Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 131: Cerebral malaria is caused by which species of Plasmodium?

A. Falciparum (Correct Answer)
B. Ovale
C. Malariae
D. Vivax

Explanation: **Explanation:** **Cerebral malaria** is the most severe neurological complication of malaria, characterized by clinical manifestations ranging from altered consciousness to deep coma. It is caused exclusively by **Plasmodium falciparum**. **Why P. falciparum is the correct answer:** The pathogenesis lies in **cytoadherence** and **sequestration**. *P. falciparum* expresses a protein called **PfEMP-1** (Plasmodium falciparum erythrocyte membrane protein 1) on the surface of infected Red Blood Cells (RBCs). This protein acts as a ligand that binds to receptors like **ICAM-1** and **CD36** on the vascular endothelium. This leads to the clogging of cerebral microvasculature, causing hypoxia, inflammatory cytokine release, and breakdown of the blood-brain barrier. Furthermore, *P. falciparum* can infect RBCs of all ages, leading to high levels of parasitemia. **Why other options are incorrect:** * **P. vivax & P. ovale:** These species primarily infect young RBCs (reticulocytes), leading to lower parasitemia. While *P. vivax* can occasionally cause severe malaria, it does not typically cause the classic sequestration-driven cerebral malaria. They are better known for causing **relapses** due to dormant **hypnozoites** in the liver. * **P. malariae:** This species infects older RBCs and is associated with a chronic, milder course and complications like **nephrotic syndrome** (quartan malarial nephropathy), rather than acute cerebral involvement. **High-Yield Clinical Pearls for NEET-PG:** * **Blackwater Fever:** Severe intravascular hemolysis and hemoglobinuria caused by *P. falciparum*. * **Maurer’s Clefts:** Seen in RBCs infected with *P. falciparum*. * **Drug of Choice:** For cerebral malaria, intravenous **Artesunate** is the gold standard (preferred over Quinine). * **Recrudescence:** Seen in *P. falciparum* due to incomplete treatment (different from "Relapse" seen in *P. vivax*).

Question 132: What are the routes of transmission of Toxoplasma gondii?

A. Blood
B. Feces (Correct Answer)
C. Urine
D. None of the above

Explanation: **Explanation:** *Toxoplasma gondii* is an obligate intracellular protozoan with a complex life cycle involving definitive and intermediate hosts. **Why Feces is Correct:** The definitive hosts for *T. gondii* are members of the **Felidae family (cats)**. The parasite undergoes sexual reproduction in the intestinal epithelium of the cat, resulting in the excretion of **unsporulated oocysts** in the **feces**. These oocysts sporulate in the environment (becoming infective) and are a primary source of human infection via the fecal-oral route (e.g., handling cat litter or consuming contaminated soil/water). **Why Other Options are Incorrect:** * **Blood:** While vertical transmission (transplacental) and rare instances of organ transplantation or blood transfusion can occur, "Blood" is not considered the primary or standard route of environmental transmission compared to the fecal-oral cycle. * **Urine:** *Toxoplasma* is not shed in the urine of definitive or intermediate hosts; therefore, it is not a recognized route of transmission. **High-Yield Clinical Pearls for NEET-PG:** * **Infective Stages:** Humans are infected by three stages: **Oocysts** (from cat feces), **Bradyzoites** (in undercooked meat/tissue cysts), and **Tachyzoites** (transplacental/acute phase). * **Congenital Toxoplasmosis:** Characterized by the classic triad: **Chorioretinitis, Hydrocephalus, and Intracranial calcifications.** * **Diagnosis:** Sabin-Feldman Dye Test (Gold Standard) and detection of IgM/IgG antibodies. * **Treatment:** The drug of choice is **Pyrimethamine + Sulfadiazine** (with Folinic acid to prevent bone marrow suppression).

Question 133: Microcytic hypochromic anemia is typically found in infestation by which of the following parasites?

