Parasitology Practice Questions

Q: What is the most common cause of cutaneous larva migrans?

Ankylostoma caninum. **Explanation:** **Cutaneous Larva Migrans (CLM)**, also known as "creeping eruption," is a zoonotic infestation caused by the larvae of animal hookworms. 1. **Why Option A is Correct:** **Ankylostoma caninum** (the dog hookworm) is the **most common** cause of CLM worldwide. **Ankylostoma braziliense** (found in both dogs and cats) is another frequent cause. Humans are accidental "dead-end" hosts; the larvae penetrate the skin (usually through contact with contaminated soil or sand) but lack the enzymes necessary to penetrate the basement membrane and reach the circulation. Consequently, they remain confined to the epidermis, migrating aimlessly and creating the characteristic serpiginous, erythematous, pruritic tracks. 2. **Why Other Options are Incorrect:** * **Options B & C (Toxocara canis/cati):** These are the causative agents of **Visceral Larva Migrans (VLM)** and Ocular Larva Migrans. Unlike CLM, these larvae migrate through internal organs rather than the skin. * **Option D (Gnathostoma):** This causes **Larva Migrans Profunda**. Unlike the superficial tracks of CLM, Gnathostomiasis typically presents as deep, migratory subcutaneous swellings (panniculitis). **High-Yield Clinical Pearls for NEET-PG:** * **Classic Presentation:** Intensely pruritic, linear or serpiginous tracks, most commonly on the feet (ground itch). * **Rate of Migration:** The larvae move at a rate of roughly **1–2 cm per day**. * **Löffler’s Syndrome:** Rare systemic involvement where larvae reach the lungs, causing transient pulmonary infiltrates and peripheral eosinophilia. * **Treatment of Choice:** **Oral Albendazole** (400 mg for 3–7 days) or **Ivermectin** (200 µg/kg single dose). Topical Thiabendazole is also an option.

Q: Chromidial bars are absent in which stage of cysts in Entamoeba?

Quadrinucleate. ### Explanation The presence and morphology of **chromidial bars** (aggregates of ribosomes) are crucial diagnostic features in the life cycle of *Entamoeba histolytica*. **Why Quadrinucleate is the correct answer:** As the cyst of *Entamoeba histolytica* matures, it undergoes nuclear division while simultaneously consuming its stored food reserves. Chromidial bars and the glycogen mass are prominent in the early stages (uninucleate and binucleate) to provide energy and protein synthesis machinery for maturation. By the time the cyst reaches the **mature quadrinucleate stage** (the infective stage), these stored reserves—including the chromidial bars—are typically **completely absorbed and disappear**. **Analysis of Incorrect Options:** * **A & B (Uninucleate & Binucleate):** These are immature stages. They characteristically contain a large glycogen mass and prominent, cigar-shaped chromidial bars with rounded ends. * **D (Octanucleate):** This stage is characteristic of *Entamoeba coli*, not *E. histolytica*. In *E. coli*, chromidial bars are often present even in the mature (octanucleate) stage, appearing splinter-like or filamentous with jagged ends. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** *E. histolytica* chromidial bars are **cigar-shaped** (rounded ends), whereas *E. coli* bars are **splinter-like** (pointed ends). * **Infective Stage:** The mature **quadrinucleate cyst** is the infective form for humans. * **Diagnostic Point:** The presence of ingested RBCs (erythrophagocytosis) in a trophozoite is pathognomonic for *E. histolytica*, distinguishing it from the commensal *E. dispar*. * **Nuclear Feature:** Look for "cartwheel appearance" (central karyosome and peripheral chromatin) in *E. histolytica*.

Q: Which of the following statements is NOT true about Kala-Azar?

