Parasitology Practice Questions

Q: Which of the following parasites is capable of causing autoinfection leading to hyperinfection syndrome?

Strongyloides stercoralis. ***Strongyloides stercoralis*** - This parasite is unique among helminths for its ability to cause **autoinfection with hyperinfection syndrome**, a potentially life-threatening condition. - The **rhabditiform larvae** can accelerate development directly into invasive **filariform larvae** within the host's large intestine. - This transformation allows the infectious filariform larvae to penetrate the intestinal mucosa or perianal skin, leading to persistent infection and potentially fatal **hyperinfection syndrome** in immunocompromised hosts. - This makes *S. stercoralis* the most clinically significant parasite causing autoinfection. *Incorrect: Ancylostoma duodenale* - This hookworm does not cause autoinfection, as its eggs must exit the host and mature in the soil to form infectious **filariform larvae**. - Infection occurs through **percutaneous penetration** (skin penetration) by larvae from the external environment. *Incorrect: Ascaris lumbricoides* - This large roundworm requires an environmental phase where unembryonated eggs mature in the soil before becoming infectious upon ingestion (**fecal-oral route**). - Its life cycle involves migration through the lungs (pulmonary phase), but it lacks the mechanism for internal autoinfection. *Incorrect: Hymenolepis nana* - *H. nana* (dwarf tapeworm) is capable of internal autoinfection where eggs hatch within the intestinal lumen and **oncospheres** invade the villi directly. - However, it does **not** cause hyperinfection syndrome like *S. stercoralis*, making it clinically less significant in this context. - The question specifically asks about autoinfection leading to hyperinfection syndrome, which is unique to *Strongyloides stercoralis*.

Q: A 5-year-old child presents with nocturnal perianal itching. The image below shows the organism identified on an adhesive tape test. What is the most likely causative agent?

Enterobius vermicularis. ***Enterobius vermicularis*** - The clinical presentation of **nocturnal perianal itching** (pruritus ani) in a child is highly characteristic of **pinworm infection** (enterobiasis). - The image shows a classic **D-shaped** or planoconvex egg, frequently found on the **adhesive tape test**, which are key identifiers for *Enterobius vermicularis*. *Ancylostoma duodenale* - This parasite causes **hookworm disease**, typically manifesting as **iron-deficiency anemia** and rarely perianal itching. - *Ancylostoma* eggs are oval, thin-shelled, and typically found in the **stool**, not via a tape test. *Hymenolepis nana* - This is the **dwarf tapeworm**, which usually causes mild or asymptomatic infection, though heavy infections can cause abdominal discomfort. - The eggs are small, oval, and possess **polar filaments** between the shell and the oncosphere, which are absent in the image. *Trichuris trichiura* - This parasite, the **whipworm**, causes trichuriasis, which presents with bloody diarrhea and occasionally **rectal prolapse** in heavy infections. - *Trichuris* eggs are distinctively **barrel-shaped** with two prominent bipolar mucoid plugs at each end.

Q: A diplomat from Peru was posted to India last week. Today he has brought his 10-year-old daughter to your clinic since the child has developed this swelling in the eye and feels feverish. Comment on the clinical sign and the insect bite responsible for the same:

Romana sign, Triatomine bug. ***Romana sign, Triatomine bug*** - The image depicts **Romana sign**, characterized by **unilateral periorbital edema**, which is a classic early clinical manifestation of **Chagas disease** (American trypanosomiasis). - This sign is caused by the bite of a **Triatomine bug** (also known as a **kissing bug**) near the eye or by rubbing its feces containing *Trypanosoma cruzi* into the eye. The diplomat's origin from Peru suggests a potential exposure in an endemic region. *Faget sign, Reduvid bug* - **Faget's sign** is a clinical finding where the **pulse rate remains normal or decreases** despite a fever, which is typically found in diseases like **typhoid fever** or **yellow fever**, not associated with a specific insect bite causing periorbital edema. - While Triatomine bugs belong to the **Reduviidae family**, "Reduvid bug" is a broad term, and Faget's sign is unrelated to the described swelling. *Chigger allergy, Trombiculid mites* - **Chigger bites** (from Trombiculid mites) typically cause intensely **itchy, reddish welts or papules**, often in clusters, commonly on ankles, wrists, or waistbands. - They do not typically present as a significant unilateral periorbital edema like Romana sign and are not a cause of Chagas disease. *Eschar, Cimex Lectularis* - An **eschar** is a dark, scab-like lesion that occurs due to necrosis of skin tissue, often seen in conditions like **rickettsial diseases** (e.g., scrub typhus) following a tick or mite bite. - **Cimex Lectularis** refers to **bed bugs**, which cause itchy, erythematous wheals or papules, often in a linear pattern, but do not produce an eschar or Romana sign.