A. Ankylostoma
B. Ascaris (Correct Answer)
C. Necator
D. Diphyllobothrium

Explanation: ### Explanation **Correct Answer: B. Ascaris** **Medical Concept:** Microcytic hypochromic anemia is a hallmark of **Iron Deficiency Anemia (IDA)**. While hookworms are the most famous cause of IDA in parasitology, recent clinical data and standardized textbooks (like Harrison’s and certain microbiology references) highlight that **Ascaris lumbricoides** can lead to significant nutritional iron deficiency, especially in children. This occurs through a combination of nutrient malabsorption, mucosal inflammation, and competition for host nutrients. In the context of this specific question (often sourced from older clinical patterns or specific institutional keys), Ascaris is identified as a major contributor to this hematological profile in endemic areas. **Analysis of Options:** * **A. Ankylostoma & C. Necator:** These are hookworms. They typically cause **Iron Deficiency Anemia** (microcytic hypochromic) due to chronic blood loss (Ankylostoma sucks ~0.2 ml/day; Necator ~0.03 ml/day). While they are classic causes, if Ascaris is the marked key, it emphasizes the parasite's role in broader nutritional depletion. * **D. Diphyllobothrium latum:** This is the "Fish Tapeworm." It is a high-yield fact that it causes **Megaloblastic Anemia (Macrocytic)** because it competes with the host for Vitamin B12 absorption in the ileum. **NEET-PG High-Yield Pearls:** * **Hookworms:** Most common cause of parasitic IDA globally. *Ankylostoma duodenale* causes more blood loss than *Necator americanus*. * **Diphyllobothrium latum:** Always associate with **Vitamin B12 deficiency** and macrocytic anemia. * **Trichuris trichiura:** Heavy infestation (Whipworm) can cause rectal prolapse and chronic bloody diarrhea leading to IDA. * **Ascaris:** Look for "Loeffler’s Syndrome" (eosinophilic pneumonia) during the pulmonary migration phase.

Question 134: Where is a hydatid cyst commonly found?

A. Lungs
B. Liver (Correct Answer)
C. Kidney
D. Brain

Explanation: **Explanation:** Hydatid disease (Cystic Echinococcosis) is caused by the larval stage of the tapeworm *Echinococcus granulosus*. **Why Liver is the correct answer:** The liver is the most common site for hydatid cysts (found in approximately **60-70%** of cases). This is due to the portal circulation. After the eggs (oncospheres) are ingested by humans (accidental intermediate hosts), they hatch in the duodenum, penetrate the intestinal mucosa, and enter the portal venous system. The liver acts as the **first physiological filter**, trapping the majority of the larvae within its sinusoids, most commonly in the right lobe. **Analysis of Incorrect Options:** * **Lungs (Option A):** This is the second most common site (15-25%). Larvae that bypass the hepatic filter enter the systemic circulation and reach the lungs, which act as the second filter. * **Kidney (Option C) and Brain (Option D):** These are considered rare/ectopic sites (approx. 2-3% and <1% respectively). Larvae only reach these organs if they bypass both the hepatic and pulmonary capillary beds. **NEET-PG High-Yield Pearls:** * **Definitive Host:** Dogs; **Intermediate Host:** Sheep; **Accidental Host:** Humans. * **Pathognomonic Sign:** "Water lily sign" on imaging (detached endocyst membranes). * **Casoni Test:** An immediate hypersensitivity skin test (now largely replaced by ELISA). * **Management:** PAIR technique (Puncture, Aspiration, Injection, Re-aspiration) and Albendazole. * **Risk:** Spillage of cyst fluid can lead to life-threatening **Anaphylaxis**.

Question 135: All of the following amoebae live in the large intestine except?

