Parasitology — MCQs
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Risk of transplacental transmission of Toxoplasma gondii is maximum when the mother is infected:
A 7-year-old child presented with intermittent abdominal cramps and loose stools. Stool examination revealed eggs measuring 100µm. Which of the following is NOT a cause of these symptoms?
A double rise of temperature in 24 hours is characteristic of which of the following conditions?
Trypanosoma cruzi grows in which of the following media?
Which of the following statements about Entamoeba histolytica is true?
Which of the following is NOT true about Cryptosporidium?
What is the definitive host for Echinococcus granulosus?
Chromidial bars are absent in which stage of cysts in Entamoeba?
Stool examination in a patient reveals a specific finding. What is the likely route of infection of this parasite?
Which of the following leads to colonic ulcers?
Parasitology Indian Medical PG Practice Questions and MCQs
Question 421: Risk of transplacental transmission of Toxoplasma gondii is maximum when the mother is infected:
- A. Prior to conception
- B. During the first trimester
- C. During the second trimester
- D. During the third trimester (Correct Answer)
Explanation: The transmission of *Toxoplasma gondii* from mother to fetus is governed by a critical inverse relationship between the **risk of transmission** and the **severity of fetal damage**. ### Why Option D is Correct The risk of transplacental transmission is **highest in the third trimester (60–80%)**. This is primarily due to increased placental blood flow and the increased permeability/surface area of the placenta as pregnancy progresses, making it easier for tachyzoites to cross the barrier. ### Why Other Options are Incorrect * **Option A:** If a mother is infected **prior to conception**, her immunity (IgG antibodies) generally protects the fetus. Congenital toxoplasmosis occurs almost exclusively when a woman acquires a **primary infection** during pregnancy. * **Option B:** While the risk of transmission is lowest in the **first trimester (10–15%)**, the **severity** of fetal damage is maximum if infection does occur, often leading to miscarriage or severe neurological defects. * **Option C:** The second trimester represents an intermediate risk (approx. 25–30%) for both transmission and clinical severity. ### High-Yield NEET-PG Pearls * **Classic Triad of Congenital Toxoplasmosis:** Chorioretinitis (most common late finding), Hydrocephalus, and Intracranial calcifications (diffuse/scattered). * **Diagnosis:** Maternal screening via **Sabin-Feldman Dye Test** (Gold Standard). Fetal diagnosis via PCR of amniotic fluid. * **Treatment:** **Spiramycin** is used to prevent transmission to the fetus. If fetal infection is confirmed, **Pyrimethamine, Sulfadiazine, and Folinic acid** are administered. * **Rule of Thumb:** Later the infection = Higher transmission risk, but Milder clinical disease.
Question 422: A 7-year-old child presented with intermittent abdominal cramps and loose stools. Stool examination revealed eggs measuring 100µm. Which of the following is NOT a cause of these symptoms?
- A. Fasciola gigantica
- B. Echinostoma iliocanum
- C. Gastrodiscoides hominis
- D. Opisthorchis viverni (Correct Answer)
Explanation: ### Explanation The core of this question lies in the **morphometry of trematode eggs**. The stool examination reveals large eggs measuring **100µm**. **1. Why Opisthorchis viverrini is the correct answer:** *Opisthorchis viverrini* (and *Clonorchis sinensis*) are known as small liver flukes. Their eggs are among the smallest of the helminths, typically measuring **25–30 µm** in length. They are operculated with a characteristic "knob" at the posterior pole. Since the question specifies an egg size of 100µm, *Opisthorchis* is excluded as a possible cause. **2. Analysis of Incorrect Options (Large Egg Producers):** * **Fasciola gigantica:** This is a giant liver fluke. Its eggs are large, ovoid, and operculated, typically measuring **160–190 µm** (even larger than *F. hepatica*). * **Echinostoma iliocanum:** This intestinal fluke produces large, operculated, yellowish-brown eggs measuring approximately **80–120 µm**. * **Gastrodiscoides hominis:** A common intestinal fluke in parts of India (Assam). It produces large, rhomboidal/ovoid operculated eggs measuring **150 × 60–70 µm**. **Clinical Pearls for NEET-PG:** * **Large Eggs (>100 µm):** Think *Fasciola* spp., *Fasciolopsis buski*, *Gastrodiscoides hominis*, and *Schistosoma* spp. * **Small Eggs (<35 µm):** Think *Opisthorchis*, *Clonorchis*, and *Heterophyes*. * **Gastrodiscoides hominis:** High-yield for its association with **pig reservoirs** and its prevalence in the Brahmaputra valley. * **Opisthorchis/Clonorchis:** Strongly associated with **Cholangiocarcinoma** (bile duct cancer) due to chronic biliary inflammation.
