Parasitology Practice Questions

Q: In which of the following parasites does a fish act as an intermediate host?

Clonorchis sinensis. **Explanation:** The correct answer is **Clonorchis sinensis** (the Chinese Liver Fluke). In its complex life cycle, this parasite requires two intermediate hosts: 1. **First Intermediate Host:** Freshwater snails (e.g., *Parafossarulus*). 2. **Second Intermediate Host:** Freshwater **fish** (specifically of the Cyprinidae family). Humans become infected by ingesting undercooked or raw fish containing **metacercariae**. **Analysis of Options:** * **Diphyllobothrium latum:** While this parasite (the Fish Tapeworm) also involves fish, it was likely excluded or ranked lower depending on the specific question context. However, in standard parasitology, *D. latum* uses a crustacean (Cyclops) as the first and fish as the second intermediate host. If this were a "multiple correct" scenario, both A and B would apply, but *Clonorchis* is a classic textbook example for trematodes. * **Hymenolepis diminuta:** This is the Rat Tapeworm. It requires an **arthropod** (like a grain beetle or flea) as an intermediate host. * **Hymenolepis nana:** This is the Dwarf Tapeworm. It is unique because it **does not require an intermediate host** (direct life cycle), though insects can occasionally serve as optional intermediate hosts. **NEET-PG Clinical Pearls:** * **Clonorchis sinensis** is strongly associated with **Cholangiocarcinoma** (bile duct cancer) due to chronic irritation of the biliary epithelium. * **Diphyllobothrium latum** is high-yield for causing **Vitamin B12 deficiency**, leading to Megaloblastic Anemia. * **H. nana** is the most common cause of all cestode infections and is the only tapeworm that can complete its entire life cycle in a single host.

Q: What is the most common cause of an amoebic lung abscess?

Direct spread from the liver. **Explanation:** Amoebic lung abscess is almost always a secondary complication of intestinal amoebiasis [1], caused by the protozoan *Entamoeba histolytica*. **Why Option B is Correct:** The most common route of pulmonary involvement is **direct extension (transdiaphragmatic spread)** from an Amoebic Liver Abscess (ALA). Because the liver is situated immediately below the diaphragm, an abscess in the superior surface of the right lobe can cause inflammatory adhesion to the diaphragm [1]. The abscess then ruptures through the diaphragm into the pleural space (causing empyema) or directly into the lung parenchyma, leading to a lung abscess [2]. This typically involves the lower lobe of the right lung. **Why Other Options are Incorrect:** * **Option A (Aspiration):** This is the most common cause of *pyogenic* lung abscesses (usually involving anaerobes), but it is not the mechanism for amoebic infections. * **Option C & D (Hematogenous spread):** While *E. histolytica* can rarely travel via the bloodstream (portal circulation to the liver or systemic circulation to the lungs/brain), this is a significantly less common route for pulmonary involvement compared to direct local extension. **NEET-PG High-Yield Pearls:** * **Sputum Appearance:** Classically described as **"Anchovy sauce"** [1] or "Chocolate" colored sputum. * **Location:** Most common in the **Right Lower Lobe** (due to the proximity of the right lobe of the liver). * **Hepatobronchial Fistula:** If the abscess ruptures into a bronchus, the patient may expectorate large amounts of "anchovy sauce" pus. * **Treatment:** The drug of choice is **Metronidazole** [2] (or Tinidazole), followed by a luminal amoebicide (e.g., Diloxanide furoate) to eradicate the intestinal cyst stage.

Q: Which of the following statements regarding malaria species is false?

P. falciparum infects young red blood cells only.. This question tests your knowledge of the **erythrocytic stage** of the *Plasmodium* life cycle, specifically the host cell selectivity of different species. ### **Explanation of the Correct Answer (Option B)** **Option B is False** because *Plasmodium falciparum* is unique in its ability to infect **red blood cells of all ages** (young, mature, and old). Because it can invade any available erythrocyte, it leads to significantly higher levels of parasitemia (>5%) compared to other species. This high parasite load is a primary reason why *P. falciparum* causes the most severe and life-threatening forms of malaria. ### **Analysis of Other Options** * **Option A & C (P. vivax and P. ovale):** These species are selective for **reticulocytes** (young RBCs). Because reticulocytes make up only about 1-2% of total circulating RBCs, the parasitemia in these infections is usually low. * **Option D (P. malariae):** This species selectively infects **senescent (old) red blood cells**. Similar to *P. vivax*, its restricted target population limits the overall parasite density. ### **NEET-PG High-Yield Pearls** * **Parasitemia Levels:** *P. falciparum* (>5%) > *P. vivax* ( *P. malariae* (<1%). * **Schuffner’s Dots:** Seen in *P. vivax* and *P. ovale*. * **Ziemann’s Dots:** Seen in *P. malariae*. * **Maurer’s Clefts:** Seen in *P. falciparum*. * **Relapse vs. Recrudescence:** *P. vivax/ovale* cause **relapse** due to dormant liver stages (**hypnozoites**). *P. falciparum/malariae* cause **recrudescence** due to the persistence of parasites in the blood. * **Receptor Match:** *P. vivax* uses the **Duffy Antigen** to enter RBCs; individuals who are Duffy-negative are resistant to *P. vivax*.