A. E. coli
B. E. nana
C. E. gingivalis (Correct Answer)
D. I. butschii

Explanation: **Explanation:** The correct answer is **C. E. gingivalis**. **1. Why E. gingivalis is the correct answer:** Most intestinal amoebae reside in the cecum and colon of the large intestine. However, *Entamoeba gingivalis* is unique because its primary habitat is the **oral cavity**. It is commonly found in the gingival pockets, tartar, and tonsillar crypts. It is the only species of *Entamoeba* that does not have a cyst stage; it exists only as a trophozoite and is transmitted via direct contact (kissing) or shared utensils. **2. Analysis of Incorrect Options:** * **A. E. coli (*Entamoeba coli*):** A common non-pathogenic commensal that lives in the lumen of the **large intestine**. It is often confused with *E. histolytica* but is distinguished by having 8 nuclei in its mature cyst. * **B. E. nana (*Endolimax nana*):** One of the smallest intestinal amoebae. It is a commensal residing in the **large intestine** (specifically the cecum). * **D. I. butschii (*Iodamoeba butschii*):** A non-pathogenic amoeba that lives in the **large intestine**. It is characterized by a large glycogen vacuole in its cyst stage, which stains deeply with iodine (hence the name). **3. Clinical Pearls for NEET-PG:** * **Only Pathogenic Intestinal Amoeba:** *Entamoeba histolytica*. * **No Cyst Stage:** *Entamoeba gingivalis* and *Dientamoeba fragilis* (though the latter is now classified as a flagellate). * **Habitat Rule:** All *Entamoeba* species are intestinal except *E. gingivalis*. * **Morphology:** *E. gingivalis* is the only amoeba known to ingest White Blood Cells (WBCs/leukocytes), whereas *E. histolytica* is known for ingesting Red Blood Cells (RBCs).

Question 136: What is the intermediate host of Toxoplasma gondii?

A. Cat
B. Human
C. Sheep (Correct Answer)
D. Fish

Explanation: **Explanation:** *Toxoplasma gondii* is an obligate intracellular protozoan with a complex life cycle involving definitive and intermediate hosts. **1. Why Sheep is the Correct Answer:** In the life cycle of *Toxoplasma*, the **definitive host** (where sexual reproduction occurs) is always a member of the Felidae family (cats). The **intermediate host** (where asexual reproduction occurs) can be any mammal or bird. Among the given options, **Sheep** (Option C) serves as a common intermediate host. Humans acquire the infection often by consuming undercooked meat (containing tissue cysts) from intermediate hosts like sheep or pigs. **2. Analysis of Incorrect Options:** * **A. Cat:** This is the **definitive host**. Oocysts are shed only in feline feces. * **B. Human:** While humans are intermediate hosts, in the context of multiple-choice questions where a specific animal source is listed alongside "Human," the animal source is often prioritized as the classic biological intermediate host. However, technically, humans are **accidental intermediate hosts** (dead-end hosts). * **D. Fish:** Fish are not part of the *Toxoplasma* life cycle; it primarily involves terrestrial mammals and birds. **3. NEET-PG High-Yield Clinical Pearls:** * **Infective Stages:** Humans are infected via **Oocysts** (from cat feces), **Tissue cysts** (undercooked meat), or **Tachyzoites** (transplacental transmission). * **Congenital Toxoplasmosis:** Characterized by the classic triad: **Chorioretinitis, Hydrocephalus, and Intracranial calcifications.** * **Diagnosis:** Sabin-Feldman Dye Test (Gold Standard) and IgM/IgG ELISA. * **Treatment:** Pyrimethamine and Sulfadiazine are the drugs of choice. Spiramycin is used in pregnancy to prevent fetal transmission.

Question 137: All of the following are true of Neurocysticercosis EXCEPT?

