Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 231: Which of the following statements is true regarding malaria?

A. Red blood cell size is enlarged in Plasmodium vivax infection. (Correct Answer)
B. Red blood cell size is enlarged in Plasmodium falciparum infection.
C. Schüffner's dots are seen in Plasmodium malariae infection.
D. Relapse occurs in Plasmodium falciparum infection.

Explanation: ### Explanation **Correct Option: A. Red blood cell size is enlarged in *Plasmodium vivax* infection.** *Plasmodium vivax* and *Plasmodium ovale* have a predilection for infecting **young erythrocytes (reticulocytes)**. Because reticulocytes are naturally larger than mature red blood cells, the infected cells appear enlarged and often distorted on a peripheral smear. **Analysis of Incorrect Options:** * **B. *Plasmodium falciparum*:** This species infects RBCs of **all ages**. Consequently, the size of the infected RBC remains **normal** (not enlarged). This leads to higher levels of parasitemia compared to other species. * **C. Schüffner's dots:** These are characteristic stippling seen in **_P. vivax_ and _P. ovale_**. In *P. malariae*, you typically see **Ziemann’s dots**, and the parasite often forms a characteristic "band shape." * **D. Relapse:** Relapse is caused by the activation of dormant liver stages called **hypnozoites**. This phenomenon is exclusive to **_P. vivax_ and _P. ovale_**. *P. falciparum* and *P. malariae* do not have a hypnozoite stage; any recurrence of symptoms in these species is termed **recrudescence** (due to surviving erythrocytic forms). **High-Yield Clinical Pearls for NEET-PG:** * **Maurer’s dots:** Coarse granulations seen in *P. falciparum* infection. * **Multiple rings & Accole forms:** Highly suggestive of *P. falciparum*. * **Treatment of Relapse:** **Primaquine** is the drug of choice to eradicate hypnozoites (ensure G6PD status is checked first). * **Infective stage:** Sporozoite (injected by female *Anopheles* mosquito). * **Diagnostic Gold Standard:** Giemsa-stained thick (for detection) and thin (for species identification) peripheral blood smears.

Question 232: Which of the following is NOT true about the peripheral blood smear findings in malaria?

A. Single ring form in Plasmodium vivax
B. Multiple ring forms in Plasmodium falciparum
C. Enlarged erythrocytes in Plasmodium vivax
D. Enlarged erythrocytes in Plasmodium falciparum (Correct Answer)

Explanation: ### Explanation The correct answer is **D (Enlarged erythrocytes in Plasmodium falciparum)** because *Plasmodium falciparum* typically infects red blood cells (RBCs) of all ages, and the infected cells remain **normal in size**. In contrast, *Plasmodium vivax* and *Plasmodium ovale* have a predilection for young RBCs (reticulocytes), which are naturally larger, and the parasite further causes the host cell to expand and become distorted. #### Analysis of Options: * **Option A (Single ring form in P. vivax):** This is a **true** statement. *P. vivax* usually presents with a single, large, thick ring (trophozoite) within the RBC. * **Option B (Multiple ring forms in P. falciparum):** This is a **true** statement and a classic diagnostic feature. *P. falciparum* often shows multiple rings within a single RBC (polyparasitism) and "accoulee" or "applique" forms (rings at the periphery of the cell). * **Option C (Enlarged erythrocytes in P. vivax):** This is **true**. Infected RBCs in *P. vivax* are significantly enlarged, pale, and often show **Schüffner’s dots**. * **Option D (Enlarged erythrocytes in P. falciparum):** This is **false**, making it the correct choice. RBCs in *P. falciparum* infections are of normal size and may show **Maurer’s clefts** (coarse granulations). #### NEET-PG High-Yield Pearls: * **P. falciparum:** Characterized by banana/crescent-shaped gametocytes, multiple rings per cell, and Maurer’s clefts. It is the most common cause of cerebral malaria. * **P. vivax:** Characterized by Schüffner’s dots, enlarged RBCs, and the presence of all stages (rings, trophozoites, schizonts) in peripheral blood. * **P. malariae:** Characterized by "Band forms" and "Ziemann’s stippling." * **Gold Standard Diagnosis:** Microscopy of **thick smears** (for detection/parasite load) and **thin smears** (for species identification).

