Parasitology Practice Questions

Q: A stool sample from a patient shows ova. How do humans typically acquire this parasitic infection?

Ingestion of contaminated food or water. ***Ingestion of contaminated food or water*** - Most intestinal parasites like **Ascaris lumbricoides** are transmitted through the **fecal-oral route** via contaminated food, water, or soil. - The parasite's **ova** survive in the environment and are ingested, leading to infection when they hatch in the intestine. *Working in contaminated water sources* - This route is specific for **Schistosoma** species, which penetrate through the **skin** during water contact. - **Ascaris** and most intestinal helminths do not infect through skin penetration but require oral ingestion. *Consumption of improperly cooked beef* - This describes the transmission of **Taenia saginata** (beef tapeworm), which requires ingestion of **cysticerci** in raw/undercooked beef. - **Ascaris** does not have an intermediate host and is transmitted directly through ingestion of embryonated eggs. *Direct contact with an infected individual* - This route is characteristic of **Enterobius vermicularis** (pinworm), which spreads through **perianal-oral** transmission. - **Ascaris** transmission does not occur through direct person-to-person contact but requires environmental contamination.

Q: A 35-year-old male presented with gross hematuria, with similar episodes occurring in the past 6 months. There was no history of fever, pain, or burning on urination, weight loss, or increased sense of urgency to void. There was no history of exposure to toxins either at work or during recreational activities. The patient underwent fiberoptic cystoscopy, and a mass was noted in the fundus of the bladder. Biopsy of the mass is shown in the figure. What is the drug of choice for the likely cause?

Praziquantel. ***Praziquantel*** - **Painless gross hematuria** with bladder mass in an endemic area strongly suggests **Schistosoma haematobium** infection, for which **praziquantel** is the drug of choice. - Praziquantel is effective against all **schistosoma species** and causes paralysis of the parasites by increasing calcium permeability. *Albendazole* - Primarily used for **intestinal nematodes** like roundworm, hookworm, and whipworm, not effective against **schistosomiasis**. - Works by inhibiting **microtubule formation** in helminths, but has no activity against **trematodes** like Schistosoma. *Mebendazole* - Another **benzimidazole anthelmintic** used for intestinal nematodes, particularly **pinworm** and **roundworm** infections. - Like albendazole, it lacks efficacy against **blood flukes** and would not treat the underlying **schistosomiasis**. *Triclabendazole* - Specifically indicated for **Fasciola hepatica** (liver fluke) infections, not for **urogenital schistosomiasis**. - While it's a **benzimidazole derivative**, its spectrum does not include **Schistosoma haematobium** which causes bladder pathology.

Q: The man-snail-crab life cycle is characteristic of which parasite?

Paragonimus westermanii. **Explanation:** The correct answer is **Paragonimus westermanii** (the Oriental Lung Fluke). This parasite follows a complex life cycle involving two intermediate hosts: 1. **First Intermediate Host:** Freshwater snails (e.g., *Semisulcospira* spp.). 2. **Second Intermediate Host:** Crustaceans like **crabs** or crayfish. Infection occurs in humans (definitive host) upon consuming raw or undercooked crab meat containing **metacercariae**. Once ingested, the larvae excyst in the duodenum, penetrate the intestinal wall, and migrate through the diaphragm to the lungs. **Analysis of Incorrect Options:** * **Fasciola hepatica (Liver fluke):** The life cycle involves a snail, but the infective metacercariae are found encysted on **aquatic vegetation** (e.g., watercress), not crabs. * **Schistosoma mansoni (Blood fluke):** This parasite has only one intermediate host (snail). Infection occurs via direct **cercarial skin penetration** while swimming in infested water; there is no second intermediate host. * **Echinococcus granulosus (Dog tapeworm):** The cycle involves dogs (definitive host) and sheep/cattle (intermediate host). Humans are accidental intermediate hosts. It does not involve snails or crabs. **NEET-PG High-Yield Pearls:** * **Clinical Presentation:** Mimics Tuberculosis (chronic cough, hemoptysis, and night sweats). * **Diagnosis:** Presence of "golden-brown," operculated eggs in **sputum** or feces. * **Chest X-ray:** May show "ring shadows" or infiltrates. * **Drug of Choice:** Praziquantel.

Q: Babesiosis is transmitted by the bite of which arthropod?

