Parasitology Practice Questions

Q: How does Ankylostoma enter the human body?

Penetration of skin. **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."

Q: Which of the following is not a coccidian parasite?

Blastomyces. **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**.

Q: Where is tapeworm mainly found?

Ileum, jejunum. **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.

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

Strongyloides stercoralis. **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.

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

Sediment. 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.

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

IgE. **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).

Q: Which of the following can cause myocarditis?

Trichinella spiralis. ### 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.

Q: 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?

Entamoeba. ### 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.

Q: What is the smallest adult intestinal nematode?

Strongyloides stercoralis. **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.

Question 1

How does Ankylostoma enter the human body?

Accepted Answer

Penetration of skin

Answer

Ingestion

Answer

Inhalation

Answer

Inoculation

Question 2

Which of the following is not a coccidian parasite?

Accepted Answer

Blastomyces

Answer

Isospora

Answer

Toxoplasma

Answer

Cyclospora

Question 3

Where is tapeworm mainly found?

Accepted Answer

Ileum, jejunum

Answer

Liver

Answer

Stomach

Answer

Caecum

Question 4

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

Accepted Answer

Strongyloides stercoralis

Answer

Trichuris trichiura

Answer

Enterobius vermicularis

Answer

Necator americanus

Question 5

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

Accepted Answer

Sediment

Answer

Ether

Answer

Fecal debris

Answer

Formal water

Question 6

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

Accepted Answer

IgE

Answer

IgA

Answer

IgG

Answer

IgM

Question 7

Which of the following can cause myocarditis?

Accepted Answer

Trichinella spiralis

Answer

Schistosoma

Answer

Ankylostoma duodenale

Answer

Trichuris trichura

Question 8

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?

Accepted Answer

Entamoeba

Answer

Giardia

Answer

Staphylococcus

Answer

Clostridium perfringens

Question 9

Which of the following statements about Giardia lamblia is correct?

Accepted Answer

It is the only protozoan parasite found in the lumen of the small intestine.

Answer

It is the only flagellate parasite without a cystic stage.

Answer

Infection occurs by ingestion of trophozoites in contaminated food and water.

Answer

It may sometimes invade the bloodstream and cause ectopic lesions.

Question 10

What is the smallest adult intestinal nematode?

Accepted Answer

Strongyloides stercoralis

Answer

Enterobius vermicularis

Answer

Necator americanus

Answer

Trichuris trichiura

Parasitology — MCQs

Parasitology — MCQs

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