by hydrophobia, aerophobia, and localized spasms of the pharyngeal muscles (furious rabies) or ascending paralysis (dumb rabies), but not classic opisthotonus. **Clinical Pearls for NEET-PG:** * **Risus Sardonicus:** The "sardonic smile" caused by spasms of the facial muscles. * **Trismus (Lockjaw):** Usually the first clinical sign of tetanus. * **Management:** Neutralize unbound toxin with **Human Tetanus Immune Globulin (HTIG)** and use **Metronidazole** (preferred over Penicillin G as Penicillin is a GABA antagonist). * **Differential:** Opisthotonus can also be seen in **strychnine poisoning** [1], **phenothiazine toxicity** (extrapyramidal side effects), and **kernicterus**.

Q: Hepatitis B infection is most commonly associated with which of the following conditions?

Serum sickness. The correct answer is **Serum sickness (Option C)**. This refers to the **prodromal, pre-icteric phase** of acute Hepatitis B virus (HBV) infection [1]. **Why Serum Sickness is Correct:** In the early stages of HBV infection, there is an excess of circulating Hepatitis B surface antigen (HBsAg) [1]. This leads to the formation of **Type III hypersensitivity immune complexes** (antigen-antibody complexes) that deposit in small vessels and joints. This manifests as a "serum sickness-like syndrome," characterized by the triad of **fever, skin rash (usually urticarial), and polyarthritis/arthralgia**. It typically resolves once jaundice appears [1]. **Analysis of Incorrect Options:** * **A. Polyarteritis nodosa (PAN):** While PAN is famously associated with HBV (10–30% of PAN cases are HBV-positive), it is a **late complication** or a chronic extrahepatic manifestation. In the context of "most common" early association or general prodromal presentation, serum sickness-like syndrome occurs more frequently during the acute phase. * **B. Systemic lupus erythematosus (SLE):** SLE is an autoimmune connective tissue disease with no direct causal link to HBV. In fact, chronic viral infections are sometimes studied as triggers for autoimmunity, but HBV is not a primary association for SLE. * **C. Polymyositis:** This is an inflammatory myopathy. While viral triggers are hypothesized, there is no established clinical association between HBV and polymyositis. **NEET-PG High-Yield Pearls:** * **Extrahepatic manifestations of HBV:** Serum sickness (most common prodrome), Polyarteritis Nodosa (PAN), and Membranous Glomerulonephritis (MGN). * **Hepatitis C associations:** Essential Mixed Cryoglobulinemia, Membranoproliferative Glomerulonephritis (MPGN), Porphyria Cutanea Tarda, and Lichen Planus. * **The "Gianotti-Crosti syndrome"** is a specific papular acrodermatitis of childhood associated with HBV.

Question 1

A patient presented with fever for 8 days and difficulty in breathing for two days. On examination, a red painless rash was found on the left side of the chest. What is the appropriate treatment?

Accepted Answer

Doxycycline

Answer

Oseltamivir

Answer

Streptomycin

Answer

Ceftriaxone

Question 2

Which of the following parasites can cause duodenal stricture?

Accepted Answer

Strongyloides stercoralis

Answer

Ascaris lumbricoides

Answer

Chlonorchis sinensis

Answer

Ankylostoma duodenale

Question 3

Painless oral ulcers are associated with which of the following conditions?

Accepted Answer

Primary syphilis

Answer

Secondary herpes

Answer

Tuberculosis

Answer

Primary herpes

Question 4

A patient with cholera experiencing diarrhea presents with a weak thready pulse, clammy skin, hypotension, and central nervous system symptoms. This clinical presentation typically occurs when the fluid loss is approximately what percentage of body weight?

Accepted Answer

>10%

Answer

2%

Answer

5%

Answer

7%

Question 5

Which of the following is FALSE regarding lymphoma in patients with Acquired Immunodeficiency Syndrome (AIDS)?

Accepted Answer

Less responsive to treatment

Answer

Intranodal involvement

Answer

Extranodal involvement

Answer

Highly aggressive nature

Question 6

Which of the following is NOT a treatment for neurocysticercosis?

Accepted Answer

Ivermectin

Answer

Albendazole

Answer

Praziquantel

Answer

Surgery

Question 7

What is common in adult parvovirus infection?

Accepted Answer

Arthropathy

Answer

Bone marrow aplasia

Answer

Pure red cell aplasia (PRCA)

Answer

Erythema infectiosum

Question 8

What is the treatment of choice for Pneumocystis jirovecii pneumonia?

Accepted Answer

Trimethoprim/sulfamethoxazole

Answer

Erythromycin

Answer

Ofloxacin

Answer

Tetracycline

Question 9

Opisthotonus is typically seen in which of the following conditions?

Accepted Answer

Tetanus

Answer

Anthrax

Answer

Tetany

Answer

Rabies

Question 10

Hepatitis B infection is most commonly associated with which of the following conditions?

Accepted Answer

Serum sickness

Answer

Polyarteritis nodosa

Answer

Systemic lupus erythematosus

Answer

Polymyositis

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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