Infectious Diseases Practice Questions

Q: A 30-year-old HIV positive patient presents with fever, dyspnoea and non-productive cough. The patient is cyanosed. His chest X-ray reveals bilateral, symmetrical interstitial infiltrates. What is the most likely diagnosis?

Pneumocystis jirovecii pneumonia. ### Explanation **Pneumocystis jirovecii Pneumonia (PCP)** is the most common opportunistic infection in HIV patients with a CD4 count <200 cells/µL. **Why Option C is Correct:** The clinical triad of **fever, progressive dyspnoea, and non-productive cough** in an HIV-positive patient is classic for PCP [1]. The presence of **cyanosis** and exercise-induced desaturation is common due to significant alveolar-capillary block. Radiologically, the hallmark is **bilateral, symmetrical perihilar interstitial infiltrates** (ground-glass opacities), which matches the description provided [1]. **Why Other Options are Incorrect:** * **A. Tuberculosis:** Usually presents with a productive cough, hemoptysis, and weight loss. Radiologically, it typically shows focal infiltrates, cavitary lesions (in the upper lobes), or miliary patterns rather than symmetrical interstitial infiltrates [1]. * **B. Cryptococcosis:** Primarily presents as meningitis in HIV patients. Pulmonary involvement is less common and usually manifests as well-defined nodules or pleural effusions . * **C. Toxoplasmosis:** Most commonly affects the CNS, presenting with seizures or focal neurological deficits and "ring-enhancing lesions" on MRI. Pulmonary toxoplasmosis is rare and clinically indistinguishable from PCP, but PCP is statistically much more likely . **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** Definitive diagnosis is made via **Gomori Methenamine Silver (GMS) stain** of induced sputum or Bronchoalveolar Lavage (BAL), showing "crushed ping-pong ball" cysts [1]. * **Lab Marker:** Elevated **Serum LDH** levels are highly sensitive but non-specific for PCP. * **Treatment:** **DOC is IV Trimethoprim-Sulfamethoxazole (TMP-SMX)** [1]. * **Steroid Indication:** Add Prednisone if $PaO_2 35$ mmHg to prevent respiratory failure triggered by dying organisms [1].

Q: A patient with undulating fever presents with features of encephalitis. He is treated successfully with doxycycline and rifampicin. What is the most probable diagnosis?

Brucellosis. ### Explanation **Correct Answer: A. Brucellosis** The clinical triad of **undulating fever** (fever that rises and falls like a wave), neurological involvement (**neurobrucellosis** presenting as encephalitis), and a dramatic response to **Doxycycline and Rifampicin** is classic for Brucellosis. Brucellosis is a zoonotic infection caused by *Brucella* species (e.g., *B. melitensis* from goats/sheep). It is an intracellular pathogen, necessitating drugs with good intracellular penetration. While osteoarticular involvement is the most common complication, neurobrucellosis occurs in 5–10% of cases and can manifest as meningitis or encephalitis [1]. The WHO-recommended regimen for uncomplicated brucellosis is Doxycycline + Rifampicin for 6 weeks; however, for neurobrucellosis, treatment is often extended and may include a third drug like Ceftriaxone [1]. **Why other options are incorrect:** * **B. Bordetella pertussis:** Causes "Whooping Cough." It presents with paroxysmal cough and post-tussive vomiting, not undulating fever or encephalitis. The treatment of choice is Macrolides (Azithromycin). * **C. Francisella tularensis:** Causes Tularemia. While it is zoonotic, it typically presents with ulceroglandular disease or oculoglandular syndromes. The drug of choice is Streptomycin or Gentamicin. * **D. Mycoplasma:** Causes "Walking Pneumonia." While it can have extrapulmonary manifestations, it does not present with an undulating fever pattern. **High-Yield Clinical Pearls for NEET-PG:** * **Most common source:** Consumption of unpasteurized dairy products or contact with infected livestock. * **Gold Standard Diagnosis:** Bone marrow culture (more sensitive than blood culture) [1]. * **Serology:** Standard Agglutination Test (SAT); titers >1:160 are significant [1]. * **Rose Bengal Test:** Used as a rapid screening tool. * **Castaneda Medium:** A specialized biphasic medium used for culturing *Brucella*.

