Parasitology — MCQs

Microscopic examination of a thin blood smear from a patient suspected of having malaria reveals numerous normal size erythrocytes without stippling but with ring stages, many with multiple ring stages and applique forms. Several erythrocytes show developing trophozoites that are spread across the erythrocytes in a band fashion. Which of the following is the most likely cause of infection?

Q676Easy

Which of the following is most severely affected in Kala-azar?

Q677Easy

Ascariasis causes which of the following complications?

Q678Easy

Which of the following parasites is known to cause anemia?

Q679Medium

A 20-year-old male goes swimming and after a few days develops diffuse itching with rashes over his body. Several weeks later, he develops lancinating pain down his legs and in all his toes. Within a few days, he develops paraparesis and problems with bowel and bladder control, resulting in urinary retention. What is your initial diagnostic approach for this patient?

Q680Easy

Which of the following parasites is capable of causing autoinfection?

Parasitology Indian Medical PG Practice Questions and MCQs

Question 671: Which of the following organisms presents with an amastigote form?

A. Leishmania (Correct Answer)
B. Plasmodium
C. Babesia
D. Ascaris

Explanation: **Explanation:** The correct answer is **Leishmania**. This organism belongs to the class of Hemoflagellates and exhibits a polymorphic life cycle consisting of two main stages: the **Amastigote** and the **Promastigote**. 1. **Why Leishmania is correct:** In the human host, *Leishmania* exists as an **amastigote** (Leishman-Donovan or LD body). This is a non-flagellated, oval, intracellular form found within the reticuloendothelial cells (macrophages). It is characterized by a nucleus and a kinetoplast. The flagellated form, the promastigote, is found in the sandfly vector (*Phlebotomus*). 2. **Why other options are incorrect:** * **Plasmodium:** This is a sporozoan that causes Malaria. Its life cycle stages include sporozoites, schizonts, merozoites, and gametocytes, but it does not have an amastigote stage. * **Babesia:** An intraerythrocytic protozoan. It typically presents as "Maltese cross" appearances (tetrads) or ring forms within RBCs, mimicking *P. falciparum*, but lacks an amastigote stage. * **Ascaris:** This is a helminth (nematode). Its life cycle involves eggs and larval stages, not protozoan morphological forms like amastigotes. **High-Yield NEET-PG Pearls:** * **Trypanosoma cruzi** (Chagas disease) is the only other major human pathogen that also exhibits an amastigote form (found in cardiac muscle). *Trypanosoma brucei* does NOT have an amastigote stage. * **Infective stage of Leishmania:** Promastigote (injected by sandfly). * **Diagnostic stage of Leishmania:** Amastigote (seen on splenic or bone marrow aspirate smears). * **Culture:** *Leishmania* is grown on **NNN (Novy-MacNeal-Nicolle) medium**, where it transforms into the promastigote form.

Question 672: What is the infective form of Plasmodium falciparum in the mosquito?

A. Merozoites
B. Sporozoites
C. Gametocytes (Correct Answer)
D. Trophozoites

Explanation: **Explanation:** The life cycle of *Plasmodium falciparum* involves two hosts: the human (intermediate host) and the female *Anopheles* mosquito (definitive host). **Why Gametocytes are correct:** For the mosquito to become infected, it must ingest the sexual stages of the parasite present in human peripheral blood. These are the **Gametocytes** (male microgametocytes and female macrogametocytes). Once inside the mosquito's midgut, these gametocytes undergo fertilization to begin the sporogonic cycle, eventually leading to the production of sporozoites. Therefore, gametocytes are the **infective form for the mosquito**. **Why other options are incorrect:** * **Sporozoites (Option B):** These are the **infective form for humans**. They are inoculated into the human bloodstream via the mosquito's saliva during a blood meal. * **Merozoites (Option A):** These are released from hepatic cells (exo-erythrocytic stage) or red blood cells (erythrocytic stage). They infect new RBCs but are digested if ingested by a mosquito. * **Trophozoites (Option D):** This is the metabolically active, feeding stage within the human RBC (e.g., "ring forms"). Like merozoites, they do not survive the mosquito's digestive tract. **High-Yield NEET-PG Pearls:** * **Definitive Host:** Female *Anopheles* mosquito (where the sexual cycle occurs). * **Intermediate Host:** Humans (where the asexual cycle/schizogony occurs). * **P. falciparum Gametocytes:** Characteristically **crescent or banana-shaped**, appearing in peripheral blood 7–10 days after the initial infection. * **Primaquine:** The drug of choice for its gametocidal action against *P. falciparum*, used to prevent the transmission of malaria back to the mosquito.