Question 233: What is the most common presenting symptom of Enterobius vermicularis infection?

A. Abdominal pain (Correct Answer)
B. Rectal prolapse
C. Urticaria
D. Vaginitis

Explanation: **Explanation:** *Enterobius vermicularis*, commonly known as **Pinworm** or **Seatworm**, is the most common helminthic infection worldwide. **Why Abdominal Pain is the Correct Answer:** While the hallmark symptom of Enterobiasis is nocturnal perianal pruritus (itching), among the options provided, **abdominal pain** is the most frequent clinical presentation. This occurs due to the presence of adult worms in the cecum and appendix, which can cause mild mucosal irritation or, in some cases, symptoms mimicking acute appendicitis. **Analysis of Incorrect Options:** * **Rectal Prolapse:** This is a classic complication associated with heavy infections of ***Trichuris trichiura* (Whipworm)**, not Enterobius. * **Urticaria:** This is more characteristic of helminths that undergo a tissue-migratory phase (e.g., *Ascaris lumbricoides* or *Strongyloides stercoralis*), leading to eosinophilic allergic responses. * **Vaginitis:** While *E. vermicularis* can cause ectopic migration into the female genital tract (leading to vulvovaginitis or salpingitis), it is a **complication** rather than the most common presenting symptom. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Gold Standard:** NIH Swab or **Scotch Tape Test** (Cellophane tape test) performed early in the morning to detect eggs. * **Egg Morphology:** Planoconvex, non-bile stained, with a "D" shape. * **Autoinfection:** Occurs via the fecal-oral route (finger-sucking or nail-biting) due to the intense perianal itching. * **Treatment:** Albendazole or Mebendazole (single dose, repeated after 2 weeks). **Treat the entire family** to prevent reinfection.

Question 234: A fisherman presents with complaints of chronic diarrhea and fatigue. His physician orders a peripheral smear, which reveals a megaloblastic anemia. What is the most likely cause?

A. Clonorchis sinensis
B. Diphyllobothrium latum (Correct Answer)
C. Echinococcus granulosus
D. Taenia saginata

Explanation: **Explanation:** The clinical presentation of chronic diarrhea, fatigue, and **megaloblastic anemia** in a fisherman is a classic description of **Diphyllobothrium latum** (Fish Tapeworm) infection. **Why Diphyllobothrium latum is correct:** * **Mechanism:** *D. latum* is the largest tapeworm infecting humans. It has a unique affinity for **Vitamin B12 (Cobalamin)**. The parasite competes with the host for B12 absorption in the small intestine, absorbing up to 80-100% of the dietary intake. * **Clinical Consequence:** Long-standing depletion of Vitamin B12 leads to impaired DNA synthesis, resulting in **megaloblastic anemia** (macrocytic anemia with hypersegmented neutrophils) and potential neurological symptoms (Subacute Combined Degeneration of the spinal cord). * **Epidemiology:** It is transmitted via the consumption of undercooked or raw freshwater fish (containing plerocercoid larvae), making it common among fishermen and sushi consumers. **Why other options are incorrect:** * **Clonorchis sinensis (Chinese Liver Fluke):** Primarily causes biliary tract diseases, including cholangitis and **cholangiocarcinoma**. It does not cause megaloblastic anemia. * **Echinococcus granulosus (Dog Tapeworm):** Causes **Hydatid cyst** disease, typically involving the liver or lungs. It presents with space-occupying lesions, not nutritional anemia. * **Taenia saginata (Beef Tapeworm):** Usually asymptomatic or causes mild GI upset. It does not interfere with Vitamin B12 absorption. **NEET-PG High-Yield Pearls:** * **Infective stage:** Plerocercoid larva. * **Diagnostic stage:** Operculated eggs in stool (bile-stained). * **Intermediate hosts:** 1st - Cyclops (Crustacean); 2nd - Freshwater fish. * **Treatment:** Praziquantel is the drug of choice. * **Key Association:** "Fish Tapeworm = Vitamin B12 deficiency."