Q: Which of the following is NOT a characteristic of acute urinary tract infection?

Elastase activity in urine. ### Explanation The diagnosis of an acute Urinary Tract Infection (UTI) relies on clinical symptoms supported by urinalysis (dipstick and microscopy) and culture [1]. **Why "Elastase activity" is the correct answer:** **Elastase** is a proteolytic enzyme primarily associated with the degradation of elastin in connective tissues. While it is a marker for conditions like acute pancreatitis (fecal elastase) or certain pulmonary diseases, it is **not** a standard marker used to diagnose or characterize a UTI. There is no significant elastase activity in the urine during a typical acute urinary infection. **Analysis of Incorrect Options:** * **Pus cells in urine (Pyuria):** This is the hallmark of UTI. The presence of ≥10 white blood cells (WBCs) per high-power field (hpf) in centrifuged urine indicates an inflammatory response to infection in the urinary tract [1]. * **Nitrite positive:** Many common uropathogens (especially Enterobacteriaceae like *E. coli*) reduce dietary nitrates to nitrites. A positive nitrite test is highly specific for bacteriuria. * **Leucocyte esterase (LE) positive:** This enzyme is produced by neutrophils. A positive LE dipstick test indicates the presence of pyuria (pus cells), even if the cells have already lysed. **Clinical Pearls for NEET-PG:** * **Sterile Pyuria:** Presence of pus cells but negative routine culture [1]. Classic causes include *Mycobacterium tuberculosis* (Renal TB), Chlamydia, or recent antibiotic use [1]. * **Nitrite False Negatives:** Occur with organisms that do not produce nitrate reductase (e.g., *Enterococcus*, *Staphylococcus saprophyticus*, and *Pseudomonas*). * **Gold Standard:** The most definitive diagnosis for UTI remains a **urine culture** showing significant bacteriuria (traditionally ≥10⁵ CFU/mL). * **Most Common Organism:** *Uropathogenic E. coli* (UPEC) remains the leading cause of both uncomplicated and complicated UTIs [2].

Q: Diagnosis of acute viral hepatitis A is primarily established by which of the following findings?

Variable increase in transaminase levels.. **Explanation:** The diagnosis of **Acute Viral Hepatitis A (HAV)** relies on a combination of clinical presentation, biochemical markers of liver injury, and serological confirmation. **Why the correct answer is right:** In acute viral hepatitis, the hallmark biochemical finding is a **variable increase in serum transaminases (ALT and AST)**. These enzymes are released into the bloodstream due to hepatocellular necrosis and inflammation. In symptomatic cases, these levels typically exceed 500 U/L and can often reach into the thousands. The degree of elevation is "variable" because it depends on the timing of the test relative to the onset of symptoms and the severity of the hepatic insult. **Analysis of Incorrect Options:** * **Option A:** While hepatic injury is present, "significant" is subjective. Transaminase levels do not always correlate linearly with the degree of liver cell necrosis or the ultimate prognosis. * **Option C:** **IgG anti-HAV** indicates past infection or immunity (post-vaccination). It is **not** used to diagnose acute infection. The gold standard serological marker for acute HAV is **IgM anti-HAV**. * **Option D:** An absence of a rise in transaminases would effectively rule out acute viral hepatitis, as these are the primary indicators of active liver inflammation. **NEET-PG High-Yield Pearls:** * **Route of Transmission:** Fecal-oral (most common). * **Incubation Period:** 15–45 days (Average: 4 weeks). * **Serology:** **IgM anti-HAV** is the diagnostic marker of choice for acute infection. It appears at the onset of symptoms and persists for 3–6 months. * **Prognosis:** HAV is typically self-limiting and **never** progresses to chronic hepatitis. * **Complication:** The most feared (though rare) complication is **Fulminant Hepatic Failure**, especially in patients with underlying chronic liver disease.

Q: Fresh water swimming can lead to which of the following infections?

