Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 301: Parasitemia is highest in which of the following types of malaria?

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

Explanation: **Explanation:** The correct answer is **Falciparum malaria (Option C)**. The degree of parasitemia in malaria is determined by the parasite's ability to invade red blood cells (RBCs) of different ages. **Why Falciparum malaria is correct:** * **Universal Invasion:** *Plasmodium falciparum* is unique because it can invade RBCs of **all ages** (young reticulocytes, mature cells, and old erythrocytes). * **High Parasitemia:** Because it is not restricted to a specific subset of cells, it can achieve extremely high levels of parasitemia (often >5%, sometimes exceeding 20-30%). * **Sequestration:** It also causes "cytoadherence," where infected RBCs stick to capillary endothelium, leading to microvascular obstruction and severe complications like cerebral malaria. **Why other options are incorrect:** * **Vivax and Ovale malaria (Options A & B):** These species are selective; they only invade **young RBCs (reticulocytes)**, which constitute only about 1-2% of total circulating RBCs. Consequently, parasitemia rarely exceeds 2%. * **Quartan malaria (Option D - *P. malariae*):** This species preferentially invades **older RBCs**. Since the population of aging erythrocytes is limited, parasitemia remains very low (usually <1%). **High-Yield NEET-PG Pearls:** * **Mnemonic for RBC Age:** **F**alciparum = **F**ull spectrum (All ages); **V**ivax = **V**ery young (Reticulocytes); **M**alariae = **M**ature (Old cells). * **Maurer’s dots** are seen in *P. falciparum*, while **Schüffner’s dots** are seen in *P. vivax/ovale*. * *P. falciparum* is the only species that causes **multiple rings** per RBC and **crescent-shaped (banana)** gametocytes. * **Recrudescence** is seen in *P. falciparum* (due to sub-optimal treatment), whereas **Relapse** is seen in *P. vivax/ovale* (due to hypnozoites in the liver).

Question 302: Which of the following statements is true regarding Acanthamoeba keratitis?

A. For the isolation of the causative agent, corneal scraping should be cultured on a nutrient agar plate.
B. The causative agent, Acanthamoeba is a helminth whose normal habitat is soil.
C. Keratitis due to Acanthamoeba is not seen in the immunocompromised patient.
D. Acanthamoeba does not depend upon a human host for the completion of its life-cycle. (Correct Answer)

Explanation: ### Explanation **Correct Option: D. Acanthamoeba does not depend upon a human host for the completion of its life-cycle.** *Acanthamoeba* is a **free-living amoeba** found ubiquitously in soil, water (tap water, swimming pools), and air. It is an **accidental pathogen** in humans. Its life cycle consists of two stages—the active **trophozoite** and the dormant **cyst**—both of which can occur entirely in the environment without requiring a human or animal host. **Analysis of Incorrect Options:** * **Option A:** For isolation, corneal scrapings should be cultured on **Non-Nutrient Agar (NNA)** seeded with a lawn of *E. coli*. The amoebae feed on the bacteria, creating characteristic "tracks." Standard nutrient agar does not support its growth effectively. * **Option B:** *Acanthamoeba* is a **protozoan**, not a helminth. While its habitat is indeed soil/water, the classification is incorrect. * **Option C:** While *Acanthamoeba* keratitis is most commonly associated with **contact lens users** (even immunocompetent ones), it can certainly occur in immunocompromised patients. In fact, in severely immunocompromised individuals, it can cause disseminated disease or **Granulomatous Amoebic Encephalitis (GAE)**. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Factor:** Over 80% of cases are associated with contact lens wear (poor hygiene or using tap water for cleaning). * **Clinical Feature:** Characterized by **intense pain** (disproportionate to clinical findings) and a pathognomonic **Ring Infiltrate** on the cornea. * **Diagnosis:** * **Gold Standard:** Culture on Non-Nutrient Agar with *E. coli*. * **Microscopy:** Calcofluor white stain or Giemsa stain showing double-walled cysts. * **Treatment:** Topical biguanides (e.g., **PHMB** - Polyhexamethylene biguanide) or Chlorhexidine.

