Parasitology Practice Questions

Q: A 20 year old female presented with abdominal pain and passage of motile segments in the stool. She claims to have barbecue pork at her friends house. No other complaints. What is the most likely causative agent?

Taenia solium. ***Taenia solium*** - Infection is acquired by ingesting **undercooked pork** containing the larval stage (cysticercus), which then develops into the adult tapeworm in the human intestine. - The passage of **motile proglottids** (segments) in the stool is a classic clinical finding of **taeniasis**. *H. nana* - Also known as the **dwarf tapeworm**, it is the most common cestode infection but is typically transmitted by ingestion of eggs from contaminated food/water. - It does not have a direct association with the consumption of **pork**. *E. vermicularis* - Commonly known as the **pinworm**, it presents primarily with intense **perianal pruritus**, especially at night, rather than abdominal pain and segment passage. - Diagnosis is typically made via the **scotch tape test** to visualize eggs in the perianal region. *T. saginata* - This species is acquired by consuming **undercooked beef**, not pork, and presents with similar tapeworm infestation symptoms. - While it also causes passage of motile segments, the patient's specific history of consuming **pork** makes *Taenia solium* the more appropriate diagnosis.

Q: A 38-year-old man with advanced HIV infection (CD4 count: 60 cells/mm³) presents with chronic watery diarrhea for 2 months, significant weight loss, intermittent fever, and fatigue. Colonoscopy is performed, and biopsy from the colonic mucosa demonstrates trophozoites with RBCs. What is the most likely causative organism?

Entamoeba histolytica. ***Entamoeba histolytica*** - The presence of **trophozoites with ingested RBCs** (erythrophagocytosis) in a colonic biopsy is pathognomonic for **amoebiasis** caused by *Entamoeba histolytica*. - This organism can invade the colonic mucosa, leading to **flask-shaped ulcers**, bloody diarrhea, and systemic symptoms, even in immunocompromised patients. *Giardia lamblia* - Typically causes **malabsorption** and fatty, foul-smelling stools rather than bloody or mucus-filled diarrhea. - Biopsy or stool examination would reveal **pear-shaped trophozoites** with two nuclei, but it does not ingest RBCs. *Cryptococcus neoformans* - Primarily presents as a fungal pneumonia or **meningoencephalitis** in patients with advanced HIV/AIDS. - While it can be disseminated, it does not typically cause primary colonic mucosal disease characterized by trophozoites. *Cryptosporidium parvum* - A very common cause of **chronic secretory diarrhea** in severely immunocompromised patients (CD4 < 100). - Diagnosis is made via **acid-fast staining** of stool, showing small oocysts, not invasive trophozoites with erythrophagocytosis.

Q: Black malarial pigment is seen in which Plasmodium species?

P. falciparum. **Explanation:** Malarial pigments, known as **hemozoin**, are insoluble crystals created by the parasite through the detoxification of heme, a byproduct of hemoglobin digestion. The color and morphology of these pigments vary across *Plasmodium* species and serve as a key diagnostic feature under light microscopy. **Why P. falciparum is correct:** In *Plasmodium falciparum* infections, the hemozoin pigment appears as **solid black or dark brown** granules. These are typically seen as a single, dense mass in the gametocyte stage (crescent-shaped) or as coarse, dark clumps in the schizont stage. The intensity of the black color is a hallmark of *P. falciparum*. **Why the other options are incorrect:** * **P. vivax:** Produces **yellowish-brown** or golden-brown pigment granules that are fine and scattered throughout the cytoplasm. * **P. malariae:** Characterized by **dark brown** pigment, often described as coarser than *P. vivax* but lacking the distinct jet-black appearance of *P. falciparum*. It often forms a central mass in the "rosette" schizont. * **P. ovale:** Similar to *P. vivax*, it produces **dark brown** granules, but they are generally fewer in number. **High-Yield Clinical Pearls for NEET-PG:** * **Maurer’s Clefts:** Coarse granulations seen in RBCs infected with *P. falciparum*. * **Schüffner’s Dots:** Fine stippling seen in *P. vivax* and *P. ovale*. * **Ziemann’s Dots:** Fine dust-like dots seen in *P. malariae*. * **Recrudescence:** Seen in *P. falciparum* and *P. malariae* due to sub-lethal parasitemia. * **Relapse:** Seen in *P. vivax* and *P. ovale* due to **hypnozoites** (latent liver stages).

