Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 381: All of the following have operculated eggs except?

A. Clonorchis sinensi
B. Diphyllobothrium latum
C. Hymenolepis dimunita (Correct Answer)
D. Fasciola hepatica

Explanation: ### Explanation The presence of an **operculum** (a lid-like structure at one pole of the egg) is a characteristic feature of most **Trematodes** (flukes) and certain **Cestodes** (tapeworms). **1. Why Hymenolepis diminuta is the correct answer:** *Hymenolepis diminuta* (rat tapeworm) belongs to the order Cyclophyllidea. Eggs of all Cyclophyllidean cestodes (including *H. nana*, *Taenia* spp., and *Echinococcus*) are **non-operculated**. They are characterized by a thick shell containing a hexacanth embryo (oncosphere). **2. Analysis of Incorrect Options:** * **Clonorchis sinensis (Option A):** This is a liver fluke (Trematode). All trematodes produce operculated eggs, with the notable **exception of Schistosoma** species. *Clonorchis* eggs are classically described as having a "convex operculum" resting on shoulders. * **Diphyllobothrium latum (Option B):** This is a Pseudophyllidean cestode (fish tapeworm). Unlike other tapeworms, Pseudophyllideans produce **operculated eggs** that resemble fluke eggs, as they must hatch in water to release a ciliated larva (coracidium). * **Fasciola hepatica (Option C):** This is a large liver fluke. It produces large, ovoid, **operculated** eggs that are unembryonated when passed in feces. **3. NEET-PG High-Yield Pearls:** * **The "Rule of Exceptions":** All Trematodes have operculated eggs **EXCEPT** *Schistosoma* (which have spines). * **The Cestode Exception:** All Cestodes have non-operculated eggs **EXCEPT** *Diphyllobothrium latum*. * **Bile Staining:** *H. diminuta* eggs are bile-stained (yellow-brown), whereas *H. nana* eggs are non-bile stained (colorless). * **Polar Filaments:** *H. nana* eggs have polar filaments; *H. diminuta* eggs **lack** polar filaments.

Question 382: What is the correct sequence of the malaria parasite life cycle?

A. Exoerythrocytic stage, Gametocytic stage, Erythrocytic stage, Sporogony
B. Exoerythrocytic stage, Erythrocytic stage, Gametocytic stage, Sporogony (Correct Answer)
C. Exoerythrocytic stage, Sporogony, Gametocytic stage, Erythrocytic stage
D. Exoerythrocytic stage, Sporogony, Erythrocytic stage, Gametocytic stage

Explanation: **Explanation:** The life cycle of *Plasmodium* involves two hosts: the **Anopheles mosquito** (definitive host) and **Humans** (intermediate host). The sequence follows a logical progression of infection, multiplication, and transmission: 1. **Exoerythrocytic Stage (Liver Stage):** Following a mosquito bite, sporozoites enter the bloodstream and invade hepatocytes. Here, they undergo asexual multiplication (schizogony) to form merozoites. 2. **Erythrocytic Stage (Blood Stage):** Merozoites are released from the liver and infect Red Blood Cells (RBCs). This cycle of multiplication causes the clinical symptoms of malaria (fever/chills). 3. **Gametocytic Stage:** Some merozoites differentiate into male and female gametocytes within the RBCs. These are the infective forms for the mosquito. 4. **Sporogony (Sexual Cycle):** When a mosquito ingests gametocytes, fertilization occurs in the mosquito’s midgut, eventually producing new sporozoites, completing the cycle. **Analysis of Incorrect Options:** * **Option A:** Incorrectly places the Gametocytic stage before the Erythrocytic stage. Gametocytes can only develop after the parasite has established an infection in the blood. * **Options C & D:** Incorrectly place Sporogony (which occurs in the mosquito) before the stages that occur in the human host. **High-Yield Clinical Pearls for NEET-PG:** * **Infective form to humans:** Sporozoite. * **Infective form to mosquito:** Gametocyte. * **Hypnozoites:** Dormant liver stages found in *P. vivax* and *P. ovale*, responsible for **relapse**. * **Recrudescence:** Seen in *P. falciparum* due to the persistence of low-level parasitemia in the blood (not liver). * **Schüffner’s dots:** Characteristic of *P. vivax* and *P. ovale*.

