Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 521: Coconut cake appearance of the rectum is seen in which parasitic infection?

A. Trichuris trichura (Correct Answer)
B. Enterobius vermicularis
C. Ancylostoma duodenale
D. Necator americanus

Explanation: **Explanation:** The "coconut cake" appearance of the rectum is a classic clinical sign of heavy infection with **Trichuris trichiura** (Whipworm). **Why Trichuris trichiura is correct:** In cases of massive infestation, particularly in children, thousands of adult worms attach to the mucosa of the large intestine and rectum. The worms embed their thin, whip-like anterior ends into the mucosa, while their thicker posterior ends hang into the lumen. On proctoscopy, these numerous white, glistening bodies of the worms against the backdrop of an inflamed, edematous, and prolapsed rectal mucosa resemble a **"coconut cake."** This heavy burden often leads to **rectal prolapse**, a high-yield clinical association for this parasite. **Why the other options are incorrect:** * **Enterobius vermicularis (Pinworm):** Primarily causes perianal pruritus (itching) at night. While it inhabits the cecum, it does not cause the mucosal changes or heavy clustering associated with the coconut cake appearance. * **Ancylostoma duodenale & Necator americanus (Hookworms):** These parasites reside in the small intestine (jejunum) and suck blood, leading to microcytic hypochromic anemia. They do not typically affect the rectum or cause rectal prolapse. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Adult worm is whip-shaped (thin anterior, thick posterior). * **Egg:** Characteristic **barrel-shaped** (lemon-shaped) with **bipolar mucus plugs**. * **Clinical Triad:** Chronic diarrhea, iron deficiency anemia, and rectal prolapse (in children). * **Treatment:** Albendazole or Mebendazole.

Question 522: What is true about Trichomonas vaginalis?

A. Flagellated parasite (Correct Answer)
B. Fungal infection
C. Curdy white discharge
D. Pruritus absent

Explanation: **Explanation:** *Trichomonas vaginalis* is a high-yield topic in NEET-PG, frequently tested under both Microbiology and Obstetrics & Gynecology. **Why Option A is Correct:** *Trichomonas vaginalis* is a **flagellated protozoan** parasite. It is unique because it exists only in the **trophozoite stage**; it does not form cysts. It possesses four anterior flagella and one posterior flagellum attached to an undulating membrane, which provides its characteristic **"jerky" or "twitching" motility** seen on a wet mount. **Why the other options are Incorrect:** * **Option B (Fungal infection):** Trichomoniasis is a parasitic (protozoal) infection, not fungal. Fungal vulvovaginitis is typically caused by *Candida albicans*. * **Option C (Curdy white discharge):** This is the hallmark of **Candidiasis**. In contrast, *Trichomonas* causes a **profuse, yellowish-green, frothy, and foul-smelling discharge**. * **Option D (Pruritus absent):** Pruritus (itching) is a common clinical feature of Trichomoniasis, along with vaginal soreness and dysuria. **High-Yield Clinical Pearls for NEET-PG:** * **Strawberry Cervix:** Colposcopy may reveal punctate hemorrhages on the cervix (colpitis macularis), a classic sign of Trichomoniasis. * **pH Factor:** Unlike the normal acidic vaginal pH, *Trichomonas* thrives when the **pH is >4.5**. * **Treatment:** The drug of choice is **Metronidazole**. Crucially, **simultaneous treatment of the sexual partner** is mandatory to prevent reinfection, as it is a Sexually Transmitted Infection (STI). * **Diagnosis:** The gold standard is **Whiv-FET Culture** (Diamond’s medium), though Point-of-Care NAAT is now preferred for its high sensitivity.

Question 523: Which of the following drugs is not required in the treatment of cysticercosis?