Question 673: Which of the following diseases are transmitted by the sandfly?

A. Kala-azar (Correct Answer)
B. Oriental sore
C. Relapsing fever
D. Oraya fever

Explanation: **Explanation:** The sandfly (genus *Phlebotomus* in the Old World and *Lutzomyia* in the New World) is a significant medical vector. The correct answer is **Kala-azar** (Visceral Leishmaniasis), caused by *Leishmania donovani*. The sandfly transmits the parasite in its **promastigote** stage through a bite, which then transforms into the **amastigote** stage within the host's macrophages. **Analysis of Options:** * **A. Kala-azar (Correct):** Transmitted by *Phlebotomus argentipes*. It is characterized by the classic triad of fever, hepatosplenomegaly, and pancytopenia. * **B. Oriental Sore:** While also transmitted by the sandfly (*P. papatasi*), it refers to **Cutaneous Leishmaniasis**. In many competitive exams, if "Kala-azar" is an option, it is prioritized as the primary disease associated with sandflies in the Indian subcontinent. * **C. Relapsing Fever:** Epidemic relapsing fever is transmitted by the **body louse** (*Pediculus humanus corporis*), while endemic relapsing fever is transmitted by **soft ticks** (*Ornithodoros*). * **D. Oroya Fever:** This is the acute febrile phase of **Carrion’s disease** (caused by *Bartonella bacilliformis*). It is indeed transmitted by the sandfly (*Lutzomyia*), but it is geographically restricted to the Andes region of South America, making Kala-azar the more globally and locally relevant answer for NEET-PG. **High-Yield Clinical Pearls:** * **Sandfly-borne diseases mnemonic (6 O's):** **O**roya fever, **O**riental sore, **O**ld world Leishmaniasis, **O**ndansetron (not related, but helps memory), **O**ther Leishmaniasis, and **O**ropouche virus. * **Sandfly characteristics:** They are small (1/4 size of a mosquito), crawl rather than fly (short hops), and are nocturnal. * **Drug of Choice for Kala-azar:** Liposomal Amphotericin B is currently the first-line treatment.

Question 674: Chaga's disease is caused by which organism?

A. Trypanosoma brucei gambiense
B. T. cruzi (Correct Answer)
C. T. rangeli
D. T. brucei brucei

Explanation: **Explanation:** **Chagas disease** (American Trypanosomiasis) is caused by the protozoan parasite **Trypanosoma cruzi**. It is primarily transmitted to humans through the feces of the **Reduviid bug** (also known as the "kissing bug" or Triatomine bug). The parasite enters the body when the bug’s feces are rubbed into the bite wound or mucous membranes. **Why the other options are incorrect:** * **Trypanosoma brucei gambiense:** This organism causes **West African Sleeping Sickness** (Chronic African Trypanosomiasis), transmitted by the Tsetse fly. * **T. brucei brucei:** This species primarily causes **Nagana** in cattle and wild animals; it does not typically cause disease in humans. * **T. rangeli:** While found in South America and transmitted by the same Reduviid bug, it is considered **non-pathogenic** to humans, though it can complicate diagnosis by co-existing with *T. cruzi*. **High-Yield NEET-PG Clinical Pearls:** 1. **Romaña’s Sign:** Unilateral painless periorbital edema is a classic early sign of acute Chagas disease. 2. **Chagoma:** A localized inflammatory nodule at the site of entry. 3. **Chronic Complications:** The "Mega" diseases—**Megacolon, Megaesophagus** (due to destruction of Auerbach’s plexus), and **Dilated Cardiomyopathy** (the leading cause of death). 4. **C-shaped Trypomastigote:** In peripheral blood smears, *T. cruzi* typically appears in a characteristic "C" or "U" shape. 5. **Amastigote Stage:** Unlike African Trypanosomes, *T. cruzi* has an intracellular amastigote stage that replicates in cardiac and smooth muscle cells.

