Parasitology Practice Questions

Q: Which of the following fits into the life cycle of the picture given below? (AIIMS May 2017)

Entamoeba histolytica. ***Entamoeba histolytica*** - The diagram illustrates the characteristic life cycle of *Entamoeba histolytica*, showing the **trophozoite** stage with pseudopodia, **binary fission**, **encystment** forming a protective cyst wall, and **excystation** producing metacystic amoebae. - Key identifying features include the **4-nucleate mature cyst** and the presence of **chromatoid bars** with rounded ends, which are pathognomonic for this parasite's life cycle. *Giardia lamblia* - This is a **flagellated protozoan** with a distinctive **pear-shaped trophozoite** containing two nuclei and eight flagella, completely different from the amoeboid forms shown. - The life cycle involves **binucleate cysts** and does not include pseudopodial movement or the amoeboid stages depicted in the diagram. *Balantidium coli* - This is a **ciliated protozoan** (the largest intestinal parasite) with a characteristic **kidney-shaped macronucleus** and numerous cilia for motility. - The trophozoite is **oval-shaped** with cilia covering the surface, lacking the pseudopodial extensions and amoeboid characteristics shown in the life cycle. *Entamoeba coli* - While also an amoeba, *E. coli* forms **8-nucleate mature cysts** (compared to 4-nucleate in *E. histolytica*) and has **chromatoid bars with splinter-like pointed ends**. - This non-pathogenic amoeba has a similar but distinct life cycle with different cyst morphology and nuclear characteristics than those depicted.

Q: Which of the following parasite's life cycle is shown below?

Fasciola hepatica. ***Fasciola hepatica (Liver Fluke)*** - The diagram clearly illustrates the key stages of the Fasciola hepatica life cycle, including **encystation in the duodenum**, migration to the **liver**, and the presence of adult worms in the **bile duct** of humans and animals - The presence of **sheep and cattle** as definitive hosts, and the involvement of **freshwater snails** (Lymnaea species) as intermediate hosts, are characteristic features of *Fasciola hepatica* - **Eggs escaping in feces** into water where miracidia develop and infect snails, followed by cercaria forming **metacercaria on aquatic vegetation** (eaten by herbivores), is pathognomonic of this fluke *Clonorchis sinensis* - This is the **Chinese liver fluke** that also inhabits bile ducts, but uses **freshwater fish** (not vegetation) as the second intermediate host - Humans acquire infection by eating **raw or undercooked fish**, not vegetation *Paragonimus westermani* - This is the **lung fluke** found in the lungs (not liver/bile ducts) - Uses **freshwater crabs or crayfish** as second intermediate hosts - Life cycle does not involve grazing animals or vegetation *Schistosoma japonicum* - This is a **blood fluke** (not a liver fluke) causing schistosomiasis - Cercaria penetrate through **intact skin** (not ingested) - Adult worms live in **mesenteric veins**, not bile ducts - No metacercarial encysted stage on vegetation

Q: A 25-year-old man undergoes routine stool examination as part of a pre-employment health check. He is asymptomatic with no history of diarrhea or abdominal pain. Microscopy of the wet mount preparation (saline) shows the cyst form depicted in the image. Identify the most likely organism.

Entamoeba dispar. ***Entamoeba dispar*** - The image shows a **cyst form** consistent with *Entamoeba* species, characterized by its **oval shape**, size (10-20 µm), and visible internal structures (nuclei). - *Entamoeba histolytica* and *Entamoeba dispar* are **morphologically indistinguishable** under light microscopy; both have cysts with up to 4 nuclei. - However, in an **asymptomatic patient** with no clinical features of invasive amebiasis (no dysentery, no extraintestinal manifestations), *Entamoeba dispar* is the **most likely diagnosis** as it is a **non-pathogenic commensal** that is far more prevalent (90% of *Entamoeba* infections). - *E. histolytica* typically causes symptomatic disease (amoebic colitis, liver abscess), while *E. dispar* remains asymptomatic. - Definitive differentiation requires **PCR or antigen detection**, but clinical context strongly suggests *E. dispar*. *Giardia intestinalis* - *Giardia* cysts are **pear-shaped** or oval with distinct internal structures resembling a **"smiley face"** pattern (flagella, median bodies, nuclei in characteristic arrangement). - These cysts are typically smaller (8-12 µm) than the depicted *Entamoeba* cyst. - The morphology shown does not match *Giardia*. *Cryptosporidium hominis* - *Cryptosporidium* oocysts are much **smaller** (4-6 µm) and **spherical**. - They require **modified acid-fast staining** for identification and appear as tiny bright red spheres. - The size and morphology in the image do not match *Cryptosporidium*. *Balantidium coli* - *Balantidium coli* cysts are significantly **larger** (40-60 µm) with a characteristic **bean-shaped macronucleus** and micronucleus. - The cyst in the image is too small and lacks these distinctive features.