A. Albendazole
B. Praziquantel
C. Levetiracetam
D. Ketoconazole (Correct Answer)

Explanation: **Explanation:** The management of **Cysticercosis** (infection by the larval stage of *Taenia solium*) involves a combination of antiparasitic drugs, corticosteroids, and anticonvulsants. **Why Ketoconazole is the correct answer:** **Ketoconazole** is an antifungal agent that inhibits ergosterol synthesis. It has no activity against helminths or the larvae of *Taenia solium*. Furthermore, Ketoconazole is a potent **CYP450 inhibitor**. This is clinically significant because it can interfere with the metabolism of other drugs, but it plays no therapeutic role in treating cysticercosis. **Analysis of other options:** * **Albendazole (Option A):** This is the **drug of choice** for neurocysticercosis. It is a cysticidal agent that crosses the blood-brain barrier effectively to kill the larvae. * **Praziquantel (Option B):** Another potent anthelmintic used as an alternative or adjunct to Albendazole. It increases the permeability of the parasite cell membrane to calcium, leading to paralysis and death of the cyst. * **Levetiracetam (Option C):** Seizures are the most common clinical presentation of neurocysticercosis. **Antiepileptic drugs (AEDs)** like Levetiracetam, Carbamazepine, or Phenytoin are essential to manage and prevent seizures during the inflammatory phase of treatment. **High-Yield Clinical Pearls for NEET-PG:** * **Steroids First:** Always administer corticosteroids (e.g., Dexamethasone) *before* starting antiparasitic drugs to prevent a severe inflammatory response (Herxheimer-like reaction) caused by dying cysts in the brain. * **Drug Interaction:** Phenytoin and Carbamazepine (enzyme inducers) can **decrease** the plasma levels of Praziquantel and Albendazole. * **Ocular Cysticercosis:** Antiparasitic drugs are generally **contraindicated** in intraocular cysticercosis as the resulting inflammation can cause permanent blindness; surgical removal is preferred.

Question 524: A patient presents with lower gastrointestinal bleed. Sigmoidoscopy shows an ulcer in the sigmoid. Biopsy from this area shows flask-shaped ulcers. Which of the following is the most appropriate treatment?

A. Intravenous ceftriaxone
B. Intravenous metronidazole (Correct Answer)
C. Intravenous steroids and sulphasalazine
D. Hydrocortisone enemas

Explanation: ### Explanation **Diagnosis: Intestinal Amoebiasis** The clinical presentation of a lower GI bleed combined with the pathognomonic finding of **"flask-shaped ulcers"** on biopsy is a classic description of **Intestinal Amoebiasis**, caused by the protozoan *Entamoeba histolytica*. **1. Why Option B is Correct:** *Entamoeba histolytica* invades the intestinal mucosa, creating a narrow neck and a broad base (flask-shaped) as it spreads laterally in the submucosa. **Metronidazole** is the drug of choice for invasive amoebiasis because it is a potent tissue amoebicide that kills the trophozoites within the intestinal wall and other extra-intestinal sites (like the liver). In cases of severe colitis or GI bleeding, the intravenous route is preferred. **2. Why Other Options are Incorrect:** * **Option A (Ceftriaxone):** This is a third-generation cephalosporin used for bacterial infections (e.g., Enteric fever or Bacillary dysentery). While Bacillary dysentery (Shigella) causes bloody diarrhea, it typically produces shallow, transverse ulcers, not flask-shaped ones. * **Options C & D (Steroids/Sulphasalazine):** These are used to treat Inflammatory Bowel Disease (IBD), specifically Ulcerative Colitis. While IBD presents with ulcers and bleeding, administering steroids in a case of Amoebiasis is dangerous and can lead to **toxic megacolon** or perforation. **3. High-Yield Clinical Pearls for NEET-PG:** * **Pathogenesis:** Trophozoites secrete **histolysin**, which dissolves host tissue. * **Microscopy:** Look for trophozoites with **ingested RBCs** (Erythrophagocytosis) in stool or biopsy—this is diagnostic of *E. histolytica*. * **Treatment Protocol:** Always follow a tissue amoebicide (Metronidazole/Tinidazole) with a **luminal amoebicide** (e.g., Diloxanide furoate, Paromomycin, or Iodoquinol) to eradicate the cyst stage and prevent relapse/transmission. * **Commonest Site:** The **Cecum** and ascending colon are the most common sites, followed by the sigmoid colon.