Q: Stool investigation of a child who presented with anemia revealed worm infestation. Which of the following worm infestations is associated with iron deficiency anemia?

Hookworm. **Explanation:** **Hookworm** (*Ancylostoma duodenale* and *Necator americanus*) is the classic cause of **Iron Deficiency Anemia (IDA)** in children. The worms attach to the small intestinal mucosa using buccal capsules (teeth or cutting plates) and suck host blood. They also secrete anticoagulants (factor Xa inhibitors), leading to persistent bleeding from attachment sites. A single *A. duodenale* can cause up to 0.2 mL of blood loss per day. Chronic infestation leads to a depletion of iron stores, resulting in microcytic hypochromic anemia. **Analysis of Incorrect Options:** * **Whipworm (*Trichuris trichiura*):** While heavy infestations can cause "Trichuris Dysentery Syndrome" and rectal prolapse, the primary hematological concern is chronic blood loss from the colon, which is generally less severe than hookworm-induced IDA. * **Roundworm (*Ascaris lumbricoides*):** These do not attach to the mucosa or suck blood. They primarily cause malnutrition by competing for nutrients or intestinal obstruction (bolus formation). * **Pinworm (*Enterobius vermicularis*):** These reside in the cecum and appendix. Their hallmark symptom is perianal pruritus; they do not cause blood loss or anemia. **Clinical Pearls for NEET-PG:** * **Route of Entry:** Filariform larvae penetrate intact skin (usually feet), often causing **Ground Itch**. * **Loeffler’s Syndrome:** Transient eosinophilic pneumonia occurring during the pulmonary migration phase of *Ascaris* or Hookworms. * **Diagnosis:** Presence of non-bile stained, oval, segmented eggs in stool. * **Treatment:** Albendazole (400 mg single dose) is the drug of choice for mass deworming.

Q: A 6-year-old child presented with perianal pruritus, skin excoriation, and nocturnal enuresis, and was found to be infected with a parasite that causes autoinfection. How is the causative agent diagnosed?

NIH swab method. The clinical presentation of **perianal pruritus** (worse at night), skin excoriation, and **nocturnal enuresis** in a child is classic for **Enterobius vermicularis** (Pinworm or Seatworm). The female worm migrates to the perianal skin at night to lay eggs, causing intense itching. Scratching leads to the transfer of eggs to the mouth, facilitating **autoinfection** and retro-infection. **Why Option A is Correct:** Standard stool microscopy is often negative because eggs are deposited on the perianal folds, not in the feces. The **NIH swab** (National Institutes of Health) or the **Scotch Tape/Cellophane Tape test** is the gold standard. It involves applying the adhesive side of the tape to the perianal area early in the morning to collect the characteristic **planoconvex (D-shaped)** eggs for microscopic examination. **Why Other Options are Incorrect:** * **B. String test (Entero-test):** Used for diagnosing parasites in the upper small intestine, primarily *Giardia lamblia* and *Strongyloides stercoralis* [1]. * **C. Hetrazan test (Mazzotti test):** Used to diagnose *Onchocerca volvulus*. It involves giving a dose of Diethylcarbamazine (DEC), which causes an intense pruritic reaction if microfilariae are present. * **D. Encysted larvae on muscle biopsy:** This is the diagnostic method for **Trichinella spiralis**, which causes trichinosis. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Albendazole or Mebendazole (single dose, repeated after 2 weeks to kill newly hatched larvae). * **Public Health:** Always treat the **entire family** simultaneously to prevent reinfection. * **Morphology:** Eggs are non-bile stained and have a double-layered shell.

Q: A 40-year-old patient developed a sudden onset of high fever. Peripheral blood film examination showed malaria parasite pigment that was yellowish-brown, and the schizonts measured 9-10 microns and contained 20 merozoites each. Which Plasmodium species is most likely responsible?

