Parasitology Practice Questions

Q: Wakana disease is caused by which of the following parasites?

Ancylostoma duodenale. **Explanation:** **Wakana Disease** is a specific clinical manifestation associated with **Ancylostoma duodenale**. It occurs when a large number of infective larvae (L3) are ingested orally, rather than entering through the skin. This phenomenon was historically documented in Japan among farmers who consumed contaminated green vegetables. 1. **Why Ancylostoma duodenale is correct:** Unlike *Necator americanus*, which primarily infects via the percutaneous route, *Ancylostoma duodenale* can infect humans through **oral ingestion**. When larvae are swallowed, they cause an immediate hypersensitivity reaction in the pharynx and upper gastrointestinal tract. Symptoms include nausea, vomiting, dyspnea, pharyngeal irritation, and cough. 2. **Why other options are incorrect:** * **Necator americanus:** Known as the "New World Hookworm," it lacks the ability to infect effectively via the oral route; it requires skin penetration and a mandatory lung migration phase. * **Strongyloides stercoralis:** While it causes "Larva Currens" (racing larvae) and autoinfection, it is not associated with the specific "Wakana" syndrome. * **Enterobius vermicularis:** This is the pinworm, which causes perianal pruritus but does not migrate through the lungs or cause pharyngeal hypersensitivity. **High-Yield Clinical Pearls for NEET-PG:** * **Hookworm Comparison:** *A. duodenale* has teeth (2 pairs), while *N. americanus* has semilunar cutting plates. * **Ground Itch:** The allergic dermatitis seen at the site of entry during percutaneous infection (more common in *Necator*). * **Loeffler’s Syndrome:** Transient eosinophilic pneumonia occurring during the lung migration phase of hookworms. * **Iron Deficiency Anemia:** The most significant complication of chronic hookworm infection due to blood-sucking (Ancylostoma sucks more blood—approx. 0.2 ml/day—than Necator).

Q: Which of the following organisms is known for its characteristic pear-shaped, flagellated appearance, and is a common cause of pelvic infections?

Trichomonas vaginalis. **Explanation:** **Trichomonas vaginalis** is the correct answer because it is a flagellated protozoan characterized by its unique **pear-shaped (pyriform)** morphology. It possesses four anterior flagella and an undulating membrane, which provides its characteristic **"jerky" motility** seen on a wet mount. It is a major cause of Trichomoniasis, a common sexually transmitted infection (STI) leading to pelvic discomfort and vaginitis. **Analysis of Incorrect Options:** * **Candida albicans:** This is a fungus (yeast). Under the microscope, it appears as budding yeast cells and **pseudohyphae**, not flagellated pear-shaped organisms. It causes "curdy white" discharge. * **Mycoplasma:** These are the smallest free-living bacteria. They lack a cell wall and are pleomorphic, but they do not have flagella or a pear-shaped structure. * **Gardnerella vaginalis:** This is a gram-variable coccobacillus associated with Bacterial Vaginosis. The hallmark microscopic finding is **"Clue cells"** (epithelial cells covered in bacteria), not flagellated protozoa. **NEET-PG High-Yield Pearls:** * **Clinical Presentation:** Characterized by a profuse, **foul-smelling, yellowish-green frothy discharge**. * **Colposcopy Finding:** **"Strawberry Cervix"** (punctate hemorrhages on the ectocervix) is a classic, highly specific sign. * **Diagnosis:** The gold standard is **culture (Whittington’s or Diamond’s medium)**, though wet mount for jerky motility is the most common initial test. * **Treatment:** Drug of choice is **Metronidazole**. Crucially, both partners must be treated simultaneously to prevent reinfection.

Q: Which of the following protozoa lacks a cyst stage in its life cycle?