Q: Which of the following Schistosoma egg is shown below?

Schistosoma hematobium. ***Schistosoma hematobium*** - The image clearly displays an **elongated, oval-shaped egg** with a characteristic **terminal spine**. - This morphology is pathognomonic for **Schistosoma hematobium**, distinguishing it from other Schistosoma species. *Schistosoma mansoni* - Eggs of *Schistosoma mansoni* are typically **oval-shaped** with a distinct **lateral spine**. - The spine is located on the side of the egg, not at one of its poles as seen in the image. *Schistosoma japonicum* - *Schistosoma japonicum* eggs are more **rounded or oval** and possess a very small, **rudimentary spine** that is often difficult to visualize or absent. - The clearly visible, prominent terminal spine in the image rules out *S. japonicum*. *Cannot be differentiated on wet mount* - The distinct morphological features (shape and spine location) of Schistosoma eggs allow for reliable differentiation on a **wet mount** microscopic examination. - These features are crucial for accurate species identification in laboratory diagnostics.

Q: The life cycle shown in the image below is characteristic of which organism?

Schistosomiasis. ***Schistosomiasis*** - The image clearly depicts the characteristic **cercariae** penetrating human skin, with subsequent migration to the portal blood and maturation into adult worms in specific venous plexuses (e.g., rectum, liver, bladder). - The presence of **miracidia** hatching from eggs and infecting snails, followed by the release of cercariae from snails, is the hallmark life cycle of *Schistosoma* species. The eggs are shown in feces and urine, indicating different species of Schistosoma. *Paragonimus* - The life cycle of *Paragonimus* (lung flukes) involves ingestion of **undercooked crustaceans** (crabs or crayfish) containing metacercariae, not skin penetration by cercariae. - Adult worms typically reside in the **lungs**, and eggs are coughed up and swallowed or passed in feces, which is different from the venous system involvement shown. *Fasciolopsis buski* - *Fasciolopsis buski* (intestinal fluke) infection occurs through ingestion of **aquatic plants** contaminated with metacercariae. - The adult worms reside in the **small intestine**, and while eggs are passed in feces, the characteristic skin penetration by cercariae is absent in its life cycle. *Fasciola hepatica* - *Fasciola hepatica* (liver fluke) is acquired by ingesting **metacercariae** on aquatic vegetation, similar to *Fasciolopsis buski*. - Adult worms inhabit the **bile ducts** of the liver, and the life cycle does not involve skin penetration by cercariae as the mode of human infection.

Q: Which of the following CNS lesions is shown below?

Neurocysticercosis. ***Neurocysticercosis*** - The top image displays multiple **cystic lesions** within the brain parenchyma, consistent with various stages of **neurocysticercosis**. - The bottom image shows an **egg of *Taenia solium***, the causative agent of cysticercosis, confirming the parasitic origin. *Cerebral toxoplasmosis* - This typically presents as **multiple ring-enhancing lesions**, often with a predilection for the **basal ganglia** in immunocompromised patients. - The pathological image shown here does not primarily depict ring-enhancing lesions but rather macroscopic cysts. *Cryptococcal meningitis* - While Cryptococcus can cause CNS lesions, they are usually **gelatinous pseudocysts** or **meningitis**, not the distinct cystic structures seen in the image. - The causative organism is a **fungus**, not a parasitic worm, so the associated egg image would be incorrect. *Hydatid cyst* - Hydatid cysts (caused by *Echinococcus granulosus*) are typically **solitary, large, well-defined cysts** with a characteristic laminated membrane. - The image shows **multiple, smaller cysts** and the egg is characteristic of *T. solium*, not *Echinococcus*.