Man has the flagellar stage of the organism. ### Explanation **Correct Answer: D. Man has the flagellar stage of the organism** **Why Option D is NOT true:** The causative agent of Kala-azar, *Leishmania donovani*, exists in two distinct morphological forms. The **flagellar stage (Promastigote)** is found only in the vector (Sandfly) and in artificial cultures. In the human host (Man), the parasite exists exclusively in the **aflagellar stage (Amastigote)**, also known as Leishman-Donovan (LD) bodies, residing within the reticuloendothelial system (macrophages). **Analysis of Other Options:** * **A. Sandfly is the vector:** This is true. The disease is transmitted by the bite of the female *Phlebotomus argentipes*. * **B. Man is the only reservoir in India:** This is true. Unlike in other parts of the world (where dogs or rodents may be reservoirs), Indian Kala-azar is **anthroponotic**, meaning humans are the sole reservoir of infection. * **C. Aldehyde test is diagnostic:** While technically a non-specific screening tool, in the context of classic medical exams, the Napier’s Aldehyde test is associated with Kala-azar. It depends on the increase in serum gamma globulins. Note: It only becomes positive after 3 months of illness. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Demonstration of LD bodies in **splenic aspirate** (highest sensitivity) or bone marrow aspirate. * **Drug of Choice:** **Liposomal Amphotericin B** (single dose of 10mg/kg is the current WHO recommendation for India). * **PKDL (Post Kala-azar Dermal Leishmaniasis):** A non-ulcerative condition appearing years after "cure"; it serves as a major parasite reservoir in the community. * **Elimination Goal:** To reduce the annual incidence to less than **1 case per 10,000 population** at the block level.

Q: Stool examination in a patient reveals a specific finding. What is the likely route of infection of this parasite?

Ingestion of food contaminated with the egg or larva. ***Ingestion of food contaminated with the egg or larva*** - **Ascaris lumbricoides** transmission occurs through the **fecal-oral route** when contaminated food or water containing **embryonated eggs** is ingested. - The eggs survive in soil for months and become **infective after 2-4 weeks** of maturation in the environment. *Insect bite* - Vector-borne transmission is characteristic of parasites like **Plasmodium** (malaria) or **Leishmania**. - **Ascaris** does not require an **arthropod vector** for transmission and spreads directly through contaminated environments. *Ingestion of improperly cooked beef* - This route is specific to **Taenia saginata** (beef tapeworm) which forms **cysticerci** in cattle muscle. - **Ascaris** does not have an **intermediate host** and does not require meat consumption for transmission. *Contact with contaminated water during swimming* - This describes **percutaneous transmission** seen in **Schistosoma** species where **cercariae** penetrate intact skin. - **Ascaris eggs** cannot penetrate skin and must be **ingested orally** to cause infection.

Q: A pregnant lady with AIDS presents with diarrhea. Stool examination reveals acid-fast positive cysts. Which organism is likely responsible for this infection?

Isospora belli. ### Explanation The clinical presentation of chronic diarrhea in an immunocompromised patient (AIDS) combined with the finding of **acid-fast positive cysts** is characteristic of the Coccidian group of parasites. **Why Isospora belli is correct:** * **Acid-fast staining:** *Isospora belli* (now *Cystoisospora belli*) produces large, oval oocysts (approx. 25–30 μm) that are **acid-fast positive** (modified Ziehl-Neelsen stain). * **Clinical Context:** It is a common cause of severe, watery diarrhea in HIV/AIDS patients. While *Cryptosporidium parvum* and *Cyclospora* are also acid-fast, *Isospora* is a classic high-yield answer for this description in competitive exams. **Why other options are incorrect:** * **Microsporidia:** These are tiny intracellular fungi (formerly classified as parasites). While they cause diarrhea in AIDS, they are **not** acid-fast; they require special stains like Modified Trichrome or Calcofluor White. * **Giardia lamblia:** This is a flagellate that causes malabsorptive "steatorrhea." It is identified by pear-shaped trophozoites or oval cysts on iodine mount, but it is **not acid-fast**. * **Entamoeba histolytica:** This causes amoebic dysentery (bloody diarrhea). Cysts are characterized by having 1–4 nuclei and chromatoid bodies, but they do **not** retain acid-fast stains. **High-Yield Clinical Pearls for NEET-PG:** 1. **Acid-fast Parasites (The "Big Three"):** *Cryptosporidium* (Small, spherical), *Cyclospora* (Mid-sized, spherical), and *Isospora* (Large, oval). 2. **Treatment of Choice:** Unlike most protozoa (treated with Metronidazole), *Isospora belli* is treated with **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. 3. **Autofluorescence:** *Isospora* and *Cyclospora* oocysts show blue-green autofluorescence under UV microscopy.

Q: The Montenegro test is performed to diagnose which of the following conditions?