Dientamoeba fragilis. ### Explanation **Correct Answer: A. Dientamoeba fragilis** **1. Why Dientamoeba fragilis is the correct answer:** In medical parasitology, most intestinal protozoa follow a life cycle involving two stages: the **Trophozoite** (motile, feeding, pathogenic stage) and the **Cyst** (non-motile, resistant, infective stage). However, *Dientamoeba fragilis* is a notable exception. It exists **only in the trophozoite stage** and does not form cysts. Because it lacks a protective cyst wall, the trophozoite is fragile and easily destroyed by gastric acid. It is hypothesized that *D. fragilis* may be transmitted via the eggs of helminths like *Enterobius vermicularis* (Pinworm), acting as a "hitchhiker" to survive the external environment. **2. Why the other options are incorrect:** * **B. Entamoeba coli:** This is a non-pathogenic commensal of the large intestine. It has a well-defined life cycle consisting of trophozoites, precysts, and mature **octanucleate cysts** (containing 8 nuclei), which are the infective forms. * **C. Entamoeba histolytica:** This is the causative agent of amoebiasis. Its life cycle includes a trophozoite stage and a **quadrinucleate cyst** stage. The mature cyst is highly resistant and is the diagnostic and infective stage found in formed stools. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Morphology:** Despite its name, *D. fragilis* is taxonomically classified as a **flagellate** (related to *Trichomonas*), not an amoeba, though it moves using pseudopodia. * **Nuclear Feature:** It typically contains **two nuclei** (hence "*Di*-entamoeba") with fragmented karyosomes. * **Other Protozoa lacking a cyst stage:** * *Trichomonas vaginalis* (transmitted sexually; no need for a resistant environmental stage). * *Entamoeba gingivalis* (found in the mouth). * *Pentatrichomonas hominis*. * **Treatment of choice:** Iodoquinol, Paromomycin, or Metronidazole.

Q: A patient was being treated with a drug that interferes with the activity of the enzyme pyruvate ferredoxin oxidoreductase. Which of the following is the most likely organism causing infection in this patient?

Cryptosporidium species. ### Explanation **Correct Answer: C. Cryptosporidium species** The enzyme **Pyruvate Ferredoxin Oxidoreductase (PFOR)** is a critical component of the anaerobic metabolic pathway. It catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA. This enzyme is the primary target of **Nitoxanide**, which is the drug of choice for treating infections caused by *Cryptosporidium parvum* and *Giardia lamblia*. Nitoxanide acts as an antiprotozoal by inhibiting PFOR, thereby disrupting the energy metabolism of the parasite. **Analysis of Incorrect Options:** * **A. Taenia saginata (Cestode):** The drug of choice is Praziquantel, which works by increasing calcium permeability of the parasite's tegument, leading to paralysis. * **B. Trichuris trichiura (Nematode):** Treated with Benzimidazoles (e.g., Albendazole/Mebendazole), which inhibit microtubule synthesis by binding to beta-tubulin. * **D. Trypanosoma species (Hemoflagellate):** Treatment depends on the species and stage (e.g., Nifurtimox, Benznidazole, or Suramin). These drugs do not primarily target the PFOR enzyme. **NEET-PG Clinical Pearls:** * **Nitoxanide** is a broad-spectrum antiparasitic used for *Cryptosporidium* in both immunocompetent and pediatric patients. * **PFOR** is also the target for **Metronidazole**; however, Metronidazole requires PFOR to reduce its nitro group into a toxic free radical. In contrast, Nitoxanide directly inhibits the enzyme's activity. * *Cryptosporidium* is a major cause of chronic, life-threatening diarrhea in **HIV/AIDS patients** (CD4 count <200 cells/mm³). * Diagnosis of *Cryptosporidium* is typically made using **Modified Acid-Fast staining** (showing red-pink oocysts).

Q: Which of the following microfilariae lacks nuclei extending to the tail tip?

Wuchereria bancrofti. ### Explanation The identification of microfilariae in peripheral blood smears is a high-yield topic for NEET-PG, primarily based on two morphological features: the presence of an **enveloping sheath** and the **distribution of nuclei in the tail**. **1. Why Wuchereria bancrofti is correct:** *Wuchereria bancrofti* is a sheathed microfilaria. Its most distinguishing feature under the microscope is that its **nuclei do not extend to the tip of the tail**. The terminal portion of the tail is empty (column of nuclei ends abruptly before the tip), which helps differentiate it from other filarial worms. **2. Analysis of Incorrect Options:** * **Loa loa (African Eye Worm):** It is sheathed, but unlike *W. bancrofti*, its **nuclei extend in a continuous row to the very tip** of the tail. * **Mansonella perstans:** This is an unsheathed microfilaria. Its **nuclei extend to the tip** of the tail, which is blunt. * **Brugia malayi:** It is sheathed but characterized by having **two distinct, terminal nuclei** that are separated from the main column of nuclei (sub-terminal and terminal nuclei). **3. High-Yield Clinical Pearls for NEET-PG:** * **Sheathed Microfilariae:** *W. bancrofti, B. malayi, Loa loa.* * **Unsheathed Microfilariae:** *Mansonella* species, *Onchocerca volvulus.* * **No Nuclei at Tail Tip:** Only *Wuchereria bancrofti*. * **Nocturnal Periodicity:** *W. bancrofti* and *B. malayi* (sampled between 10 PM – 2 AM). * **Diurnal Periodicity:** *Loa loa* (sampled during the day). * **Drug of Choice:** Diethylcarbamazine (DEC) is the standard treatment for most, except *Onchocerca* (where Ivermectin is preferred).

