Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 291: How does Ankylostoma enter the human body?

A. Ingestion
B. Inhalation
C. Penetration of skin (Correct Answer)
D. Inoculation

Explanation: **Explanation:** The correct answer is **C. Penetration of skin**. *Ankylostoma duodenale* (Hookworm) primarily enters the human body through the **penetration of intact skin** by the third-stage **filariform larva**. These larvae typically reside in damp soil and penetrate the skin of barefoot individuals (most commonly through the interdigital spaces of the feet). Once inside, they enter the venous circulation, travel to the lungs, ascend the trachea, are swallowed, and finally mature into adults in the small intestine. **Analysis of Incorrect Options:** * **A. Ingestion:** While *Ankylostoma duodenale* can occasionally be transmitted via ingestion of larvae in contaminated food/water (unlike *Necator americanus*), skin penetration remains the classic and primary route. * **B. Inhalation:** There is no known respiratory transmission route for hookworms; larvae only reach the lungs via the bloodstream during their migratory cycle. * **C. Inoculation:** This refers to entry via an arthropod vector (e.g., Malaria via mosquitoes) or needle sticks, which does not apply to the hookworm life cycle. **High-Yield Clinical Pearls for NEET-PG:** * **Ground Itch:** The local pruritic dermatitis at the site of larval entry. * **Loeffler’s Syndrome:** Transient pulmonary symptoms (cough, wheezing, eosinophilia) during the larval migration phase through the lungs. * **Iron Deficiency Anemia (IDA):** The hallmark of chronic infection. *Ankylostoma* causes significantly more blood loss (~0.15–0.2 ml/day) compared to *Necator americanus* (~0.03 ml/day). * **Morphology:** *Ankylostoma* has "teeth" (ventral hooks), whereas *Necator* has "cutting plates."

Question 292: Which of the following is not a coccidian parasite?

A. Isospora
B. Toxoplasma
C. Blastomyces (Correct Answer)
D. Cyclospora

Explanation: **Explanation:** The correct answer is **Blastomyces** because it is a **dimorphic fungus**, not a parasite. Coccidian parasites belong to the Phylum Apicomplexa and are characterized by a complex life cycle involving both sexual and asexual reproduction, often occurring within the intestinal epithelium or tissues of the host. **Analysis of Options:** * **Blastomyces (Correct Answer):** It is a fungal pathogen (specifically *Blastomyces dermatitidis*) that causes Blastomycosis. It exists as a mold in the environment and as a broad-based budding yeast in human tissues at 37°C. * **Isospora (now *Cystoisospora belli*):** A classic intestinal coccidian parasite. It is a significant cause of diarrhea in immunocompromised individuals (e.g., HIV/AIDS) and is identified by acid-fast staining of oocysts in stool. * **Toxoplasma (*Toxoplasma gondii*):** A tissue coccidian. While its sexual cycle occurs only in cats (definitive host), it is a major human pathogen causing congenital infections and encephalitis in AIDS patients. * **Cyclospora (*Cyclospora cayetanensis*):** An intestinal coccidian known for causing waterborne or foodborne outbreaks of diarrhea. Like Isospora, it is also acid-fast. **NEET-PG High-Yield Pearls:** 1. **Intestinal Coccidians:** Remember the "Big Three" that cause diarrhea in AIDS patients: *Cryptosporidium parvum*, *Cystoisospora belli*, and *Cyclospora*. 2. **Staining:** All intestinal coccidians are **Modified Acid-Fast positive**. 3. **Blastomyces Key Feature:** On microscopy, look for **"Broad-Based Budding"** yeast cells—a favorite "buzzword" in exams. 4. **Drug of Choice:** For most coccidian parasites (except Cryptosporidium), the treatment of choice is **Cotrimoxazole**.

Question 293: Where is tapeworm mainly found?

A. Liver
B. Stomach
C. Caecum
D. Ileum, jejunum (Correct Answer)

Explanation: **Explanation:** The correct answer is **Ileum and Jejunum**. Most adult cestodes (tapeworms) that infect humans, such as *Taenia saginata* (beef tapeworm), *Taenia solium* (pork tapeworm), and *Diphyllobothrium latum* (fish tapeworm), reside in the **small intestine**. **Why Ileum and Jejunum?** Tapeworms lack a digestive system of their own. They absorb pre-digested nutrients directly through their body wall (tegument). The jejunum and ileum are the primary sites of nutrient absorption in the human host, providing an environment rich in glucose and amino acids. The worms use their scolex (head) to attach to the mucosal lining to resist peristalsis. **Analysis of Incorrect Options:** * **A. Liver:** While the larval stages of certain tapeworms (e.g., *Echinococcus granulosus* causing Hydatid cyst) are commonly found in the liver, the adult "tapeworm" itself does not reside there. * **B. Stomach:** The acidic environment (low pH) of the stomach is hostile to the survival of the adult worm; it is primarily a site where the protective cyst wall of the larvae is digested to release the parasite. * **C. Caecum:** This is the site for parasites like *Trichuris trichiura* (whipworm) and *Enterobius vermicularis* (pinworm), but not the primary habitat for adult tapeworms. **Clinical Pearls for NEET-PG:** * **Taenia saginata:** Most common tapeworm in India; lacks hooks on scolex (unarmed). * **Diphyllobothrium latum:** Can cause **Vitamin B12 deficiency**, leading to megaloblastic anemia, as it competes with the host for B12 absorption in the ileum. * **Hymenolepis nana:** The smallest and most common intestinal cestode; it is unique because it does not require an intermediate host.

