Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 211: Chagas disease is a parasitic disease that affects the intestine. What is the vector for this disease?

A. Reduvid bug (Correct Answer)
B. Tse tse fly
C. Sand fly
D. Hard tick

Explanation: **Explanation:** **Chagas Disease (American Trypanosomiasis)** is caused by the protozoan parasite *Trypanosoma cruzi*. 1. **Why the Reduvid bug is correct:** The primary vector is the **Reduvid bug** (also known as the Triatomine bug, "kissing bug," or assassin bug). The parasite is transmitted not through the bite itself, but via the bug's **feces**. The bug typically bites the face (near the lips) and defecates simultaneously; the host then accidentally rubs the infective metacyclic trypomastigotes into the bite wound or mucous membranes. 2. **Analysis of Incorrect Options:** * **Tse-tse fly (*Glossina*):** Vector for **African Trypanosomiasis** (Sleeping Sickness) caused by *Trypanosoma brucei*. * **Sand fly (*Phlebotomus*):** Vector for **Leishmaniasis** (Kala-azar). * **Hard tick (*Ixodid*):** Vector for diseases like Babesiosis, Kyasanur Forest Disease (KFD), and Lyme disease. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Features:** * **Acute Phase:** **Romaña’s sign** (unilateral painless periorbital edema) and Chagoma (localized skin swelling). * **Chronic Phase:** Affects hollow viscera leading to **Megaesophagus** and **Megacolon** (due to destruction of Auerbach’s plexus) and **Dilated Cardiomyopathy** (most common cause of death). * **Diagnosis:** C-shaped trypomastigotes in peripheral blood (acute); Xenodiagnosis or Serology (chronic). * **Treatment:** Benznidazole or Nifurtimox.

Question 212: A patient with prolonged diarrhea undergoes esophagogastroduodenoscopy. Biopsy of the small intestine demonstrates numerous crescent-shaped protozoa adjacent to the epithelial brush border. Which of the following organisms is the most likely pathogen?

A. Entamoeba histolytica
B. Escherichia coli
C. Giardia lamblia (Correct Answer)
D. Naegleria fowleri

Explanation: ### Explanation **Correct Answer: C. Giardia lamblia** The clinical presentation and histopathological findings are classic for **Giardiasis**. * **Mechanism:** *Giardia lamblia* (or *G. duodenalis*) trophozoites are pear-shaped or **crescent-shaped** (when viewed laterally) and possess a ventral sucking disc. They attach to the **brush border of the duodenal and jejunal enterocytes** but do not invade the mucosa. * **Pathology:** This attachment leads to the blunting of villi and malabsorption, resulting in foul-smelling, non-bloody, fatty diarrhea (steatorrhea). The biopsy finding of crescentic organisms "falling off" or "clinging to" the epithelial surface is a high-yield diagnostic feature. **Analysis of Incorrect Options:** * **A. Entamoeba histolytica:** Primarily affects the **colon** (not the small intestine). Histology shows "flask-shaped ulcers" and trophozoites with ingested RBCs (erythrophagocytosis). * **B. Escherichia coli:** This is a bacterium, not a protozoan. While ETEC/EPEC cause diarrhea, they would not appear as large crescent-shaped protozoa on biopsy. * **D. Naegleria fowleri:** This is a free-living amoeba that causes **Primary Amoebic Meningoencephalitis (PAM)**. It enters through the cribriform plate via nasal inhalation and does not cause intestinal disease. **High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** Duodenum and upper jejunum (acidic pH favors excystation). * **Diagnosis:** Stool microscopy (cysts/trophozoites), String test (Entero-test), or biopsy. * **Morphology:** Trophozoite has a "Monkey face" or "Owl's eye" appearance (2 nuclei, 4 pairs of flagella). * **Risk Factors:** IgA deficiency (predisposes to chronic giardiasis). * **Treatment:** Metronidazole or Tinidazole.

Question 213: What is the gold standard diagnostic test for babesiosis?