Q: What is the average blood loss in ankylostomiasis per worm per day?

0.15 - 0.25 ml/day. **Explanation:** Ankylostomiasis (Hookworm infection) is a leading cause of iron-deficiency anemia in tropical regions. The blood loss occurs because the adult worms attach to the small intestinal mucosa using their buccal capsules, secreting anticoagulants (like factor Xa inhibitors) to facilitate continuous feeding. **Why Option D is Correct:** The amount of blood loss depends specifically on the species of hookworm. For ***Ancylostoma duodenale*** (Old World hookworm), the average blood loss is **0.15 to 0.25 ml per worm per day**. This species is more pathogenic than *Necator americanus* because it has teeth (rather than cutting plates) and consumes significantly more blood. **Analysis of Incorrect Options:** * **Option A (0.2 - 0.3 ml/day):** This is slightly higher than the standard range cited in major textbooks like Paniker’s Parasitology. * **Option B (2 - 4 ml/day):** This is an extreme overestimate. Such loss would lead to rapid exsanguination and death in heavy infections. * **Option C (0.33 - 1 ml/day):** This range is incorrect for human hookworms; however, it is sometimes confused with the higher blood loss seen in certain animal hookworms. **High-Yield Clinical Pearls for NEET-PG:** * ***Necator americanus* blood loss:** Significantly lower, approximately **0.03 to 0.05 ml per worm per day**. * **Anemia type:** Microcytic hypochromic anemia (Iron deficiency). * **Ground Itch:** The allergic reaction at the site of filariform larvae penetration. * **Löffler's Syndrome:** Can occur during the pulmonary migration phase of the larvae. * **Drug of Choice:** Albendazole (400 mg single dose).

Q: A sandfly transmits all of the following diseases EXCEPT?

Relapsing fever. **Explanation:** The correct answer is **Relapsing fever** because it is not transmitted by the sandfly (*Phlebotomus* species). Relapsing fever is caused by *Borrelia* species and is transmitted by either the **body louse** (*Pediculus humanus corporis*), which causes Epidemic Relapsing Fever, or **soft ticks** (*Ornithodoros*), which cause Endemic Relapsing Fever. **Analysis of Options:** * **Oriental sore (Option A):** Also known as Cutaneous Leishmaniasis, it is caused by *Leishmania tropica* and is transmitted by the bite of an infected female sandfly. * **Leishmaniasis (Option B):** This is the umbrella term for diseases caused by *Leishmania* parasites. All forms (Cutaneous, Mucocutaneous, and Visceral) are transmitted via the sandfly vector. * **Kala-azar (Option C):** Also known as Visceral Leishmaniasis, it is caused by *Leishmania donovani*. In India, the specific vector is the sandfly ***Phlebotomus argentipes***. **High-Yield Clinical Pearls for NEET-PG:** * **Sandfly Characteristics:** They are small, moth-like flies that fly in short hops and are nocturnal. Only the **female** sandfly takes a blood meal. * **Other diseases transmitted by Sandfly:** Sandfly fever (Pappataci fever) and Oroya fever (Bartonellosis). * **Infective Stage:** For Leishmaniasis, the sandfly injects the **promastigote** stage into the human host. * **Vector Control:** Sandflies are highly susceptible to DDT residual spraying, which is a mainstay in Kala-azar elimination programs.

Q: Which of the following parasites requires three hosts in its life cycle?