Question 235: Cholangiocarcinoma has been associated with infection by which of the following parasites?

A. Paragonimus westermani
B. Clonorchis sinensis (Correct Answer)
C. Loa Loa
D. Schistosoma haematobium

Explanation: **Explanation:** The correct answer is **Clonorchis sinensis**. **1. Why Clonorchis sinensis is correct:** *Clonorchis sinensis* (the Chinese Liver Fluke) and *Opisthorchis viverrini* are well-established biological carcinogens. These parasites reside in the **distal biliary passages**. Chronic infection leads to mechanical irritation, production of proline-like substances, and chronic inflammation of the bile duct epithelium. This results in adenomatous hyperplasia, which can progress to **Cholangiocarcinoma** (bile duct cancer). Transmission occurs via the ingestion of undercooked freshwater fish containing metacercariae. **2. Analysis of Incorrect Options:** * **Paragonimus westermani (Lung Fluke):** Associated with pulmonary infections mimicking tuberculosis (hemoptysis, cavitary lesions). It does not involve the biliary tract. * **Loa Loa (African Eye Worm):** A nematode transmitted by the *Chrysops* fly. It causes Calabar swellings and subconjunctival migration; it has no association with malignancy. * **Schistosoma haematobium (Bladder Fluke):** While it is associated with cancer, it causes **Squamous Cell Carcinoma of the Urinary Bladder**, not cholangiocarcinoma. It resides in the vesical venous plexuses. **3. NEET-PG High-Yield Clinical Pearls:** * **Drug of Choice:** Praziquantel is the treatment for all trematodes (flukes) except *Fasciola hepatica* (Triclabendazole). * **Intermediate Hosts:** *C. sinensis* requires two intermediate hosts: 1st - Snail (Parafossarulus), 2nd - Freshwater fish. * **Imaging:** On ultrasound/CT, chronic infection may show "ductal dilatation with eccentric wall thickening." * **Other Parasite-Cancer Link:** Remember *Schistosoma japonicum* is occasionally linked to colorectal cancer.

Question 236: Romana's sign is seen in?

A. Toxoplasma
B. Trypanosoma cruzi (Correct Answer)
C. Loa loa
D. Wuchereria

Explanation: **Explanation:** **Romana’s sign** is a classic clinical hallmark of **acute Chagas disease**, caused by the protozoan parasite ***Trypanosoma cruzi***. It occurs when the parasite (transmitted via the feces of the Reduviid/Triatomine bug) enters through the conjunctiva or the skin near the eye. It is characterized by unilateral, painless periorbital edema, conjunctivitis, and local lymphadenopathy (pre-auricular nodes). **Why the other options are incorrect:** * **Toxoplasma gondii:** Typically presents as asymptomatic infection, lymphadenopathy, or chorioretinitis in immunocompromised patients, but does not cause Romana’s sign. * **Loa loa (African Eye Worm):** Known for **Calabar swellings** (transient subcutaneous angioedema) and the visible migration of the adult worm across the subconjunctiva. * **Wuchereria bancrofti:** The primary cause of Lymphatic Filariasis, leading to hydrocele, lymphedema, and elephantiasis, but not acute periorbital swelling. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Reduviid bug (also called Triatomine or "Kissing bug"). * **Chagas Disease Triad (Chronic):** Achalasia cardia (Megaesophagus), Megacolon, and Dilated Cardiomyopathy (most common cause of death). * **Chagoma:** A localized inflammatory swelling at the site of entry on the skin (distinct from Romana's sign, which is specifically ophthalmic). * **Diagnosis:** C-shaped trypomastigotes on peripheral blood smear (acute phase) or Xenodiagnosis. * **Treatment:** Benznidazole or Nifurtimox.