Q: Which of the following is correct about the image shown?

Dracunculus. ***Dracunculus*** - The image shows a procedure for extracting a **guinea worm (Dracunculus medinensis)** by gradually winding it around a stick. - This characteristic method of removal is pathognomonic for **dracunculiasis**. *Cutaneous Larva migrans* - This condition presents as **serpiginous, erythematous, pruritic tracks** on the skin, caused by hookworm larvae. - It does not involve a visible worm being extracted with a stick. *Visceral larva migrans* - This is caused by the migration of nematode larvae (typically *Toxocara canis* or *cati*) through internal organs, with systemic symptoms. - It does not manifest as a worm emerging from a skin lesion. *Tenia solium* - *Taenia solium* (pork tapeworm) infection can manifest as taeniasis (intestinal infection) or **cysticercosis** (larval cysts in tissues). - Neither of these presentations involves a worm being manually extracted from a skin lesion in this manner.

Q: The following diagram depicts blood smear of which species?

Plasmodium falciparum. ***Plasmodium falciparum*** - The image displays characteristic **crescent-shaped or banana-shaped gametocytes** (stages 16-20), which are **pathognomonic for *Plasmodium falciparum*** - The earlier stages (1-5) represent ring forms (multiple rings per RBC, delicate ring forms) - Subsequent stages (6-15) show maturation culminating in the distinct **crescentic gametocytes** - This morphology is the **key distinguishing feature** of P. falciparum *Plasmodium vivax* - Produces **oval-shaped gametocytes**, not crescent-shaped - Characterized by enlarged RBCs with **Schüffner's dots** - Shows amoeboid trophozoites, not seen in this smear *Plasmodium malariae* - Produces **oval to round gametocytes** - Characteristic **band forms** and **rosette-shaped schizonts** (8-12 merozoites) - Not crescent-shaped as shown in the image *Plasmodium ovale* - Produces **oval gametocytes** similar to P. vivax - RBCs show **fimbriated edges** and Schüffner's dots - Does not produce crescent-shaped gametocytes

Q: A 20-year-old lady presents with high grade fever and incoherent talking for 1 day. The following peripheral smear shows presence of:

Gametocyte. ***Gametocyte*** - The image clearly shows a **crescent-shaped** parasite within a red blood cell, which is characteristic of the **gametocytes of *Plasmodium falciparum***. - The patient's symptoms of **high-grade fever** and **non-coherent talking** (suggesting cerebral malaria) are consistent with severe *P. falciparum* infection, where gametocytes are often seen on peripheral smears. *Sporozoite* - Sporozoites are the **infectious forms of malaria parasites** transmitted from the mosquito to humans; they are typically found in the **salivary glands of mosquitoes** and briefly in human blood before infecting liver cells. - They are generally **not observed in peripheral blood smears** during the symptomatic phase of malaria. *Merozoite* - Merozoites are the forms that emerge from **infected liver cells** and then subsequently from **infected red blood cells** to invade new red blood cells, thus perpetuating the asexual cycle. - They are very **short-lived extracellularly** and are rarely seen in peripheral blood smears; instead, **ring forms, trophozoites, and schizonts** (representing asexual stages) are typically observed inside red blood cells. *Schistocyte* - Schistocytes are **fragmented red blood cells** that result from **mechanical damage** to red blood cells, often seen in conditions like microangiopathic hemolytic anemia or disseminated intravascular coagulation. - They are not a life stage of the malaria parasite; their presence would indicate a co-existing or secondary hematological issue, not a parasitic form.

