Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 701: In the context of Filariasis, all statements are true EXCEPT:

A. The definitive host is man.
B. Worms colonize the lymphatic system.
C. The most common causative agent is W. bancrofti.
D. It is transmitted by Aedes aegypti mosquito. (Correct Answer)

Explanation: ### Explanation The correct answer is **D**. In Lymphatic Filariasis, the primary vector for *Wuchereria bancrofti* is the **Culex quinquefasciatus** mosquito (especially in urban and semi-urban areas). While *Aedes* and *Anopheles* species can transmit certain types of filariasis in specific geographic pockets (like the Pacific islands), *Aedes aegypti* is classically associated with viral diseases like Dengue, Chikungunya, and Zika, not the primary transmission of Bancroftian filariasis in the Indian subcontinent. **Analysis of other options:** * **Option A:** True. Humans are the **definitive host** because they harbor the adult sexual stages of the parasite. There is no known animal reservoir for *W. bancrofti*. * **Option B:** True. Adult worms reside in the **afferent lymphatic vessels** and lymph nodes, where they cause mechanical obstruction and inflammatory reactions leading to elephantiasis. * **Option C:** True. *Wuchereria bancrofti* is responsible for approximately **90%** of all lymphatic filariasis cases worldwide, followed by *Brugia malayi*. **High-Yield NEET-PG Pearls:** * **Infective Stage:** Third-stage larvae (**L3**) introduced during a mosquito bite. * **Diagnostic Stage:** Microfilariae found in peripheral blood (usually with **nocturnal periodicity**, between 10 PM and 2 AM). * **Drug of Choice:** **Diethylcarbamazine (DEC)**; however, it is contraindicated in Onchocerciasis due to the Mazzotti reaction. * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity response to filarial antigens characterized by nocturnal cough, wheezing, and high peripheral eosinophilia.

Question 702: Giardiasis is associated with which of the following conditions?

A. Common variable immunodeficiency (Correct Answer)
B. C1 esterase deficiency
C. C8 deficiency
D. Anaemia

Explanation: **Explanation:** **Giardiasis** is caused by the flagellated protozoan *Giardia lamblia*. The primary host defense against this parasite in the small intestine is **Secretory IgA**, which prevents the attachment of trophozoites to the intestinal mucosa. **1. Why Option A is Correct:** **Common Variable Immunodeficiency (CVID)** is characterized by hypogammaglobulinemia (low levels of IgG, IgA, and IgM). The profound deficiency of **IgA** in these patients removes the primary barrier against *Giardia* colonization. Consequently, patients with CVID are highly susceptible to chronic, recurrent, and severe giardiasis, often leading to malabsorption and villous atrophy. **2. Why the Other Options are Incorrect:** * **Option B (C1 esterase deficiency):** This leads to **Hereditary Angioedema** due to the overproduction of bradykinin. It does not predispose patients to parasitic infections. * **Option C (C8 deficiency):** Deficiencies in late complement components (C5-C9) impair the formation of the Membrane Attack Complex (MAC), specifically predisposing individuals to recurrent **Neisserial infections** (Meningitis and Gonorrhea). * **Option D (Anaemia):** While chronic malabsorption from giardiasis can theoretically lead to nutritional deficiencies, it is not a predisposing "condition" for the infection itself. In contrast, *Hookworm* infection is more classically associated with iron-deficiency anemia. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** *Giardia* trophozoites are pear-shaped, have a "falling leaf" motility, and possess a characteristic "owl’s eye" appearance (two nuclei). * **Diagnosis:** Stool microscopy for cysts/trophozoites or the **Entero-test (String test)**. * **Drug of Choice:** Tinidazole (preferred) or Metronidazole. * **Association:** Giardiasis is the most common intestinal parasitic pathogen identified in patients with primary immunodeficiency.

Question 703: Naegleria fowleri is commonly acquired by:

A. Saltwater living
B. Freshwater living (Correct Answer)
C. Sulfur springs
D. Swimming pools

Explanation: **Explanation:** *Naegleria fowleri*, commonly known as the **"brain-eating amoeba,"** is a thermophilic, free-living amoeba found globally. **Why Freshwater living is correct:** The primary habitat for *N. fowleri* is **warm freshwater** (lakes, rivers, and ponds). Infection occurs when water containing the trophozoites or cysts is forcefully inhaled through the nose, typically during diving or swimming. The organism penetrates the **cribriform plate** and migrates along the olfactory nerves to the brain, leading to **Primary Amoebic Meningoencephalitis (PAM)**, a rapidly fatal condition. **Why the other options are incorrect:** * **Saltwater living:** *N. fowleri* cannot survive in high salinity; it is strictly a freshwater organism. * **Sulfur springs:** While *N. fowleri* is thermophilic (thriving up to 45°C), the specific chemical composition and high mineral content of sulfur springs are generally not its typical reservoir compared to stagnant or slow-moving freshwater. * **Swimming pools:** While possible if pools are inadequately chlorinated and filled with freshwater, "Freshwater living" is the broader, more definitive ecological niche and the standard textbook answer for its primary source. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Rapidly progressive meningoencephalitis with a history of swimming in the last 7–10 days. * **Diagnosis:** Wet mount of **CSF** shows motile trophozoites (look for "slug-like" pseudopodia). Note: Cysts are never seen in brain tissue, only trophozoites. * **Drug of Choice:** **Amphotericin B** (often combined with Miltefosine). * **Key Feature:** It is the only amoeba with a **flagellated stage** in its life cycle (though the trophozoite is the infective form).