Question 303: Which of the following diseases is transmitted by egg ingestion?

A. Taeniasis
B. Trichinosis
C. Hydatidosis (Correct Answer)
D. Strongyloidosis

Explanation: **Explanation:** The correct answer is **Hydatidosis** (Cystic Echinococcosis). This disease is caused by the larval stage of the dog tapeworm, *Echinococcus granulosus*. Humans serve as accidental intermediate hosts and acquire the infection by **ingesting embryonated eggs** passed in the feces of definitive hosts (dogs). Once ingested, the eggs hatch in the small intestine, releasing oncospheres that migrate to the liver and lungs to form hydatid cysts. **Analysis of Incorrect Options:** * **Taeniasis (A):** Caused by *Taenia saginata* or *Taenia solium*. It is transmitted by the **ingestion of larvae** (Cysticercus bovis/cellulosae) in undercooked beef or pork. (Note: Ingesting *T. solium* eggs causes Cysticercosis, not Taeniasis). * **Trichinosis (B):** Caused by *Trichinella spiralis*. It is transmitted by the **ingestion of encysted larvae** in undercooked meat (usually pork). * **Strongyloidosis (D):** Caused by *Strongyloides stercoralis*. Transmission occurs via **filariform larvae penetrating the skin** from contaminated soil, not by egg ingestion. **High-Yield Clinical Pearls for NEET-PG:** * **Modes of Transmission Mnemonic:** Remember **"EAT"** for organisms transmitted by egg ingestion: **E**nterobius, **A**scaris, **T**richuris, and *Echinococcus*. * **Hydatid Cyst:** Characterized by "Water lily sign" on imaging (detached endocyst) and managed via the **PAIR** technique (Puncture, Aspiration, Injection, Re-aspiration). * **Casoni’s Test:** An immediate hypersensitivity skin test used for diagnosis (though largely replaced by serology).

Question 304: All are seen in the cyst of E. Histolytica except?

A. Glycogen mass
B. Chromatid bars
C. Eccentric nucleus
D. Refractile nucleus (Correct Answer)

Explanation: ### Explanation The correct answer is **D. Refractile nucleus**. In the life cycle of *Entamoeba histolytica*, the cyst is the infective stage. In a **fresh, unstained wet mount preparation**, the nuclei of the cyst are **not visible** (non-refractile). They only become visible when stained with iodine or hematoxylin. In contrast, the nucleus of the **trophozoite** stage is often described as having a delicate, refractile nuclear membrane in some clinical contexts, but specifically for the cyst, the "refractile" property is not a characteristic feature. **Analysis of Options:** * **A. Glycogen mass:** Immature cysts (unicucleated and binucleated) contain a dense mass of glycogen which serves as a food reserve. This stains mahogany brown with iodine. It disappears as the cyst matures into the quadrinucleate stage. * **B. Chromatid bars:** These are oblong, cigar-shaped structures composed of ribonucleoproteins. They are characteristic of *E. histolytica* cysts and have rounded ends (unlike *E. coli* which has splintered ends). They also disappear in the mature stage. * **C. Eccentric nucleus:** While the nucleus of *E. histolytica* typically features a **central karyosome**, the nuclear positioning within the cytoplasm of a developing cyst can appear eccentric, especially when pushed aside by a large glycogen vacuole. **NEET-PG High-Yield Pearls:** * **Infective Stage:** Mature quadrinucleate cyst. * **Diagnostic Stage:** Trophozoite (in acute dysentery) or Cyst (in chronic cases/carriers). * **Chromatid Bars:** "Cigar-shaped" in *E. histolytica*; "Splinter-like/Frayed" in *E. coli*. * **Nuclear Morphology:** Small, central karyosome with fine, uniform peripheral chromatin (described as a "cartwheel appearance"). * **Staining:** Iodine is used to visualize nuclei and glycogen; Trichrome or Iron-hematoxylin is used for permanent smears.

