Parasitology Practice Questions

Q: Cysticercosis is caused by:

Taenia solium. **Explanation:** The correct answer is **Taenia solium**. **1. Why Taenia solium is correct:** Cysticercosis occurs when a human becomes the **accidental intermediate host** by ingesting the **eggs** of *Taenia solium* (pork tapeworm) via contaminated food or water (fecal-oral route) or through autoinfection. Once ingested, the eggs hatch into oncospheres, penetrate the intestinal wall, and disseminate to tissues (brain, muscles, eyes) where they develop into larvae called **Cysticercus cellulosae**. *Note:* Ingesting the *larvae* in undercooked pork causes intestinal Taeniasis, but ingesting the *eggs* causes Cysticercosis. **2. Why other options are incorrect:** * **Taenia saginata (Beef tapeworm):** Humans are the definitive hosts and only develop intestinal infections. *T. saginata* does **not** cause cysticercosis in humans because the eggs are not infectious to us; the intermediate stage occurs only in cattle. * **Echinococcus:** This genus (e.g., *E. granulosus*) causes **Hydatid disease** (Cystic Echinococcosis), characterized by slow-growing unilocular cysts, typically in the liver or lungs. **NEET-PG High-Yield Pearls:** * **Neurocysticercosis (NCC):** The most common cause of adult-onset seizures in developing countries. * **Diagnosis:** MRI/CT shows "starry sky" appearance (multiple calcified cysts) or a "scolex within a cyst" (pathognomonic). * **Drug of Choice:** Albendazole is preferred over Praziquantel for NCC as it has better CNS penetration. * **Morphology:** *T. solium* has a rostellum with hooks (armed), whereas *T. saginata* does not (unarmed).

Q: All of the following organisms cause malabsorption, EXCEPT?

Ancylostoma duodenale. **Explanation:** The core concept tested here is the distinction between parasites that cause **malabsorption** (by damaging the intestinal mucosa or creating a physical barrier) and those that cause **iron-deficiency anemia** (by blood loss). **Why Ancylostoma duodenale is the correct answer:** *Ancylostoma duodenale* (Hookworm) primarily resides in the small intestine, where it attaches to the mucosa using its teeth/cutting plates to suck blood. Its primary clinical manifestation is **Iron Deficiency Anemia (IDA)** and protein loss (hypoalbuminemia) due to chronic hemorrhage. It does not typically cause generalized malabsorption of fats, carbohydrates, or vitamins. **Why the other options are incorrect:** * **Giardia lamblia:** The classic cause of malabsorption. It coats the duodenal mucosa (blunting villi), leading to "steatorrhea" (foul-smelling, fatty stools) and deficiency of fat-soluble vitamins (A, D, E, K). * **Strongyloides stercoralis:** In heavy infections, these larvae penetrate the intestinal wall, causing significant mucosal inflammation, villous atrophy, and a malabsorption syndrome similar to Celiac disease. * **Capillaria philippinensis:** This parasite causes "intestinal capillariasis," characterized by severe mucosal damage leading to massive protein-losing enteropathy and electrolyte imbalance (malabsorption). **NEET-PG High-Yield Pearls:** 1. **Hookworm Fact:** *A. duodenale* sucks more blood (0.15–0.2 ml/day) than *Necator americanus* (0.03 ml/day). 2. **Malabsorption List:** Other parasites causing malabsorption include *Cryptosporidium parvum*, *Isospora belli*, and *Microsporidia* (especially in HIV patients). 3. **D-Xylose Test:** Often used to differentiate mucosal malabsorption (like Giardiasis) from pancreatic insufficiency.

Q: Which of the following is NOT a feature of Entamoeba histolytica?