Q: Which of the following life cycles is shown below?

Hymenolepis nana. ***Hymenolepis nana*** - The image clearly depicts the life cycle of *Hymenolepis nana*, showing direct human infection from ingesting **fertile eggs**, leading to the development of an **oncosphere** and then a **cercocyst** within the human host before maturing into an adult tapeworm in the intestine. - The presence of an "alternative rodent host (rat, mouse) of minor importance" is a characteristic feature of *Hymenolepis nana*, which can infect both humans and rodents. *Echinococcus granulosus* - This parasite's life cycle involves **dogs (definitive host)** and **sheep/humans (intermediate hosts)**, where humans develop **hydatid cysts**, which is not shown here. - The depiction of an adult tapeworm developing directly in humans after ingestion of eggs, with a rodent as an alternative host, is inconsistent with *Echinococcus granulosus*. *Ascaris lumbricoides* - This is a **roundworm (nematode)**, not a tapeworm, and its life cycle involves **lung migration** of larvae before returning to the intestines to mature, which is not illustrated. - The image shows development from an oncosphere to a cercocyst and then to an adult tapeworm, which is specific to certain **cestodes**. *Toxocara canis* - This is another **roundworm** primarily affecting **dogs**, and humans become **incidental hosts** by ingesting embryonated eggs, leading to visceral larva migrans, where larvae migrate through tissues but do not develop into adult worms in the human intestine. - The illustrated life cycle details, particularly the formation of an oncosphere and cercocyst within the human leading to an adult tapeworm, are not indicative of *Toxocara canis*.

Q: Which is correct of the parasite shown below?

$A=$ Dipylidium caninum, $B=$ Hymenolepis nana. ***A = Dipylidium caninum, B = Hymenolepis nana*** - Image A displays a **scolex with four prominent suckers and a rostellum armed with hooks**, which is characteristic of *Dipylidium caninum*. - Image B shows a **scolex with four suckers and a distinct retractable rostellum armed with a single circlet of hooks**, a key morphological feature of *Hymenolepis nana*. *A = Taenia solium, B = Taenia saginata* - *Taenia solium* scolex (pork tapeworm) typically has **four suckers and a rostellum with a double crown of hooks**, not the single retractile coronet seen in B. - *Taenia saginata* scolex (beef tapeworm) is **unarmed (lacks hooks)** and only possesses four suckers, which contradicts both images. *A = Taenia saginata, B = Taenia solium* - This option is incorrect because *Taenia saginata* is an **unarmed tapeworm**, meaning it lacks hooks, which are clearly visible in Image A. - *Taenia solium* has a **scolex with hooks**, but Image B's scolex with a single circlet of hooks is more consistent with *Hymenolepis nana*. *A = Hymenolepis nana, B = Dipylidium caninum* - The scolex in Image A possesses a **double-crown rostellum with hooks clustered in rows**, which is characteristic of *Dipylidium caninum*, not *Hymenolepis nana*. - The scolex in Image B with four suckers and a retractile rostellum with a single circlet of hooks is indicative of *Hymenolepis nana*, not *Dipylidium caninum*.

Q: Which of the following parasite is shown below?

Echinococcus granulosus. ***Echinococcus granulosus*** - The image displays a **hydatid cyst**, characterized by its thick, laminated outer wall (ectocyst) and an inner germinal layer (endocyst) from which **brood capsules** and **protoscolices** (seen as invaginations) bud off. - This morphology is pathognomonic for **Echinococcus granulosus**, the causative agent of **cystic echinococcosis** (hydatid disease). *Cysticercosis cellulosae* - Cysts of *Cysticercus cellulosae* (larval stage of *Taenia solium*) typically appear as a fluid-filled bladder with a single **invaginated scolex** lacking the complex brood capsule arrangement seen in the image. - They also generally have a thinner cyst wall compared to *Echinococcus* cysts. *E. Histolytica* - *Entamoeba histolytica* is a **protozoan parasite** that causes amoebiasis, presenting as trophozoites or cysts; it does not form macroscopic cysts with complex internal structures like the one shown. - Amoebic abscesses are typically necrotic lesions, not true cysts with parasitic structures within. *Fasciola hepatica* - *Fasciola hepatica* is a **trematode (fluke)**, and its larval stages or adult worms do not form cysts with this characteristic morphology. - Liver flukes would appear as tissue sections of the flatworm itself in infected organs, not as a large, spherical cyst with internal budding structures.