A. Peripheral blood smear examination (Correct Answer)
B. Blood culture
C. Polymerase chain reaction (PCR)
D. Enzyme-linked immunosorbent assay (ELISA)

Explanation: **Explanation:** **1. Why Peripheral Blood Smear (PBS) is the Gold Standard:** The definitive diagnosis of babesiosis relies on the direct visualization of *Babesia* parasites within host erythrocytes. A **Giemsa or Wright-stained peripheral blood smear** (both thick and thin) is considered the gold standard because it allows for the identification of pathognomonic features: * **Maltese Cross Appearance:** Tetrads of merozoites (highly specific for *Babesia microti*). * **Pleomorphic Ring Forms:** These can mimic *Plasmodium falciparum* but are distinguished by the absence of malarial pigment (hemozoin) and the presence of extracellular ring forms. **2. Why other options are incorrect:** * **Blood Culture (B):** While *Babesia* can be isolated via specialized automated systems or hamster inoculation, these methods are time-consuming, expensive, and not used in routine clinical practice. * **PCR (C):** PCR is more sensitive than microscopy, especially in cases of low parasitemia or for monitoring treatment response. However, it is not yet the "gold standard" due to limited availability and lack of standardization across all laboratories. * **ELISA (D):** Serology detects antibodies (IgM/IgG) and is useful for epidemiological studies or chronic infections. It cannot distinguish between an active and a past infection. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Ixodes scapularis* tick (same as Lyme disease and Anaplasmosis). * **Clinical Presentation:** Fever, hemolytic anemia, and hemoglobinuria. Severe in asplenic patients. * **Microscopy Tip:** Unlike Malaria, *Babesia* lacks gametocytes and intracellular pigment. * **Treatment:** Atovaquone + Azithromycin (preferred) or Clindamycin + Quinine (for severe cases).

Question 214: Which parasite remains alive without development or multiplication?

A. Definitive host
B. Intermediate host
C. Paratenic host (Correct Answer)
D. None of the above

Explanation: ### Explanation In parasitology, hosts are classified based on the role they play in the parasite's life cycle. The correct answer is **Paratenic host** (also known as a transport host). **1. Why Paratenic Host is Correct:** A paratenic host is an "accidental" or "substitute" host where the parasite enters but **does not undergo any development or multiplication**. The parasite remains in a dormant or encysted state, staying alive and infective until the paratenic host is consumed by the definitive host. It serves primarily as a bridge to close an ecological gap between the intermediate and definitive hosts. * *Example:* Small fish acting as paratenic hosts for *Diphyllobothrium latum* plerocercoid larvae. **2. Why Other Options are Incorrect:** * **Definitive Host:** This is the host in which the parasite reaches **sexual maturity** and undergoes sexual reproduction (e.g., Humans for *Taenia saginata*). * **Intermediate Host:** This is the host in which the parasite undergoes **essential development** or asexual reproduction (e.g., Freshwater snails for *Schistosoma*). Unlike a paratenic host, the parasite *must* change stages here to continue its life cycle. **3. Clinical Pearls for NEET-PG:** * **Reservoir Host:** An animal host that maintains the parasite cycle in nature and serves as a source of infection to humans (e.g., dogs for *Leishmania*). * **Accidental Host:** A host that is not suitable for the parasite's normal development; the parasite often reaches a "dead-end" (e.g., Humans for *Echinococcus granulosus*). * **High-Yield Example:** In **Toxocariasis** (Visceral Larva Migrans), humans act as paratenic hosts because the larvae migrate through tissues but never mature into adult worms.

Question 215: Which of the following is NOT true of Giardiasis?