Question 237: Which of the following is true about the mature cyst of E. histolytica?

A. Endoplasm and ectoplasm are clearly defined.
B. Contains eight chromatid bodies.
C. Shows chromatid bodies and glycogen mass.
D. Nuclear structure retains characteristics of the trophozoite. (Correct Answer)

Explanation: ### Explanation **1. Why the Correct Answer is Right** The diagnostic hallmark of *Entamoeba histolytica* (both in trophozoite and cyst stages) is its unique nuclear morphology. The nucleus features a **small, central karyosome** and **fine, uniform peripheral chromatin** distributed along the inner nuclear membrane (often described as a "cartwheel appearance"). Even as the parasite matures from a trophozoite to a quadrinucleate cyst, these specific nuclear characteristics remain constant, allowing for definitive microscopic identification. **2. Why the Other Options are Wrong** * **Option A:** Differentiation into ectoplasm (clear) and endoplasm (granular) is a characteristic feature of the **trophozoite** stage, which is actively motile via pseudopodia. Cysts have a rigid cell wall and do not show this differentiation. * **Option B:** A mature cyst of *E. histolytica* contains **one to four** nuclei. It is *Entamoeba coli* that typically possesses eight nuclei in its mature cyst stage. * **Option C:** Chromatid bodies (cigar-shaped) and the glycogen mass are features of the **immature (uninucleate or binucleate) cyst**. As the cyst matures into the quadrinucleate stage, these nutrient reserves are consumed and usually disappear. **3. NEET-PG High-Yield Pearls** * **Infective Stage:** Mature quadrinucleate cyst. * **Diagnostic Stage:** Trophozoite (in acute dysentery) or Cyst (in chronic cases/carriers). * **Chromatid Bodies:** In *E. histolytica*, they have **rounded/frounded ends** (cigar-shaped), whereas in *E. coli*, they are filamentous with **splintered/frayed ends**. * **Trophozoite Identification:** The presence of ingested RBCs (**erythrophagocytosis**) is pathognomonic for *E. histolytica* and distinguishes it from the non-pathogenic *E. dispar*.

Question 238: Which of the following parasites is commonly found in muscles?

A. Trichuris trichiura
B. Trichinella spiralis (Correct Answer)
C. Schistosomiasis
D. Ancylostoma duodenale

Explanation: **Explanation:** The correct answer is **Trichinella spiralis**. This parasite is the causative agent of **Trichinellosis**. Its unique life cycle involves the same animal acting as both the definitive and intermediate host. After ingestion of undercooked meat (usually pork) containing encysted larvae, the larvae mature in the small intestine. The newborn larvae then migrate via the bloodstream to **striated muscles**, where they encyst. These "nurse cells" are most commonly found in highly active muscles such as the diaphragm, extraocular muscles, and deltoids. **Why the other options are incorrect:** * **Trichuris trichiura (Whipworm):** This is a soil-transmitted helminth that resides in the **large intestine (caecum)**. It does not have a tissue migration phase involving muscles. * **Schistosomiasis (Blood Flukes):** These trematodes reside in the **venous plexuses** (e.g., vesical plexus for *S. haematobium* and mesenteric veins for *S. mansoni*). They do not encyst in muscles. * **Ancylostoma duodenale (Hookworm):** These parasites reside in the **small intestine**, where they attach to the mucosa to suck blood. While they migrate through the lungs (Loeffler’s syndrome), they do not settle in muscle tissue. **NEET-PG High-Yield Pearls:** * **Clinical Triad of Trichinellosis:** Myalgia, periorbital edema, and eosinophilia. * **Diagnosis:** Muscle biopsy (showing coiled larvae) or the **Bachman intradermal test**. * **Other parasites in muscle:** *Taenia solium* (Cysticercosis) also forms cysts in muscles and the brain. * **Key Lab Finding:** Elevated **Creatine Phosphokinase (CPK)** due to muscle damage.

