Parasitology Practice Questions

Q: Which of the following parasitic infections is associated with Salmonella?

Schistosoma hematobium. **Explanation:** The association between **Salmonella** and **Schistosomiasis** is a classic example of a pathogen-parasite interaction. The correct answer is **Schistosoma haematobium** (and other species like *S. mansoni*). **Why it is correct:** Salmonella species (particularly *S. typhi* and *S. typhimurium*) have a unique ability to adhere to and colonize the **tegument** (outer surface) of adult Schistosoma worms. The bacteria utilize the parasite as a protected niche, leading to **chronic salmonellosis**. This synergy results in prolonged bacteremia that is often refractory to standard antibiotic therapy until the underlying parasitic infection is treated. While *S. mansoni* is more commonly linked to intestinal salmonellosis, *S. haematobium* is frequently associated with persistent urinary tract colonization and "urinary carriers" of Salmonella. **Why other options are incorrect:** * **Paragonimus (Lung fluke):** Associated with pulmonary symptoms mimicking tuberculosis; it does not have a recognized symbiotic relationship with Salmonella. * **Taenia solium (Pork tapeworm):** Primarily associated with neurocysticercosis or intestinal taeniasis; no specific link to Salmonella bacteremia. * **Hymenolepis nana (Dwarf tapeworm):** The most common cause of all cestode infections, but it does not serve as a reservoir for Salmonella. **High-Yield Clinical Pearls for NEET-PG:** * **Chronic Carrier State:** Always suspect Schistosomiasis in a patient with recurrent enteric fever who fails to respond to antibiotics. * **Mechanism:** Salmonella pili bind to the mannose-resistant receptors on the schistosome surface. * **Other Salmonella Associations:** * **Sickle Cell Anemia:** Predisposes to Salmonella Osteomyelitis. * **Chronic Gallbladder Disease:** Associated with the chronic carrier state of *S. typhi*.

Q: A girl complained of abdominal pain with the passage of foul-smelling stool that does not wash away easily. There is a history of swimming in contaminated water. What is the likely causative organism?

Giardia lamblia. The clinical presentation described is a classic case of **Giardiasis**, caused by the flagellated protozoan **Giardia lamblia**. **Why Giardia lamblia is correct:** The hallmark of Giardiasis is **steatorrhea** (fatty, foul-smelling stools that float and are difficult to flush/wash away). This occurs because the parasite attaches to the duodenal and jejunal mucosa via a ventral sucking disc, causing blunting of villi and malabsorption of fats. The history of **swimming in contaminated water** (lakes, streams, or pools) is a high-yield risk factor, as Giardia cysts are resistant to standard chlorine levels [1]. **Why the other options are incorrect:** * **Naegleria fowleri:** Known as the "brain-eating amoeba," it is also associated with contaminated water but causes Primary Amoebic Meningoencephalitis (PAM), not gastrointestinal symptoms. * **Amoeba (Entamoeba histolytica):** Causes amoebic dysentery characterized by bloody stools (haematochezia) and flask-shaped ulcers. It does not typically cause steatorrhea [2]. * **Shigella:** A bacterial cause of inflammatory diarrhea (dysentery). It presents with high fever, tenesmus, and stools containing blood and mucus, rather than foul-smelling, fatty stools. **High-Yield Clinical Pearls for NEET-PG:** * **Site of infection:** Primarily the **Duodenum** and upper Jejunum (Giardia "likes" the alkaline environment) [1]. * **Diagnosis:** Stool microscopy (cysts or pear-shaped trophozoites with "falling leaf" motility). **Entero-test (String test)** can be used if stool samples are negative. * **Drug of Choice:** **Tinidazole** (preferred over Metronidazole due to single-dose efficacy). * **Common Association:** Increased incidence in patients with **IgA deficiency**.

Q: A stool sample from a patient shows ova. How do humans typically acquire this parasitic infection?

Ingestion of contaminated food or water. ***Ingestion of contaminated food or water*** - Most intestinal parasites like **Ascaris lumbricoides** are transmitted through the **fecal-oral route** via contaminated food, water, or soil. - The parasite's **ova** survive in the environment and are ingested, leading to infection when they hatch in the intestine. *Working in contaminated water sources* - This route is specific for **Schistosoma** species, which penetrate through the **skin** during water contact. - **Ascaris** and most intestinal helminths do not infect through skin penetration but require oral ingestion. *Consumption of improperly cooked beef* - This describes the transmission of **Taenia saginata** (beef tapeworm), which requires ingestion of **cysticerci** in raw/undercooked beef. - **Ascaris** does not have an intermediate host and is transmitted directly through ingestion of embryonated eggs. *Direct contact with an infected individual* - This route is characteristic of **Enterobius vermicularis** (pinworm), which spreads through **perianal-oral** transmission. - **Ascaris** transmission does not occur through direct person-to-person contact but requires environmental contamination.