Kala-azar. **Explanation:** The **Montenegro test** (also known as the Leishmanin skin test) is a delayed-type hypersensitivity (Type IV) reaction used to detect prior exposure to *Leishmania* parasites, the causative agents of **Kala-azar** (Visceral Leishmaniasis). **Why Kala-azar is correct:** The test involves the intradermal injection of a suspension of killed *Leishmania* promastigotes. A positive result (induration ≥5 mm after 48–72 hours) indicates a cell-mediated immune response. It is important to note that the test is typically **negative** during active visceral leishmaniasis (due to suppressed cell-mediated immunity) but becomes **positive** after successful treatment or in cases of Cutaneous Leishmaniasis and Post-Kala-azar Dermal Leishmaniasis (PKDL). **Why other options are incorrect:** * **Hydatid disease:** Diagnosed primarily via imaging (USG/CT) and the **Casoni’s test** (though now largely replaced by serology like ELISA). * **Taeniasis:** Diagnosed by stool microscopy for eggs or proglottids; no specific skin test is used for routine diagnosis. * **Filariasis:** Diagnosed by demonstrating microfilariae in peripheral blood (night samples) or using the ICT (Immunochromatographic test) for circulating filarial antigen. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Sandfly (*Phlebotomus argentipes*). * **Drug of Choice:** Liposomal Amphotericin B (current standard). * **RK-39 Immunochromatographic test:** The rapid diagnostic test of choice for active Kala-azar in field settings. * **Aldehyde Test (Napier’s test):** Based on hypergammaglobulinemia; it is non-specific but used for screening.

Q: Wakana disease is caused by which of the following parasites?

Ancylostoma duodenale. **Explanation:** **Wakana Disease** is a specific clinical manifestation associated with **Ancylostoma duodenale**. It occurs when a large number of infective larvae (L3) are ingested orally, rather than entering through the skin. This phenomenon was historically documented in Japan among farmers who consumed contaminated green vegetables. 1. **Why Ancylostoma duodenale is correct:** Unlike *Necator americanus*, which primarily infects via the percutaneous route, *Ancylostoma duodenale* can infect humans through **oral ingestion**. When larvae are swallowed, they cause an immediate hypersensitivity reaction in the pharynx and upper gastrointestinal tract. Symptoms include nausea, vomiting, dyspnea, pharyngeal irritation, and cough. 2. **Why other options are incorrect:** * **Necator americanus:** Known as the "New World Hookworm," it lacks the ability to infect effectively via the oral route; it requires skin penetration and a mandatory lung migration phase. * **Strongyloides stercoralis:** While it causes "Larva Currens" (racing larvae) and autoinfection, it is not associated with the specific "Wakana" syndrome. * **Enterobius vermicularis:** This is the pinworm, which causes perianal pruritus but does not migrate through the lungs or cause pharyngeal hypersensitivity. **High-Yield Clinical Pearls for NEET-PG:** * **Hookworm Comparison:** *A. duodenale* has teeth (2 pairs), while *N. americanus* has semilunar cutting plates. * **Ground Itch:** The allergic dermatitis seen at the site of entry during percutaneous infection (more common in *Necator*). * **Loeffler’s Syndrome:** Transient eosinophilic pneumonia occurring during the lung migration phase of hookworms. * **Iron Deficiency Anemia:** The most significant complication of chronic hookworm infection due to blood-sucking (Ancylostoma sucks more blood—approx. 0.2 ml/day—than Necator).

Q: Which of the following organisms is known for its characteristic pear-shaped, flagellated appearance, and is a common cause of pelvic infections?

Trichomonas vaginalis. **Explanation:** **Trichomonas vaginalis** is the correct answer because it is a flagellated protozoan characterized by its unique **pear-shaped (pyriform)** morphology. It possesses four anterior flagella and an undulating membrane, which provides its characteristic **"jerky" motility** seen on a wet mount. It is a major cause of Trichomoniasis, a common sexually transmitted infection (STI) leading to pelvic discomfort and vaginitis. **Analysis of Incorrect Options:** * **Candida albicans:** This is a fungus (yeast). Under the microscope, it appears as budding yeast cells and **pseudohyphae**, not flagellated pear-shaped organisms. It causes "curdy white" discharge. * **Mycoplasma:** These are the smallest free-living bacteria. They lack a cell wall and are pleomorphic, but they do not have flagella or a pear-shaped structure. * **Gardnerella vaginalis:** This is a gram-variable coccobacillus associated with Bacterial Vaginosis. The hallmark microscopic finding is **"Clue cells"** (epithelial cells covered in bacteria), not flagellated protozoa. **NEET-PG High-Yield Pearls:** * **Clinical Presentation:** Characterized by a profuse, **foul-smelling, yellowish-green frothy discharge**. * **Colposcopy Finding:** **"Strawberry Cervix"** (punctate hemorrhages on the ectocervix) is a classic, highly specific sign. * **Diagnosis:** The gold standard is **culture (Whittington’s or Diamond’s medium)**, though wet mount for jerky motility is the most common initial test. * **Treatment:** Drug of choice is **Metronidazole**. Crucially, both partners must be treated simultaneously to prevent reinfection.