Leptospirosis. **Explanation:** **Leptospirosis** is a zoonotic infection caused by the spirochete *Leptospira interrogans*. The bacteria are shed in the **urine of infected animals** (most commonly rodents, dogs, and livestock) [1]. These spirochetes can survive for weeks in **fresh water and moist soil** [1]. Human infection occurs through direct contact with contaminated water or soil via skin abrasions or mucous membranes. Activities like **freshwater swimming**, kayaking, or wading in floodwaters are classic risk factors frequently tested in exams [1]. **Analysis of Incorrect Options:** * **A. Brucellosis:** Primarily transmitted through the consumption of unpasteurized dairy products or direct contact with infected livestock (cattle, goats, sheep). It is an occupational hazard for veterinarians and slaughterhouse workers, not associated with swimming. * **C. Babesiosis:** A malaria-like illness caused by *Babesia microti*. It is transmitted by the bite of the **Ixodes tick** (the same vector for Lyme disease). * **D. Lassa Fever:** A viral hemorrhagic fever transmitted through contact with food or household items contaminated with the urine or feces of infected **Mastomys rats** (multimammate rats), primarily in West Africa. **High-Yield Clinical Pearls for NEET-PG:** * **Weil’s Disease:** The severe form of Leptospirosis characterized by the triad of **Jaundice, Renal failure, and Hemorrhage**. * **Clinical Feature:** Look for **conjunctival suffusion** (redness without exudate), which is a highly specific sign. * **Biphasic illness:** It typically presents with an initial septicemic phase followed by an immune phase (meningitis/uveitis). * **Treatment:** **Doxycycline** is the drug of choice for prophylaxis and mild cases; IV **Penicillin G** is preferred for severe disease.

Q: Opportunistic infections are seen in which of the following conditions?

All of the above. **Explanation:** Opportunistic infections (OIs) occur in individuals with compromised immune systems [2]. These pathogens, which typically do not cause disease in healthy hosts, take advantage of a weakened immune response (cellular or humoral). * **AIDS (Option A):** This is the classic example of profound immunosuppression. HIV targets and destroys **CD4+ T-lymphocytes**. When the CD4 count falls below 200 cells/mm³, the risk for OIs like *Pneumocystis jirovecii* pneumonia, Toxoplasmosis, and Cryptococcosis increases significantly [3]. * **Autoimmune Diseases (Option B):** While the diseases themselves involve immune dysregulation, the primary risk for OIs stems from **iatrogenic immunosuppression** [2]. Patients are often treated with long-term corticosteroids, Methotrexate, or Biologicals (e.g., TNF-alpha inhibitors), which suppress the body's ability to fight latent or environmental pathogens. * **Organ Transplantation (Option C):** To prevent graft rejection, transplant recipients must take lifelong **immunosuppressive therapy** (e.g., Cyclosporine, Tacrolimus, Mycophenolate) [1]. This creates a "window of vulnerability" where patients are highly susceptible to Cytomegalovirus (CMV), BK virus, and fungal infections [1]. **Conclusion:** Since all three conditions involve a state of immunosuppression (either primary or secondary), **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Most common OI in AIDS:** *Pneumocystis jirovecii* (PCP) [3]. * **Post-Transplant Period:** The first month is dominated by surgical/bacterial infections; months 1–6 are the peak period for OIs like CMV and *Nocardia*. * **TNF-alpha Inhibitors:** Always screen for **Latent Tuberculosis** before starting these drugs for autoimmune conditions (e.g., Rheumatoid Arthritis), as they significantly increase the risk of TB reactivation.

Q: Which parasite causes 'River blindness'?