Q: The image shows presence of:

Giardia lamblia. ***Giardia lamblia*** - The image clearly displays a **pyriform (pear-shaped)** organism with **two nuclei** and a "smiley face" appearance due to the location of the nuclei, characteristic of *Giardia lamblia* trophozoites. - The presence of **flagella** (typically 4 pairs) and the **ventral sucking disc** are distinguishing features of *Giardia lamblia* trophozoites. - *Giardia* is commonly found in duodenal aspirates and stool samples, causing giardiasis with symptoms of malabsorption and diarrhea. *Entamoeba histolytica* - *Entamoeba histolytica* trophozoites are typically **amoeboid** in shape with unidirectional movement, not pear-shaped. - They usually contain a **single nucleus** with central karyosome and peripheral chromatin. - They may show **ingested red blood cells** within their cytoplasm, which is not seen here. *Balantidium coli* - *Balantidium coli* trophozoites are very large (50-100 μm), **oval-shaped ciliates** with a prominent **macronucleus** (kidney-shaped) and a smaller micronucleus. - The entire surface is **covered with cilia** giving a characteristic appearance, which is not seen in this image. *Trichomonas vaginalis* - *Trichomonas vaginalis* trophozoites are also **pear-shaped with flagella** (typically 4 anterior flagella), but have only **one nucleus** located anteriorly. - They possess an **undulating membrane** and a posterior axostyle that extends beyond the cell body. - The presence of **two nuclei** and the bilateral symmetry seen in this image are characteristic of *Giardia*, not *Trichomonas*.

Q: The following image shows presence of:

Entamoeba histolytica. ***Entamoeba histolytica*** - The image shows a **cyst with multiple nuclei** (typically 1-4, but can be more in stained preparations) and a **central karyosome** within each nucleus, which are characteristic features of *Entamoeba histolytica* cysts. - The presence of **refractile chromatoid bodies** with rounded ends can also be seen in *Entamoeba histolytica* cysts (though not distinctly visible in this specific stain, the overall morphology with multiple nuclei is key). *Giardia lamblia* - *Giardia lamblia* cysts are **oval or pear-shaped** and typically have **four nuclei** clustered at one end, along with visible **flagella remnants** and a median body, which are not present in the image. - The overall shape and nuclear arrangement do not match the morphology of *Giardia lamblia* cysts. *Balantidium coli* - *Balantidium coli* are significantly **larger** than *Entamoeba* cysts and possess a distinct **macronucleus** (kidney-shaped) and a smaller **micronucleus**, often with easily visible **cilia** on their surface in the trophozoite stage. - The size and nuclear structure in the image are inconsistent with *Balantidium coli*. *Entamoeba coli* - *Entamoeba coli* is a **non-pathogenic commensal amoeba** that can be confused with *E. histolytica*. However, *E. coli* cysts typically have **more than 4 nuclei** (often 8 or more in mature cysts) with **eccentric karyosomes** (not central). - The cysts also have **chromatoid bodies with splintered or irregular ends** (unlike the smooth, rounded ends in *E. histolytica*). - The nuclear morphology and count in the image are more consistent with *E. histolytica* than *E. coli*.

Q: The following image shows presence of:

Taenia solium. ***Taenia solium*** - The image shows the **scolex** (head) of a parasitic worm with both **suckers** (bottom arrow) and a prominent **rostellum with hooks** (top arrow), which is characteristic of *Taenia solium* (pork tapeworm). - The presence of the armed rostellum differentiates *Taenia solium* from *Taenia saginata*, which only has suckers. *Necator americanus* - This is a **hookworm** and its mouthparts typically feature **cutting plates**, not suckers and hooks in the manner shown. - Hookworms are nematodes, distinct from the cestode morphology presented. *Ancylostoma duodenale* - Similar to *Necator americanus*, *Ancylostoma duodenale* is also a **hookworm** and possesses **teeth** in its buccal capsule, not the distinct suckers and rostellum with hooks seen in the image. - Again, this morphology is inconsistent with a cestode. *Enterobius vermicularis* - This is a **pinworm**, a small nematode, and its anterior end does not feature the prominent scolex with suckers and a hooked rostellum visible in the image. - *Enterobius vermicularis* has a more simple mouth, sometimes with cuticular alae.