Question 704: Charcot leyden crystals in stool are typically seen in which of the following conditions?

A. Bacillary dysentery
B. Amoebic dysentery (Correct Answer)
C. Giardiasis
D. Cholera

Explanation: **Explanation:** **Charcot-Leyden crystals** are slender, needle-like, diamond-shaped crystals formed from the breakdown products of **eosinophils** (specifically the enzyme Galectin-10). Their presence in stool indicates an inflammatory process involving eosinophilic infiltration. 1. **Why Amoebic Dysentery is correct:** In *Entamoeba histolytica* infection, there is significant tissue destruction and an inflammatory response. While the stool in amoebic dysentery is typically characterized by "clumps" of RBCs and few pus cells (unlike bacillary dysentery), the presence of Charcot-Leyden crystals is a classic diagnostic hallmark that helps differentiate it from bacterial causes. 2. **Why other options are incorrect:** * **Bacillary Dysentery:** Caused by *Shigella*, this presents with numerous pus cells (neutrophils) and macrophages, but Charcot-Leyden crystals are characteristically **absent**. * **Giardiasis:** This is a non-invasive infection of the small intestine causing malabsorption and steatorrhea. It does not typically involve significant eosinophilic inflammation or blood in the stool. * **Cholera:** Caused by *Vibrio cholerae* enterotoxin, it results in "rice-water stools" which are watery and contain mucus and epithelial cells, but no inflammatory cells or crystals. **High-Yield Clinical Pearls for NEET-PG:** * **Amoebic Dysentery Stool:** Acidic, contains RBCs in clumps, Charcot-Leyden crystals present, and motile trophozoites with ingested RBCs (pathognomonic). * **Bacillary Dysentery Stool:** Alkaline, numerous pus cells, RBCs in discrete rows, and crystals are absent. * **Other locations:** Charcot-Leyden crystals are also found in the **sputum** of patients with **Bronchial Asthma** and in cases of tissue-invasive helminthic infections.

Question 705: What is the natural habitat of Schistosoma (blood flukes)?

A. Veins of the urinary bladder
B. Portal and pelvic veins
C. Vesical plexuses
D. All of the above (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. All of the above**. Schistosomes, unlike other trematodes (flukes), are unique because they reside in the **venous system** of their definitive host (humans) rather than the intestine or liver. They are dioecious (separate sexes) and live in permanent copulation within the veins. 1. **Why the answer is correct:** The term "Schistosoma" refers to a genus that includes several species with specific anatomical preferences. * ***S. haematobium*** primarily inhabits the **vesical and pelvic venous plexuses** (surrounding the urinary bladder). * ***S. mansoni*** and ***S. japonicum*** reside in the **portal venous system** and mesenteric veins. Since the question asks for the habitat of "Schistosoma" (the genus) generally, all listed venous sites are correct. 2. **Analysis of Options:** * **Option A & C:** These are the specific habitats for *S. haematobium*. Eggs are deposited in the bladder wall, leading to terminal hematuria. * **Option B:** The portal vein is the site where schistosomes mature, and the pelvic/mesenteric veins are where they reside as adults. **High-Yield NEET-PG Pearls:** * **Infective stage:** Cercaria (enters via skin penetration, often during swimming). * **Diagnostic stage:** Non-operculated eggs with characteristic spines (*S. haematobium*: Terminal spine; *S. mansoni*: Lateral spine; *S. japonicum*: Rudimentary spine). * **Intermediate host:** Freshwater snails (*Biomphalaria*, *Bulinus*, *Oncomelania*). * **Clinical Association:** *S. haematobium* is a known risk factor for **Squamous Cell Carcinoma of the bladder**. * **Treatment of choice:** Praziquantel.

Question 706: Specific diagnosis of Ascaris is made by?

