Parasitology Practice Questions

Q: Abdominal pain, fat malabsorption, and frothy stools suggest which of the following conditions?

Giardiasis. **Explanation:** The clinical presentation of abdominal pain, fat malabsorption (steatorrhea), and frothy, foul-smelling stools is characteristic of **Giardiasis**, caused by the flagellated protozoan *Giardia lamblia*. **Why Giardiasis is correct:** *Giardia* trophozoites attach to the duodenal and jejunal mucosa using a ventral sucking disc. This attachment leads to the **blunting of intestinal villi** and inflammation, which physically and chemically interferes with the absorption of fats and fat-soluble vitamins. The unabsorbed fat undergoes bacterial fermentation in the gut, resulting in **steatorrhea**—characterized by bulky, frothy, greasy, and foul-smelling stools that often float. Unlike invasive pathogens, *Giardia* does not cause blood or mucus in the stool. **Why other options are incorrect:** * **Amoebiasis (*Entamoeba histolytica*):** Typically presents as amoebic dysentery with blood and mucus in the stool ("red currant jelly" stools) due to mucosal invasion and flask-shaped ulcers. It does not cause malabsorption. * **Bacillary dysentery (*Shigella* spp.):** This is an acute bacterial infection characterized by high fever, severe abdominal cramps, and small-volume stools containing blood, pus, and mucus. It is an inflammatory process, not a malabsorptive one. **High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** Duodenum and upper jejunum (acidic environment). * **Diagnosis:** Stool microscopy (Trophozoites with "falling leaf motility" or Cysts); **Entero-test** (String test) is used if stool exams are negative. * **Morphology:** Trophozoite is pear-shaped with 4 pairs of flagella and two nuclei (**"Monkey face" appearance**). * **Drug of Choice:** Tinidazole or Metronidazole. * **Association:** Common in patients with **IgA deficiency**.

Q: All of the following are true of neurocysticercosis EXCEPT?

It is more common in vegetarians.. **Explanation:** Neurocysticercosis (NCC) is caused by the larval stage of the pork tapeworm, **_Taenia solium_** [1]. **1. Why Option B is the correct answer (False statement):** A common misconception is that NCC only occurs in pork eaters. In reality, NCC is acquired through the **fecal-oral route** by ingesting eggs (oncospheres) shed in the feces of a human tapeworm carrier [1]. This occurs via contaminated food, water, or poor hand hygiene. Therefore, **vegetarians are at equal or even higher risk** if they consume vegetables or water contaminated with human feces. Eating undercooked pork leads to intestinal taeniasis (adult worm), not NCC [1]. **2. Analysis of other options:** * **Option A:** **Albendazole** is the drug of choice (DOC) for parenchymal NCC as it has better CNS penetration than Praziquantel. Steroids are usually co-administered to reduce inflammation caused by dying cysts. * **Option C:** NCC is the most common cause of **intracerebral calcification** and acquired epilepsy in developing countries. As the cysticerci die (colloidal/granular stage), they eventually mineralize into calcified nodules. * **Option D:** In the life cycle of *T. solium*, **Man is the definitive host** (harbors the adult worm) [1], while pigs are the intermediate hosts. However, in the case of NCC, man acts as an **accidental intermediate host**. **Clinical Pearls for NEET-PG:** * **Most common presentation:** New-onset seizures (focal or generalized). * **Imaging:** "Starry sky appearance" on CT/MRI (multiple small enhancing lesions/calcifications). * **Scudder’s sign:** Presence of a "scolex" (eccentric dot) within a cyst on MRI is pathognomonic. * **Contraindication:** Do not give cysticidal drugs in **cysticercotic encephalitis** (diffuse brain edema) or **subretinal cysts** (risk of retinal detachment).

Q: A person presents with diarrhea of six months' duration. Acid-fast organisms, approximately 10 microns in size, are found in the stool. What is the most likely cause?