Tick. **Explanation:** **Babesiosis** is a malaria-like parasitic disease caused by protozoa of the genus *Babesia* (most commonly *Babesia microti*). It is a zoonotic infection primarily transmitted by the bite of the **Ixodes scapularis tick** (also known as the black-legged tick or deer tick). This tick is the same vector responsible for transmitting Lyme disease and Anaplasmosis, often leading to co-infections. **Why the other options are incorrect:** * **Mosquito:** Vectors for Malaria (*Plasmodium*), Filariasis, and various viral fevers (Dengue, Zika), but not Babesiosis. * **Sandfly:** The vector for Leishmaniasis (Kala-azar). * **Reduviid bug:** Also known as the "kissing bug," it transmits *Trypanosoma cruzi*, the causative agent of Chagas disease. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** In a peripheral blood smear, *Babesia* appears as pleomorphic ring forms. A pathognomonic feature is the **"Maltese Cross" appearance** (tetrads formed by four daughter cells), which distinguishes it from *Plasmodium falciparum*. * **Clinical Presentation:** It causes hemolytic anemia and hemoglobinuria. It is particularly severe or fatal in **asplenic patients**, as the spleen is responsible for clearing infected erythrocytes. * **Diagnosis:** Giemsa-stained thick and thin peripheral smears are the gold standard. * **Treatment:** The preferred regimen is a combination of **Atovaquone and Azithromycin** (unlike Malaria, which uses Chloroquine/Artemisinin).

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: 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).

Question 1

A stool sample from a patient shows ova. How do humans typically acquire this parasitic infection?

Accepted Answer

Ingestion of contaminated food or water

Answer

Working in contaminated water sources

Answer

Consumption of improperly cooked beef

Answer

Direct contact with an infected individual

Question 2

A 35-year-old male presented with gross hematuria, with similar episodes occurring in the past 6 months. There was no history of fever, pain, or burning on urination, weight loss, or increased sense of urgency to void. There was no history of exposure to toxins either at work or during recreational activities. The patient underwent fiberoptic cystoscopy, and a mass was noted in the fundus of the bladder. Biopsy of the mass is shown in the figure. What is the drug of choice for the likely cause?

Accepted Answer

Praziquantel

Answer

Albendazole

Answer

Mebendazole

Answer

Triclabendazole

Question 3

The man-snail-crab life cycle is characteristic of which parasite?

Accepted Answer

Paragonimus westermanii

Answer

Fasciola hepatica

Answer

Schistosoma mansoni

Answer

Echinococcus granulosus

Question 4

Which of the following is NOT true about Plasmodium falciparum?

Accepted Answer

The parasitic burden can be estimated by peripheral parasitemia.

Answer

The duration of the erythrocytic cycle is 48 hours.

Answer

An exo-erythrocytic phase is absent.

Answer

It causes rosette formation.

Question 5

Babesiosis is transmitted by the bite of which arthropod?

Accepted Answer

Tick

Answer

Mosquito

Answer

Sandfly

Answer

Reduviid bug

Question 6

Which of the following inhibits digestion in the intestinal mucosa?

Accepted Answer

Giardia lamblia

Answer

Vibrio cholerae

Answer

Enterokinase

Answer

Schistosoma haematobium

Question 7

Which of the following is NOT a cause of malabsorption?

Accepted Answer

Ascariasis

Answer

Giardia lamblia

Answer

Mycobacterium avium-intracellulare

Answer

Microsporidium

Question 8

A 3-year-old girl presents with acute abdominal pain, a 5-day history of vomiting and abdominal distension, and absence of stool passage. She has been vomiting bilious material for the past day. Physical examination reveals a lethargic child with a firm, tender abdomen and peritoneal signs. Intraoperative findings include resection of approximately 20 cm of markedly distended small intestine containing a tightly knotted ball of nematodes (15-35 cm in length, tapered ends without hooks). The patient's parasite has a life cycle stage where larvae hatch in the duodenum, penetrate the small intestinal wall, and migrate. The passage of these migrating larvae most commonly produces symptomatic disease in which of the following organs?

Accepted Answer

Lungs

Answer

Heart

Answer

Liver

Answer

Pancreas

Question 9

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 10

Giardia lambia infection is common in which of the following conditions?

Accepted Answer

Selective IgA deficiency

Answer

Selective IgM deficiency

Answer

Common variable hypogammaglobulinemia

Answer

Severe combined immunodeficiency

Parasitology — MCQs

Parasitology — MCQs

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