Question 525: What type of life cycle does Filaria have?

A. Cyclodevelopmental (Correct Answer)
B. Cyclopropagative
C. Propagative
D. Transovarian

Explanation: ### Explanation In medical parasitology, the classification of life cycles within vectors is determined by whether the parasite undergoes **multiplication**, **developmental changes**, or both. **1. Why Cyclodevelopmental is correct:** Filarial worms (e.g., *Wuchereria bancrofti*) exhibit a **Cyclodevelopmental** life cycle. This means the parasite undergoes essential **developmental changes** (morphological transformation) within the vector (mosquito) but does **not multiply** in number. Specifically, the microfilariae ingested by the mosquito transform from the L1 stage to the infective L3 stage (filariform larva) without increasing their count. One microfilaria ingested results in only one infective larva. **2. Analysis of Incorrect Options:** * **Cyclopropagative:** The parasite undergoes both **developmental changes and multiplication**. Example: *Plasmodium* (Malaria) in the Anopheles mosquito. * **Propagative:** The parasite **multiplies** in number but undergoes **no developmental change**. Example: *Yersinia pestis* (Plague) in rat fleas or Arboviruses in mosquitoes. * **Transovarian:** This refers to the vertical transmission of a pathogen from the parent vector to its offspring via eggs. Example: *Rickettsia rickettsii* in ticks or Dengue virus in *Aedes* mosquitoes. **Clinical Pearls for NEET-PG:** * **Infective stage of Filaria:** L3 (Filariform) larva. * **Diagnostic stage:** Microfilaria (usually detected in peripheral blood during nocturnal periodicity, 10 PM – 2 AM). * **Vector for W. bancrofti:** *Culex quinquefasciatus* (in India). * **Key distinction:** Remember, for Filaria, the number of larvae that enter the mosquito is the maximum number that can come out; there is no "amplification" inside the vector.

Question 526: Calabar swellings are characteristic of infection with which parasite?

A. Ascaris
B. Hymenolepis
C. Loa Loa (Correct Answer)
D. Strongyloides

Explanation: **Explanation:** **Loa loa** (the African Eye Worm) is the correct answer. **Calabar swellings** are transient, localized, subcutaneous edematous areas that typically appear on the extremities. They represent a **Type I hypersensitivity reaction** to the metabolic products of the migrating adult worms or the worms themselves as they move through the subcutaneous connective tissue. **Analysis of Options:** * **Loa loa (Correct):** Transmitted by the **Chrysops fly** (deer fly/mango fly). It is characterized by Calabar swellings and the visible migration of the adult worm across the subconjunctiva of the eye. * **Ascaris lumbricoides:** Primarily causes intestinal obstruction or Loeffler’s syndrome (eosinophilic pneumonia) during its pulmonary phase, but does not cause migratory subcutaneous swellings. * **Hymenolepis nana:** The dwarf tapeworm. It resides in the small intestine and typically causes vague abdominal symptoms or is asymptomatic; it has no migratory tissue phase involving the skin. * **Strongyloides stercoralis:** Known for causing **Larva Currens**, a rapidly moving serpiginous cutaneous eruption (creeping eruption) caused by migrating larvae, distinct from the localized, puffy Calabar swellings. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Chrysops* fly (day-biting). * **Microfilariae:** Exhibit **diurnal periodicity** (found in peripheral blood during the day, usually 10 AM – 4 PM). * **Diagnosis:** Identification of microfilariae in a peripheral blood smear or visualization of the adult worm in the eye. * **Treatment:** **Diethylcarbamazine (DEC)** is the drug of choice, but caution is required if microfilarial load is high due to the risk of encephalopathy.