Question 675: Microscopic examination of a thin blood smear from a patient suspected of having malaria reveals numerous normal size erythrocytes without stippling but with ring stages, many with multiple ring stages and applique forms. Several erythrocytes show developing trophozoites that are spread across the erythrocytes in a band fashion. Which of the following is the most likely cause of infection?

A. Plasmodium vivax
B. Plasmodium malariae
C. Plasmodium falciparum
D. A mixed infection with two plasmodium species (Correct Answer)

Explanation: This question tests your ability to differentiate Plasmodium species based on morphological features in a peripheral blood smear. The correct answer is **D (Mixed infection)** because the smear displays characteristic features of two distinct species simultaneously. ### 1. Why the Correct Answer is Right The description provides a "morphological mosaic" that cannot be explained by a single species: * **Plasmodium falciparum features:** The presence of **multiple rings** per erythrocyte and **applique (accolé) forms** (parasites appearing on the periphery of the RBC) are classic hallmarks of *P. falciparum*. * **Plasmodium malariae features:** The presence of **band-form trophozoites** (parasites stretching across the diameter of the RBC) is the pathognomonic feature of *P. malariae*. * **RBC Morphology:** The erythrocytes are **normal-sized** and lack stippling (Schüffner’s dots), which is consistent with both *P. falciparum* and *P. malariae*, but rules out *P. vivax*. ### 2. Why Other Options are Wrong * **A. P. vivax:** Typically infects young RBCs (reticulocytes), causing them to appear **enlarged**. It also shows **Schüffner’s dots** and amoeboid trophozoites, not band forms. * **B. P. malariae:** While it explains the band forms, it rarely shows multiple rings per cell or applique forms, which are specific to *P. falciparum*. * **C. P. falciparum:** While it explains the multiple rings and applique forms, it does not typically form band-shaped trophozoites in the peripheral blood (as mature stages usually sequester in deep capillaries). ### 3. NEET-PG High-Yield Pearls * **Band Forms:** Pathognomonic for *P. malariae*. * **Applique/Accolé Forms:** Pathognomonic for *P. falciparum*. * **Maurer’s Clefts:** Seen in *P. falciparum*; **Schüffner’s dots:** Seen in *P. vivax/ovale*. * **Mixed Infections:** Most common combination is *P. falciparum* + *P. vivax*. Always look for "conflicting" morphological clues in the question stem.

Question 676: Which of the following is most severely affected in Kala-azar?

A. Spleen (Correct Answer)
B. Liver
C. Adrenal gland
D. Bone marrow

Explanation: **Explanation:** **Kala-azar (Visceral Leishmaniasis)**, caused by *Leishmania donovani*, is characterized by the massive proliferation of the parasite within the **Reticuloendothelial System (RES)**. **Why the Spleen is the correct answer:** The spleen is the organ most severely affected in Kala-azar. The amastigote form of the parasite multiplies within the splenic macrophages, leading to intense reactive hyperplasia of the lymphoid tissue and congestion. This results in **massive splenomegaly** (often extending to the iliac fossa), which is a hallmark clinical feature of the disease. The spleen becomes soft, friable, and dark (hence the name "Black Fever"). **Analysis of Incorrect Options:** * **B. Liver:** While the liver is frequently enlarged (hepatomegaly) due to the proliferation of Kupffer cells, the degree of enlargement and structural alteration is significantly less than that of the spleen. * **C. Adrenal gland:** Though the RES is involved systemically, the adrenal glands are not a primary site of pathology in Visceral Leishmaniasis. * **D. Bone marrow:** The bone marrow is indeed involved, leading to pancytopenia (anemia, leucopenia, and thrombocytopenia). However, in terms of gross organ pathology and severity of enlargement, the spleen remains the most prominently affected organ. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Splenic aspiration is the most sensitive diagnostic method (>95% yield) but carries a risk of hemorrhage. Bone marrow aspiration is safer and more commonly performed. * **Hematological Finding:** Characterized by **pancytopenia** and **hypergammaglobulinemia** (reversed Albumin:Globulin ratio). * **Vector:** Transmitted by the bite of the female **Sandfly (*Phlebotomus argentipes*)**. * **Drug of Choice:** Liposomal Amphotericin B is currently the preferred treatment.