Question 305: What is the most common parasite causing myocarditis?

A. Trichinella (Correct Answer)
B. Trypanosome
C. Ascaris
D. Plasmodium

Explanation: **Explanation:** **Trichinella spiralis** is recognized as the most common parasitic cause of myocarditis worldwide. While the adult worms reside in the intestines, the larvae migrate via the bloodstream to encyst in striated skeletal muscles. During this migratory phase, larvae frequently pass through the myocardium. Unlike skeletal muscle, the larvae do not encyst in the heart; instead, they provoke a severe inflammatory response (eosinophilic infiltration), leading to interstitial myocarditis. This is the most serious complication of trichinosis and the leading cause of death in these patients. **Analysis of Incorrect Options:** * **Trypanosoma cruzi:** While *T. cruzi* (Chagas disease) is a classic cause of chronic dilated cardiomyopathy and acute myocarditis, it is geographically restricted to Central and South America. *Trichinella* is more globally prevalent as a cause of parasitic myocarditis. * **Ascaris lumbricoides:** These larvae undergo heart-lung migration, but they typically pass through the pulmonary circulation without causing significant myocardial inflammation. Their primary pathology is intestinal obstruction or Loeffler’s syndrome (pneumonitis). * **Plasmodium:** While severe Malaria (especially *P. falciparum*) can cause microvascular sequestration and "malarial heart" in rare cases, it is not a primary or common cause of myocarditis. **Clinical Pearls for NEET-PG:** * **Triad of Trichinosis:** Myositis (muscle pain), periorbital edema, and marked peripheral eosinophilia. * **Diagnosis:** Muscle biopsy (showing encysted larvae in skeletal muscle) or Bachman intradermal test. * **Key Distinction:** Larvae **encyst** in skeletal muscle but **never encyst** in cardiac muscle (they cause inflammation and then die or move on).

Question 306: The mature cyst of Entamoeba histolytica differs from Entamoeba coli, except in which of the following features?

A. Size 6 to 15 microns
B. Nuclei are 1 to 4 in number
C. Karyosome is central in position
D. Chromatid bars seen (Correct Answer)

Explanation: ### Explanation The question asks for the feature that is **common** to both *Entamoeba histolytica* (E. histolytica) and *Entamoeba coli* (E. coli), as the other options represent points of differentiation. **1. Why "Chromatid bars seen" is the correct answer:** Both *E. histolytica* and *E. coli* possess **chromatoid bodies (bars)** in their immature cyst stages. While their morphology differs (cigar-shaped in *E. histolytica* vs. splinter-like in *E. coli*), the **presence** of these structures is a shared characteristic. Therefore, they do not "differ" in the fact that chromatid bars are seen. **2. Analysis of Incorrect Options (Points of Differentiation):** * **Size (Option A):** *E. histolytica* cysts are smaller (10–15 µm) compared to the larger *E. coli* cysts (15–30 µm). * **Number of Nuclei (Option B):** A mature cyst of *E. histolytica* contains **4 nuclei** (quadrinucleate). In contrast, a mature cyst of *E. coli* contains **8 nuclei** (octanucleate). * **Karyosome Position (Option C):** In *E. histolytica*, the karyosome is **small and central**, with fine, uniform peripheral chromatin. In *E. coli*, the karyosome is **large and eccentric** (off-center), with coarse, irregular peripheral chromatin. **3. High-Yield Clinical Pearls for NEET-PG:** * **E. histolytica:** Pathogenic; causes amoebic dysentery and liver abscesses. Look for **ingested RBCs** in the trophozoite (pathognomonic). * **E. coli:** Non-pathogenic commensal; its presence indicates fecal contamination of food/water. * **Stain of choice:** Iron-hematoxylin or Trichrome stain is used to visualize nuclear details clearly. * **Infective stage:** The **mature cyst** is the infective stage for both parasites, transmitted via the fecal-oral route.