A. Complement fixation test is diagnostic (Correct Answer)
B. Stool contains only cysts
C. Habitat is the colon
D. Trophozoites and cysts are found in the duodenum

Explanation: ### Explanation **Giardiasis** is caused by the flagellated protozoan *Giardia lamblia* (also known as *G. intestinalis* or *G. duodenalis*). **1. Why Option A is the Correct Answer (The False Statement):** Diagnosis of Giardiasis primarily relies on **microscopic examination** of stool (detecting cysts or trophozoites) or **antigen detection** (ELISA/Immunochromatography). Serological tests like the **Complement Fixation Test (CFT)** are **not diagnostic** because Giardia is a luminal parasite that does not typically invade the tissues; therefore, it does not elicit a significant systemic antibody response useful for routine diagnosis. **2. Analysis of Other Options:** * **Option B (Stool contains only cysts):** In formed stools, only the resistant **cyst** stage is typically found. Trophozoites are usually only seen in liquid or diarrheic stools because they disintegrate rapidly outside the body. * **Option C (Habitat is the colon):** This is a **technically incorrect statement** in many textbooks (as the primary habitat is the duodenum and upper jejunum), but in the context of this specific MCQ, Option A is the "most" false/intended answer because CFT has no role in diagnosis. *Note: Some older sources incorrectly grouped intestinal protozoa together, but for NEET-PG, remember the habitat is the Duodenum.* * **Option D (Trophozoites and cysts are found in the duodenum):** The duodenum is the primary site of excystation and multiplication. Both stages can be recovered via **Entero-test (String test)** or duodenal aspiration. **Clinical Pearls for NEET-PG:** * **Morphology:** Trophozoite is pear-shaped, has a "falling leaf" motility, and a "tennis racket" or "old man with glasses" appearance (due to two nuclei and suction discs). * **Pathogenesis:** Causes malabsorption (steatorrhea) by "carpeting" the duodenal mucosa, leading to blunting of villi. * **Drug of Choice:** Tinidazole (preferred over Metronidazole). * **Association:** Increased incidence in patients with **Common Variable Immunodeficiency (CVID)** due to IgA deficiency.

Question 216: Novy-McNeal-Nicolle medium is used for which of the following organisms?

A. Giardia lamblia
B. Leishmania donovani (Correct Answer)
C. Echinococcus
D. Toxoplasma gondii

Explanation: **Explanation:** The **Novy-McNeal-Nicolle (NNN) medium** is the classic culture medium used for the isolation of **Leishmania donovani** and *Trypanosoma cruzi*. It is a biphasic medium consisting of a solid phase (blood agar made with rabbit blood) and a liquid phase (overlay of saline or broth). 1. **Why Leishmania donovani is correct:** In NNN medium, the amastigote forms (found in patient samples like bone marrow or splenic aspirates) transform into the motile **promastigote** forms. These promastigotes multiply in the condensation fluid of the medium. Cultivation is essential for definitive diagnosis in cases where smears are inconclusive and for research purposes. 2. **Why other options are incorrect:** * **Giardia lamblia:** This is an intestinal protozoan usually diagnosed via stool microscopy (cysts/trophozoites) or string tests. It is cultured in specialized axenic media like **Diamond’s medium**, not NNN. * **Echinococcus:** This is a helminth (Cestode) causing Hydatid cyst disease. Diagnosis relies on imaging (USG/CT) and serology (Casoni’s test/ELISA). It is not routinely cultured. * **Toxoplasma gondii:** An obligate intracellular parasite. It cannot grow on cell-free media like NNN; it requires living systems such as **tissue culture** or mouse inoculation. **High-Yield Clinical Pearls for NEET-PG:** * **NNN Medium Composition:** Agar, Salt, and **Rabbit Blood** (defibrinated). * **Other Media for Leishmania:** Schneider’s Drosophila medium (liquid). * **Gold Standard for Kala-azar:** Splenic aspirate (highest sensitivity) followed by Bone marrow aspirate. * **Diagnostic Stage in Culture:** Promastigote (long, slender with a single anterior flagellum).

Question 217: A patient presented with subcutaneous nodules over the Iliac Crest and snowflake opacity in the eye. Skin scraping contains microfilaria and adult worms. Which parasite is likely responsible?