A. Adult worm in stool
B. Egg detection
C. Antigen detection
D. Antibody detection (Correct Answer)

Explanation: ### Explanation The specific diagnosis of *Ascaris lumbricoides* infection, particularly in the context of systemic involvement or early-stage infection, is best achieved through **Antibody detection**. **1. Why Antibody Detection is Correct:** While stool microscopy is the most common method for routine diagnosis, **Antibody detection (Serology)** using ELISA is considered the "specific" diagnostic tool for detecting exposure and early infection. It is particularly useful during the **larval migratory phase** (Löffler’s syndrome), where the larvae are present in the lungs but have not yet matured into egg-laying adults in the intestine. At this stage, stool samples will be negative for eggs, making serology the definitive way to confirm the diagnosis. **2. Why Other Options are Incorrect:** * **Adult worm in stool (A):** While adult worms may occasionally be passed in stool or vomitus, this is an incidental finding rather than a standard or specific diagnostic protocol. * **Egg detection (B):** This is the **most common** method (standard stool microscopy) for diagnosing intestinal ascariasis. However, it has a "window period" of 2–3 months post-infection before eggs appear in the stool. It cannot diagnose the early migratory phase. * **Antigen detection (C):** While research is ongoing, antigen detection is not a standard or widely utilized specific diagnostic test for *Ascaris* compared to antibody detection. **3. Clinical Pearls for NEET-PG:** * **Löffler’s Syndrome:** Characterized by fever, cough, wheezing, and eosinophilia during larval migration through the lungs. Diagnosis at this stage is via **sputum microscopy** (finding larvae/Charcot-Leyden crystals) or **Serology**. * **Most Common Helminthic Infection:** *Ascaris lumbricoides* is the largest and most common soil-transmitted helminth globally. * **Fertilized vs. Unfertilized Eggs:** Fertilized eggs are ovoid, bile-stained (golden brown), with a thick mammillated shell. Unfertilized eggs are more elongated and have a thinner shell. * **Treatment:** Albendazole (Drug of Choice) or Mebendazole. In cases of intestinal obstruction, Piperazine is preferred.

Question 707: Diphyllobothrium latum is transmitted by which of the following modes?

A. Ingestion of cercariae through copepods
B. Ingestion of cercariae through fish meal
C. Ingestion of plerocercoids through raw or undercooked fish (Correct Answer)
D. Ingestion of metacercariae in copepods

Explanation: **Explanation:** *Diphyllobothrium latum* (the Fish Tapeworm) is the largest parasite infecting humans. Its complex life cycle involves two intermediate hosts: first, a **copepod** (crustacean), and second, a **freshwater fish**. **1. Why Option C is Correct:** The infective stage for humans is the **Plerocercoid larva** (also known as the sparganum). After a fish consumes an infected copepod, the larvae migrate into the fish's muscle. Humans acquire the infection by **ingesting raw or undercooked fish** containing these plerocercoids. Once inside the human intestine, they develop into adult worms. **2. Why the Other Options are Incorrect:** * **Options A & B:** **Cercariae** are the infective stages for Trematodes (Flukes), such as *Schistosoma*, not Cestodes (Tapeworms). In the *D. latum* cycle, the stage found in copepods is the *procercoid* larva, not cercariae. * **Option D:** **Metacercariae** are the infective stages for hermaphroditic flukes (e.g., *Fasciola hepatica*, *Clonorchis sinensis*). While copepods are involved in the life cycle of *D. latum*, they harbor *procercoids*, not metacercariae. **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** and subacute combined degeneration of the spinal cord. * **Operculated Eggs:** It is the only human tapeworm that produces operculated eggs (similar to fluke eggs) and has a ciliated larval stage called **Coracidium**. * **Treatment:** Praziquantel is the drug of choice.

Question 708: What is the basis for the 'Dipstick Test' used for the rapid diagnosis of Plasmodium falciparum?

A. Arginine-rich protein
B. Serine-rich protein
C. Tyrosine-rich protein
D. Histidine-rich protein (Correct Answer)

Explanation: ### Explanation The correct answer is **D. Histidine-rich protein (HRP-2)**. **1. Why Histidine-rich protein is correct:** Rapid Diagnostic Tests (RDTs) for Malaria, often called the 'Dipstick Test', utilize immunochromatographic methods to detect specific circulating antigens. **Histidine-rich protein 2 (HRP-2)** is a water-soluble protein produced specifically by the asexual stages and young gametocytes of ***Plasmodium falciparum***. Because HRP-2 is secreted into the host’s bloodstream, it serves as a highly sensitive biomarker for diagnosing *P. falciparum* infections, even when parasite density is low. **2. Why the other options are incorrect:** * **Arginine, Serine, and Tyrosine-rich proteins:** While *Plasmodium* species do possess various proteins rich in these amino acids (e.g., Serine-repeat antigen), they are not utilized in commercial rapid diagnostic dipsticks. HRP-2 is uniquely targeted because of its high expression levels and specificity to the *falciparum* species. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Target Antigens:** * **HRP-2:** Specific for *P. falciparum* only. * **pLDH (Parasite Lactate Dehydrogenase):** Produced by all four species (*P. falciparum, P. vivax, P. ovale, P. malariae*). It indicates the presence of **viable** parasites. * **Persistence:** HRP-2 can persist in the blood for **2–4 weeks** even after successful treatment. Therefore, a positive dipstick test immediately after treatment may represent a "false positive" for active infection. * **Prozone Effect:** Very high parasitemia can sometimes lead to a false-negative result in RDTs due to the prozone phenomenon. * **Gold Standard:** Despite the convenience of RDTs, **Microscopy** (Peripheral Smear) remains the gold standard for malaria diagnosis.