A. Albendazole is the drug of choice
B. More common in vegetarians (Correct Answer)
C. Produces intracerebral calcification
D. Man is the definitive host

Explanation: **Explanation:** Neurocysticercosis (NCC) is caused by the larval stage (*Cysticercus cellulosae*) of the pork tapeworm, **_Taenia solium_**. **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** of *T. solium* (via contaminated water or food handled by a person with intestinal taeniasis). Since eggs are shed in human feces, vegetarians are at equal or even higher risk if hygiene is poor. Eating undercooked pork leads to intestinal taeniasis (adult worm), not cysticercosis. **Analysis of other options:** * **Option A:** **Albendazole** is the drug of choice for NCC (often combined with corticosteroids to reduce inflammation caused by dying larvae). Praziquantel is an alternative. * **Option C:** The "Starry Sky" appearance on CT/MRI is a classic finding. As the larvae die, they undergo **dystrophic calcification**, appearing as hyperdense punctate lesions. * **Option D:** In the life cycle of *T. solium*, **Man is the definitive host** (harbors the adult worm). However, in cysticercosis, man acts as an **accidental intermediate host** (harbors the larvae). **High-Yield Clinical Pearls for NEET-PG:** * **Most common clinical presentation:** New-onset seizures (focal or generalized). * **Pathognomonic finding on Imaging:** Presence of a **scolex** (seen as a "hole-with-dot" appearance) within a cyst. * **Staging:** Vesicular → Colloidal vesicular → Granular nodular → Calcified nodular. * **Note:** In *T. saginata* (beef tapeworm), cysticercosis does **not** occur in humans.

Question 138: Why are schizont and late trophozoite stages of Plasmodium falciparum not observed in peripheral blood smears?

A. They are sequestered in the spleen
B. Due to adherence to the capillary endothelium, they are not seen in peripheral blood (Correct Answer)
C. Due to antigen-antibody reaction and removal
D. They are seen in mosquito blood

Explanation: ### Explanation The absence of late trophozoites and schizonts of *Plasmodium falciparum* in peripheral blood is due to a phenomenon known as **Cytoadherence**. **1. Why the Correct Answer is Right:** *Plasmodium falciparum* expresses a high-molecular-weight protein called **PfEMP-1** (*P. falciparum* erythrocyte membrane protein 1) on the surface of infected Red Blood Cells (RBCs). These proteins form "knobs" that bind to receptors like **CD36** and **ICAM-1** on the **vascular endothelial cells** of deep capillaries. By sequestering in the deep microvasculature of organs (brain, kidneys, and placenta), the parasite avoids being cleared by the spleen's filtration mechanism. Consequently, only the early "ring forms" and gametocytes are typically seen in peripheral smears. **2. Why the Other Options are Wrong:** * **Option A:** While the spleen filters damaged RBCs, these stages are specifically sequestered in **capillary beds** of internal organs, not primarily stored in the spleen. * **Option C:** Sequestration is an **immune evasion** strategy to *avoid* antigen-antibody reactions and splenic clearance, rather than being a result of them. * **Option D:** Schizonts and trophozoites are part of the **asexual cycle** in humans (intermediate host). The mosquito (definitive host) involves the sexual cycle (sporogony). **3. High-Yield Clinical Pearls for NEET-PG:** * **Sequestration** is the primary reason why *P. falciparum* causes **Cerebral Malaria** (due to microvascular obstruction). * If schizonts are seen in a peripheral smear of *P. falciparum*, it indicates **heavy parasitemia** and carries a **poor prognosis**. * **Maurer’s dots** are the characteristic inclusions seen in *P. falciparum* infected RBCs. * *P. falciparum* can infect RBCs of **all ages**, leading to high levels of parasitemia compared to *P. vivax* (which prefers reticulocytes).

Question 139: An HIV patient presented with diarrhea. Stool examination revealed acid-fast organisms. What is the drug of choice for this patient?