Cyclospora. The diagnosis of chronic diarrhea in the presence of acid-fast oocysts depends primarily on the **size** of the organism. ### **1. Why Cyclospora is Correct** * **Size:** *Cyclospora cayetanensis* oocysts are typically **8–10 microns** in diameter. This is the defining characteristic in the question. * **Staining:** They are **variably acid-fast**, meaning some oocysts stain red while others appear as "ghosts" on a Modified Ziehl-Neelsen (ZN) stain. * **Clinical Context:** It causes prolonged, watery diarrhea, often associated with contaminated water or fresh produce (e.g., berries). ### **2. Why Other Options are Incorrect** * **Cryptosporidium (Option A):** These are also acid-fast but significantly smaller, measuring **4–6 microns**. They are a common cause of diarrhea in HIV/AIDS patients. * **Isospora (Cystoisospora) (Option B):** These are much larger (**25–30 microns**) and have a characteristic **ellipsoid/oval shape**, unlike the spherical shape of Cyclospora. * **Giardia (Option D):** *Giardia lamblia* is **not acid-fast**. It is identified by its characteristic pear-shaped trophozoites or oval cysts on a routine iodine mount. ### **3. High-Yield Clinical Pearls for NEET-PG** * **Size Comparison (The "Rule of 5s"):** * *Cryptosporidium:* ~5 µm (Smallest) * *Cyclospora:* ~10 µm (Medium) * *Isospora:* ~25–30 µm (Largest & Oval) * **Autofluorescence:** Under UV microscopy, *Cyclospora* oocysts exhibit **blue-green autofluorescence**, a key diagnostic feature. * **Treatment:** Unlike *Cryptosporidium* (Nitazoxanide), *Cyclospora* and *Isospora* are treated with **Trimethoprim-Sulfamethoxazole (Cotrimoxazole)**.

Q: The Maltese cross formation is characteristic of which of the following infections?

Babesiosis. **Explanation:** The **Maltese cross formation** is a pathognomonic finding in **Babesiosis**, an infection caused by the protozoan *Babesia microti*. Inside the host's erythrocytes, the parasite undergoes asexual reproduction (budding), resulting in four daughter cells (merozoites) that remain attached by their bases. This tetrad arrangement resembles a "Maltese cross" and is a high-yield diagnostic feature on a Giemsa-stained peripheral blood smear. **Analysis of Options:** * **Babesiosis (Correct):** Characterized by intra-erythrocytic tetrads. It is often confused with *Plasmodium falciparum*, but Babesia lacks malarial pigment (hemozoin) and intracellular gametocytes. * **Schistosomiasis:** Known for characteristic eggs with spines (e.g., terminal spine in *S. haematobium* and lateral spine in *S. mansoni*), not tetrad formations. * **Cryptococcosis:** *Cryptococcus neoformans* is a budding yeast with a thick polysaccharide capsule. While it shows "Maltese cross" appearance under **polarized light** in urinalysis (due to lipiduria), the classic morphological description in tissue is a "narrow-based bud." * **Sporotrichosis:** Caused by *Sporothrix schenckii*, it typically presents as "cigar-shaped" yeast cells in tissue. **NEET-PG High-Yield Pearls:** 1. **Vector:** *Ixodes* tick (same vector as Lyme disease and Anaplasmosis). 2. **Clinical Presentation:** Fever, hemolytic anemia, and hemoglobinuria; severe in asplenic patients. 3. **Drug of Choice:** Atovaquone + Azithromycin (or Clindamycin + Quinine for severe cases). 4. **Distinction:** Unlike Malaria, *Babesia* can show extracellular rings.

Q: Which of the following is true about Giardia?

May cause traveler's diarrhea. **Explanation:** **1. Why Option A is Correct:** *Giardia lamblia* (also known as *G. intestinalis* or *G. duodenalis*) is a common cause of **Traveler’s Diarrhea**, particularly in individuals consuming contaminated water in endemic areas. The diarrhea is typically non-bloody, foul-smelling, and associated with steatorrhea (fatty stools) due to malabsorption caused by the parasite coating the intestinal mucosa. **2. Why Other Options are Incorrect:** * **Option B:** Giardia primarily inhabits the **duodenum and upper jejunum**, not the ileum. It prefers the acidic environment of the upper small intestine. * **Option C:** The **Cyst** is the infective stage for humans. Trophozoites are the vegetative, feeding stage found in the intestine; if passed in feces, they cannot survive the external environment or gastric acidity, making them non-infective upon ingestion. **3. NEET-PG High-Yield Clinical Pearls:** * **Morphology:** The trophozoite is "pear-shaped" or "heart-shaped" with a **"Falling Leaf" motility** and a characteristic "Monkey Face" appearance (due to two nuclei and four pairs of flagella). * **Pathogenesis:** It causes malabsorption by blunting villi and inhibiting enzymes like disaccharidases. It does **not** invade the bloodstream (no extraintestinal manifestations). * **Diagnosis:** Stool microscopy (cysts/trophozoites) or the **String Test (Entero-test)** to sample duodenal fluid. * **Immunology:** Patients with **IgA deficiency** are highly susceptible to chronic giardiasis. * **Treatment:** Drug of choice is **Metronidazole** or Tinidazole.