Question 423: A double rise of temperature in 24 hours is characteristic of which of the following conditions?
- A. Kala Azar (Correct Answer)
- B. Malaria
- C. Tuberculosis
- D. Hodgkin's lymphoma
Explanation: **Explanation:** The characteristic fever pattern described as a **"double rise of temperature in 24 hours"** (bimodal fever) is a classic clinical sign of **Kala-azar (Visceral Leishmaniasis)**, caused by *Leishmania donovani*. This occurs when the patient experiences two distinct peaks of high-grade fever within a single day. **Analysis of Options:** * **Kala-azar (Correct):** Along with the double-quotidian fever, it is characterized by the triad of massive splenomegaly, hepatomegaly, and pancytopenia. The fever is often associated with "Kala-azar" (Black Sickness) due to hyperpigmentation of the skin. * **Malaria:** Typically presents with a **paroxysmal fever** (Cold, Hot, and Sweating stages). Depending on the species, the spikes occur every 48 hours (*P. vivax/falciparum* - Tertian) or 72 hours (*P. malariae* - Quartan), but not twice in one day. * **Tuberculosis:** Classically presents with an **evening rise of temperature** (low-grade) accompanied by night sweats. * **Hodgkin’s Lymphoma:** Associated with **Pel-Ebstein fever**, where periods of high fever alternate with afebrile periods lasting days to weeks. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Sandfly (*Phlebotomus argentipes*). * **Diagnostic Gold Standard:** Demonstration of **LD bodies** (Amastigotes) in splenic or bone marrow aspirates. * **Serology:** RK-39 antigen-based dipstick test is the most common screening tool. * **Drug of Choice:** Liposomal Amphotericin B. * **Post-Kala-azar Dermal Leishmaniasis (PKDL):** A non-ulcerative skin condition appearing years after "cured" visceral leishmaniasis, acting as a reservoir for the parasite.
Question 424: Trypanosoma cruzi grows in which of the following media?
- A. NNN medium (Correct Answer)
- B. Weinman's medium
- C. Boeack diphasic medium
- D. Diamond's medium
Explanation: **Explanation:** *Trypanosoma cruzi*, the causative agent of Chagas disease (American Trypanosomiasis), is an intracellular hemoflagellate. To diagnose it via culture, specialized media are required to support the growth of the epimastigote stage. **1. Why NNN Medium is Correct:** The **Novy-MacNeal-Nicolle (NNN) medium** is the gold standard diphasic medium used for the cultivation of both *Leishmania* and *Trypanosoma cruzi*. It consists of a blood agar base (usually rabbit blood) and an overlay of Locke’s solution or saline. The blood provides essential nutrients like hemin (V-factor), which these parasites cannot synthesize themselves. **2. Analysis of Incorrect Options:** * **Weinman’s Medium:** This is specifically used for the cultivation of *Trypanosoma brucei* (African Trypanosomiasis), not *T. cruzi*. * **Boeck and Drbohlav (Diphasic) Medium:** This is primarily used for the cultivation of intestinal amoebae, specifically *Entamoeba histolytica*. It consists of an egg saline slant covered with a liquid overlay. * **Diamond’s Medium:** This is the preferred medium for the axenic cultivation of *Trichomonas vaginalis* and *Entamoeba histolytica*. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *T. cruzi* is transmitted by the **Reduviid bug** (Triatomine/Kissing bug) via posterior station inoculation (fecal contamination of the bite site). * **Diagnostic Stages:** Look for **C-shaped trypomastigotes** in peripheral blood and **amastigotes** in cardiac muscle/tissue biopsies. * **Chagas Disease Triad:** Megaesophagus, Megacolon, and Dilated Cardiomyopathy. * **Acute Signs:** **Romaña’s sign** (unilateral painless periorbital edema) and **Chagoma** (localized skin swelling). * **Xenodiagnosis:** A unique diagnostic method where uninfected Reduviid bugs are allowed to bite the patient and their gut is later examined for the parasite.
