Parasitology Practice Questions

Q: Flame cells are seen in which of the following groups of organisms?

Cestodes. **Explanation:** **Flame cells** (also known as protonephridia) are specialized excretory cells found in the simplest freshwater invertebrates, including **Platyhelminthes** (flatworms). 1. **Why Cestodes is correct:** Cestodes (tapeworms) belong to the phylum Platyhelminthes. These organisms lack a circulatory system and a body cavity (acoelomates). To manage waste and maintain osmotic balance, they utilize a primitive excretory system composed of **flame cells**. These cells have a cluster of cilia that flicker like a flame, creating a filtration pressure that pushes waste fluids through canals and out of the body through excretory pores. 2. **Why other options are incorrect:** * **Protozoa:** These are unicellular organisms. They do not have specialized multicellular organs or cells like flame cells; instead, they rely on simple diffusion or contractile vacuoles for osmoregulation. * **Nematodes:** These are roundworms. They possess a more advanced excretory system consisting of **Renette cells** or a tubular system (H-shaped canals), but they do not possess ciliated flame cells. **High-Yield Clinical Pearls for NEET-PG:** * **Flame Cells:** Characteristic of Platyhelminthes (both **Cestodes** and **Trematodes**). * **Renette Cells:** Characteristic of **Nematodes**. * **Solenocytes:** Another term for specialized excretory cells (often used interchangeably with flame cells in certain primitive chordates/invertebrates). * **Cestodes vs. Trematodes:** Remember that while both have flame cells, Cestodes are segmented (proglottids) and lack a digestive tract, whereas Trematodes (flukes) are unsegmented and leaf-like.

Q: What is the name of the test involving an intradermal injection of sterilised fluid from an infectious cyst?

Casoni's test. **Explanation:** **Correct Answer: A. Casoni’s test** Casoni’s test is an immediate hypersensitivity (Type I) skin test used for the diagnosis of **Hydatid disease** (caused by *Echinococcus granulosus*). The test involves the intradermal injection of 0.2 ml of sterile hydatid fluid (obtained from human or sheep cysts). A positive result is indicated by the formation of a large wheal (>2 cm) with pseudopodia within 15–20 minutes. While historically significant, it has largely been replaced by more specific serological assays (ELISA, IHA) and imaging (USG/CT) due to its low specificity and risk of anaphylaxis. **Analysis of Incorrect Options:** * **B. Schick test:** Used to determine immunity against **Diphtheria** (*Corynebacterium diphtheriae*). It detects the presence of circulating antitoxin. * **C. Patch test:** A diagnostic tool used to identify the cause of **Contact Dermatitis** (Type IV hypersensitivity). It involves applying allergens to the skin under adhesive patches for 48 hours. * **D. Dick’s test:** A skin test used to determine susceptibility to **Scarlet Fever**, caused by the erythrogenic toxin of *Streptococcus pyogenes*. **High-Yield Clinical Pearls for NEET-PG:** * **Hydatid Cyst:** Look for "Water lily sign" or "Camelot sign" on imaging. * **Treatment of Choice:** Surgical excision (PAIR technique) combined with **Albendazole**. * **Other Parasitological Skin Tests:** * **Montenegro (Leishmanin) test:** For Kala-azar (Delayed hypersensitivity). * **Bachman intradermal test:** For Trichinellosis. * **Fairley's test:** For Schistosomiasis.

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: 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: Which of the following helminths has a larval form that is typically found in stool?

Strongyloides. **Explanation:** The correct answer is **Strongyloides stercoralis**. This is a high-yield concept in parasitology because *Strongyloides* is unique among intestinal nematodes regarding its life cycle and diagnostic stage. **1. Why Strongyloides is correct:** In most soil-transmitted helminths, eggs are passed in the stool and hatch in the soil. However, in *Strongyloides stercoralis*, the eggs hatch into **rhabditiform larvae** within the intestinal mucosa. Therefore, the diagnostic stage found in a fresh stool sample is the **larva**, not the egg. This larva can also transform into the infectious filariform stage within the host, leading to **autoinfection**, which can cause life-threatening hyperinfection syndrome in immunocompromised patients. **2. Why the other options are incorrect:** * **Ancylostoma duodenale (Hookworm) & Necator americanus:** These parasites excrete **eggs** in the stool. The eggs only hatch into larvae once they reach warm, moist soil. Finding larvae in stool for hookworms usually only occurs if the stool sample is left at room temperature for a prolonged period. * **Ascaris lumbricoides:** The diagnostic stage is the characteristic **bile-stained, mammillated egg**. Larvae are never seen in the stool; they migrate through the lungs (causing Löffler’s syndrome) but mature into adults in the small intestine. **NEET-PG High-Yield Pearls:** * **Diagnostic Method:** The **Baermann technique** or agar plate culture is used to concentrate *Strongyloides* larvae from stool. * **Drug of Choice:** **Ivermectin** is the preferred treatment for Strongyloidiasis (Albendazole is second-line). * **Clinical Sign:** **Larva currens** (a rapidly moving serpiginous cutaneous eruption) is pathognomonic for chronic *Strongyloides* infection.