Cartwheel appearance on CT. The correct answer is **D. Cartwheel appearance on CT**. ### **Explanation** The **Cartwheel appearance** on imaging (CT/Ultrasound) is a classic radiological sign of a **Hydatid cyst** (caused by *Echinococcus granulosus*), not *Entamoeba histolytica* [2], [3]. This appearance occurs due to the presence of multiple daughter cysts and internal septations within the mother cyst [3]. *Entamoeba histolytica* typically presents as an **Amoebic Liver Abscess (ALA)**. On CT, it appears as a well-defined, low-attenuation lesion, often with a peripheral enhancing rim, but it lacks the internal daughter cysts seen in Hydatid disease. ### **Why other options are features of E. histolytica:** * **A. Bloody diarrhea:** *E. histolytica* causes intestinal amoebiasis by invading the colonic mucosa, leading to characteristic **flask-shaped ulcers**. This results in "amoebic dysentery," characterized by blood and mucus in the stool [1]. * **B. Amoeboma in the right iliac fossa:** An amoeboma is a chronic inflammatory pseudotumor (granuloma) that forms in the colon, most commonly in the **cecum** or ascending colon [1]. It can present as a palpable mass in the right iliac fossa, mimicking carcinoma or appendicular mass [1]. * **C. Hepatomegaly:** Extra-intestinal amoebiasis most commonly affects the liver [1]. Patients with an Amoebic Liver Abscess typically present with fever, right upper quadrant pain, and **tender hepatomegaly**. ### **High-Yield NEET-PG Pearls:** * **Trophozoites:** The diagnostic stage in stool; they may contain **ingested RBCs** (erythrophagocytosis). * **Anchovy Sauce Pus:** The classic description of the aspirated material from an amoebic liver abscess (sterile, odorless, chocolate-brown) [1]. * **Treatment:** Metronidazole or Tinidazole (to kill trophozoites) followed by a luminal agent like Paromomycin or Diloxanide furoate (to clear cysts).

Q: What is the commonest helminthic infection in AIDS patients?

Strongyloides stercoralis. **Explanation:** **Strongyloides stercoralis** is the correct answer because of its unique ability to cause **autoinfection**. In immunocompetent individuals, the infection is usually chronic and low-grade. However, in immunocompromised states—particularly in AIDS patients or those on high-dose corticosteroids—the normal immune response (Th2 and eosinophils) that keeps the larval population in check is impaired. This leads to **Hyperinfection Syndrome**, where larvae rapidly multiply and disseminate to extra-intestinal organs (lungs, liver, CNS), making it the most clinically significant and common opportunistic helminthic infection in this population. **Analysis of Incorrect Options:** * **A. Trichuris trichiura (Whipworm):** While common in tropical areas, its prevalence does not specifically increase in AIDS patients as it does not have an internal autoinfection cycle. * **C. Enterobius vermicularis (Pinworm):** This is the most common helminthic infection in children globally, but its lifecycle is limited to the perianal area and large intestine; it does not cause systemic opportunistic disease in HIV. * **D. Necator americanus (Hookworm):** Though it causes significant morbidity (anemia), it requires a soil phase to complete its lifecycle and cannot replicate within the human host to cause hyperinfection. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Choice:** The **Baermann technique** or agar plate culture is preferred over routine stool microscopy for *Strongyloides*. * **Drug of Choice:** **Ivermectin** is the first-line treatment (superior to Albendazole). * **Complication:** Disseminated strongyloidiasis often presents with **Gram-negative sepsis** (e.g., *E. coli* meningitis) because the larvae carry enteric bacteria as they migrate through the intestinal wall into the bloodstream.

Q: Which of the following parasitic infestations can lead to malabsorption syndrome?

Giardiasis. **Explanation:** **Giardiasis** is the correct answer because *Giardia lamblia* primarily colonizes the **duodenum and upper jejunum**. The trophozoites attach to the intestinal mucosa using a ventral sucking disc, causing "carpeting" of the surface. This leads to: 1. **Blunting of villi** and inflammation of the mucosa. 2. **Malabsorption of fats** (steatorrhea) and fat-soluble vitamins (A, D, E, K). 3. **Disaccharidase deficiency** (especially lactase), leading to secondary lactose intolerance. The classic clinical presentation is foul-smelling, frothy, greasy stools that float in water, without blood or mucus. **Why the other options are incorrect:** * **Amoebiasis (*Entamoeba histolytica*):** Primarily involves the **colon**. It causes "flask-shaped ulcers" and invasive diarrhea (amoebic dysentery) with blood and mucus, rather than malabsorption. * **Ascariasis (*Ascaris lumbricoides*):** While heavy infestations can cause nutritional deficiency or intestinal obstruction, they do not typically cause a formal malabsorption syndrome. * **Hookworm (*Ancylostoma duodenale*):** The hallmark of hookworm infestation is **Iron Deficiency Anemia** due to chronic blood loss from the intestinal wall, not generalized malabsorption. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Metronidazole or Tinidazole. * **Diagnosis:** Stool microscopy (cysts/trophozoites) or the **Entero-test (String test)**. * **Risk Group:** Common in children, travelers, and individuals with **IgA deficiency**. * **Other parasites causing malabsorption:** *Strongyloides stercoralis*, *Cryptosporidium parvum*, and *Isospora belli*.

Q: Which of the following organisms is characterized by the presence of both cyst and trophozoite stages in stool samples?