Question 307: Chandler index is an important tool in epidemiology. Which of the following is its least likely use?

A. Determining case severity and prognosis (Correct Answer)
B. Impact of control programme
C. Endemicity
D. Load of infection in the community

Explanation: **Explanation:** The **Chandler Index** is a classic epidemiological tool used specifically for **Hookworm infection** (*Ancylostoma duodenale* and *Necator americanus*). It represents the average number of eggs per gram (EPG) of stool calculated from a representative sample of the community. **Why Option A is the correct answer:** The Chandler Index is a **population-based metric**, not a clinical one. While it measures the "worm burden" of a community, it is **not used to determine individual case severity or prognosis**. Clinical severity in an individual depends on factors like nutritional status, iron stores, and host immunity, rather than just the egg count. Prognosis is determined by clinical response to anthelmintic treatment and iron supplementation. **Analysis of Incorrect Options:** * **B. Impact of control programme:** By comparing the Chandler Index before and after an intervention (e.g., mass drug administration or improved sanitation), health authorities can quantify the effectiveness of the program. * **C. Endemicity:** The index categorizes the level of infection in a region. A Chandler Index **< 200** is considered suggestive of low endemicity/potential disappearance, while **> 500** indicates a significant public health problem. * **D. Load of infection in the community:** This is the primary definition of the index. It estimates the total intensity of the parasite reservoir within a specific population. **High-Yield Clinical Pearls for NEET-PG:** * **Formula:** Chandler Index = (Total number of eggs in all samples) / (Total number of samples). * **Hookworm & Anemia:** The primary morbidity is **Microcytic Hypochromic Anemia** due to chronic blood loss (Ancylostoma: 0.15–0.2 ml/day; Necator: 0.03 ml/day). * **Ground Itch:** The allergic reaction at the site of larval entry (L3 - Filariform larva). * **Drug of Choice:** Albendazole (400 mg single dose).

Question 308: Which of the following is known as the lung fluke?

A. Schistosoma mansoni
B. Schistosoma haematobium
C. Paragonimus spp (Correct Answer)
D. Clonorchis sinensis

Explanation: **Explanation:** The correct answer is **Paragonimus spp.** (specifically *Paragonimus westermani*), which is the most common cause of human paragonimiasis. It is known as the **lung fluke** because the adult worms reside in the parenchyma of the lungs, often encapsulated within fibrous cysts. **Why Paragonimus spp. is correct:** Humans typically acquire the infection by consuming raw or undercooked crustaceans (crabs or crayfish) containing metacercariae. Once ingested, the larvae excyst in the duodenum, penetrate the intestinal wall, and migrate through the diaphragm into the lungs. Clinically, it presents with a chronic cough and **hemoptysis** (rusty sputum), often mimicking pulmonary tuberculosis—a high-yield "masking" clinical scenario for NEET-PG. **Analysis of Incorrect Options:** * **Schistosoma mansoni:** Known as the **intestinal fluke** (or blood fluke). It resides in the inferior mesenteric veins and causes intestinal schistosomiasis and portal hypertension. * **Schistosoma haematobium:** Known as the **vesical blood fluke**. It resides in the venous plexus of the urinary bladder and is classically associated with hematuria and squamous cell carcinoma of the bladder. * **Clonorchis sinensis:** Known as the **Chinese liver fluke**. It inhabits the bile ducts and is a significant risk factor for cholangiocarcinoma. **NEET-PG High-Yield Pearls:** * **Diagnostic Stage:** Eggs are found in sputum or feces (golden-brown, operculated). * **Intermediate Hosts:** 1st host is a Snail; 2nd host is a Crab/Crayfish. * **Drug of Choice:** Praziquantel is the treatment for most trematodes, including *Paragonimus*. * **Radiology:** May show "ring-shadow" opacities or infiltrates in the lungs.