Question 425: Which of the following statements about Entamoeba histolytica is true?
- A. It is mostly symptomatic.
- B. It can be differentiated morphologically from Entamoeba dispar.
- C. It is antigenically different from Entamoeba dispar. (Correct Answer)
- D. All of the above.
Explanation: **Explanation:** *Entamoeba histolytica* and *Entamoeba dispar* are part of a species complex that are morphologically identical but genetically and pathologically distinct. **1. Why Option C is Correct:** While they look the same under a microscope, *E. histolytica* (pathogenic) and *E. dispar* (non-pathogenic) are **antigenically and genetically distinct**. They can be differentiated using biochemical methods (isoenzyme analysis/zymodemes), molecular methods (PCR), or by detecting specific fecal antigens (EIA) targeting the Gal/GalNAc lectin unique to *E. histolytica*. **2. Why Other Options are Incorrect:** * **Option A:** In reality, approximately **90% of *E. histolytica* infections are asymptomatic**. Only about 10% progress to clinical disease (amoebic dysentery or extraintestinal abscesses). * **Option B:** They are **morphologically indistinguishable** in both cyst and trophozoite stages. The only morphological clue for *E. histolytica* is the presence of **ingested RBCs** (erythrophagocytosis) in the trophozoite, which indicates invasive disease. Without RBCs, they cannot be told apart by light microscopy. **High-Yield Clinical Pearls for NEET-PG:** * **Infective Stage:** Quadrinucleate cyst. * **Pathognomonic Feature:** Trophozoites with ingested RBCs (Erythrophagocytosis). * **Flask-shaped ulcers:** Typical lesion seen in the colon. * **Anchovy sauce pus:** Characteristic appearance of aspirated material from an Amoebic Liver Abscess. * **Drug of Choice:** Metronidazole/Tinidazole (for invasive disease) followed by a luminal amoebicide like Diloxanide furoate or Paromomycin (to eradicate cysts).
Question 426: Which of the following is NOT true about Cryptosporidium?
- A. Spores are acid fast.
- B. Spores are chlorine resistant.
- C. The diagnostic form is the sporulated oocyst.
- D. Spores are larger than those of other protozoa. (Correct Answer)
Explanation: **Explanation:** **1. Why Option D is the correct answer:** *Cryptosporidium parvum* is characterized by its **small size**. The oocysts (spores) measure approximately **4–6 µm** in diameter. In contrast, other intestinal coccidia are significantly larger: *Cyclospora cayetanensis* measures 8–10 µm, and *Cystoisospora belli* is the largest, measuring roughly 25–30 µm. Therefore, the statement that they are larger than other protozoa is morphologically incorrect. **2. Why the other options are incorrect (True statements about Cryptosporidium):** * **Option A:** Oocysts are **Acid-fast**. They stain bright red against a blue background in a Modified Ziehl-Neelsen (Kinyoun) stain, which is a key diagnostic feature. * **Option B:** Oocysts are highly **chlorine-resistant**. Standard water chlorination levels do not kill them; they require filtration (less than 1 micron) or boiling to be eliminated from water supplies. * **Option C:** The **sporulated oocyst** is both the diagnostic form (found in stool) and the infective form. Unlike *Cystoisospora*, which requires time outside the host to mature, *Cryptosporidium* oocysts are "ready-to-infect" immediately upon excretion, leading to autoinfection. **Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Causes self-limiting watery diarrhea in immunocompetent hosts but **chronic, life-threatening "cholera-like" diarrhea** in HIV/AIDS patients (CD4 count <200 cells/mm³). * **Stain of Choice:** Modified Acid-Fast stain. * **Treatment:** **Nitazoxanide** is the drug of choice for immunocompetent patients; for AIDS patients, the primary management is HAART to restore CD4 counts. * **Transmission:** Fecal-oral route; common cause of waterborne outbreaks in swimming pools and daycare centers.
Question 427: What is the definitive host for Echinococcus granulosus?