Question 294: What is the most common helminth infection in patients with AIDS?

A. Trichuris trichiura
B. Strongyloides stercoralis (Correct Answer)
C. Enterobius vermicularis
D. Necator americanus

Explanation: **Explanation:** The correct answer is **Strongyloides stercoralis**. This is because *S. stercoralis* is a unique helminth capable of completing its entire life cycle within the human host through a process called **autoinfection**. In immunocompromised individuals, particularly those with HIV/AIDS or those on corticosteroids, this autoinfection can accelerate uncontrollably, leading to **Hyperinfection Syndrome** and **Disseminated Strongyloidiasis**. While HIV patients are susceptible to many parasites, *Strongyloides* is the most clinically significant and frequently reported helminthic opportunistic infection in this demographic. **Analysis of Incorrect Options:** * **A. Trichuris trichiura (Whipworm):** While common in tropical areas, it is a soil-transmitted helminth that does not have an internal autoinfective cycle. Its prevalence in AIDS patients reflects geographic endemicity rather than an opportunistic relationship with immunosuppression. * **C. Enterobius vermicularis (Pinworm):** This is the most common helminth infection in children worldwide, but it does not cause systemic or severe opportunistic disease in AIDS patients. * **D. Necator americanus (Hookworm):** Like *Trichuris*, hookworms require a period of development in the soil. They do not multiply within the host, so the worm burden does not increase exponentially due to immunosuppression. **High-Yield NEET-PG Pearls:** * **Diagnostic Stage:** Rhabditiform larvae in stool (not eggs). * **Infective Stage:** Filariform larvae (penetrate intact skin). * **Hyperinfection Clue:** Gram-negative sepsis/meningitis (due to enteric bacteria "hitchhiking" on larvae migrating from the gut to the lungs). * **Drug of Choice:** Ivermectin (preferred over Albendazole). * **Association:** Strongly associated with **HTLV-1 infection**, which predisposes patients to severe disseminated disease even more than HIV.

Question 295: In the formol-ether concentration technique, which layer contains the parasites?

A. Ether
B. Fecal debris
C. Formal water
D. Sediment (Correct Answer)

Explanation: The **Formol-Ether Concentration Technique** (also known as the Ritchie technique) is a gold-standard method used in parasitology to increase the yield of eggs, cysts, and larvae in stool samples, especially when the parasitic load is low. ### Why the Correct Answer is Right The principle of this technique relies on **specific gravity**. When a fecal suspension is centrifuged with ether and formalin: * **Ether** dissolves and extracts fats and lipids from the stool. * **Formalin** fixes and preserves the parasites. * **Centrifugation** forces the heavier elements—specifically the **parasitic eggs, cysts, and larvae**—to the bottom of the tube due to their higher density. Therefore, the **Sediment (Option D)** is the layer where parasites are concentrated and collected for microscopic examination. ### Why Other Options are Wrong After centrifugation, four distinct layers are formed (from top to bottom): * **A. Ether:** The topmost layer containing dissolved fats and organic solvents. * **B. Fecal debris:** A "plug" of organic matter that rests at the interface of ether and formalin. * **C. Formal water (Formalin):** The liquid column between the debris and the sediment. It contains the preservative but not the concentrated parasites. ### NEET-PG High-Yield Pearls * **Advantage:** It preserves the morphology of most cysts and eggs and is excellent for field studies. * **Disadvantage:** It is not ideal for detecting **trophozoites** (as they are destroyed) or *Strongyloides* larvae (which may lose motility). * **Alternative:** The **Zinc Sulfate Flotation** technique is another concentration method, but there, parasites are found in the **surface film** (top layer) because the solution has a higher specific gravity than the parasites. * **Safety Note:** Ethyl acetate is often used as a safer, non-flammable substitute for ether in modern laboratories.

Question 296: Which one of the following immunoglobulins is characteristically elevated in filariasis?