A. Onchocerca volvulus (Correct Answer)
B. Loa loa
C. Brugia timori
D. Mansonella ozzardi

Explanation: ### Explanation The correct answer is **Onchocerca volvulus**. This parasite is the causative agent of **Onchocerciasis (River Blindness)**. #### Why Onchocerca volvulus is correct: The clinical presentation is classic for Onchocerciasis. * **Subcutaneous Nodules:** Known as **Onchocercomas**, these contain both adult worms and microfilariae. They typically occur over bony prominences like the iliac crest or skull. * **Ocular Involvement:** Microfilariae migrating to the eye cause **Snowflake Opacities** (punctate keratitis), which are reversible inflammatory lesions. Chronic infection leads to sclerosing keratitis and blindness. * **Diagnosis:** Unlike other filarial worms, *O. volvulus* microfilariae are found in **skin snips/scrapings**, not in the blood. #### Why other options are incorrect: * **Loa loa (African Eye Worm):** Characterized by transient **Calabar swellings** and the visible migration of the adult worm across the subconjunctiva. Microfilariae are found in the **blood** (diurnal periodicity). * **Brugia timori:** Causes lymphatic filariasis (elephantiasis) primarily in the lower limbs. Microfilariae are found in the **blood** and have a nocturnal periodicity. * **Mansonella ozzardi:** Generally asymptomatic or causes mild skin rashes/joint pain. Microfilariae are found in the **blood** and lack a sheath. #### High-Yield Clinical Pearls for NEET-PG: * **Vector:** *Simulium* fly (Blackfly), which breeds in fast-flowing rivers. * **Skin Changes:** "Leopard skin" (patchy depigmentation) and "Lizard skin" (atrophy/thickening). * **Hanging Groin:** Loss of elasticity in the inguinal skin leading to pendulous lymph nodes. * **Drug of Choice:** **Ivermectin** (Note: Diethylcarbamazine is contraindicated as it can trigger a severe Mazzotti reaction). * **Wolbachia:** An endosymbiotic bacteria required for the fertility of the adult worm; targeting it with Doxycycline can sterilize the parasite.

Question 218: In malaria, what is the form of the parasite that remains in the human reservoir?

A. Merozoite
B. Sporozoite
C. Trophozoite
D. None of the above (Correct Answer)

Explanation: **Explanation:** The correct answer is **None of the above** because the form of the malaria parasite that remains in the human reservoir (specifically in the liver) is the **Hypnozoite**. 1. **Why "None of the above" is correct:** In infections caused by *Plasmodium vivax* and *Plasmodium ovale*, some sporozoites do not immediately undergo exo-erythrocytic schizogony. Instead, they enter a dormant phase in the hepatocytes known as **hypnozoites**. These forms can remain "latent" for months or years, serving as a reservoir that leads to clinical **relapse** when they eventually reactivate. Since "Hypnozoite" is not listed among the options, "None of the above" is the correct choice. 2. **Why other options are incorrect:** * **Merozoite:** These are released from hepatic or erythrocytic schizonts to infect Red Blood Cells (RBCs). They are transient and do not serve as a long-term reservoir. * **Sporozoite:** This is the **infective stage** introduced by the female Anopheles mosquito. They stay in the human circulation for only about 30 minutes before entering the liver. * **Trophozoite:** This is the active, feeding stage of the parasite within the RBC (e.g., ring forms). It is responsible for clinical symptoms but is not a dormant reservoir. **NEET-PG High-Yield Pearls:** * **Relapse vs. Recrudescence:** Relapse is due to **hypnozoites** (*P. vivax/ovale*). Recrudescence is due to the persistence of low-level parasitemia in the blood (*P. falciparum/malariae*). * **Drug of Choice:** **Primaquine** (or Tafenoquine) is the only drug effective against hypnozoites (radical cure). * **G6PD Deficiency:** Always screen for G6PD deficiency before administering Primaquine to avoid acute hemolysis.