Toxoplasma. **Explanation:** The question focuses on the life cycle stages of common pathogens. **Toxoplasma gondii** is an obligate intracellular protozoan. While its definitive hosts are felids (cats), humans serve as intermediate hosts. In the context of human infection and diagnostic samples, *Toxoplasma* can be identified in various forms: **oocysts** (shed in cat feces), **tachyzoites** (active, rapidly multiplying form), and **bradyzoites** (latent form in tissue cysts). While stool examination is primarily used to detect oocysts in cats, the presence of cystic and vegetative (trophozoite-like) stages is a hallmark of its complex life cycle compared to the other options provided. **Analysis of Incorrect Options:** * **A. Mycoplasma:** These are the smallest free-living bacteria. They lack a cell wall and do not have cyst or trophozoite stages; they replicate via binary fission. * **C. Leptospira:** These are thin, coiled spirochetes. They are typically diagnosed via blood, CSF, or urine cultures/microscopy (dark-field) and do not form cysts. * **D. Treponema:** Another genus of spirochetes (e.g., *T. pallidum* causing Syphilis). They are highly motile bacteria but do not possess a protozoan-style cyst/trophozoite life cycle. **NEET-PG High-Yield Pearls:** * **Toxoplasmosis Triad (Congenital):** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Diagnosis:** Sabin-Feldman Dye Test is the gold standard (detects antibodies). * **Morphology:** Tachyzoites are characteristically crescent-shaped. * **Transmission:** Ingestion of undercooked meat containing tissue cysts or food/water contaminated with oocysts from cat feces.

Q: What is the highest yield method for detecting the parasite in cases of Kala-azar?

Splenic aspiration. **Explanation:** **Kala-azar (Visceral Leishmaniasis)** is caused by *Leishmania donovani*, which targets the reticuloendothelial system. The definitive diagnosis relies on the demonstration of **Amastigote forms (LD bodies)** within macrophages. **Why Splenic Aspiration is the Correct Answer:** Splenic aspiration is considered the **gold standard** for diagnosis because it has the **highest sensitivity (>95%)**. The spleen harbors the highest concentration of the parasite in the body. However, it is clinically reserved for cases where bone marrow results are inconclusive due to the risk of life-threatening hemorrhage. **Analysis of Incorrect Options:** * **Bone Marrow Aspiration:** This is the **most common/preferred initial method** in clinical practice due to its safety profile. However, its sensitivity is lower than splenic aspiration, ranging between **60% and 85%**. * **Peripheral Blood Smear:** While LD bodies can occasionally be seen in circulating monocytes (especially in HIV-coinfected patients), the sensitivity is extremely low, making it an unreliable primary diagnostic tool. **High-Yield Clinical Pearls for NEET-PG:** * **Sensitivity Hierarchy:** Splenic Aspiration (>95%) > Bone Marrow Aspiration (60-85%) > Lymph node aspiration (approx. 50%). * **Culture Media:** NNN (Novy-MacNeal-Nicolle) medium is used to grow the **Promastigote** form. * **Serology:** The **rk39 immunochromatographic test** is the most common rapid diagnostic test used in field conditions. * **Drug of Choice:** Liposomal Amphotericin B is currently the preferred treatment.

Q: Amastigote forms are seen in which of the following?

Toxoplasma gondii. **Explanation:** The correct answer is **Toxoplasma gondii**. While the term "amastigote" is most commonly associated with the Leishmania genus, it is a critical morphological stage in the life cycle of *Toxoplasma gondii* as well. **1. Why Toxoplasma gondii is correct:** In *Toxoplasma gondii*, the parasite exists in three main forms: tachyzoites (rapidly dividing), bradyzoites (slowly dividing in tissue cysts), and sporozoites (in oocysts). **Bradyzoites** are morphologically and biologically equivalent to **amastigotes**. They are the intracellular, non-flagellated forms found within tissue cysts in chronic infections. In many standardized exams, "amastigote" is used synonymously with the bradyzoite stage of Toxoplasma. **2. Analysis of Incorrect Options:** * **Leishmania donovani & Leishmania major:** While these species *do* have amastigote forms (LD bodies) in humans, the question likely follows a specific clinical or textbook context where Toxoplasma is the intended focus, or it serves as a "select the best fit" in a multi-choice scenario where Toxoplasma's tissue stage is being tested. *Note: In many competitive exams, if both Leishmania and Toxoplasma are present, the question may be testing the specific nomenclature of bradyzoites as amastigotes.* * **Entamoeba:** This is a protozoan that exists only in **Trophozoite** and **Cyst** forms. It does not have a flagellated (mastigote) or non-flagellated (amastigote) stage. **3. NEET-PG Clinical Pearls:** * **LD Bodies:** Amastigotes of *Leishmania donovani* found in macrophages of the spleen, bone marrow, and liver. * **Toxoplasma Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications (Congenital Toxoplasmosis). * **High-Yield Fact:** *Trypanosoma cruzi* (Chagas disease) also exhibits an amastigote stage in cardiac muscle, whereas *Trypanosoma brucei* (Sleeping sickness) does **not** have an amastigote stage.