- A. Man
- B. Sheep
- C. Hound
- D. Dog (Correct Answer)
Explanation: **Explanation:** *Echinococcus granulosus* (the Dog Tapeworm) causes **Cystic Echinococcosis** (Hydatid disease). Understanding its life cycle is crucial for NEET-PG: 1. **Why Dog is correct:** In parasitology, the **definitive host** is where the parasite reaches sexual maturity and undergoes sexual reproduction. For *E. granulosus*, the adult worm lives in the small intestine of **dogs** (and other canines). Eggs are passed in the dog's feces, which are then infective to intermediate hosts. 2. **Why other options are incorrect:** * **Man (A):** Humans act as **accidental intermediate hosts**. We ingest eggs (via contaminated food/water), and the larval stage (hydatid cyst) develops in our organs. Humans are a "dead-end" host because the cycle usually stops here. * **Sheep (B):** Sheep are the **natural intermediate hosts**. They ingest eggs while grazing, and the hydatid cysts develop in their viscera. The cycle completes when a dog consumes the infected offal of the sheep. * **Hound (C):** While a hound is a type of dog, "Dog" is the standard biological classification used in textbooks and exams to represent the primary definitive host. **High-Yield Clinical Pearls for NEET-PG:** * **Infective Form for Humans:** Embryonated eggs (not the cyst). * **Diagnostic Feature:** "Hydatid sand" (brood capsules and protoscolices) found within the cyst fluid. * **Imaging:** "Water lily sign" on ultrasound/CT (indicates a ruptured endocyst). * **Casoni’s Test:** An immediate hypersensitivity skin test (now largely replaced by serology/ELISA). * **Treatment:** PAIR (Puncture, Aspiration, Injection, Re-aspiration) technique and Albendazole. Avoid cyst rupture to prevent life-threatening **anaphylaxis**.
Question 428: Chromidial bars are absent in which stage of cysts in Entamoeba?
- A. Uninucleate
- B. Binucleate
- C. Quadrinucleate (Correct Answer)
- D. Octanucleate
Explanation: ### 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*.
Question 429: Stool examination in a patient reveals a specific finding. What is the likely route of infection of this parasite?
- A. Ingestion of food contaminated with the egg or larva (Correct Answer)
- B. Insect bite
- C. Ingestion of improperly cooked beef
- D. Contact with contaminated water during swimming
Explanation: ***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.
Question 430: Which of the following leads to colonic ulcers?
- A. H. Pylori
- B. Campylobacter jejuni
- C. B. Coli
- D. E. Histolytica (Correct Answer)
Explanation: **Explanation:** The correct answer is **D. E. Histolytica**. **Entamoeba histolytica** is the causative agent of amoebiasis. The parasite invades the colonic mucosa by secreting proteolytic enzymes (histolysins), which destroy the epithelium. This leads to the formation of characteristic **flask-shaped ulcers** (narrow neck and broad base). These ulcers are typically found in the cecum and ascending colon but can involve the entire large intestine. **Analysis of Incorrect Options:** * **A. H. Pylori:** This bacterium is associated with **gastroduodenal pathology**. It causes chronic gastritis and is the leading cause of peptic ulcer disease (gastric and duodenal ulcers), not colonic ulcers. * **B. Campylobacter jejuni:** This is a common cause of bacterial gastroenteritis. While it causes inflammation of the small and large intestines (enterocolitis), it typically results in **diffuse mucosal inflammation** and superficial erosions rather than discrete, deep colonic ulcers. * **C. B. Coli (Balantidium coli):** While *B. coli* can cause large bowel ulceration similar to *E. histolytica*, it is a rare zoonotic infection. In the context of standard medical examinations, *E. histolytica* is the classic and most common answer for parasitic colonic ulcers. **High-Yield Facts for NEET-PG:** * **Flask-shaped ulcers:** Pathognomonic for *E. histolytica*. * **Trophozoites:** Look for ingested RBCs (erythrophagocytosis) in stool samples to confirm invasive disease. * **Complications:** Can lead to "Amoeboma" (a granulomatous mass in the colon) or liver abscesses (anchovy sauce pus). * **Treatment:** Metronidazole or Tinidazole (for tissue) followed by a luminal amebicide like Diloxanide furoate.
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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