Question 383: A patient with AIDS experienced an acute episode of diarrhea. Stool examination revealed an oval structure, 8 to 9 micrometers in diameter, that was acid-fast and fluoresced blue under ultraviolet light. What is the most likely identification of this organism?

A. Cryptosporidium
B. Cyclospora (Correct Answer)
C. Enterocytozoon
D. Giardia

Explanation: **Explanation:** The clinical presentation of acute diarrhea in an immunocompromised (AIDS) patient, combined with specific morphologic and staining characteristics, points directly to **Cyclospora cayetanensis**. **Why Cyclospora is correct:** The key diagnostic features provided are: 1. **Size:** Cyclospora oocysts are typically **8–10 μm** in diameter (twice the size of *Cryptosporidium*). 2. **Staining:** They are **variably acid-fast** (some stain pink/red, others remain ghost-like). 3. **Autofluorescence:** This is the pathognomonic "clincher" for NEET-PG. Under UV light (330–365 nm), Cyclospora oocysts exhibit **intense blue/green autofluorescence** due to the presence of phenolic compounds in the oocyst wall. **Why other options are incorrect:** * **Cryptosporidium:** While also acid-fast and common in AIDS, the oocysts are significantly smaller (**4–6 μm**) and **do not** exhibit autofluorescence. * **Enterocytozoon (Microsporidia):** These are much smaller (1–3 μm) and are not acid-fast; they require specialized stains like Modified Trichrome or Calcofluor White. * **Giardia:** These are flagellated protozoa (cysts are 8–12 μm) but are **not acid-fast** and do not fluoresce. They typically present with foul-smelling, fatty stools (steatorrhea). **High-Yield Clinical Pearls for NEET-PG:** * **Size Comparison:** *Cryptosporidium* (4–6 μm) < *Cyclospora* (8–10 μm) < *Isospora/Cystoisospora* (25–30 μm). * **Treatment:** Unlike *Cryptosporidium* (Nitazoxanide), *Cyclospora* is treated with **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. * **Transmission:** Often associated with contaminated imported soft fruits (raspberries, strawberries) and leafy vegetables.

Question 384: What causes swollen belly syndrome?

A. Ascaris lumricoides
B. Strongyloides stercoralis
C. Strongyloides fuelleborni (Correct Answer)
D. Wucheraria bancrofti

Explanation: **Explanation:** **Strongyloides fuelleborni** is the causative agent of **Swollen Belly Syndrome (SBS)**, a specific clinical entity primarily reported in infants in Papua New Guinea and parts of Africa. **Why it is the correct answer:** *S. fuelleborni* is a parasite of non-human primates that can infect humans. In infants, heavy infection leads to a severe protein-losing enteropathy. This results in profound **hypoalbuminemia**, which causes generalized edema and massive ascites, giving the characteristic "swollen belly" appearance. It is often associated with respiratory distress and high mortality if untreated. **Analysis of Incorrect Options:** * **A. *Ascaris lumbricoides*:** While heavy Ascaris infections can cause abdominal distension due to a large bolus of worms (intestinal obstruction), it does not cause the specific clinical triad of SBS (ascites/hypoalbuminemia). * **B. *Strongyloides stercoralis*:** This is the common human threadworm. It causes "Hyperinfection Syndrome" in immunocompromised hosts but is not the specific cause of the SBS clinical entity. * **D. *Wuchereria bancrofti*:** This filarial nematode causes lymphatic filariasis. While it can cause "Chylous ascites" in rare cases, its hallmark is elephantiasis of the limbs and scrotum, not Swollen Belly Syndrome. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** *S. fuelleborni* is unique because it can be transmitted via **breast milk** (transmammary transmission), which explains why it affects very young infants. * **Diagnosis:** Identification of eggs in the stool (unlike *S. stercoralis*, where larvae are usually found). * **Treatment:** Albendazole or Ivermectin. * **Key Association:** Always link "Swollen Belly Syndrome" + "Infant" + "Papua New Guinea" to *Strongyloides fuelleborni*.