Question 239: What is true about the peripheral blood smear of Plasmodium vivax?

A. Single ring with cytoplasm condensed around in each erythrocyte. (Correct Answer)
B. Mature or old erythrocytes are affected.
C. Parasitized erythrocytes are of the same size as normal erythrocytes.
D. Only ring and gametocytes are seen.

Explanation: ### Explanation **1. Why Option A is Correct:** In *Plasmodium vivax* infections, the early trophozoite (ring stage) typically appears as a **single ring** within the erythrocyte. The cytoplasm is often described as being condensed or "chunky" around the central vacuole, and the red blood cell (RBC) may show **Schüffner’s dots** (stippling) as the parasite matures. Unlike *P. falciparum*, multiple rings per RBC are rare in *P. vivax*. **2. Why the Other Options are Incorrect:** * **Option B:** *P. vivax* has a predilection for **young erythrocytes (reticulocytes)**. It uses the Duffy blood group antigen as a receptor. In contrast, *P. malariae* affects old RBCs, and *P. falciparum* affects RBCs of all ages. * **Option C:** Parasitized RBCs in *P. vivax* are **enlarged and pale**. The parasite causes the host cell membrane to become flexible and distended. If the RBC is the same size as a normal one, it points toward *P. falciparum* or *P. malariae*. * **Option D:** In *P. vivax*, **all stages** (rings, developing trophozoites, schizonts, and gametocytes) can be seen in the peripheral blood smear. This is a key differentiator from *P. falciparum*, where typically only rings and crescent-shaped gametocytes are seen (as mature stages are sequestered in deep capillaries). **3. NEET-PG High-Yield Pearls:** * **Duffy Negative Status:** Individuals lacking Duffy antigens (common in West Africa) are resistant to *P. vivax*. * **Relapse:** Caused by **hypnozoites** (latent stages in the liver). Treatment requires **Primaquine** or **Tafenoquine** for radical cure. * **Schüffner’s Dots:** Characteristic stippling seen in *P. vivax* and *P. ovale*. * **Amoeboid Trophozoite:** The growing trophozoite of *P. vivax* is highly irregular and "amoeboid" in shape.

Question 240: Romana's sign occurs in which condition?

A. Babesiosis
B. Leishmaniasis
C. Trypanosomiasis (Correct Answer)
D. Schistosomiasis

Explanation: **Explanation:** **Romana’s sign** is a classic clinical hallmark of **American Trypanosomiasis (Chagas disease)**, caused by the protozoan parasite *Trypanosoma cruzi*. It refers to the painless, unilateral periorbital edema and conjunctivitis that occurs when the parasite (transmitted via the feces of the **Reduviid/Triatomine bug**) enters through the conjunctiva or a nearby bite wound. **Why the other options are incorrect:** * **Babesiosis:** Caused by *Babesia microti* (transmitted by *Ixodes* ticks), it typically presents with a malaria-like illness (fever, hemolytic anemia) and is characterized by "Maltese cross" appearances in RBCs, not localized facial swelling. * **Leishmaniasis:** While Cutaneous Leishmaniasis causes skin ulcers and Visceral Leishmaniasis (Kala-azar) causes hepatosplenomegaly, they do not present with Romana’s sign. A similar-sounding sign, the "Chagoma," is the skin equivalent of Romana’s sign in Chagas disease. * **Schistosomiasis:** This helminthic infection is associated with "Swimmer’s itch" (cercarial dermatitis) and Katayama fever, but not periorbital edema. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Reduviid bug (also known as the Kissing bug or Assassin bug). * **Transmission:** Occurs via the **feces** of the bug being rubbed into a wound or mucous membrane (Stercorarian transmission). * **Chronic Chagas Disease:** Look for "Mega" syndromes—**Megaesophagus, Megacolon**, and **Dilated Cardiomyopathy** (the leading cause of death in these patients). * **Diagnosis:** C-shaped trypomastigotes in peripheral blood (acute) or Amastigotes in tissue (Leishmanial stage).

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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