A. IgA
B. IgE (Correct Answer)
C. IgG
D. IgM

Explanation: **Explanation:** In helminthic infections like **Filariasis** (caused by *Wuchereria bancrofti* or *Brugia malayi*), the immune system primarily mounts a **Type 2 helper T cell (Th2) response**. This response is characterized by the secretion of cytokines such as IL-4 and IL-5. IL-4 induces B-cell class switching to produce **IgE**, while IL-5 leads to the recruitment and activation of **eosinophils**. Elevated serum IgE levels and peripheral blood eosinophilia are hallmark laboratory findings in lymphatic filariasis and Tropical Pulmonary Eosinophilia (TPE). **Analysis of Options:** * **IgE (Correct):** It is the primary immunoglobulin involved in the defense against multicellular parasites. It binds to mast cells and basophils, triggering the release of inflammatory mediators that help combat the larvae. * **IgA:** Primarily involved in mucosal immunity (secretory IgA). While it may be present in the gut during intestinal helminthiasis, it is not the characteristic marker for systemic filarial infection. * **IgG:** While filarial-specific IgG (especially IgG4) increases during chronic infection, it is not as characteristically diagnostic or pathognomonic as the elevation of IgE in the context of the Th2 allergic-type response. * **IgM:** This is the first antibody produced in an acute infection (primary response) but is not specifically associated with the chronic, eosinophilic nature of parasitic infestations. **High-Yield Pearls for NEET-PG:** * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to microfilariae in the lungs, characterized by massive elevation of IgE (>1000 IU/mL) and extreme eosinophilia. * **Drug of Choice:** Diethylcarbamazine (DEC) is the standard treatment for filariasis. * **Diagnostic Gold Standard:** Demonstration of microfilariae in a **peripheral blood smear** (collected at night, between 10 PM and 2 AM, due to nocturnal periodicity).

Question 297: Which of the following can cause myocarditis?

A. Schistosoma
B. Ankylostoma duodenale
C. Trichuris trichura
D. Trichinella spiralis (Correct Answer)

Explanation: ### Explanation **Correct Option: D. *Trichinella spiralis*** *Trichinella spiralis* is a tissue nematode acquired by consuming undercooked meat (usually pork) containing encysted larvae. While the larvae typically encyst in striated skeletal muscle, they can migrate through various organs during the parenteral phase. **Myocarditis** is the most serious and potentially fatal complication of Trichinellosis. **Medical Concept:** Although the larvae do not encyst in the heart (as cardiac muscle lacks the necessary regenerative capacity/satellite cells to form "nurse cells"), their migration through the myocardium triggers a severe inflammatory response (eosinophilic infiltration), leading to arrhythmias or heart failure. **Why other options are incorrect:** * **A. *Schistosoma*:** These are blood flukes. Their primary complications involve the venous plexuses (vesical or portal), leading to hematuria, portal hypertension, or "Katayama fever," but not typically myocarditis. * **B. *Ankylostoma duodenale* (Hookworm):** These reside in the small intestine and cause iron deficiency anemia and hypoalbuminemia due to chronic blood loss. Cardiac involvement is usually limited to "high-output heart failure" secondary to severe anemia, not direct myocarditis. * **C. *Trichuris trichura* (Whipworm):** This large intestinal parasite is primarily associated with rectal prolapse (in children) and chronic diarrhea/dysentery. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad of Trichinellosis:** Myalgia, Periorbital edema, and Eosinophilia. * **Diagnosis:** Muscle biopsy (showing coiled larvae in nurse cells) or Bachman intradermal test. * **Drug of Choice:** Albendazole or Mebendazole (Steroids are added if myocarditis is present to reduce inflammation). * **Other Parasites causing Myocarditis:** *Trypanosoma cruzi* (Chagas disease) is the most common parasitic cause globally.

Question 298: A patient presents with complaints of lower abdominal pain, fever, and repeated stools containing little fecal matter, blood, and mucus. Microscopy of the stool shows a paucity of WBCs and a positive test for heme. Which is the likely causative organism?

