Parasitology Practice Questions

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.

Q: Which of the following is not a cause of lymphatic filariasis?

Loa loa. **Explanation:** Lymphatic filariasis is caused by filarial nematodes that reside in the lymphatic vessels and lymph nodes, leading to obstruction and characteristic clinical features like elephantiasis and hydrocele. **Why Loa loa is the correct answer:** * **Loa loa** (the African eye worm) is the causative agent of **Subcutaneous Filariasis**, not lymphatic filariasis. The adult worms migrate through the subcutaneous tissues, causing transient localized swellings known as **Calabar swellings**. It is also famous for its subconjunctival migration across the eye. **Why the other options are incorrect:** * **Wuchereria bancrofti:** This is the most common cause of lymphatic filariasis worldwide (responsible for ~90% of cases). It primarily affects the lower limbs and genital lymphatics. * **Brugia malayi:** A major cause of lymphatic filariasis in South and Southeast Asia. Unlike *W. bancrofti*, it rarely involves the genitals. * **Brugia timori:** A localized cause of lymphatic filariasis found specifically in the Timor Islands of Indonesia. **High-Yield Clinical Pearls for NEET-PG:** 1. **Vector:** *W. bancrofti* is primarily transmitted by the **Culex** mosquito (in urban areas), while *Brugia* species are often transmitted by **Mansonia** or *Anopheles*. 2. **Diagnosis:** The gold standard is the demonstration of **microfilariae** in a peripheral blood smear. Due to **nocturnal periodicity**, blood collection should ideally occur between **10 PM and 2 AM**. 3. **Drug of Choice:** **Diethylcarbamazine (DEC)** is the mainstay of treatment. However, in areas co-endemic with *Loa loa* or *Onchocerca*, DEC is avoided due to the risk of severe encephalopathy or Mazzotti reaction. 4. **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by nocturnal cough, wheezing, and high peripheral eosinophilia.

Q: Man is the definitive host for which of the following parasites?

Measles. In parasitology, the **definitive host** is defined as the host in which the parasite undergoes its sexual cycle or reaches sexual maturity. **Explanation of the Correct Answer:** While **Measles** is a viral infection and not a parasite, in the context of this specific question (often seen in older NEET-PG/AIIMS patterns), it is the correct choice because humans are the **only natural reservoir and host**. Unlike the other options provided, there is no intermediate host or vector involved in the life cycle of the Measles virus; it is transmitted directly from human to human. **Analysis of Incorrect Options:** * **A. Malaria (*Plasmodium*):** Man is the **Intermediate Host** because only the asexual cycle (Schizogony) occurs in humans. The Female *Anopheles* mosquito is the definitive host (where the sexual cycle/Sporogony occurs). * **B. Filariasis (*Wuchereria bancrofti*):** Man is the **Definitive Host** (adult worms live in lymphatics), but since Measles is a "dead-end" human-only pathogen, it is often prioritized in MCQ logic. However, technically, humans are definitive hosts for Filaria, while mosquitoes are the intermediate hosts. * **D. Tapeworm (*Taenia solium*):** Man is the **Definitive Host** when harboring the adult worm (Taeniasis), but can also be an **Intermediate Host** (Cysticercosis) if eggs are ingested. **NEET-PG High-Yield Pearls:** * **General Rule:** For most protozoa, the mosquito/insect is the definitive host. For most helminths (except *Echinococcus*), man is the definitive host. * **Exception:** In *Echinococcus granulosus* (Hydatid cyst), man is the **Accidental Intermediate Host**, while the dog is the definitive host. * **Toxoplasma gondii:** Man is the intermediate host; the cat is the definitive host.

Q: What is the host receptor for Entamoeba histolytica?

N-acetylglucosamine. **Explanation:** The pathogenesis of *Entamoeba histolytica* depends on its ability to adhere to the host’s colonic mucosa. This attachment is mediated by a specific parasite surface protein called the **Gal/GalNAc lectin**. This lectin binds specifically to **N-acetylglucosamine (GlcNAc)** and N-acetylgalactosamine residues present on the surface of human colonic epithelial cells. Once adhesion is established, the amoeba can initiate tissue destruction through the release of pore-forming proteins (amoebapores) and cysteine proteases, leading to the characteristic "flask-shaped" ulcers. **Analysis of Incorrect Options:** * **Glycophorin A:** This is the primary receptor on human erythrocytes for the EBA-175 protein of *Plasmodium falciparum*. It is crucial for malarial merozoite invasion, not amoebiasis. * **Heparan sulfate:** This glycosaminoglycan serves as a common attachment factor for various viruses (like HSV and HPV) and certain bacteria, but it is not the specific target for *E. histolytica* lectin. * **Asialo-GM1:** This is a ganglioside receptor often associated with the binding of *Pseudomonas aeruginosa* and certain toxins (like *Vibrio cholerae* toxin), but it does not mediate primary *E. histolytica* attachment. **NEET-PG High-Yield Pearls:** * **Virulence Factor:** The Gal/GalNAc lectin is the most important virulence factor for colonization. * **Trophy vs. Cyst:** Only the **trophozoite** form is invasive and possesses these receptors; the cyst is the infective but non-motile stage. * **Diagnostic Clue:** In stool microscopy, the presence of **ingested RBCs (erythrophagocytosis)** within a trophozoite is pathognomonic for *E. histolytica*, distinguishing it from the non-pathogenic *E. dispar*.

Question 1

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 2

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 3

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 4

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 5

A sandfly transmits all of the following diseases EXCEPT?

Accepted Answer

Relapsing fever

Answer

Oriental sore

Answer

Leishmaniasis

Answer

Kala-azar

Question 6

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 7

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.

Question 8

Which of the following is not a cause of lymphatic filariasis?

Accepted Answer

Loa loa

Answer

Wuchereria bancrofti

Answer

Brugia malayi

Answer

Brugia timori

Question 9

Man is the definitive host for which of the following parasites?

Accepted Answer

Measles

Answer

Malaria

Answer

Filariasis

Answer

Tapeworm

Question 10

What is the host receptor for Entamoeba histolytica?

Accepted Answer

N-acetylglucosamine

Answer

Glycophorin A

Answer

Heparan sulfate

Answer

Asialo-GM1

Parasitology — MCQs

Parasitology — MCQs

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