Question 677: Ascariasis causes which of the following complications?

A. Appendicitis
B. Intestinal obstruction
C. Bile duct obstruction
D. All of the above (Correct Answer)

Explanation: **Explanation:** *Ascaris lumbricoides* (the giant roundworm) is the most common helminthic infection worldwide. The complications of Ascariasis are primarily due to the **mechanical effects** of the adult worms, which are large (20–35 cm), highly mobile, and have a tendency to migrate into narrow openings. 1. **Intestinal Obstruction:** This is the most common serious complication. A heavy worm burden can lead to the formation of a "bolus" or tangled mass of worms that physically blocks the lumen of the small intestine (usually the ileum), leading to acute mechanical obstruction. 2. **Bile Duct Obstruction:** Adult worms are known for their "wandering" nature. They can migrate through the Ampulla of Vater into the biliary tract, causing biliary colic, cholecystitis, or obstructive jaundice. 3. **Appendicitis:** If a wandering worm enters the narrow lumen of the appendix, it can cause luminal obstruction, leading to acute appendicitis. **Why "All of the above" is correct:** Since *Ascaris* is a large, motile parasite capable of both mass-aggregation and ectopic migration, it can cause mechanical blockage in the intestine, the biliary tree, and the appendix simultaneously or independently. **High-Yield Clinical Pearls for NEET-PG:** * **Loeffler’s Syndrome:** Characterized by transient pulmonary infiltrates and peripheral eosinophilia during the larval migration phase through the lungs. * **Diagnosis:** The gold standard is the detection of characteristic bile-stained (brown), mamillated eggs in stool microscopy. * **Imaging:** On Barium meal, a "String sign" or "Railway track appearance" may be seen due to the presence of worms in the intestine. * **Drug of Choice:** Albendazole (single dose) or Mebendazole.

Question 678: Which of the following parasites is known to cause anemia?

A. Entamoeba histolytica
B. Isospora belli
C. Trichomonas vaginalis
D. Diphyllobothrium latum (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Diphyllobothrium latum** **Medical Concept:** *Diphyllobothrium latum*, also known as the **Fish Tapeworm**, is the largest parasite infecting humans. It causes a specific type of anemia known as **Megaloblastic Anemia** (Vitamin B12 deficiency). The parasite competes with the host for Vitamin B12 (Cyanocobalamin) in the proximal small intestine. It absorbs approximately 80–100% of the dietary B12, leading to host depletion. This results in macrocytic anemia and, in severe cases, neurological symptoms similar to Subacute Combined Degeneration of the Spinal Cord (SCD). **Analysis of Incorrect Options:** * **A. Entamoeba histolytica:** This protozoan causes amoebic dysentery and liver abscesses. While chronic dysentery can lead to iron deficiency, it is not classically associated with a specific anemia syndrome like *D. latum*. * **B. Isospora belli (Cystoisospora):** An opportunistic coccidian parasite primarily causing self-limiting or chronic watery diarrhea, especially in HIV/AIDS patients. It does not cause anemia. * **C. Trichomonas vaginalis:** A flagellated protozoan that causes urogenital infections (vaginitis/urethritis). It is a localized infection and does not have systemic hematological effects. **NEET-PG High-Yield Pearls:** * **Infection Source:** Consumption of undercooked/raw freshwater fish (containing **Plerocercoid larvae**). * **Diagnosis:** Presence of **operculated eggs** (bile-stained) in stool. * **Other Parasites causing Anemia:** * **Hookworms** (*Ancylostoma duodenale/Necator americanus*): Iron Deficiency Anemia (Microcytic Hypochromic). * **Malaria** (*Plasmodium*): Hemolytic Anemia. * **Trichuris trichiura**: Microcytic anemia due to mucosal bleeding in heavy infestations (Whipworm). * **Drug of Choice:** Praziquantel.

Question 679: A 20-year-old male goes swimming and after a few days develops diffuse itching with rashes over his body. Several weeks later, he develops lancinating pain down his legs and in all his toes. Within a few days, he develops paraparesis and problems with bowel and bladder control, resulting in urinary retention. What is your initial diagnostic approach for this patient?

