Parasitology Practice Questions

Q: Which of the following inhibits digestion in the intestinal mucosa?

Giardia lamblia. **Explanation:** **Giardia lamblia** is the correct answer because it causes malabsorption by physically and biochemically interfering with the intestinal mucosa. The trophozoites attach to the duodenal and jejunal mucosa using a ventral sucking disc. This attachment, combined with the "carpeting" effect of high parasitic loads, leads to the **blunting of microvilli** and the **inhibition of brush border enzymes** (such as disaccharidases). This disruption inhibits the final stages of digestion and absorption, resulting in characteristic foul-smelling, fatty stools (steatorrhea). **Analysis of Incorrect Options:** * **Vibrio cholerae:** Causes secretory diarrhea via the cholera toxin, which increases cAMP levels. It leads to massive water and electrolyte loss but does not primarily inhibit the digestion of nutrients or damage the brush border enzymes. * **Enterokinase:** This is a physiological enzyme (not a pathogen) produced by the duodenum that converts trypsinogen to trypsin. It is essential *for* digestion, not an inhibitor of it. * **Schistosoma haematobium:** This is a blood fluke that primarily affects the venous plexus of the urinary bladder, leading to hematuria. It does not inhabit the intestinal mucosa or interfere with digestion. **NEET-PG High-Yield Pearls:** * **Habitat:** Duodenum and upper jejunum (acidic environment). * **Diagnosis:** Stool microscopy shows "falling leaf" motility (trophozoites) or cysts. String test (Entero-test) can be used for sampling. * **Antigen Detection:** Immunochromatographic assays for Giardia-specific antigen (GSA 65) are highly sensitive. * **Drug of Choice:** Tinidazole or Metronidazole. * **Association:** Common in patients with IgA deficiency.

Q: What is the scientific name for the pinworm (seat worm)?

Enterobius. **Explanation:** The correct answer is **Enterobius vermicularis**, commonly known as the **pinworm, seat worm, or threadworm**. It is a nematode that primarily inhabits the human cecum and appendix. The name "seat worm" is derived from the intense perianal itching (pruritus ani) it causes, typically at night when the gravid female migrates out of the anus to deposit eggs on the perianal skin. **Analysis of Options:** * **Enterobius (Correct):** The most common helminthic infection in developed countries. It is unique because it is transmitted via the fecal-oral route or retroinfection and is diagnosed using the **NIH swab or Scotch Tape test** rather than routine stool examination. * **Dracunculus medinensis:** Known as the **Guinea worm**. It is transmitted by drinking water containing infected *Cyclops* (copepods) and is characterized by a blister on the lower limb through which the adult worm emerges. * **Ankylostoma duodenale:** Known as the **Old World Hookworm**. It causes iron deficiency anemia due to blood-sucking at the intestinal mucosa. * **Necator americanus:** Known as the **New World Hookworm**. Like *Ankylostoma*, it is transmitted via larval penetration of the skin (ground itch). **NEET-PG High-Yield Pearls:** * **Drug of Choice:** Albendazole or Mebendazole (treat the entire family to prevent reinfection). * **Diagnostic Feature:** Eggs are non-bile stained and have a characteristic **"D-shape"** (flattened on one side). * **Clinical Sign:** Nocturnal enuresis and perianal pruritus in children. * **Autoinfection:** Common due to the "scratch-and-mouth" cycle.

Q: Which of the following is NOT a zoonotic disease?