Question 527: Which of the following is FALSE regarding Giardia lamblia?

A. The quadrinucleate cyst is the infective form.
B. Cysts can survive in water for up to 3 months.
C. The trophozoite has an axostyle for adherence to surfaces. (Correct Answer)
D. It exhibits falling leaf motility.

Explanation: **Explanation:** The correct answer is **C** because it contains a factual error regarding the morphology of *Giardia lamblia*. While the trophozoite does possess an **axostyle** (a central supporting rod), it is **not** used for adherence. Adherence to the intestinal mucosa is mediated by a specialized **ventral sucking disc** (adhesive disc). The axostyle functions as a structural cytoskeleton. **Analysis of Options:** * **Option A (True):** The **quadrinucleate cyst** is indeed the infective stage. It is resistant to environmental stressors and gastric acid. * **Option B (True):** Cysts are highly resilient and can survive in cold water for approximately **3 months**, making waterborne transmission common. * **Option D (True):** Under a microscope, the trophozoite exhibits a characteristic **"falling leaf" motility**, which is a classic diagnostic feature in stool wet mounts. **Clinical Pearls for NEET-PG:** * **Morphology:** The trophozoite is pear-shaped (pyriform) and described as having a **"Monkey face"** or **"Old man with glasses"** appearance due to its two nuclei. * **Pathogenesis:** It causes **malabsorption** (especially of fats) by coating the duodenal and jejunal mucosa, leading to **steatorrhea** (foul-smelling, greasy stools). It does not invade the bloodstream. * **Diagnosis:** The **String Test (Entero-test)** can be used to sample duodenal contents. Antigen detection (ELISA) is now the preferred method. * **Treatment:** Drug of choice is **Tinidazole** or Metronidazole. Nitazoxanide is an alternative.

Question 528: Which of the following is a true mode of transmission of Toxoplasma?

A. Vertical transmission
B. Ingestion of uncooked cysts
C. Organ transplantation
D. All of the above (Correct Answer)

Explanation: **Explanation:** *Toxoplasma gondii* is an obligate intracellular protozoan with a complex life cycle involving multiple modes of transmission to humans (the intermediate hosts). The correct answer is **All of the above** because *Toxoplasma* can be transmitted through several distinct routes: 1. **Ingestion of Oocysts/Tissue Cysts:** This is the most common route. Humans can ingest **sporulated oocysts** from soil or water contaminated by feline feces (definitive host) or **tissue cysts (bradyzoites)** found in undercooked meat (e.g., pork or lamb). 2. **Vertical Transmission:** Tachyzoites can cross the placenta if a woman acquires a primary infection during pregnancy, leading to **Congenital Toxoplasmosis**. 3. **Organ Transplantation & Blood Transfusion:** Though less common, the parasite can be transmitted via infected donor organs (containing tissue cysts) or through blood transfusions (containing tachyzoites). **Why other options are included:** Options A, B, and C are all scientifically accurate modes of transmission. In NEET-PG multiple-choice formats, when three distinct, valid mechanisms are listed, "All of the above" is the definitive choice. **High-Yield Clinical Pearls for NEET-PG:** * **Definitive Host:** Domestic cat (where the sexual cycle occurs). * **Infective Stages:** Oocysts (feces), Tissue cysts (meat), and Tachyzoites (transplacental). * **Congenital Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Diagnosis:** Sabin-Feldman Dye Test (Gold Standard) and PCR for amniotic fluid. * **Treatment:** Pyrimethamine and Sulfadiazine (Spiramycin is used in pregnancy to prevent transmission).

Question 529: Which of the following parasite eggs consists of polar filaments arising from either end of the ambryophore?