Q: A 35-year-old male presented with gross hematuria, with similar episodes occurring in the past 6 months. There was no history of fever, pain, or burning on urination, weight loss, or increased sense of urgency to void. There was no history of exposure to toxins either at work or during recreational activities. The patient underwent fiberoptic cystoscopy, and a mass was noted in the fundus of the bladder. Biopsy of the mass is shown in the figure. What is the drug of choice for the likely cause?

Praziquantel. ***Praziquantel*** - **Painless gross hematuria** with bladder mass in an endemic area strongly suggests **Schistosoma haematobium** infection, for which **praziquantel** is the drug of choice. - Praziquantel is effective against all **schistosoma species** and causes paralysis of the parasites by increasing calcium permeability. *Albendazole* - Primarily used for **intestinal nematodes** like roundworm, hookworm, and whipworm, not effective against **schistosomiasis**. - Works by inhibiting **microtubule formation** in helminths, but has no activity against **trematodes** like Schistosoma. *Mebendazole* - Another **benzimidazole anthelmintic** used for intestinal nematodes, particularly **pinworm** and **roundworm** infections. - Like albendazole, it lacks efficacy against **blood flukes** and would not treat the underlying **schistosomiasis**. *Triclabendazole* - Specifically indicated for **Fasciola hepatica** (liver fluke) infections, not for **urogenital schistosomiasis**. - While it's a **benzimidazole derivative**, its spectrum does not include **Schistosoma haematobium** which causes bladder pathology.

Q: The man-snail-crab life cycle is characteristic of which parasite?

Paragonimus westermanii. **Explanation:** The correct answer is **Paragonimus westermanii** (the Oriental Lung Fluke). This parasite follows a complex life cycle involving two intermediate hosts: 1. **First Intermediate Host:** Freshwater snails (e.g., *Semisulcospira* spp.). 2. **Second Intermediate Host:** Crustaceans like **crabs** or crayfish. Infection occurs in humans (definitive host) upon consuming raw or undercooked crab meat containing **metacercariae**. Once ingested, the larvae excyst in the duodenum, penetrate the intestinal wall, and migrate through the diaphragm to the lungs. **Analysis of Incorrect Options:** * **Fasciola hepatica (Liver fluke):** The life cycle involves a snail, but the infective metacercariae are found encysted on **aquatic vegetation** (e.g., watercress), not crabs. * **Schistosoma mansoni (Blood fluke):** This parasite has only one intermediate host (snail). Infection occurs via direct **cercarial skin penetration** while swimming in infested water; there is no second intermediate host. * **Echinococcus granulosus (Dog tapeworm):** The cycle involves dogs (definitive host) and sheep/cattle (intermediate host). Humans are accidental intermediate hosts. It does not involve snails or crabs. **NEET-PG High-Yield Pearls:** * **Clinical Presentation:** Mimics Tuberculosis (chronic cough, hemoptysis, and night sweats). * **Diagnosis:** Presence of "golden-brown," operculated eggs in **sputum** or feces. * **Chest X-ray:** May show "ring shadows" or infiltrates. * **Drug of Choice:** Praziquantel.

Q: Babesiosis is transmitted by the bite of which arthropod?

Tick. **Explanation:** **Babesiosis** is a malaria-like parasitic disease caused by protozoa of the genus *Babesia* (most commonly *Babesia microti*). It is a zoonotic infection primarily transmitted by the bite of the **Ixodes scapularis tick** (also known as the black-legged tick or deer tick). This tick is the same vector responsible for transmitting Lyme disease and Anaplasmosis, often leading to co-infections. **Why the other options are incorrect:** * **Mosquito:** Vectors for Malaria (*Plasmodium*), Filariasis, and various viral fevers (Dengue, Zika), but not Babesiosis. * **Sandfly:** The vector for Leishmaniasis (Kala-azar). * **Reduviid bug:** Also known as the "kissing bug," it transmits *Trypanosoma cruzi*, the causative agent of Chagas disease. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** In a peripheral blood smear, *Babesia* appears as pleomorphic ring forms. A pathognomonic feature is the **"Maltese Cross" appearance** (tetrads formed by four daughter cells), which distinguishes it from *Plasmodium falciparum*. * **Clinical Presentation:** It causes hemolytic anemia and hemoglobinuria. It is particularly severe or fatal in **asplenic patients**, as the spleen is responsible for clearing infected erythrocytes. * **Diagnosis:** Giemsa-stained thick and thin peripheral smears are the gold standard. * **Treatment:** The preferred regimen is a combination of **Atovaquone and Azithromycin** (unlike Malaria, which uses Chloroquine/Artemisinin).