Q: Which of the following may cause biliary obstruction?

Clonorchis. **Explanation:** The correct answer is **Clonorchis sinensis** (the Chinese Liver Fluke). **Why Clonorchis is correct:** *Clonorchis sinensis* is a trematode that primarily inhabits the **distal bile ducts**. The adult worms cause mechanical obstruction, chronic inflammation, and hyperplasia of the biliary epithelium. Long-term infection leads to biliary stasis, stone formation (pigment stones), and recurrent pyogenic cholangitis. Crucially for NEET-PG, chronic irritation by *Clonorchis* is a major risk factor for **Cholangiocarcinoma** (bile duct cancer). **Why the other options are incorrect:** * **Ancylostoma duodenale (Hookworm):** These reside in the small intestine (jejunum) and attach to the mucosa to suck blood, leading to iron deficiency anemia. They do not migrate into the biliary tree. * **Enterobius vermicularis (Pinworm):** These primarily inhabit the cecum and appendix. Their main clinical manifestation is perianal pruritus; they do not cause biliary pathology. * **Strongyloides stercoralis:** These reside in the mucosal tunnels of the duodenum and upper jejunum. While they can cause severe autoinfection in immunocompromised hosts (Hyperinfection syndrome), they are not a cause of biliary obstruction. **NEET-PG High-Yield Pearls:** 1. **Biliary Parasites:** Apart from *Clonorchis*, the other major parasite causing biliary obstruction is ***Ascaris lumbricoides*** (due to its tendency to migrate into the Ampulla of Vater) and ***Fasciola hepatica***. 2. **Intermediate Hosts:** *Clonorchis* requires two intermediate hosts: 1st - Snail (Parafossarulus); 2nd - Freshwater fish (Cyprinidae family). 3. **Infective Stage:** Metacercariae found in undercooked fish. 4. **Drug of Choice:** Praziquantel is the gold standard treatment for *Clonorchis* and most trematodes.

Question 1

A 20 year old female presented with abdominal pain and passage of motile segments in the stool. She claims to have barbecue pork at her friends house. No other complaints. What is the most likely causative agent?

Accepted Answer

Taenia solium

Answer

H. nana

Answer

E. vermicularis

Answer

T. saginata

Question 2

A 38-year-old man with advanced HIV infection (CD4 count: 60 cells/mm³) presents with
chronic watery diarrhea for 2 months, significant weight loss, intermittent fever, and fatigue.
Colonoscopy is performed, and biopsy from the colonic mucosa demonstrates trophozoites with
RBCs. What is the most likely causative organism?

Accepted Answer

Entamoeba histolytica

Answer

Giardia lamblia

Answer

Cryptococcus neoformans

Answer

Cryptosporidium parvum

Question 3

A young female presents with fatigue, pallor, and symptoms suggestive of iron deficiency
anemia. A microscopic image of her stool examination is provided. Which of the following
statements is correct regarding the parasite identified?

Accepted Answer

Infection occurs by active penetration of infective larvae through the skin

Answer

Infection occurs by ingestion of cysts in contaminated food or water

Answer

The image represents eggs of Enterobius vermicularis

Answer

The parasite shown is Ascaris lumbricoides

Question 4

Black malarial pigment is seen in which Plasmodium species?

Accepted Answer

P. falciparum

Answer

P. vivax

Answer

P. malariae

Answer

P. ovale

Question 5

Which of the following may cause biliary obstruction?

Accepted Answer

Clonorchis

Answer

Ancylostoma

Answer

Enterobius

Answer

Strongyloides

Parasitology — MCQs

Parasitology — MCQs

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