Plasmodium vivax. ### Explanation The correct answer is **Plasmodium vivax**. This diagnosis is based on the specific morphology of the schizont and the characteristics of the malarial pigment. **1. Why Plasmodium vivax is correct:** * **Schizont Size:** *P. vivax* schizonts are large, typically measuring **9–10 microns**, almost filling the enlarged infected erythrocyte. * **Merozoite Count:** They contain **12–24 merozoites** (average 16–20), which matches the 20 merozoites mentioned in the question. * **Pigment:** The malarial pigment (hemozoin) in *P. vivax* is typically **yellowish-brown** and fine. **2. Why other options are incorrect:** * **P. falciparum:** Schizonts are rarely seen in peripheral blood (due to sequestration). When present, they are smaller (approx. 8 microns) and contain **8–36 merozoites** with a single mass of dark pigment. * **P. malariae:** The schizont is smaller (6.5–7 microns) and contains fewer merozoites (**6–12**), often arranged in a characteristic **"Rosette" or "Daisy-head" pattern**. The pigment is dark brown/black. * **P. ovale:** While it has a similar merozoite count to *P. vivax* (average 8–10, up to 12), the infected RBC is typically oval with **fimbriated edges**, and the schizont is smaller (approx. 6 microns). **High-Yield Clinical Pearls for NEET-PG:** * **Schüffner’s dots:** Seen in *P. vivax* and *P. ovale*. * **Ziemann’s dots:** Seen in *P. malariae*. * **Maurer’s clefts:** Seen in *P. falciparum*. * **Relapse:** Occurs in *P. vivax* and *P. ovale* due to dormant **hypnozoites** in the liver (treated with Primaquine). * **Recrudescence:** Occurs in *P. falciparum* and *P. malariae* due to the persistence of erythrocytic stages.

Q: Which is the only living part of a Hydatid cyst?

Germinal epithelium. ### Explanation A Hydatid cyst, caused by the larval stage of ***Echinococcus granulosus***, consists of three distinct layers. Understanding these layers is crucial for identifying the biological activity of the parasite. **1. Why Germinal Epithelium is Correct:** The **Germinal layer (Endocyst)** is the innermost layer of the cyst wall. It is the **only metabolically active and living component** of the parasite. It is responsible for: * Secretory functions (producing the hydatid fluid). * Asexual reproduction (forming brood capsules and scolices). * Formation of the outer laminated membrane. **2. Why the other options are incorrect:** * **Adventitia (Pericyst):** This is the outermost layer, formed by the **host’s inflammatory response** (fibrous tissue). It is not part of the parasite itself. * **Laminated membrane (Ectocyst):** This is the middle, acellular, white chitinous layer. While it provides structural support and protects the parasite from the host's immune system, it is **non-living**. * **Parenchyma of the organ:** This refers to the host tissue (e.g., liver or lung) surrounding the cyst, not a component of the cyst wall. ### NEET-PG High-Yield Pearls: * **Hydatid Sand:** Refers to the sediment found in the cyst fluid, consisting of free scolices, brood capsules, and hooklets. * **Casoni Test:** An immediate hypersensitivity skin test (historically used, now largely replaced by serology/imaging). * **Water Lily Sign:** Seen on imaging when the endocyst ruptures and the membranes float in the fluid. * **Surgical Caution:** During surgery (PAIR technique), scolicidal agents (e.g., hypertonic saline) are used to kill the germinal layer and prevent secondary hydatidosis or anaphylaxis due to spillage.

Q: A patient presents with diarrhea. Analysis of stool on wet mount shows mobile protozoa without RBCs and pus cells. What is the most likely diagnosis?

Giardiasis. ### Explanation The correct answer is **Giardiasis**. **Why Giardiasis is correct:** The clinical presentation of diarrhea with a stool wet mount showing **mobile protozoa** but **no RBCs or pus cells** is characteristic of *Giardia lamblia*. Giardia is a non-invasive parasite that colonizes the duodenum and upper jejunum. Because it does not invade the intestinal mucosa or cause ulceration, it results in **non-inflammatory diarrhea** (steatorrhea). Therefore, the stool typically lacks inflammatory markers like Red Blood Cells (RBCs) and pus cells (leukocytes). On a wet mount, the trophozoites exhibit a characteristic "falling leaf" motility. **Analysis of Incorrect Options:** * **Entamoeba histolytica:** This is an invasive parasite that causes amoebic dysentery. It produces "flask-shaped ulcers," leading to the presence of **RBCs (erythrophagocytosis)** and cellular debris in the stool. * **Balantidium coli:** This is the largest protozoan infecting humans and is invasive. It causes mucosal ulceration similar to *E. histolytica*, typically resulting in blood and mucus in the stool. * **Trichomonas hominis:** While found in the human colon as a commensal and possessing motility, it is generally considered non-pathogenic and is not a primary cause of clinical diarrhea. **NEET-PG High-Yield Pearls:** * **Motility:** *Giardia* = Falling leaf motility; *Balantidium* = Boring/Rotary motility; *E. histolytica* = Purposeful/Unidirectional pseudopodial motility. * **Stool Microscopy:** *Giardia* is associated with malabsorption and fatty stools (steatorrhea). * **Drug of Choice:** Metronidazole is the treatment of choice for Giardiasis, though Tinidazole is often preferred for its single-dose efficacy. * **String Test (Entero-test):** A classic diagnostic method used for *Giardia* and *Strongyloides* when stool exams are negative.