Q: What is the lifespan of microfilaria in human blood?

3 Months. **Explanation:** The correct answer is **3 Months (Option B)**. This question tests the fundamental knowledge of the life cycle of *Wuchereria bancrofti* and *Brugia malayi*, the primary causative agents of Lymphatic Filariasis. **1. Why 3 Months is Correct:** Microfilariae are the embryonic stages produced by the adult female filarial worms residing in the lymphatic system. Once released into the peripheral bloodstream, their primary goal is to be ingested by a mosquito vector (Culex, Anopheles, or Aedes) to continue the life cycle. In the human host, microfilariae do not multiply and have a limited survival period, which is typically **3 to 6 months**. For examination purposes (standard textbooks like Paniker’s), **3 months** is the most frequently cited and accepted duration for their lifespan in human blood. **2. Analysis of Incorrect Options:** * **Option A (2 Months):** This is too short. While some microfilariae may die early due to immune responses, the average population persists longer. * **Option C & D (4 & 6 Months):** While some literature suggests survival up to 6 months, standard medical entrance exams follow the conservative estimate of 3 months as the baseline physiological lifespan. **3. High-Yield Clinical Pearls for NEET-PG:** * **Lifespan of Adult Worm:** Unlike microfilariae, the adult worms live for **5 to 10 years** in the lymphatic vessels. * **Nocturnal Periodicity:** Microfilariae of *W. bancrofti* usually appear in the blood between **10 PM and 2 AM**, coinciding with the biting habits of the vector. * **Diagnostic Gold Standard:** Direct demonstration of microfilariae in a **peripheral blood smear** (thick film) collected at night. * **Drug of Choice:** **Diethylcarbamazine (DEC)** is the standard treatment, which is effective against both microfilariae and adult worms.

Q: Multiple infection of red blood cells is seen with which Plasmodium species?

Plasmodium falciparum. **Explanation:** The correct answer is **Plasmodium falciparum**. **Why it is correct:** *Plasmodium falciparum* is characterized by high levels of parasitemia because it can infect red blood cells (RBCs) of all ages (young reticulocytes to old erythrocytes). A hallmark morphological feature seen on a peripheral blood smear is **multiple infection**, where more than one trophozoite (ring form) is seen within a single RBC. This occurs because of the high density of parasites in the blood. Additionally, *P. falciparum* rings are often fine, delicate, and may show "appliqué" or "accole" forms (positioned at the periphery of the RBC). **Why other options are incorrect:** * **Plasmodium vivax:** Primarily infects only young RBCs (reticulocytes). While it causes RBC enlargement and shows Schüffner’s dots, multiple infection of a single RBC is rare. * **Plasmodium ovale:** Similar to *P. vivax*, it prefers reticulocytes. It is characterized by oval-shaped RBCs with fimbriated (tufted) edges. * **Plasmodium malariae:** Prefers older RBCs. It is known for "band forms" of trophozoites and "rosette" schizonts, but not multiple infections. **High-Yield Clinical Pearls for NEET-PG:** * **Maurer’s dots:** Coarse granulations seen in RBCs infected with *P. falciparum*. * **Cerebral Malaria:** Caused by *P. falciparum* due to the expression of **PfEMP-1**, which leads to cytoadherence and sequestration of RBCs in deep capillaries. * **Banana-shaped gametocytes:** Pathognomonic for *P. falciparum*. * **Recrudescence:** Seen in *P. falciparum* and *P. malariae* due to sub-optimal treatment; **Relapse** is seen in *P. vivax* and *P. ovale* due to dormant **hypnozoites** in the liver.

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).

Question 1

Flame cells are seen in which of the following groups of organisms?

Accepted Answer

Cestodes

Answer

Protozoa

Answer

Nematodes

Answer

None of the above

Question 2

What is the name of the test involving an intradermal injection of sterilised fluid from an infectious cyst?

Accepted Answer

Casoni's test

Answer

Schick test

Answer

Patch test

Answer

Dick's test

Question 3

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 4

In giardiasis, malabsorption is due to all of the following except:

Accepted Answer

Loss of brush border enzymes

Answer

Bacterial overgrowth

Answer

Lactose intolerance

Answer

Hypogammaglobulinaemia

Question 5

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 6

Which of the following helminths has a larval form that is typically found in stool?

Accepted Answer

Strongyloides

Answer

Ancylostoma duodenale

Answer

Ascaris lumbricoides

Answer

Necator americanus

Question 7

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 8

What is the lifespan of microfilaria in human blood?

Accepted Answer

3 Months

Answer

2 Months

Answer

4 Months

Answer

6 Months

Question 9

Multiple infection of red blood cells is seen with which Plasmodium species?

Accepted Answer

Plasmodium falciparum

Answer

Plasmodium ovale

Answer

Plasmodium vivax

Answer

Plasmodium malariae

Question 10

Babesiosis is transmitted by the bite of which arthropod?

Accepted Answer

Tick

Answer

Mosquito

Answer

Sandfly

Answer

Reduviid bug

Parasitology — MCQs

Parasitology — MCQs

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