Dracunculiasis (Guinea worm). **Explanation:** A **zoonosis** is defined as an infectious disease that is naturally transmissible from vertebrate animals to humans. The key to answering this question lies in identifying the natural reservoir of the pathogen. **Why Dracunculiasis is the correct answer:** Dracunculiasis (Guinea worm disease), caused by the nematode *Dracunculus medinensis*, is **not** a zoonotic disease because humans are the **only definitive host**. The life cycle involves humans and intermediate hosts (Cyclops/water fleas), but there is no animal reservoir involved in the natural transmission cycle. This unique characteristic made it a prime candidate for eradication; India was certified free of Guinea worm in 2000. **Analysis of Incorrect Options:** * **Leptospirosis:** A classic zoonosis caused by *Leptospira interrogans*. It is transmitted to humans via contact with water contaminated by the urine of infected animals (primarily rodents/rats). * **Rabies:** A viral zoonosis transmitted through the saliva of infected mammals (dogs, bats, monkeys). It is nearly 100% fatal once symptoms appear. * **Plague:** Caused by *Yersinia pestis*, it is a zoonotic infection of rodents transmitted to humans via the bite of an infected rat flea (*Xenopsylla cheopis*). **NEET-PG High-Yield Pearls:** * **Eradicated/Eliminated in India:** Smallpox (1977), Guinea worm (2000), Polio (2014), and Maternal & Neonatal Tetanus (2015). * **Intermediate Host of Guinea Worm:** *Cyclops* (Water flea). * **Infective Stage:** Third-stage (L3) larvae within the Cyclops. * **Diagnostic sign:** A painful blister, usually on the lower limb, from which the adult female worm emerges.

Q: Protozoan cysts are typically stored in which of the following solutions for preservation?

Formalin. ### Explanation **Correct Option: D (Formalin)** Formalin (typically as a 5% or 10% buffered solution) is the gold standard for preserving protozoan cysts, eggs, and larvae in stool samples. The underlying medical concept is **fixation**: Formalin acts by cross-linking proteins, which preserves the morphology of the cysts and prevents further development or decomposition. It is the primary component of the **Formalin-Ether Concentration Technique**, the most widely used method in diagnostic parasitology to increase the yield of cysts and ova. **Analysis of Incorrect Options:** * **A. Saline:** Normal saline (0.85% NaCl) is used for **direct wet mounts** to observe the motility of trophozoites (e.g., *Entamoeba histolytica*). However, it is not a preservative; samples in saline will eventually degenerate due to bacterial overgrowth. * **B. Phenol:** While phenol has antiseptic properties, it is too caustic and causes significant morphological distortion, making it unsuitable for preserving delicate protozoan structures for microscopic identification. * **C. Sodium hypochlorite:** This is a strong disinfectant and bleaching agent. It is used for surface decontamination but would destroy the internal structures of protozoan cysts, rendering them unidentifiable. **Clinical Pearls for NEET-PG:** * **Trophozoites vs. Cysts:** Formalin preserves cysts well but is poor for trophozoites. For trophozoites, **PVA (Polyvinyl Alcohol)** or **SDA (Sodium acetate-acetic acid-formalin)** is preferred. * **Concentration Technique:** The Formalin-Ether technique is preferred over Zinc Sulfate flotation for heavy eggs (like *Ascaris*) and operculated eggs. * **Safety:** Formalin-fixed specimens are generally non-infectious (except for certain coccidian oocysts like *Cryptosporidium*), making them safer for transport.

Q: Napier's aldehyde test is used in the diagnosis of which condition?

Kala azar. **Explanation:** **Napier’s Aldehyde Test** (also known as the Formol-gel test) is a non-specific biochemical test used for the presumptive diagnosis of **Kala-azar (Visceral Leishmaniasis)**. **Why Kala-azar is correct:** The underlying principle of this test is the detection of **hypergammaglobulinemia** (a massive increase in IgG levels). In chronic Kala-azar, there is a profound polyclonal B-cell activation leading to excessive serum globulins. When 1–2 drops of 40% formaldehyde are added to 1 mL of the patient's serum, the serum undergoes gelification and becomes opaque (resembling the white of a boiled egg) within 2 to 20 minutes. A positive result typically appears only after the disease has been present for at least 3 months. **Why other options are incorrect:** * **Malaria:** Diagnosis is primarily made via peripheral blood smears (thick and thin) or Rapid Diagnostic Tests (RDTs) detecting HRP-2 or LDH antigens. * **Typhus Fever:** Diagnosed using the **Weil-Felix test** (a heterophile agglutination test) or molecular methods like PCR. * **Enteric Fever:** Diagnosed via the **Widal test** (detecting O and H antibodies) or gold-standard blood/bone marrow cultures. **High-Yield Clinical Pearls for NEET-PG:** * **Chopra’s Antimony Test:** Another non-specific test for Kala-azar using urea stibamine (positive result = profuse flocculent precipitate). * **Specific Diagnosis:** The gold standard for Kala-azar is the demonstration of **LD bodies** (amastigotes) in splenic or bone marrow aspirates. * **rK39 Immunochromatographic Strip Test:** The most common rapid diagnostic test used in the field today due to its high sensitivity and specificity. * **Montenegro Skin Test:** Negative in active Kala-azar but becomes positive after recovery (indicates delayed hypersensitivity).