A. Giardia
B. Entamoeba (Correct Answer)
C. Staphylococcus
D. Clostridium perfringens

Explanation: ### Explanation The clinical presentation of lower abdominal pain, fever, and frequent small-volume stools containing blood and mucus is classic for **Amoebic Dysentery**, caused by *Entamoeba histolytica*. **Why Entamoeba is correct:** The defining feature in this question is the **"paucity of WBCs"** (pus cells) in the stool. *E. histolytica* produces a cytotoxin that lyses leukocytes (leukocytolysis). Therefore, despite being an invasive infection, the stool microscopy shows few inflammatory cells, RBCs in clumps (due to erythrophagocytosis), and a positive heme test. This contrasts with Bacillary Dysentery (e.g., *Shigella*), which presents with numerous pus cells. **Why other options are incorrect:** * **Giardia:** Causes malabsorptive "steatorrhea" (foul-smelling, fatty stools). It is non-invasive, so it does **not** cause blood or mucus in the stool. * **Staphylococcus & Clostridium perfringens:** These typically cause **food poisoning** characterized by watery diarrhea and vomiting due to preformed toxins or enterotoxins. They do not typically cause a dysenteric picture with blood and mucus. **NEET-PG High-Yield Pearls:** * **Stool Microscopy:** Look for **Trophozoites with ingested RBCs** (pathognomonic for *E. histolytica*). * **Flask-shaped ulcers:** The characteristic lesion formed in the colon. * **Charcot-Leyden crystals:** Often found in the stool due to eosinophil breakdown. * **Treatment:** Metronidazole or Tinidazole (Tissue amoebicides) followed by Diloxanide furoate (Luminal amoebicide) to clear the carrier state.

Question 299: Which of the following statements about Giardia lamblia is correct?

A. It is the only flagellate parasite without a cystic stage.
B. Infection occurs by ingestion of trophozoites in contaminated food and water.
C. It is the only protozoan parasite found in the lumen of the small intestine. (Correct Answer)
D. It may sometimes invade the bloodstream and cause ectopic lesions.

Explanation: **Explanation:** **1. Why the correct answer is right:** *Giardia lamblia* (also known as *G. duodenalis* or *G. intestinalis*) is unique because it is the **only protozoan parasite** that inhabits the **lumen of the human small intestine** (specifically the duodenum and upper jejunum). While other protozoa like *Entamoeba histolytica* reside in the large intestine, Giardia thrives in the alkaline environment of the small bowel, attaching to the mucosal surface via its ventral sucking disc. **2. Why the incorrect options are wrong:** * **Option A:** Incorrect. *Giardia* has a well-defined life cycle consisting of both **trophozoites and cysts**. The cyst is the infective stage and the form responsible for survival in the environment. (Note: *Trichomonas vaginalis* is an example of a flagellate that lacks a cystic stage). * **Option B:** Incorrect. Infection occurs by the ingestion of **mature cysts**, not trophozoites. Trophozoites are fragile and are usually destroyed by gastric acid if ingested. * **Option C:** Incorrect. *Giardia* is a **non-invasive** parasite. It remains limited to the intestinal lumen and does not invade the bloodstream or cause extra-intestinal (ectopic) lesions, unlike *Entamoeba histolytica*. **3. High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Trophozoite is **pear-shaped** (pyriform) with a "falling leaf" motility and a characteristic **"monkey-face"** appearance (due to two nuclei and four pairs of flagella). * **Clinical Presentation:** Causes **steatorrhea** (foul-smelling, fatty stools) and malabsorption (especially of Vitamin A and fats) due to the "carpeting" of the intestinal mucosa. * **Diagnosis:** Stool microscopy (cysts/trophozoites) or **String Test** (Entero-test). * **Drug of Choice:** Tinidazole or Metronidazole.

Question 300: What is the smallest adult intestinal nematode?

A. Enterobius vermicularis
B. Necator americanus
C. Strongyloides stercoralis (Correct Answer)
D. Trichuris trichiura

Explanation: **Explanation:** The correct answer is **Strongyloides stercoralis**. In medical parasitology, size is a high-yield morphological feature used to differentiate helminths. **Why Strongyloides stercoralis is correct:** *Strongyloides stercoralis* (Threadworm) is recognized as the **smallest intestinal nematode** infecting humans. The parasitic female measures approximately **2.0 to 2.5 mm** in length. A unique feature of this parasite is that only the females are parasitic in the human intestine, and they reproduce via parthenogenesis. **Analysis of Incorrect Options:** * **Enterobius vermicularis (Pinworm):** While small, the adult female is significantly larger than *Strongyloides*, measuring about **8–13 mm**. It is the most common helminthic infection in developed countries. * **Necator americanus (Hookworm):** Adult females measure approximately **9–11 mm** in length. They are known for causing iron deficiency anemia. * **Trichuris trichiura (Whipworm):** These are much larger, with adults measuring between **30–50 mm**. They are characterized by a whip-like shape (thin anterior and thick posterior). **High-Yield Clinical Pearls for NEET-PG:** * **Autoinfection:** *S. stercoralis* is unique because its larvae can mature into the filariform stage within the host's intestine, leading to internal autoinfection. * **Hyperinfection Syndrome:** In immunocompromised patients (especially those on steroids), autoinfection can lead to massive dissemination. * **Diagnostic Stage:** Unlike most nematodes, the diagnostic stage in stool is the **Rhabditiform larva**, not the egg. * **Larva Currens:** A rapidly moving serpiginous cutaneous eruption is pathognomonic for Strongyloidiasis.

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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