Q: A 5-year-old girl presents to the Emergency Department with sudden onset of difficulty in breathing, fever, and pruritus. She has no past history of lung infection or recent travel, but has a history of pica. On examination, wheezing and hepatomegaly are present. Peripheral smear shows marked eosinophilia and leukocytosis. What is the best test to aid in the diagnosis?

ELISA for Toxocara. **Explanation:** The clinical presentation of fever, wheezing (mimicking asthma), hepatomegaly, and marked peripheral eosinophilia in a child with a history of **pica** is classic for **Visceral Larva Migrans (VLM)**, caused by the migration of *Toxocara canis* or *Toxocara cati* larvae through human tissues. **Why ELISA for Toxocara is correct:** Humans (accidental hosts) ingest eggs from soil contaminated with dog or cat feces. The larvae hatch in the intestine and migrate to the liver and lungs, but cannot complete their life cycle, leading to an intense inflammatory response. Since the larvae do not mature into adults in humans, **stool examination for eggs is always negative**. Therefore, the diagnosis relies on serology. **ELISA for Toxocara excretory-secretory (TES) antigens** is the gold standard for diagnosis due to its high sensitivity and specificity. **Why other options are incorrect:** * **Tuberculin skin test:** Used for Tuberculosis. While TB can cause fever and lung findings, it does not typically present with sudden wheezing, pica, and profound eosinophilia. * **Histoplasmin test:** Used for Histoplasmosis (fungal infection). It is rarely used for acute diagnosis and does not explain the eosinophilic response seen here. * **Silver stain of gastric aspirate:** Used to identify *Pneumocystis jirovecii* or *Mycobacterium tuberculosis*. It has no role in diagnosing Toxocariasis. **NEET-PG High-Yield Pearls:** * **Classic Triad of VLM:** Hepatomegaly, marked eosinophilia, and hypergammaglobulinemia. * **Ocular Larva Migrans (OLM):** A variant where larvae migrate to the eye, often presenting as a retinal granuloma mimicking retinoblastoma. * **Treatment:** Albendazole is the drug of choice; corticosteroids are added if there is severe pulmonary or ocular involvement to reduce inflammation.

Q: What is the intermediate host where the larval form of Taenia solium is typically found?

Pig. **Explanation:** The life cycle of **_Taenia solium_ (Pork Tapeworm)** involves two hosts. Humans serve as the **definitive host**, harboring the adult tapeworm in the small intestine. **Pigs** serve as the **intermediate host**, where the ingested eggs hatch into oncospheres, penetrate the intestinal wall, and migrate to the muscles to develop into the larval stage, known as **Cysticercus cellulosae**. Humans become infected by consuming undercooked pork containing these larvae. **Analysis of Options:** * **A. Pig (Correct):** The natural intermediate host for _T. solium_. Note: Humans can also act as accidental intermediate hosts if they ingest eggs (via feco-oral route), leading to **Cysticercosis**. * **B. Cattle:** This is the intermediate host for **_Taenia saginata_ (Beef Tapeworm)**. _T. saginata_ does not cause cysticercosis in humans. * **C. Dog:** The definitive host for **_Echinococcus granulosus_** (Hydatid disease). Humans and sheep act as intermediate hosts here. * **D. Cat:** Primarily associated with **_Toxoplasma gondii_** (definitive host) or _Opisthorchis_ species, but not involved in the _Taenia_ life cycle. **High-Yield Clinical Pearls for NEET-PG:** * **Neurocysticercosis (NCC):** The most common cause of adult-onset seizures worldwide, caused by the larval stage of _T. solium_ in the brain. * **Diagnosis:** Stool microscopy for eggs/proglottids (Taeniasis) or MRI/CT showing "hole-with-dot" appearance (NCC). * **Treatment:** Praziquantel for intestinal infection; Albendazole + Steroids for NCC. * **Key Distinction:** In _T. solium_, the gravid uterus has **7–13 lateral branches**, whereas _T. saginata_ has **15–30**.

Q: A veterinarian presents with a chief complaint of thin, watery, non-bloody diarrhea for the past two weeks. He appears fatigued and mildly dehydrated. Stool examination is negative for leukocytes and culture for bacterial pathogens is negative. Acid-fast stain of the stool demonstrates oocysts that are 5-7 microns in diameter. Where does the sexual phase of this organism's life cycle occur?