Question 385: What is the largest protozoan?

A. Entamoeba histolytica
B. Balantidium coli (Correct Answer)
C. Escherichia coli
D. Plasmodium

Explanation: **Explanation:** **Balantidium coli** is the correct answer because it is the **largest protozoan** known to infect humans. It is the only member of the ciliate group (Phylum Ciliophora) that is pathogenic to humans. The trophozoite stage is massive, typically measuring **50–200 μm** in length and **40–70 μm** in width, making it easily visible under low-power microscopy. **Analysis of Incorrect Options:** * **Entamoeba histolytica:** This is a common intestinal amoeba, but it is significantly smaller than *B. coli*, with trophozoites measuring only **10–60 μm**. * **Escherichia coli:** This is a **bacterium**, not a protozoan. While it shares a species name with *B. coli*, it is a prokaryote and much smaller (approx. 1–2 μm). * **Plasmodium:** These are intracellular blood parasites (sporozoans). They are microscopic and much smaller than ciliates, typically residing within red blood cells (approx. 7–8 μm). **High-Yield Clinical Pearls for NEET-PG:** * **Natural Reservoir:** Pigs are the primary reservoir; infection is common in pig farmers (fecal-oral route). * **Morphology:** It is unique for having **two nuclei**: a large kidney-shaped **macronucleus** (vegetative functions) and a small **micronucleus** (reproductive functions). * **Locomotion:** It moves via rows of hair-like **cilia**. * **Clinical Presentation:** It causes "Balantidial dysentery," which mimics amoebiasis by producing **flask-shaped ulcers** in the large intestine. * **Treatment:** The drug of choice is **Tetracycline**.

Question 386: Man serves as the secondary host for which of the following?

A. Malaria (Correct Answer)
B. Tuberculosis
C. Filariasis
D. Relapsing fever

Explanation: **Explanation:** In parasitology, the classification of hosts is determined by the stage of the parasite's life cycle. A **Definitive (Primary) Host** is where the parasite undergoes its sexual cycle, while an **Intermediate (Secondary) Host** is where the parasite undergoes its asexual cycle or larval stage. **1. Why Malaria is Correct:** In the life cycle of *Plasmodium* species, the **sexual cycle (sporogony)** occurs within the female *Anopheles* mosquito, making it the definitive host. The **asexual cycle (schizogony)** occurs in humans (within hepatocytes and erythrocytes). Therefore, **man serves as the intermediate/secondary host** for Malaria. **2. Analysis of Incorrect Options:** * **Filariasis:** In *Wuchereria bancrofti*, humans are the **definitive host** because the adult worms (sexual stage) reside in the human lymphatic system. The mosquito acts as the intermediate host. * **Tuberculosis:** This is caused by *Mycobacterium tuberculosis*, a bacterium. The concept of definitive/intermediate hosts applies to parasites (protozoa and helminths), not bacteria. Humans are the primary reservoir. * **Relapsing Fever:** Caused by *Borrelia* species (spirochetes). Like TB, this is a bacterial infection where humans are either the primary reservoir (louse-borne) or accidental hosts (tick-borne). **Clinical Pearls for NEET-PG:** * **Exception to the Rule:** In most parasitic infections, man is the definitive host. Malaria and **Hydatid disease (*Echinococcus granulosus*)** are the two classic exceptions where man is the intermediate host. * **Accidental Host:** In Hydatid disease, man is an "accidental" intermediate host and a "dead-end" host because the life cycle is not naturally completed through humans. * **Vector vs. Host:** Always distinguish between the vector (the transmitter) and the biological host (where development occurs). In Malaria, the mosquito is both the vector and the definitive host.

Question 387: What is the gold standard investigation for diagnosing cystic echinococcosis?