A. Taenia saginata
B. Taenia solium
C. Echinococcus granulosus
D. Hymenolepis nana (Correct Answer)

Explanation: **Explanation:** The correct answer is **Hymenolepis nana** (Dwarf Tapeworm). **Why H. nana is correct:** The morphology of *Hymenolepis nana* eggs is a high-yield topic in parasitology. These eggs are characterized by an oval shape with a double membrane. The inner membrane (embryophore) encloses the oncosphere (hexacanth embryo) and possesses two distinct **polar thickenings**. From these thickenings, **4 to 8 polar filaments** arise and spread into the space between the inner and outer shells. This is a pathognomonic feature used to differentiate *H. nana* from *H. diminuta* (which lacks polar filaments). **Why other options are incorrect:** * **Taenia saginata & Taenia solium:** The eggs of both *Taenia* species are morphologically identical. They are spherical, brown, and have a thick, radially striated wall (embryophore) resembling a "wagon wheel." They do **not** possess polar filaments. * **Echinococcus granulosus:** The eggs of *Echinococcus* are morphologically indistinguishable from *Taenia* species (radially striated embryophore). Diagnosis is usually made via imaging or serology, as eggs are not typically found in human feces (humans are intermediate hosts). **NEET-PG High-Yield Pearls:** * **Smallest Cestode:** *H. nana* is the smallest intestinal cestode infecting humans. * **Direct Life Cycle:** It is unique among tapeworms because it does not require an intermediate host (though insects can act as optional ones). * **Autoinfection:** It is the only cestode capable of completing its entire life cycle in a single host, leading to internal autoinfection and heavy worm burdens. * **Treatment:** Praziquantel is the drug of choice.

Question 530: Which of the following statements about Entamoeba histolytica is FALSE?

A. Cysts are typically 8-nucleated. (Correct Answer)
B. Cysts are typically 4-nucleated.
C. Trophozoites colonize the colon.
D. Chromatid bodies are stained by iodides.

Explanation: ### Explanation **1. Why Option A is the Correct (False) Statement:** The mature cyst of *Entamoeba histolytica* is characteristically **quadrinucleate** (contains 4 nuclei). An 8-nucleated cyst is the hallmark of *Entamoeba coli*, a non-pathogenic commensal. Distinguishing between these two is a classic high-yield point: *E. histolytica* has 1–4 nuclei, while *E. coli* has 1–8 nuclei. **2. Analysis of Other Options:** * **Option B (Cysts are typically 4-nucleated):** This is a **true** statement. The life cycle involves the ingestion of mature quadrinucleate cysts, which are the infective stage. * **Option C (Trophozoites colonize the colon):** This is **true**. Trophozoites reside in the lumen of the large intestine (colon and cecum). They can invade the mucosa to cause "flask-shaped ulcers" or spread extra-intestinally (most commonly to the liver). * **Option D (Chromatid bodies are stained by iodides):** This is **true**. In young cysts, chromatid bodies (ribonucleoprotein aggregates) appear as dark-staining structures. In iodine mounts, the glycogen mass stains golden brown, and the nuclei/chromatid bodies become visible, aiding identification. **3. High-Yield Clinical Pearls for NEET-PG:** * **Infective Stage:** Mature quadrinucleate cyst. * **Diagnostic Stage:** Trophozoites (in acute dysentery) or Cysts (in chronic cases/carriers). * **Morphology:** Trophozoites show **"crawling" pseudopodial movement** and may contain ingested RBCs (erythrophagocytosis), which is pathognomonic for *E. histolytica*. * **Anchovy Sauce Pus:** Characteristic appearance of liver abscess aspirate caused by *E. histolytica*. * **Treatment:** Metronidazole/Tinidazole (for tissue stages) followed by a luminal amoebicide like Paromomycin or Diloxanide furoate (to eradicate cysts).

Practice by Chapter

Classification of Parasites

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Intestinal Protozoa

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Blood and Tissue Protozoa

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Malaria Parasites

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Leishmaniasis

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Intestinal Helminths: Nematodes

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Tissue Nematodes

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Trematodes

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Cestodes

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Ectoparasites

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Antiparasitic Drugs

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Laboratory Diagnosis of Parasitic Infections

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