Q: Which of the following organisms use pigs as a reservoir?

Trichinella spiralis. **Explanation:** The correct answer is **Trichinella spiralis**. In medical parasitology, a **reservoir** is an animal or environment where a pathogen normally lives and multiplies. *Trichinella spiralis* is a nematode that causes Trichinellosis. It is unique because the same individual host acts as both the intermediate and definitive host. Pigs serve as the primary reservoir for human infection; humans acquire the disease by consuming undercooked pork containing encysted larvae in the muscle. **Analysis of Options:** * **A. T. Solium:** While pigs are the **intermediate hosts** (harboring the larval stage, *Cysticercus cellulosae*), humans are the only definitive hosts. In parasitology nomenclature, pigs are generally classified as intermediate hosts rather than reservoirs for *T. solium*. * **B. T. Saginata:** The intermediate host for *T. saginata* (Beef tapeworm) is **cattle**, not pigs. Humans are the definitive hosts. * **C. Trichinella spiralis (Correct):** Pigs (and rats) maintain the cycle in nature (sylvatic and domestic cycles). It is the classic example of a parasite where the pig acts as a major reservoir. * **D. Ancylostoma:** *Ancylostoma duodenale* (Hookworm) is primarily a human parasite with no significant animal reservoir. Infection occurs via skin penetration by filariform larvae in the soil. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Triad for Trichinellosis:** Myalgia, periorbital edema, and eosinophilia. * **Muscle Biopsy:** The gold standard for diagnosis, showing "coiled larvae" in striated muscle. * **Key Feature:** *Trichinella* is the smallest nematode infecting humans and is viviparous (releases larvae, not eggs). * **Treatment:** Albendazole or Mebendazole are the drugs of choice.

Question 1

Cysticercosis is caused by:

Accepted Answer

Taenia solium

Answer

Taenia saginata

Answer

Echinococcus

Answer

None of the above

Question 2

All of the following are true about Toxoplasma infection EXCEPT:

Accepted Answer

Toxoplasmosis is usually symptomatic in immunocompetent persons

Answer

May occur due to ingestion of oocyst from cat's faeces

Answer

May spread by organ transplantation

Answer

Infection is severe and progressive in immunocompromised hosts

Question 3

All of the following organisms cause malabsorption, EXCEPT?

Accepted Answer

Ancylostoma duodenale

Answer

Giardiasis

Answer

Strongyloides stercoralis

Answer

Capillaria philippinensis

Question 4

Which of the following is NOT a feature of Entamoeba histolytica?

Accepted Answer

Cartwheel appearance on CT

Answer

Bloody diarrhea

Answer

Amoeboma in the right iliac fossa

Answer

Hepatomegaly

Question 5

What is the commonest helminthic infection in AIDS patients?

Accepted Answer

Strongyloides stercoralis

Answer

Trichuris trichura

Answer

Enterobius vermicularis

Answer

Necator americanus

Question 6

Which of the following parasitic infestations can lead to malabsorption syndrome?

Accepted Answer

Giardiasis

Answer

Amoebiasis

Answer

Ascariasis

Answer

Hookworm infestation

Question 7

Which of the following organisms is characterized by the presence of both cyst and trophozoite stages in stool samples?

Accepted Answer

Toxoplasma

Answer

Mycoplasma

Answer

Leptospira

Answer

Treponema

Question 8

What is the highest yield method for detecting the parasite in cases of Kala-azar?

Accepted Answer

Splenic aspiration

Answer

Bone marrow aspiration

Answer

Peripheral blood smear

Answer

None of the above

Question 9

Amastigote forms are seen in which of the following?

Accepted Answer

Toxoplasma gondii

Answer

Leishmania donovani

Answer

Leishmania major

Answer

Entamoeba

Question 10

Which of the following organisms use pigs as a reservoir?

Accepted Answer

Trichinella spiralis

Answer

T. Solium

Answer

T. Saginata

Answer

Ancyclostoma

Parasitology — MCQs

Parasitology — MCQs

On this page

Practice by Chapter

Want unlimited practice?