A. Ultrasound (USG) (Correct Answer)
B. X-ray
C. ELISA
D. CT scan

Explanation: **Explanation:** **Cystic Echinococcosis (Hydatid Disease)** is caused by the larval stage of *Echinococcus granulosus*. **Why Ultrasound (USG) is the Gold Standard:** Ultrasound is the primary diagnostic tool and the "gold standard" because it is highly sensitive, non-invasive, and cost-effective. It allows for the visualization of pathognomonic features such as daughter cysts, "hydatid sand," and the "water lily sign" (detached endocyst). Furthermore, the **WHO-IWGE classification**, which guides the management (surgery vs. PAIR vs. medical therapy), is based entirely on USG findings. **Analysis of Incorrect Options:** * **X-ray:** While it may show calcification of the cyst wall or a "double contour" sign in lung hydatids, it lacks the sensitivity and detail required for a definitive diagnosis or staging. * **ELISA:** Serology is a supportive investigation. It is useful for confirming the diagnosis but can yield false negatives in intact or calcified cysts and false positives due to cross-reactivity with other helminths. * **CT scan:** CT is superior for detecting calcification and identifying cysts in extra-hepatic locations (e.g., bone, brain), but it is not the first-line gold standard for routine abdominal screening and staging. **High-Yield Clinical Pearls for NEET-PG:** * **Definitive Host:** Dog; **Intermediate Host:** Sheep (Man is an accidental dead-end host). * **Most common site:** Liver (Right lobe > Left lobe), followed by the Lungs. * **Casoni’s Test:** An immediate hypersensitivity skin test (now largely replaced by ELISA). * **Management:** Small, inactive cysts (CE4/CE5) are monitored; active cysts are treated with **Albendazole** and/or the **PAIR** technique (Puncture, Aspiration, Injection, Re-aspiration).

Question 388: Donovanosis is caused by which bacterium?

A. Calymmatobacterium granulomatosis (Correct Answer)
B. Legionella
C. Chlamydia
D. Rickettsia

Explanation: **Explanation:** **Donovanosis**, also known as **Granuloma Inguinale**, is a chronic, progressive bacterial infection of the genital and perianal skin. It is caused by **Klebsiella granulomatis** (formerly known as **Calymmatobacterium granulomatosis**). 1. **Why Option A is correct:** The causative agent is a Gram-negative, pleomorphic, intracellular bacillus. In clinical practice, the diagnosis is confirmed by identifying **Donovan bodies**—safety-pin-shaped organisms seen within the cytoplasm of large mononuclear cells (macrophages) on a Wright-Giemsa or Leishman stain. 2. **Why the other options are incorrect:** * **Legionella:** Causes Legionnaires' disease (atypical pneumonia) and Pontiac fever; it is not associated with sexually transmitted genital ulcers. * **Chlamydia:** Specifically *Chlamydia trachomatis* (serotypes L1-L3), causes **Lymphogranuloma Venereum (LGV)**. While LGV also causes genital lesions, it is characterized by painful inguinal lymphadenopathy (Buboes) and the "Groove sign," unlike the painless ulcers of Donovanosis. * **Rickettsia:** These are obligate intracellular bacteria transmitted by arthropod vectors (ticks, lice, fleas) causing typhus and spotted fevers, not genital infections. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Characterized by **painless, beefy-red, velvety ulcers** that bleed easily on touch (friable). * **Key Feature:** There is **no inguinal lymphadenopathy**; however, "pseudobuboes" (subcutaneous granulation tissue) may occur in the groin. * **Microscopy:** Look for the "Safety-pin appearance" of Donovan bodies. * **Treatment of Choice:** Azithromycin (1g orally once a week or 500mg daily) for at least 3 weeks or until lesions heal.

Question 389: A 50-year-old male presented with various subcutaneous nodules over the right iliac crest, measuring approximately 1 cm in diameter. Adult worms and microfilariae were detected within the excised nodules. Which of the following organisms is likely the causative agent?