In the brush border of the intestinal epithelium of humans. **Explanation:** The clinical presentation of chronic watery diarrhea in a veterinarian, combined with the finding of **acid-fast oocysts (5–7 µm)** in the stool, is diagnostic of ***Cryptosporidium parvum***. **1. Why the Correct Answer is Right:** *Cryptosporidium* is unique among coccidian parasites because it occupies an **intracellular but extracytoplasmic** niche. It resides within the **brush border of the intestinal epithelium** (primarily the small intestine). Both the asexual (schizogony) and **sexual (gametogony)** phases of its life cycle occur in this specific location within the host. This leads to villous atrophy and malabsorptive diarrhea. **2. Analysis of Incorrect Options:** * **Option A:** Swine are hosts for *Balantidium coli*, which causes dysentery and inhabits the large intestine, but it is a ciliate, not an acid-fast oocyst. * **Option B:** Muskrats and beavers are reservoirs for *Giardia lamblia*. While *Giardia* is extracellular, it is a flagellate and does not stain acid-fast. * **Option C:** Felines (cats) are the **definitive hosts** for *Toxoplasma gondii*. The sexual phase of *Toxoplasma* occurs in the feline gut, but *Toxoplasma* does not cause primary diarrheal illness in humans; it presents as systemic infection. **3. High-Yield Clinical Pearls for NEET-PG:** * **Stain:** Modified Kinyoun’s Acid-Fast stain is the gold standard. * **Size Matters:** *Cryptosporidium* (5–7 µm) is smaller than *Cyclospora* (8–10 µm) and *Isospora* (25–30 µm). * **Immunocompromised Patients:** In HIV/AIDS (CD4 <100), it causes severe, life-threatening cholera-like diarrhea. * **Transmission:** Highly resistant to chlorination; common in swimming pools and among animal handlers (veterinarians). * **Treatment:** **Nitazoxanide** is the drug of choice in immunocompetent patients.

Question 1

Abdominal pain, fat malabsorption, and frothy stools suggest which of the following conditions?

Accepted Answer

Giardiasis

Answer

Amoebiasis

Answer

Bacillary dysentery

Answer

All of the above

Question 2

All of the following are true of neurocysticercosis EXCEPT?

Accepted Answer

It is more common in vegetarians.

Answer

Albendazole is the drug of choice.

Answer

It produces intracerebral calcification.

Answer

Man is the definitive host.

Question 3

Which of the following conditions is characterized by a "strawberry vagina" and a vaginal pH greater than 4.5?

Accepted Answer

Trichomoniasis

Answer

Entamoeba histolytica infection

Answer

Giardiasis

Answer

Toxoplasmosis

Question 4

A person presents with diarrhea of six months' duration. Acid-fast organisms, approximately 10 microns in size, are found in the stool. What is the most likely cause?

Accepted Answer

Cyclospora

Answer

Cryptosporidium

Answer

Isospora

Answer

Giardia

Question 5

The Maltese cross formation is characteristic of which of the following infections?

Accepted Answer

Babesiosis

Answer

Schistosomiasis

Answer

Cryptococcosis

Answer

Sporotrichosis

Question 6

Which of the following is true about Giardia?

Accepted Answer

May cause traveler's diarrhea

Answer

Giardia inhabits mainly the ileum

Answer

Trophozoites are infective to humans

Answer

None of the above

Question 7

A 5-year-old girl presents to the Emergency Department with sudden onset of difficulty in breathing, fever, and pruritus. She has no past history of lung infection or recent travel, but has a history of pica. On examination, wheezing and hepatomegaly are present. Peripheral smear shows marked eosinophilia and leukocytosis. What is the best test to aid in the diagnosis?

Accepted Answer

ELISA for Toxocara

Answer

Tuberculin skin test

Answer

Histoplasmin test

Answer

Silver stain of gastric aspirate

Question 8

What is the intermediate host where the larval form of Taenia solium is typically found?

Accepted Answer

Pig

Answer

Cattle

Answer

Dog

Answer

Cat

Question 9

A veterinarian presents with a chief complaint of thin, watery, non-bloody diarrhea for the past two weeks. He appears fatigued and mildly dehydrated. Stool examination is negative for leukocytes and culture for bacterial pathogens is negative. Acid-fast stain of the stool demonstrates oocysts that are 5-7 microns in diameter. Where does the sexual phase of this organism's life cycle occur?

Accepted Answer

In the brush border of the intestinal epithelium of humans

Answer

Attached to the colonic mucosa of swine

Answer

Extracellularly in the small intestine of muskrats and beavers

Answer

Intracellularly in the intestinal mucosa of felines

Question 10

Multilocular hydatid cysts are caused by which organism?

Accepted Answer

E. multilocularis

Answer

E. granulosus

Answer

Clonorchis sinensis

Answer

Paragonimus westermani

Parasitology — MCQs

Parasitology — MCQs

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