Q: Senescent red blood cells are primarily attacked in which type of malaria?

Quartan malaria. **Explanation:** The preference of *Plasmodium* species for specific ages of red blood cells (RBCs) is a high-yield concept in parasitology. **1. Why Option D is Correct:** **Quartan malaria**, caused by ***Plasmodium malariae***, has a unique predilection for **senescent (old) erythrocytes**. Because the population of aging RBCs in the peripheral blood is relatively small, the parasitemia levels in *P. malariae* infections remain low (usually <1%). This species is also characterized by a 72-hour erythrocytic cycle, leading to paroxysms every fourth day. **2. Why Other Options are Incorrect:** * **Options A & B (P. vivax and P. ovale):** These species selectively infect **young RBCs (reticulocytes)**. They utilize the Duffy blood group antigen (specifically *P. vivax*) to invade immature cells. Since reticulocytes comprise only about 1–2% of total RBCs, parasitemia is limited. * **Option C (P. falciparum):** This is the most "promiscuous" species; it invades **RBCs of all ages** (young, mature, and old). This leads to high levels of parasitemia and the severe clinical manifestations associated with malignant tertian malaria. **NEET-PG High-Yield Pearls:** * **P. falciparum:** All ages of RBCs; highest parasitemia; "Maurer’s clefts." * **P. vivax/ovale:** Reticulocytes; "Schüffner’s dots"; presence of hypnozoites (relapse). * **P. malariae:** Old RBCs; "Ziemann’s dots"; characteristic "Band form" trophozoites. * **P. knowlesi:** All ages of RBCs; 24-hour cycle (quotidian fever).

Question 1

In which of the following parasites does a fish act as an intermediate host?

Accepted Answer

Clonorchis sinensis

Answer

Diphyllobothrium latum

Answer

Hymenolepis diminuta

Answer

Hymenolepis nana

Question 2

What is the most common cause of an amoebic lung abscess?

Accepted Answer

Direct spread from the liver

Answer

Aspiration

Answer

Hematogenous spread from the liver

Answer

Hematogenous spread from the gut

Question 3

Which of the following statements regarding malaria species is false?

Accepted Answer

P. falciparum infects young red blood cells only.

Answer

P. vivax infects reticulocytes.

Answer

P. ovale selectively infects reticulocytes.

Answer

P. malariae infects old red blood cells.

Question 4

Which of the following statements best describes the diagnostic characteristics of Plasmodium falciparum?

Accepted Answer

Except in infections with very high parasitemia, only ring forms of early trophozoites and the gametocytes are seen in the peripheral blood.

Answer

An important diagnostic feature is the irregular appearance of the edges of the infected RBC.

Answer

A period of 72 hours is required for the development of the mature schizont, which resembles a rosette with only 8 to 10 oval merozoites.

Answer

Schuffner stippling is routinely seen in RBCs that harbor parasites.

Question 5

Stool investigation of a child who presented with anemia revealed worm infestation. Which of the following worm infestations is associated with iron deficiency anemia?

Accepted Answer

Hookworm

Answer

Whipworm

Answer

Roundworm

Answer

Pinworm

Question 6

A 6-year-old child presented with perianal pruritus, skin excoriation, and nocturnal enuresis, and was found to be infected with a parasite that causes autoinfection. How is the causative agent diagnosed?

Accepted Answer

NIH swab method

Answer

String test

Answer

Hetrazan test

Answer

Encysted larvae on muscle biopsy

Question 7

A 40-year-old patient developed a sudden onset of high fever. Peripheral blood film examination showed malaria parasite pigment that was yellowish-brown, and the schizonts measured 9-10 microns and contained 20 merozoites each. Which Plasmodium species is most likely responsible?

Accepted Answer

Plasmodium vivax

Answer

Plasmodium falciparum

Answer

Plasmodium malariae

Answer

Plasmodium ovale

Question 8

Which is the only living part of a Hydatid cyst?

Accepted Answer

Germinal epithelium

Answer

Adventitia

Answer

Laminated membrane

Answer

Parenchyma of the organ

Question 9

A patient presents with diarrhea. Analysis of stool on wet mount shows mobile protozoa without RBCs and pus cells. What is the most likely diagnosis?

Accepted Answer

Giardiasis

Answer

Balantidium coli

Answer

Trichomonas hominis

Answer

Entamoeba histolytica

Question 10

Senescent red blood cells are primarily attacked in which type of malaria?

Accepted Answer

Quartan malaria

Answer

Vivax malaria

Answer

Ovale malaria

Answer

Falciparum malaria

Parasitology — MCQs

Parasitology — MCQs

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