A. Onchocerca volvulus
B. Loa Loa (Correct Answer)
C. Mansonella
D. Brugia malayi

Explanation: ### Explanation The correct answer is **Loa loa** (African Eye Worm). **1. Why Loa loa is correct:** The clinical presentation of subcutaneous nodules containing both **adult worms and microfilariae** is characteristic of *Loa loa*. While *Loa loa* is famous for subconjunctival migration (Calabar swellings), the adult worms reside in the subcutaneous tissues. A unique diagnostic feature of Loiasis is that the female worm releases **sheathed microfilariae** directly into the subcutaneous tissue or blood. Finding both stages in an excised nodule confirms the presence of the gravid adult worm in its natural habitat. **2. Why other options are incorrect:** * **Onchocerca volvulus:** While it causes subcutaneous nodules (Onchocercomas), the microfilariae are typically found in the **skin (dermis)** and the eye, not primarily within the nodule alongside the adult in a way that distinguishes it from Loa loa in this specific question context. Furthermore, *O. volvulus* microfilariae are **unsheathed**. * **Brugia malayi:** This is a lymphatic filarial worm. It resides in the **lymphatic vessels and nodes**, causing elephantiasis of the distal limbs. It does not typically present as isolated subcutaneous nodules over the iliac crest. * **Mansonella:** *M. streptocerca* can cause skin changes, but the nodules are less common, and the microfilariae are **unsheathed** and usually found in the skin snips. **3. NEET-PG High-Yield Pearls:** * **Vector:** *Loa loa* is transmitted by the **Chrysops** fly (Deer fly/Mango fly). * **Microfilariae Periodicity:** *Loa loa* exhibits **diurnal periodicity** (found in peripheral blood during the day). * **Calabar Swellings:** These are transient, localized subcutaneous edemas (angioedema) caused by a hypersensitivity reaction to the metabolic products of the migrating adult worm. * **Drug of Choice:** **Diethylcarbamazine (DEC)** is the treatment of choice, but caution is required if microfilarial load is high (risk of encephalopathy).

Question 390: Enterotest is used for the diagnosis of which of the following?

A. E. histolytica
B. N. fowleri
C. T. Cruzi
D. Giardia lambia (Correct Answer)

Explanation: **Explanation:** **Enterotest (String Test)** is a diagnostic procedure used to sample the contents of the upper gastrointestinal tract. In this test, a patient swallows a gelatin capsule containing a weighted nylon string. The capsule dissolves in the stomach, and the string uncoils into the duodenum and jejunum. After several hours, the string is withdrawn, and the bile-stained mucus adhering to it is examined microscopically for motile trophozoites. **Why Giardia lamblia is correct:** *Giardia lamblia* primarily colonizes the **duodenum and upper jejunum**. Since these parasites are often firmly attached to the intestinal mucosa via their ventral sucking discs, they may not always be seen in routine stool examinations (which often require three samples due to erratic shedding). The Enterotest provides a direct sample from the parasite’s primary habitat, making it a highly specific diagnostic tool for Giardiasis. **Why other options are incorrect:** * **E. histolytica:** Primarily affects the **large intestine** (colon). Diagnosis is typically made via stool microscopy for cysts/trophozoites or colonoscopic biopsy. * **N. fowleri:** An amoeba that causes Primary Amoebic Meningoencephalitis (PAM). Diagnosis involves **CSF analysis** (wet mount) to look for motile trophozoites. * **T. cruzi:** The causative agent of Chagas disease. It is a blood and tissue parasite diagnosed via peripheral blood smears, serology, or xenodiagnosis, not intestinal sampling. **High-Yield Clinical Pearls for NEET-PG:** * **Other uses:** Enterotest can also be used to diagnose *Strongyloides stercoralis* and *Cryptosporidium*. * **Giardia Morphology:** Look for "falling leaf motility" on wet mounts and a "pear-shaped" trophozoite with two nuclei (resembling a "monkey face" or "old man with glasses"). * **Drug of Choice:** Metronidazole or Tinidazole. * **Stool findings:** Characterized by foul-smelling, greasy stools (steatorrhea) without blood or mucus (non-invasive).

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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