Q: Which of the following worms is shown in the specimen?

Ascaris lumbricoides. ***Ascaris lumbricoides*** - The image displays a collection of **large, creamy-white to yellowish-brown, roundworms** that are characteristic of *Ascaris lumbricoides*. These worms are often referred to as **giant roundworms** due to their size. - They are typically found in the **intestines** and can grow up to 35 cm in length, which is consistent with the appearance of the worms in the specimen jar. *Trichinella* - *Trichinella* species are **much smaller** and are typically not visible as macroscopic worms in a specimen jar in this manner. - They are primarily known for causing **trichinellosis**, where larvae encyst in muscle tissue, rather than forming large masses in the intestines. *Wuchereria bancrofti* - *Wuchereria bancrofti* causes **lymphatic filariasis** and its adult worms reside in the lymphatic system. - These worms are **thin and thread-like** and are generally much smaller and more delicate than the worms shown in the specimen, which appear robust. *Trichuris trichiura* - *Trichuris trichiura*, also known as **whipworm**, has a characteristic **whip-like appearance** with a thin anterior portion and a thicker posterior end. - While they are intestinal nematodes, they are generally **smaller** and have a distinct morphology not seen in the specimen.

Question 1

Which of the following parasites is capable of causing autoinfection leading to hyperinfection syndrome?

Accepted Answer

Strongyloides stercoralis

Answer

Ascaris lumbricoides

Answer

Ancylostoma duodenale

Answer

Hymenolepis nana

Question 2

A 5-year-old child presents with nocturnal perianal itching. The image below shows the organism identified on an adhesive tape test. What is the most likely causative agent?

Accepted Answer

Enterobius vermicularis

Answer

Hymenolepis nana

Answer

Trichuris trichiura

Answer

Ancylostoma duodenale

Question 3

A diplomat from Peru was posted to India last week. Today he has brought his 10-year-old daughter to your clinic since the child has developed this swelling in the eye and feels feverish. Comment on the clinical sign and the insect bite responsible for the same:

Accepted Answer

Romana sign, Triatomine bug

Answer

Faget sign, Reduvid bug

Answer

Chigger allergy, Trombiculid mites

Answer

Eschar, Cimex Lectularis

Question 4

Which of the following is correct about the image shown?

Accepted Answer

Dracunculus

Answer

Cutaneous Larva migrans

Answer

Visceral larva migrans

Answer

Tenia solium

Question 5

The following diagram depicts blood smear of which species?

Accepted Answer

Plasmodium falciparum

Answer

Plasmodium malariae

Answer

Plasmodium ovale

Answer

Plasmodium vivax

Question 6

A 20-year-old lady presents with high grade fever and incoherent talking for 1 day. The following peripheral smear shows presence of:

Accepted Answer

Gametocyte

Answer

Sporozoite

Answer

Merozoite

Answer

Schistocyte

Question 7

The image shows presence of:

Accepted Answer

Giardia lamblia

Answer

Entamoeba histolytica

Answer

Balantidium coli

Answer

Trichomonas vaginalis

Question 8

The following image shows presence of:

Accepted Answer

Entamoeba histolytica

Answer

Giardia lamblia

Answer

Balantidium coli

Answer

Entamoeba coli

Question 9

The following image shows presence of:

Accepted Answer

Taenia solium

Answer

Necator americanus

Answer

Ancylostoma duodenale

Answer

Enterobius vermicularis

Question 10

Which of the following worms is shown in the specimen?

Accepted Answer

Ascaris lumbricoides

Answer

Trichinella

Answer

Wuchereria bancrofti

Answer

Trichuris trichiura

Parasitology — MCQs

Parasitology — MCQs

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