Parasitology Practice Questions

Q: What is typically true in large tapeworm infestations?

Eggs are frequently detected in the stools.. **Explanation:** Large tapeworms (Cestodes) such as *Taenia saginata* (beef tapeworm) and *Taenia solium* (pork tapeworm) primarily inhabit the human small intestine. **Why Option C is correct:** The definitive diagnosis of an adult tapeworm infestation relies on the microscopic demonstration of **eggs or proglottids in the stool**. Gravid proglottids detach from the distal end of the worm and pass out with feces, often rupturing to release characteristic bile-stained, radially striated eggs. Therefore, stool examination is the gold standard for confirming intestinal taeniasis. **Why other options are incorrect:** * **Option A:** The **Sabin-Feldman Dye Test** is a highly specific serological gold standard used for the diagnosis of **Toxoplasmosis**, not tapeworm infestations. * **Option B:** While large tapeworms can reach several meters in length, they are flexible and usually exist as a single worm. **Intestinal obstruction is rare.** Most patients are asymptomatic or present with vague abdominal pain and "passage of segments" per rectum. Obstruction is more classically associated with a heavy bolus of *Ascaris lumbricoides* (roundworms). **High-Yield Clinical Pearls for NEET-PG:** * **Taenia saginata:** Known as the "hungry tapeworm"; it has no hooks on the scolex (unarmed) and more than 15 lateral uterine branches. * **Taenia solium:** Possesses a rostellum with hooks (armed); it is more dangerous because ingestion of eggs can lead to **Cysticercosis** (larval stage in tissues). * **Treatment:** **Praziquantel** is the drug of choice for adult tapeworm infections. Niclosamide is an alternative.

Q: Ingested RBCs (erythrophagy) are seen in which of the following parasitic infections?

Entamoeba histolytica. **Explanation:** The presence of ingested red blood cells (erythrophagy) within the cytoplasm of a trophozoite is the **pathognomonic** feature of **Entamoeba histolytica**. **1. Why Entamoeba histolytica is correct:** * **Concept:** *E. histolytica* is an invasive parasite. The trophozoites produce proteolytic enzymes (histolysins) that destroy host tissues and cause mucosal ulceration. * **Mechanism:** During this invasive process, the trophozoites ingest host erythrocytes. Finding these "hematophagous" trophozoites in a stool sample or biopsy is the gold standard for differentiating the pathogenic *E. histolytica* from the morphologically identical but non-pathogenic *E. dispar*. **2. Why other options are incorrect:** * **Entamoeba coli:** This is a commensal amoeba. It does not invade tissues and lacks the machinery to ingest RBCs. Its trophozoites typically contain ingested bacteria and debris. * **Naegleria fowleri:** Known as the "brain-eating amoeba," it causes Primary Amoebic Meningoencephalitis (PAM). While highly destructive to brain tissue, erythrophagy is not its defining diagnostic characteristic in clinical samples. * **Acanthamoeba:** This free-living amoeba causes Granulomatous Amoebic Encephalitis (GAE) and Keratitis. It does not typically exhibit erythrophagy. **Clinical Pearls for NEET-PG:** * **Morphology:** *E. histolytica* trophozoites show **unidirectional motility** via pseudopodia and a nucleus with a **central karyosome** and fine peripheral chromatin. * **Stain:** Erythrophagy is best visualized using **Iron-hematoxylin** or Trichrome stain. * **Culture:** The **Robinson’s medium** and **NIH medium** are used for cultivation. * **Key Distinction:** Remember the "Rule of 4": *E. histolytica* cysts have a maximum of **4 nuclei**, whereas *E. coli* cysts have up to **8 nuclei**.

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

Trichuris trichura. **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.

Q: Calabar swellings are characteristic of infection with which parasite?

Loa Loa. **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.

Q: Which of the following is FALSE regarding Giardia lamblia?

The trophozoite has an axostyle for adherence to surfaces.. **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.

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

Fasciola hepatica. ***Fasciola hepatica*** - The life cycle involves **Lymnaea snails** as intermediate hosts and **metacercariae** encysted on aquatic vegetation like watercress. - Adult flukes migrate through **liver parenchyma** before settling in **bile ducts**, causing hepatic damage and biliary obstruction. *Paragonimus westermani* - Uses **freshwater crabs** or **crayfish** as second intermediate hosts, not aquatic vegetation. - Adults reside in **lung cysts**, not bile ducts, causing pulmonary symptoms and hemoptysis. *Clonorchis sinensis* - Requires **freshwater fish** as second intermediate hosts where metacercariae encyst in muscle tissue. - Adults migrate directly to **bile ducts** without liver parenchyma migration phase seen in Fasciola. *Fasciolopsis buski* - Metacercariae encyst on **aquatic plants** similar to Fasciola but adults remain in the **small intestine**. - Does not involve **liver migration** or bile duct colonization, causing primarily intestinal symptoms.

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

All of the above. **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 1

What is typically true in large tapeworm infestations?

Accepted Answer

Eggs are frequently detected in the stools.

Answer

The diagnosis is confirmed by Sabin Feldman dye test.

Answer

Intestinal obstruction is usually the presenting feature.

Answer

None of the above.

Question 2

Ingested RBCs (erythrophagy) are seen in which of the following parasitic infections?

Accepted Answer

Entamoeba histolytica

Answer

Naegleria fowleri

Answer

Entamoeba coli

Answer

Acanthamoeba

Question 3

Which of the following statements about amoebiasis is NOT true?

Accepted Answer

Amoebic abscesses are primarily caused by pyogenic bacterial co-infection leading to suppuration.

Answer

An amoebic liver abscess occurs in about 10% of cases in the tropics.

Answer

The portal venous system acts as an efficient filter for Entamoeba histolytica.

Answer

The wall of an amoebic abscess is a suitable site for culturing Entamoeba histolytica.

Question 4

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

Accepted Answer

Trichuris trichura

Answer

Enterobius vermicularis

Answer

Ancylostoma duodenale

Answer

Necator americanus

Question 5

Calabar swellings are characteristic of infection with which parasite?

Accepted Answer

Loa Loa

Answer

Ascaris

Answer

Hymenolepis

Answer

Strongyloides

Question 6

Cholangiocarcinoma has been associated with infection by which of the following organisms?

Accepted Answer

Clonorchis sinensis

Answer

Paragonimus westermani

Answer

Loa Loa

Answer

Schistosoma haematobium

Question 7

Which of the following is FALSE regarding Giardia lamblia?

Accepted Answer

The trophozoite has an axostyle for adherence to surfaces.

Answer

The quadrinucleate cyst is the infective form.

Answer

Cysts can survive in water for up to 3 months.

Answer

It exhibits falling leaf motility.

Question 8

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

Accepted Answer

Fasciola hepatica

Answer

Paragonimus westermani

Answer

Clonorchis sinensis

Answer

Fasciolopsis buski

Question 9

Malaria recrudescence is defined as:

Accepted Answer

Reappearance of parasitemia after a period of subpatent parasitemia during treatment

Answer

Parasitemia resistant to treatment

Answer

Relapse of infection from dormant liver forms

Answer

Relapse specifically in Plasmodium vivax and ovale infections

Question 10

Which of the following is a true mode of transmission of Toxoplasma?

Accepted Answer

All of the above

Answer

Vertical transmission

Answer

Ingestion of uncooked cysts

Answer

Organ transplantation

Parasitology — MCQs

Parasitology — MCQs

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