A. Initiate anticoagulation
B. Perform spinal angiography
C. Order an MRI scan (Correct Answer)
D. Perform sensory evoked potential testing

Explanation: ### Explanation **Diagnosis: Neuroschistosomiasis (Spinal Schistosomiasis)** The patient presents with a classic progression of **Schistosomiasis** (likely *S. mansoni* or *S. haematobium*). The initial "swimmer’s itch" (cercarial dermatitis) followed weeks later by acute neurological deficits (paraparesis, bowel/bladder dysfunction) suggests **acute transverse myelitis** caused by the deposition of schistosome eggs in the spinal cord. **1. Why "Order an MRI scan" is correct:** In any patient presenting with acute or subacute spinal cord symptoms (paraparesis and autonomic dysfunction), the immediate priority is to visualize the spinal cord to rule out compressive lesions and confirm inflammation. MRI with gadolinium is the **gold standard** for diagnosing spinal schistosomiasis. It typically shows spinal cord enlargement, T2-hyperintensity, and a characteristic "arborized" (tree-like) enhancement pattern in the lower thoracic cord or conus medullaris. **2. Why other options are incorrect:** * **Initiate anticoagulation:** This is used for vascular events like spinal cord infarction. However, the history of swimming and rashes points toward an infectious/inflammatory etiology. * **Perform spinal angiography:** This is the investigation of choice for spinal dural arteriovenous fistulas (SDAVF). While SDAVF can cause similar symptoms, the clinical history here strongly favors a parasitic cause. * **Perform sensory evoked potential testing:** This tests the integrity of sensory pathways but is not diagnostic for the underlying anatomical or infectious cause of paraparesis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Etiology:** *Schistosoma mansoni* is the most common cause of spinal neuroschistosomiasis (due to the proximity of the inferior mesenteric plexus to the Batson’s vertebral venous plexus). * **Pathogenesis:** Eggs reach the spinal cord via retrograde flow through the **Batson’s plexus** (valveless veins). * **Clinical Stages:** 1. *Cercarial dermatitis* (Itch) 2. *Katayama fever* (Systemic hypersensitivity) 3. *Chronic/Ectopic stage* (Neuroschistosomiasis). * **Treatment:** Praziquantel + Corticosteroids (to reduce the inflammatory response to dying eggs).

Question 680: Which of the following parasites is capable of causing autoinfection?

A. Giardia lamblia
B. Isospora belli
C. Balantidium coli
D. Taenia solium (Correct Answer)

Explanation: **Explanation:** The concept of **autoinfection** occurs when an individual serves as both the intermediate and definitive host, leading to a cycle of reinfection without the parasite leaving the body or via fecal-oral contamination from one's own stool. **Why Taenia solium is correct:** *Taenia solium* (Pork tapeworm) is unique because it can cause two distinct diseases: **Taeniasis** (intestinal infection with the adult worm) and **Cysticercosis** (tissue infection with larvae). Autoinfection occurs via the fecal-oral route (external) or reverse peristalsis (internal), where eggs produced by the adult worm in the intestine are ingested or pushed back into the stomach. These eggs hatch into oncospheres, penetrate the intestinal wall, and migrate to tissues (brain, muscles), leading to **Neurocysticercosis**. **Why the other options are incorrect:** * **Giardia lamblia & Balantidium coli:** These are protozoa transmitted via the fecal-oral route through contaminated food or water. While they cause reinfection if hygiene is poor, they do not exhibit a true biological "autoinfection" cycle where the parasite's life stage matures within the same host to cause a different clinical pathology. * **Isospora belli (Cystoisospora):** This requires a period of maturation (sporulation) outside the host in the environment to become infective. Therefore, immediate autoinfection is not possible. **NEET-PG High-Yield Pearls:** * **Other parasites causing autoinfection:** *Strongyloides stercoralis* (most common), *Enterobius vermicularis*, *Hymenolepis nana*, and *Cryptosporidium hominis*. * **Strongyloides stercoralis** is notorious for "Hyperinfection syndrome" in immunocompromised patients due to internal autoinfection. * **H. nana** is the only cestode (besides *T. solium*) that can complete its entire life cycle in a single host.

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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