Q: Which of the following protozoa lacks a cyst stage in its life cycle?

Dientamoeba fragilis. ### Explanation **Correct Answer: A. Dientamoeba fragilis** **1. Why Dientamoeba fragilis is the correct answer:** In medical parasitology, most intestinal protozoa follow a life cycle involving two stages: the **Trophozoite** (motile, feeding, pathogenic stage) and the **Cyst** (non-motile, resistant, infective stage). However, *Dientamoeba fragilis* is a notable exception. It exists **only in the trophozoite stage** and does not form cysts. Because it lacks a protective cyst wall, the trophozoite is fragile and easily destroyed by gastric acid. It is hypothesized that *D. fragilis* may be transmitted via the eggs of helminths like *Enterobius vermicularis* (Pinworm), acting as a "hitchhiker" to survive the external environment. **2. Why the other options are incorrect:** * **B. Entamoeba coli:** This is a non-pathogenic commensal of the large intestine. It has a well-defined life cycle consisting of trophozoites, precysts, and mature **octanucleate cysts** (containing 8 nuclei), which are the infective forms. * **C. Entamoeba histolytica:** This is the causative agent of amoebiasis. Its life cycle includes a trophozoite stage and a **quadrinucleate cyst** stage. The mature cyst is highly resistant and is the diagnostic and infective stage found in formed stools. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Morphology:** Despite its name, *D. fragilis* is taxonomically classified as a **flagellate** (related to *Trichomonas*), not an amoeba, though it moves using pseudopodia. * **Nuclear Feature:** It typically contains **two nuclei** (hence "*Di*-entamoeba") with fragmented karyosomes. * **Other Protozoa lacking a cyst stage:** * *Trichomonas vaginalis* (transmitted sexually; no need for a resistant environmental stage). * *Entamoeba gingivalis* (found in the mouth). * *Pentatrichomonas hominis*. * **Treatment of choice:** Iodoquinol, Paromomycin, or Metronidazole.

Question 1

What is the most common cause of cutaneous larva migrans?

Accepted Answer

Ankylostoma caninum

Answer

Toxocara canis

Answer

Toxocara cati

Answer

Gnathostoma

Question 2

Chromidial bars are absent in which stage of cysts in Entamoeba?

Accepted Answer

Quadrinucleate

Answer

Uninucleate

Answer

Binucleate

Answer

Octanucleate

Question 3

Which of the following statements is NOT true about Kala-Azar?

Accepted Answer

Man has the flagellar stage of the organism

Answer

Sandfly is the vector

Answer

Man is the only reservoir in India

Answer

Aldehyde test is diagnostic

Question 4

Stool examination in a patient reveals a specific finding. What is the likely route of infection of this parasite?

Accepted Answer

Ingestion of food contaminated with the egg or larva

Answer

Insect bite

Answer

Ingestion of improperly cooked beef

Answer

Contact with contaminated water during swimming

Question 5

A pregnant lady with AIDS presents with diarrhea. Stool examination reveals acid-fast positive cysts. Which organism is likely responsible for this infection?

Accepted Answer

Isospora belli

Answer

Microsporidia

Answer

Giardia lamblia

Answer

Entamoeba histolytica

Question 6

The Montenegro test is performed to diagnose which of the following conditions?

Accepted Answer

Kala-azar

Answer

Hydatid disease

Answer

Taeniasis

Answer

Filariasis

Question 7

Which of the following organisms presents with acid-fast oocysts?

Accepted Answer

All of the above

Answer

Cryptosporidium

Answer

Isospora

Answer

Cyclospora

Question 8

Wakana disease is caused by which of the following parasites?

Accepted Answer

Ancylostoma duodenale

Answer

Necator americanus

Answer

Strongyloides

Answer

Enterobius vermicularis

Question 9

Which of the following organisms is known for its characteristic pear-shaped, flagellated appearance, and is a common cause of pelvic infections?

Accepted Answer

Trichomonas vaginalis

Answer

Candida albicans

Answer

Mycoplasma

Answer

Gardenella

Question 10

Which of the following protozoa lacks a cyst stage in its life cycle?

Accepted Answer

Dientamoeba fragilis

Answer

Entamoeba coli

Answer

Entamoeba histolytica

Answer

All of the above

Parasitology — MCQs

Parasitology — MCQs

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