Q: Xenodiagnosis is used in the diagnosis of a disease that is transmitted by the bite of which of the following vectors?

Reduviid bug. **Explanation:** **Xenodiagnosis** is a specialized diagnostic technique where a laboratory-bred, pathogen-free vector is allowed to feed on a patient suspected of having a specific infection. The vector is later dissected to check for the multiplication of the parasite. 1. **Why Reduviid bug is correct:** Xenodiagnosis is the classic diagnostic method for **Chagas disease** (American Trypanosomiasis), caused by *Trypanosoma cruzi*. The vector for this disease is the **Reduviid bug** (also known as the Triatomine or "kissing" bug). In chronic stages of the disease, when parasitemia is too low to be detected by standard blood smears, uninfected Reduviid bugs are allowed to bite the patient. If *T. cruzi* is present, it multiplies in the bug's hindgut and is detected in its feces after 2–4 weeks. 2. **Why other options are incorrect:** * **Body louse:** Transmits Epidemic typhus (*Rickettsia prowazekii*) and Relapsing fever. Diagnosis is usually via serology or PCR. * **Deer tick (*Ixodes*):** Transmits Lyme disease and Babesiosis. Diagnosis relies on clinical presentation (Erythema migrans) and serology (ELISA/Western Blot). * **Mosquito:** Transmits Malaria, Filariasis, and various viral fevers. Diagnosis is typically via peripheral blood smears (Malaria) or antigen detection. **High-Yield Clinical Pearls for NEET-PG:** * **Chagas Disease Triad:** Cardiomyopathy (apical aneurysm), Megaesophagus, and Megacolon. * **Romaña’s sign:** Unilateral painless periorbital swelling (portal of entry through the conjunctiva). * **C-shaped Trypomastigotes:** Characteristic morphology of *T. cruzi* on peripheral smears. * **NNN Medium:** The specialized culture medium used for both *Leishmania* and *Trypanosoma*.

Q: Which of the following parasites is NOT included in the class Coccidia?

Naegleria. ### Explanation The correct answer is **Naegleria**. **1. Why Naegleria is the correct answer:** The class **Coccidia** (belonging to the Phylum Apicomplexa) consists of intracellular protozoa that typically undergo a complex life cycle involving both sexual (sporogony) and asexual (schizogony) reproduction. **Naegleria fowleri** is not a coccidian; it is a **Free-living Amoeba** (specifically an excavate amoeboflagellate). It is known as the "brain-eating amoeba" and causes Primary Amoebic Meningoencephalitis (PAM), a rapidly fatal CNS infection. **2. Why the other options are incorrect:** * **Cryptosporidium (C. parvum):** A classic coccidian parasite. It is a major cause of self-limiting diarrhea in immunocompetent individuals and chronic, life-threatening diarrhea in AIDS patients. * **Isospora (now Cystoisospora belli):** A coccidian parasite that causes intestinal infections. It is characterized by large, oval oocysts that stain acid-fast. * **Cyclospora (C. cayetanensis):** Another coccidian parasite associated with waterborne or foodborne (e.g., contaminated berries) outbreaks of diarrhea. **3. NEET-PG Clinical Pearls:** * **Acid-Fast Staining:** All intestinal coccidia (Cryptosporidium, Cyclospora, and Cystoisospora) are **Modified Acid-Fast positive**. * **Oocyst Sizes (High-Yield):** * *Cryptosporidium:* 4–6 µm (Smallest) * *Cyclospora:* 8–10 µm * *Cystoisospora:* 25–30 µm (Largest) * **Naegleria fowleri:** Usually contracted via intranasal entry during swimming in warm freshwater. Diagnosis is made by seeing motile trophozoites in a **wet mount of CSF**. * **Treatment:** Drug of choice for intestinal coccidia (except Cryptosporidium) is **Cotrimoxazole**. For Naegleria, **Amphotericin B** is used.