Question 219: A 32-year-old female is suffering from scabies due to Sarcoptes scabiei. Which of the following drugs is prescribed for her?

A. Diethylcarbamazine (DEC) 6 mg/kg body weight for 12 days
B. Diethylcarbamazine (DEC) 9 mg/kg body weight for 12 days
C. Ivermectin 200 mcg/kg body weight (Correct Answer)
D. Ivermectin 100 mg/kg body weight

Explanation: **Explanation:** **Sarcoptes scabiei** is an ectoparasite that causes scabies by burrowing into the stratum corneum. While topical 5% Permethrin is the first-line treatment, oral **Ivermectin** is the systemic drug of choice, particularly for institutional outbreaks, crusted (Norwegian) scabies, or patients who cannot tolerate topical therapy. * **Correct Option (C):** The standard therapeutic dose of Ivermectin for scabies is **200 mcg/kg body weight** as a single oral dose. A second dose is usually repeated after 7–14 days to kill newly hatched nymphs, as the drug is not ovicidal. * **Incorrect Options (A & B):** **Diethylcarbamazine (DEC)** is the drug of choice for lymphatic filariasis (caused by *W. bancrofti* or *B. malayi*) and Tropical Pulmonary Eosinophilia (TPE). It is ineffective against the *Sarcoptes* mite. * **Incorrect Option (D):** The dosage **100 mg/kg** is incorrect and potentially toxic. Ivermectin is measured in **micrograms (mcg)**, not milligrams (mg), per kilogram of body weight. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Ivermectin acts by binding to glutamate-gated chloride channels, leading to hyperpolarization and paralysis of the parasite. * **Contraindication:** Ivermectin should be avoided in children weighing <15 kg and pregnant/lactating women (due to potential disruption of the blood-brain barrier). * **Crusted Scabies:** In severe, crusted (Norwegian) scabies, a combination of oral Ivermectin and topical Permethrin is required. * **Classical Site:** The most common site for scabies burrows is the **interdigital webs** of the hands.

Question 220: Schuffner's dots are seen in infection due to which Plasmodium species?

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

Explanation: **Explanation:** **Schuffner’s dots** are fine, pinkish-red stippling (granules) seen on the surface of infected red blood cells (RBCs) when stained with Romanowsky stains (like Giemsa). They represent morphological changes in the RBC membrane caused by the parasite. **1. Why Plasmodium vivax is correct:** Schuffner’s dots are a hallmark diagnostic feature of **Plasmodium vivax**. In P. vivax infections, the parasite preferentially infects young RBCs (reticulocytes), causing the host cell to become enlarged and pale. The presence of these dots helps differentiate it from other species under light microscopy. **2. Why other options are incorrect:** * **Plasmodium falciparum:** Characterized by **Maurer’s clefts** (coarse, irregular dots). The infected RBCs remain normal in size but may show "comma-shaped" or "crescent-shaped" gametocytes. * **Plasmodium malariae:** Characterized by **Ziemann’s stippling** (fine, dusty dots). The RBCs are usually normal or slightly smaller in size. * **Plasmodium ovale:** While P. ovale also shows Schuffner’s dots (sometimes specifically called **James’ dots**), the question typically refers to P. vivax as the primary association. P. ovale is distinguished by its characteristic oval-shaped host cells with fimbriated (tufted) edges. **High-Yield Clinical Pearls for NEET-PG:** * **RBC Size:** Enlarged in *P. vivax* and *P. ovale*; normal/small in *P. falciparum* and *P. malariae*. * **Relapse:** *P. vivax* and *P. ovale* form **hypnozoites** in the liver, requiring Primaquine for a radical cure. * **Recrudescence:** Seen in *P. falciparum* and *P. malariae* due to persistent erythrocytic cycles. * **Duffy Antigen:** Individuals lacking Duffy blood group antigens are resistant to *P. vivax* infection.

Practice by Chapter

Classification of Parasites

Practice Questions

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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