Q: Which of the following inhibits digestion in the intestinal mucosa?

Giardia lamblia. **Explanation:** **Giardia lamblia** is the correct answer because it causes malabsorption by physically and biochemically interfering with the intestinal mucosa. The trophozoites attach to the duodenal and jejunal mucosa using a ventral sucking disc. This attachment, combined with the "carpeting" effect of high parasitic loads, leads to the **blunting of microvilli** and the **inhibition of brush border enzymes** (such as disaccharidases). This disruption inhibits the final stages of digestion and absorption, resulting in characteristic foul-smelling, fatty stools (steatorrhea). **Analysis of Incorrect Options:** * **Vibrio cholerae:** Causes secretory diarrhea via the cholera toxin, which increases cAMP levels. It leads to massive water and electrolyte loss but does not primarily inhibit the digestion of nutrients or damage the brush border enzymes. * **Enterokinase:** This is a physiological enzyme (not a pathogen) produced by the duodenum that converts trypsinogen to trypsin. It is essential *for* digestion, not an inhibitor of it. * **Schistosoma haematobium:** This is a blood fluke that primarily affects the venous plexus of the urinary bladder, leading to hematuria. It does not inhabit the intestinal mucosa or interfere with digestion. **NEET-PG High-Yield Pearls:** * **Habitat:** Duodenum and upper jejunum (acidic environment). * **Diagnosis:** Stool microscopy shows "falling leaf" motility (trophozoites) or cysts. String test (Entero-test) can be used for sampling. * **Antigen Detection:** Immunochromatographic assays for Giardia-specific antigen (GSA 65) are highly sensitive. * **Drug of Choice:** Tinidazole or Metronidazole. * **Association:** Common in patients with IgA deficiency.

Question 1

What is true about the peripheral blood smear of Plasmodium vivax?

Accepted Answer

Single ring with cytoplasm condensed around in each erythrocyte.

Answer

Mature or old erythrocytes are affected.

Answer

Parasitized erythrocytes are of the same size as normal erythrocytes.

Answer

Only ring and gametocytes are seen.

Question 2

Which of the following parasitic infections is associated with Salmonella?

Accepted Answer

Schistosoma hematobium

Answer

Paragonimus

Answer

Taenia solium

Answer

Hymenolepis nana

Question 3

A girl complained of abdominal pain with the passage of foul-smelling stool that does not wash away easily. There is a history of swimming in contaminated water. What is the likely causative organism?

Accepted Answer

Giardia lamblia

Answer

Naegleria

Answer

Amoeba

Answer

Shigella

Question 4

A stool sample from a patient shows ova. How do humans typically acquire this parasitic infection?

Accepted Answer

Ingestion of contaminated food or water

Answer

Working in contaminated water sources

Answer

Consumption of improperly cooked beef

Answer

Direct contact with an infected individual

Question 5

A 35-year-old male presented with gross hematuria, with similar episodes occurring in the past 6 months. There was no history of fever, pain, or burning on urination, weight loss, or increased sense of urgency to void. There was no history of exposure to toxins either at work or during recreational activities. The patient underwent fiberoptic cystoscopy, and a mass was noted in the fundus of the bladder. Biopsy of the mass is shown in the figure. What is the drug of choice for the likely cause?

Accepted Answer

Praziquantel

Answer

Albendazole

Answer

Mebendazole

Answer

Triclabendazole

Question 6

The man-snail-crab life cycle is characteristic of which parasite?

Accepted Answer

Paragonimus westermanii

Answer

Fasciola hepatica

Answer

Schistosoma mansoni

Answer

Echinococcus granulosus

Question 7

Which of the following is NOT true about Plasmodium falciparum?

Accepted Answer

The parasitic burden can be estimated by peripheral parasitemia.

Answer

The duration of the erythrocytic cycle is 48 hours.

Answer

An exo-erythrocytic phase is absent.

Answer

It causes rosette formation.

Question 8

Babesiosis is transmitted by the bite of which arthropod?

Accepted Answer

Tick

Answer

Mosquito

Answer

Sandfly

Answer

Reduviid bug

Question 9

Which of the following inhibits digestion in the intestinal mucosa?

Accepted Answer

Giardia lamblia

Answer

Vibrio cholerae

Answer

Enterokinase

Answer

Schistosoma haematobium

Question 10

Which of the following is NOT a cause of malabsorption?

Accepted Answer

Ascariasis

Answer

Giardia lamblia

Answer

Mycobacterium avium-intracellulare

Answer

Microsporidium

Parasitology — MCQs

Parasitology — MCQs

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