Q: True about Babesiosis?

Caused by Babesia microti. **Explanation:** **Babesiosis** is a malaria-like parasitic disease caused by protozoa of the genus *Babesia*. In humans, the most common species responsible for infection is **Babesia microti**. 1. **Why Option A is Correct:** *Babesia microti* is the primary causative agent of human babesiosis (transmitted by the *Ixodes scapularis* tick). It is an intraerythrocytic parasite that invades red blood cells, making this option the definitive true statement. 2. **Why Option B & C are Incorrect:** While *Babesia* does reside in **RBCs** (making Option B technically true in a biological sense), in the context of multiple-choice questions, the species name (Option A) is the most specific "textbook" fact. Option C is incorrect because *Babesia* does **not** infect white blood cells (WBCs). 3. **Why Option D is Incorrect:** Unlike Malaria, **Chloroquine is ineffective** against Babesiosis. The treatment of choice is a combination of **Atovaquone plus Azithromycin** (for mild-to-moderate cases) or **Quinine plus Clindamycin** (for severe cases). **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Ixodes* tick (the same vector for Lyme disease and Anaplasmosis; co-infections are common). * **Morphology:** On a Giemsa-stained peripheral smear, look for the characteristic **"Maltese Cross" appearance** (tetrads of merozoites). Unlike *P. falciparum*, there is no pigment (hemozoin) or gametocytes. * **Risk Factors:** Asplenic patients are at high risk for severe, life-threatening disease. * **Diagnosis:** Gold standard is the peripheral thin smear; PCR is more sensitive for low parasitemia.

Question 1

Which of the following inhibits digestion in the intestinal mucosa?

Accepted Answer

Giardia lamblia

Answer

Vibrio cholerae

Answer

Enterokinase

Answer

Schistosoma haematobium

Question 2

What is the scientific name for the pinworm (seat worm)?

Accepted Answer

Enterobius

Answer

Dracunculus

Answer

Ankylostoma

Answer

Necator

Question 3

Which of the following is NOT a cause of malabsorption?

Accepted Answer

Ascariasis

Answer

Giardia lamblia

Answer

Mycobacterium avium-intracellulare

Answer

Microsporidium

Question 4

Which of the following is NOT a zoonotic disease?

Accepted Answer

Dracunculiasis (Guinea worm)

Answer

Leptospirosis

Answer

Rabies

Answer

Plague

Question 5

Protozoan cysts are typically stored in which of the following solutions for preservation?

Accepted Answer

Formalin

Answer

Saline

Answer

Phenol

Answer

Sodium hypochlorite

Question 6

Napier's aldehyde test is used in the diagnosis of which condition?

Accepted Answer

Kala azar

Answer

Malaria

Answer

Typhus fever

Answer

Enteric fever

Question 7

Xenodiagnosis is used in the diagnosis of a disease that is transmitted by the bite of which of the following vectors?

Accepted Answer

Reduviid bug

Answer

Body louse

Answer

Deer tick

Answer

Mosquito

Question 8

Which of the following parasites is NOT included in the class Coccidia?

Accepted Answer

Naegleria

Answer

Cryptosporidium

Answer

Isospora

Answer

Cyclospora

Question 9

Which of the following statements concerning malaria is TRUE?

Accepted Answer

Red cells negative for the Duffy blood group antigen are resistant to Plasmodium vivax.

Answer

Malaria caused by each of the four plasmodial species can relapse after initial illness.

Answer

Renal impairment is a grave prognostic sign in falciparum malaria.

Answer

Plasmodium malariae can cause immune-mediated nephropathy.

Question 10

True about Babesiosis?

Accepted Answer

Caused by Babesia microti

Answer

Resides in RBC

Answer

Resides in WBC

Answer

Chloroquine is the treatment of choice

Parasitology — MCQs

Parasitology — MCQs

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