Q: Which of the following life cycle is shown below?

Clonorchiasis. ***Clonorchiasis*** - The diagram displays metacercariae (infective stage) in freshwater fish being ingested by a human host, a defining characteristic of the Clonorchis sinensis life cycle. - The life cycle involves freshwater snails (first intermediate host) and freshwater fish (second intermediate host), which aligns with the image showing cercariae encysting in fish. *Diphylobothrium latum* - The infective stage for *Diphylobothrium latum* (fish tapeworm) is the **plerocercoid larva** in raw or undercooked freshwater fish, not metacercariae. - While it also involves freshwater fish, its larval forms and overall life cycle stages are distinct from what is depicted. *Echinococcus granulosus* - This parasite causes **hydatid disease** and has a life cycle involving canids (definitive host) and herbivores (intermediate host), with humans being accidental intermediate hosts. - The life cycle does not involve freshwater fish or metacercariae for human infection. *Tenia solium* - The human is the definitive host for **Taenia solium** (pork tapeworm), acquiring infection by ingesting undercooked pork containing **cysticerci**. - The intermediate host is pigs, and the life cycle does not involve freshwater fish or metacercariae.

Question 1

Which of the following fits into the life cycle of the picture given below? (AIIMS May 2017)

Accepted Answer

Entamoeba histolytica

Answer

Giardia lamblia

Answer

Balantidium coli

Answer

Entamoeba coli

Question 2

Which of the following parasite's life cycle is shown below?

Accepted Answer

Fasciola hepatica

Answer

Clonorchis sinensis

Answer

Paragonimus westermani

Answer

Schistosoma japonicum

Question 3

A 25-year-old man undergoes routine stool examination as part of a pre-employment health check. He is asymptomatic with no history of diarrhea or abdominal pain. Microscopy of the wet mount preparation (saline) shows the cyst form depicted in the image. Identify the most likely organism.

Accepted Answer

Entamoeba dispar

Answer

Giardia intestinalis

Answer

Cryptosporidium hominis

Answer

Balantidium coli

Question 4

Which of the following Schistosoma egg is shown below?

Accepted Answer

Schistosoma hematobium

Answer

Schistosoma mansoni

Answer

Schistosoma japonicum

Answer

Cannot be differentiated on wet mount

Question 5

The life cycle shown in the image below is characteristic of which organism?

Accepted Answer

Schistosomiasis

Answer

Paragonimus

Answer

Fasciolopsis buski

Answer

Fasciola hepatica

Question 6

Which of the following CNS lesions is shown below?

Accepted Answer

Neurocysticercosis

Answer

Cerebral toxoplasmosis

Answer

Cryptococcal meningitis

Answer

Hydatid cyst

Question 7

Which of the following life cycles is shown below?

Accepted Answer

Hymenolepis nana

Answer

Echinococcus granulosus

Answer

Ascaris lumbricoides

Answer

Toxocara canis

Question 8

Which is correct of the parasite shown below?

Accepted Answer

$A=$ Dipylidium caninum, $B=$ Hymenolepis nana

Answer

A = Taenia saginata, B = Taenia solium

Answer

$A=$ Hymenolepis nana, $B=$ Dipylidium caninum

Answer

A = Taenia solium, B = Taenia saginata

Question 9

Which of the following parasite is shown below?

Accepted Answer

Echinococcus granulosus

Answer

Cysticercosis cellulosae

Answer

E. Histolytica

Answer

Fasciola hepatica

Question 10

Which of the following life cycle is shown below?

Accepted Answer

Clonorchiasis

Answer

Diphylobothrium latum

Answer

Echinococcus granulosus

Answer

Tenia solium

Parasitology — MCQs

Parasitology — MCQs

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