Diphyllobothrium latum. **Explanation:** The correct answer is **Diphyllobothrium latum** (the Fish Tapeworm). This parasite is unique among common human helminths because it requires **three different hosts** to complete its complex life cycle: 1. **First Intermediate Host:** A freshwater crustacean (*Cyclops*), which ingests the ciliated larva (coracidium). 2. **Second Intermediate Host:** Freshwater fish (e.g., pike, trout), which ingest the *Cyclops* and develop the infective **plerocercoid larva**. 3. **Definitive Host:** Humans (or other fish-eating mammals), who ingest undercooked fish containing the plerocercoid larva. **Why the other options are incorrect:** * **Taenia solium (Pork Tapeworm):** Requires **two hosts**—Humans (Definitive) and Pigs (Intermediate). * **Entamoeba histolytica:** Requires only **one host** (Humans). It is a protozoan transmitted via the fecal-oral route (monoxenous life cycle). * **Trichuris trichiura (Whipworm):** Requires only **one host** (Humans). It is a soil-transmitted helminth with no intermediate host. **High-Yield Clinical Pearls for NEET-PG:** * **Vitamin B12 Deficiency:** *D. latum* competes with the host for Vitamin B12 absorption in the jejunum, leading to **Megaloblastic Anemia** (resembling Pernicious Anemia). * **Operculated Eggs:** It is the only human tapeworm that produces operculated eggs (similar to trematodes) and lacks a rostellum/hooks. * **Diagnosis:** Identification of characteristic operculated eggs or proglottids (with a "rosette-shaped" uterus) in stool. * **Treatment:** Praziquantel is the drug of choice.

Question 1

Wakana disease is caused by which of the following parasites?

Accepted Answer

Ancylostoma duodenale

Answer

Necator americanus

Answer

Strongyloides

Answer

Enterobius vermicularis

Question 2

Which of the following organisms is known for its characteristic pear-shaped, flagellated appearance, and is a common cause of pelvic infections?

Accepted Answer

Trichomonas vaginalis

Answer

Candida albicans

Answer

Mycoplasma

Answer

Gardenella

Question 3

Which of the following protozoa lacks a cyst stage in its life cycle?

Accepted Answer

Dientamoeba fragilis

Answer

Entamoeba coli

Answer

Entamoeba histolytica

Answer

All of the above

Question 4

A patient was being treated with a drug that interferes with the activity of the enzyme pyruvate ferredoxin oxidoreductase. Which of the following is the most likely organism causing infection in this patient?

Accepted Answer

Cryptosporidium species

Answer

Taenia saginata (beef tapeworm)

Answer

Trichuris trichiura (whipworm)

Answer

Trypanosoma species

Question 5

An HIV+ patient with a CD4 count of 47 cells/mL presents with diarrhea. Acid-fast oocysts are found in the stool. What is the most likely diagnosis and its typical course?

Accepted Answer

Cryptosporidiosis, which can be unrelenting even with optimal treatment in immunocompromised individuals.

Answer

Cryptosporidiosis, which is usually self-limiting and requires no treatment.

Answer

Cystoisosporiasis, which should resolve in 3-6 days with appropriate antibiotic therapy.

Answer

Toxoplasmosis, which will only resolve with antituberculous drugs and may take weeks.

Question 6

Which of the following microfilariae lacks nuclei extending to the tail tip?

Accepted Answer

Wuchereria bancrofti

Answer

Loa loa

Answer

Mansonella perstans

Answer

Brugia malayi

Question 7

What is the average blood loss in ankylostomiasis per worm per day?

Accepted Answer

0.15 - 0.25 ml/day

Answer

0.2 - 0.3 ml/day

Answer

2 - 4 ml/day

Answer

0.33 - 1 ml/day

Question 8

A sandfly transmits all of the following diseases EXCEPT?

Accepted Answer

Relapsing fever

Answer

Oriental sore

Answer

Leishmaniasis

Answer

Kala-azar

Question 9

Which of the following parasites requires three hosts in its life cycle?

Accepted Answer

Diphyllobothrium latum

Answer

Taenia solium

Answer

Entamoeba histolytica

Answer

Trichuris trichiura

Question 10

Taenia saginata (beef tapeworm) causes less serious infection than Taenia solium (pork tapeworm) because:

Accepted Answer

Unlike T. saginata, T. solium produces neurocysticercosis, which results in serious lesions in humans due to toxic byproducts formed.

Answer

Acute intestinal blockage is less common in beef tapeworm infection.

Answer

Larval invasion does not occur in beef tapeworm infection.

Answer

The adult beef tapeworms are smaller.

Parasitology — MCQs

Parasitology — MCQs

On this page

Practice by Chapter

Want unlimited practice?