Question 309: Schistosomiasis infects humans at which of the following stages of its life cycle?

A. Egg
B. Miracidia
C. Cercariae (Correct Answer)
D. All of the above

Explanation: **Explanation:** The correct answer is **Cercariae**. Schistosomiasis (Bilharzia) is unique among trematodes because it infects humans via **direct skin penetration** rather than ingestion. 1. **Why Cercariae is correct:** The infective stage for humans is the **fork-tailed cercaria**. These are released from the intermediate host (freshwater snails) into water. When a human comes into contact with contaminated water, the cercariae penetrate the intact skin using proteolytic enzymes. During penetration, they lose their tails to become **schistosomulae**, which then migrate through the venous circulation to the liver and eventually the vesical or mesenteric venous plexuses. 2. **Why other options are incorrect:** * **Egg:** Eggs are the **diagnostic stage** excreted in human feces or urine. They are not infective to humans; instead, they must reach water to hatch into miracidia. * **Miracidia:** This is the infective stage for the **intermediate host (snail)**. Miracidia hatch from eggs in water and seek out specific snail species (e.g., *Biomphalaria*, *Bulinus*) to continue the life cycle. **High-Yield NEET-PG Pearls:** * **Intermediate Hosts:** *S. haematobium* (Bulinus snail), *S. mansoni* (Biomphalaria snail), *S. japonicum* (Oncomelania snail). * **Clinical Presentation:** Initial infection often presents as **"Swimmer’s Itch"** (dermatitis at the site of cercarial entry). Chronic *S. haematobium* is a major risk factor for **Squamous Cell Carcinoma of the urinary bladder**. * **Morphology:** Schistosomes are non-hermaphroditic (dioecious) "blood flukes" where the female resides in the **gynecophoric canal** of the male.

Question 310: T. trichuria maintains its position in the intestinal tract by:

A. Penetration into tissues
B. Anchorage with its anterior portion (Correct Answer)
C. Retention in the folds of the mucosa
D. Attachment with its cutting plate

Explanation: ### Explanation **Correct Answer: B. Anchorage with its anterior portion** *Trichuris trichiura* (Whipworm) has a characteristic morphology where the **anterior three-fifths** of the body is thin and hair-like, while the posterior two-fifths is thick and bulbous. To maintain its position in the large intestine (primarily the cecum), the worm uses its thin, needle-like anterior end to **thread itself into the mucosal epithelium**. It creates a tunnel within the superficial layers of the mucosa, effectively "stitching" itself into the intestinal wall. This mechanical anchorage prevents the worm from being expelled by peristalsis. **Analysis of Incorrect Options:** * **A. Penetration into tissues:** While the anterior end enters the mucosa, it does not deeply penetrate into the systemic tissues or organs like *Strongyloides* or *Trichinella*. It remains localized to the superficial mucosal layers. * **C. Retention in the folds of the mucosa:** This is a passive mechanism. *T. trichiura* uses an active mechanical anchorage rather than simply hiding in the crypts or folds. * **D. Attachment with its cutting plate:** This is the mechanism used by **Hookworms** (*Ancylostoma duodenale*), which possess teeth or cutting plates to attach to the villi. *Trichuris* lacks these structures. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Known as the "Whipworm" due to its whip-like shape. * **Egg Morphology:** Characteristic **Barrel-shaped** (lemon-shaped) eggs with **bipolar mucus plugs**. * **Clinical Presentation:** Heavy infections in children can lead to **Rectal Prolapse** due to increased peristalsis and straining. * **Anemia:** Unlike hookworms, *Trichuris* causes blood loss primarily through mucosal oozing at the site of attachment, leading to Iron Deficiency Anemia in heavy loads. * **Treatment:** Albendazole or Mebendazole are the drugs of choice.

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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