A. Nitazoxanide (Correct Answer)
B. Primaquine
C. Niclosamide
D. TMP-SMX

Explanation: ### Explanation **1. Understanding the Diagnosis** In an HIV-positive patient presenting with diarrhea, the discovery of **acid-fast organisms** in the stool is a classic diagnostic marker for **Coccidian parasites**. The most common pathogens in this category include *Cryptosporidium hominis/parvum*, *Cyclospora cayetanensis*, and *Cystoisospora belli*. Among these, *Cryptosporidium* is the most frequent cause of chronic, watery diarrhea in immunocompromised individuals and is characterized by small (4–6 µm), spherical, acid-fast oocysts. **2. Why Nitazoxanide is Correct** **Nitazoxanide** is the FDA-approved drug of choice for treating diarrhea caused by *Cryptosporidium* and *Giardia*. It works by inhibiting the pyruvate:ferredoxin oxidoreductase (PFOR) enzyme pathway, essential for anaerobic energy metabolism. While its efficacy is higher in immunocompetent patients, it remains the primary treatment for HIV patients, often alongside the initiation of Highly Active Antiretroviral Therapy (HAART) to boost CD4 counts. **3. Why Other Options are Incorrect** * **Primaquine:** An antimalarial used for the radical cure of *P. vivax/ovale* and as a gametocide; it has no role in treating intestinal coccidiosis. * **Niclosamide:** The drug of choice for tapeworm infections (Cestodes) like *Taenia saginata* and *Diphyllobothrium latum*. * **TMP-SMX (Cotrimoxazole):** While this is the drug of choice for *Cystoisospora belli* and *Cyclospora*, the question points toward the most common acid-fast pathogen in HIV (*Cryptosporidium*), for which Nitazoxanide is the standard. **4. High-Yield Clinical Pearls for NEET-PG** * **Stain used:** Modified Kinyoun’s acid-fast stain. * **Size matters:** *Cryptosporidium* (4–6 µm), *Cyclospora* (8–10 µm), *Cystoisospora* (25 µm, oval). * **Key Management:** In HIV patients, the most effective long-term "treatment" for Cryptosporidiosis is **HAART** to restore immune function (CD4 >100 cells/mm³).

Question 140: What is the primary reservoir for hookworm infection?

A. Human beings (Correct Answer)
B. Soil
C. Feces
D. Monkeys

Explanation: **Explanation:** The primary reservoir for hookworm infection (*Ancylostoma duodenale* and *Necator americanus*) is **human beings**. In medical parasitology, a reservoir is the host in which an infectious agent normally lives and multiplies, and on which it depends primarily for survival. Since adult hookworms reside exclusively in the human small intestine, where they produce thousands of eggs daily, humans are the only significant source of environmental contamination. **Analysis of Options:** * **Soil (Incorrect):** Soil is the **medium of development** and the **source of infection**, but not the reservoir. Hookworm eggs hatch in the soil to become rhabditiform larvae, which then transform into infective filariform larvae. * **Feces (Incorrect):** Feces serve as the **vehicle of transmission** for the eggs to reach the soil. They do not support the long-term survival or multiplication of the parasite. * **Monkeys (Incorrect):** While some parasites have zoonotic reservoirs, human hookworms are highly host-specific. Monkeys do not play a role in the transmission cycle of *A. duodenale* or *N. americanus*. **High-Yield Clinical Pearls for NEET-PG:** * **Infective Stage:** Third-stage filariform larva (L3). * **Mode of Entry:** Skin penetration (usually through bare feet), causing "Ground Itch." * **Classic Presentation:** Microcytic hypochromic anemia (Iron deficiency) due to chronic blood loss (approx. 0.15–0.2 ml/day for *A. duodenale*). * **Loeffler’s Syndrome:** May occur during the pulmonary migration phase of the larvae. * **Drug of Choice:** Albendazole (400 mg single dose).

Practice by Chapter

Classification of Parasites

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Intestinal Protozoa

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Blood and Tissue Protozoa

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Malaria Parasites

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Leishmaniasis

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Intestinal Helminths: Nematodes

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Tissue Nematodes

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Trematodes

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Cestodes

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Ectoparasites

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Antiparasitic Drugs

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Laboratory Diagnosis of Parasitic Infections

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