Onchocerca volvulus. **Onchocerca volvulus** is the causative agent of **River Blindness** (Onchocerciasis). It is a filarial nematode transmitted to humans through the bite of an infected **Blackfly (*Simulium* genus)**, which breeds in fast-flowing rivers—hence the name. The pathology is primarily caused by the host's inflammatory response to dying **microfilariae**. These larvae migrate to the skin (causing severe pruritus and "leopard skin" appearance) and the eyes, where chronic inflammation leads to sclerosing keratitis and eventual blindness [1]. **Analysis of Incorrect Options:** * **Schistosoma haematobium:** A trematode (blood fluke) that causes urinary schistosomiasis [2]. It is associated with terminal hematuria and is a significant risk factor for **Squamous Cell Carcinoma of the bladder**. * **Fasciola hepatica:** Known as the "Sheep liver fluke," it causes hepatobiliary disease after ingestion of contaminated watercress. It typically presents with right upper quadrant pain and eosinophilia. * **Opisthorchis viverrini:** A Southeast Asian liver fluke associated with the consumption of raw fish. Chronic infection is a major risk factor for **Cholangiocarcinoma** (bile duct cancer). **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Blackfly (*Simulium*) [1]. * **Drug of Choice:** **Ivermectin** (kills microfilariae but not adults) [1]. * **Diagnosis:** Skin snip preparation to visualize microfilariae. * **Wolbachia:** *Onchocerca* harbors symbiotic *Wolbachia* bacteria; treating with Doxycycline can sterilize adult female worms [1]. * **Mazzotti Reaction:** A severe systemic reaction (fever, hypotension) that can occur after treating onchocerciasis with diethylcarbamazine (DEC).

Question 1

A 30-year-old HIV positive patient presents with fever, dyspnoea and non-productive cough. The patient is cyanosed. His chest X-ray reveals bilateral, symmetrical interstitial infiltrates. What is the most likely diagnosis?

Accepted Answer

Pneumocystis jirovecii pneumonia

Answer

Tuberculosis

Answer

Cryptococcosis

Answer

Toxoplasmosis

Question 2

A patient with undulating fever presents with features of encephalitis. He is treated successfully with doxycycline and rifampicin. What is the most probable diagnosis?

Accepted Answer

Brucellosis

Answer

Bordetella pertussis

Answer

Francisella tularensis

Answer

Mycoplasma

Question 3

Which of the following is NOT a characteristic of acute urinary tract infection?

Accepted Answer

Elastase activity in urine

Answer

Pus cells in urine

Answer

Nitrite positive

Answer

Leucocyte esterase positive

Question 4

Diagnosis of acute viral hepatitis A is primarily established by which of the following findings?

Accepted Answer

Variable increase in transaminase levels.

Answer

Significant hepatic injury indicated by transaminase levels.

Answer

Detection of IgG anti-HAV antibodies.

Answer

Absence of any rise in transaminase levels.

Question 5

Fresh water swimming can lead to which of the following infections?

Accepted Answer

Leptospirosis

Answer

Brucellosis

Answer

Babesiosis

Answer

Lassa fever

Question 6

Which of the following hepatitis viruses can cause chronic liver disease?

Accepted Answer

Hepatitis C

Answer

Hepatitis B

Answer

Hepatitis A

Answer

Hepatitis E

Question 7

All of the following are true regarding typhoid ulcers except:

Accepted Answer

Multiple ulcers and transverse

Answer

Mainly affects the ileum

Answer

Perforation occurs at the 3rd week

Answer

Perforation is treated by surgery

Question 8

Opportunistic infections are seen in which of the following conditions?

Accepted Answer

All of the above

Answer

AIDS

Answer

Autoimmune diseases

Answer

Organ transplantation

Question 9

A 36-year-old man with AIDS develops right-sided weakness involving the lower, but not the upper, limb. MRI scans reveal a ring-enhancing lesion within the white matter of the left frontal lobe. A biopsy showed coagulative necrosis of brain parenchyma with macrophage-rich chronic inflammatory infiltration admixed with microscopic cysts that contain characteristic bradyzoites. What is the most common source of this type of infection?

Accepted Answer

Cats

Answer

Anopheles mosquitoes

Answer

Bird droppings

Answer

Cooling systems

Question 10

Which parasite causes 'River blindness'?

Accepted Answer

Onchocerca volvulus

Answer

Schistosoma haematobium

Answer

Fasciola hepatica

Answer

Opisthorchis viverrini

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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