Question 709: Which of the following is false about Echinococcus granulosus?

A. Man is the dead-end host
B. It causes hydatid disease
C. Casoni's test is sensitive
D. Hydatid fluid is secreted by the ectocyst (Correct Answer)

Explanation: **Explanation:** The correct answer is **D**. In *Echinococcus granulosus* (Hydatid disease), the cyst wall consists of three layers. The **ectocyst** is the outermost, thick, fibrous layer formed by the **host’s inflammatory response**. It is not a part of the parasite itself and does not secrete fluid. The hydatid fluid is actually secreted by the **endocyst** (germinal layer), which is the innermost, metabolically active layer of the parasite. **Analysis of Options:** * **A. Man is the dead-end host:** True. Humans act as accidental intermediate hosts. Since the life cycle is broken (human-to-dog transmission does not occur), they are considered dead-end hosts. * **B. It causes hydatid disease:** True. *E. granulosus* is the causative agent of cystic echinococcosis, commonly known as hydatid disease, primarily affecting the liver and lungs. * **C. Casoni's test is sensitive:** True. This is an immediate hypersensitivity skin test. While it has high sensitivity (approx. 90%), it is rarely used today due to low specificity and the risk of anaphylaxis; it has been replaced by serology (ELISA) and imaging. **High-Yield Clinical Pearls for NEET-PG:** * **Definitive Host:** Dog (adult worm lives in the intestine). * **Intermediate Host:** Sheep (natural) and Man (accidental). * **Infective Stage:** Embryonated eggs (found in dog feces). * **Hydatid Sand:** Consists of free scolices, daughter cysts, and hooklets found within the fluid. * **Water Lily Sign:** Seen on imaging when the endocyst ruptures and floats within the ectocyst. * **Treatment:** PAIR (Puncture, Aspiration, Injection, Re-aspiration) technique and Albendazole. Avoid cyst rupture to prevent life-threatening **anaphylactic shock**.

Question 710: A patient diagnosed with malaria has a peripheral blood smear showing all stages of schizonts with 14-20 merozoites and yellowish-brown pigment. What is the most likely type of malaria?

A. Plasmodium falciparum
B. Plasmodium malariae
C. Plasmodium vivax (Correct Answer)
D. Plasmodium ovale

Explanation: ### Explanation The correct answer is **Plasmodium vivax**. The diagnosis of malaria species via peripheral blood smear relies on specific morphological characteristics of the parasite and the infected Red Blood Cells (RBCs). **Why Plasmodium vivax is correct:** * **Schizont Morphology:** *P. vivax* schizonts are large and typically contain **12–24 merozoites** (matching the 14–20 range in the question). * **Pigment:** It characteristically shows **yellowish-brown (golden-brown)** hemozoin pigment. * **RBC Appearance:** *P. vivax* infects young RBCs (reticulocytes), causing the cells to become **enlarged/hypertrophied** and often showing Schüffner’s dots. * **Stages Present:** Unlike *P. falciparum*, all stages (trophozoites, schizonts, and gametocytes) are commonly seen in the peripheral blood. **Why the other options are incorrect:** * **P. falciparum:** Typically, only ring forms and crescent-shaped gametocytes are seen in peripheral blood. Schizonts are rarely seen as they are sequestered in deep capillaries. When present, they contain 8–36 merozoites and dark black pigment. * **P. malariae:** Schizonts typically show a **"Rosette appearance"** with only **6–12 merozoites**. The pigment is usually dark brown/black. It infects older RBCs, so the cells are not enlarged. * **P. ovale:** While it also shows Schüffner’s dots and 6–12 merozoites, the infected RBCs are typically **oval-shaped with fimbriated (tufted) edges**. **High-Yield NEET-PG Pearls:** * **P. vivax & P. ovale:** Associated with **Hypnozoites** (latent liver stages) causing relapses; treated with Primaquine. * **P. falciparum:** Associated with **Maurer’s dots** and multiple rings per RBC (Accole/Applique forms). * **P. malariae:** Associated with **Ziemann’s dots** and "Band forms." * **P. knowlesi:** A zoonotic malaria showing a 24-hour erythrocytic cycle (quotidian fever).

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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