Parasitology Practice Questions

Q: The amastigote form is seen in which of the following cell types?

Reticuloendothelial cells. **Explanation:** The **amastigote** is the intracellular, non-flagellated stage of parasites belonging to the genera *Leishmania* and *Trypanosoma cruzi*. In the case of *Leishmania donovani* (the causative agent of Kala-azar), the parasite specifically targets and multiplies within the **Reticuloendothelial system (RES)**. **1. Why Reticuloendothelial cells are correct:** The RES consists of phagocytic cells located in the liver (Kupffer cells), spleen, bone marrow, and lymph nodes. Once the promastigote form enters the human body via a sandfly bite, it is engulfed by phagocytes. Inside these cells, it transforms into the amastigote (Leishman-Donovan or LD bodies). While macrophages are the primary host cells, the term "Reticuloendothelial cells" is the most comprehensive and accurate description of the entire system involved in the pathogenesis of Visceral Leishmaniasis. **2. Why other options are incorrect:** * **Macrophages (Option A):** While technically correct as macrophages are the specific cells involved, "Reticuloendothelial cells" is the preferred broader anatomical classification in standard parasitology textbooks for this specific question type. * **Lymphocytes (Option C):** These are part of the adaptive immune system (T and B cells) and are not the primary hosts for amastigote replication. * **Red blood cells (Option D):** RBCs are the target for *Plasmodium* (Malaria) and *Babesia*, but they lack the machinery and phagocytic nature required by *Leishmania*. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Phlebotomus argentipes* (Sandfly). * **Infective stage:** Promastigote (flagellated, found in the sandfly midgut). * **Diagnostic stage:** Amastigote (found in splenic or bone marrow aspirates). * **Culture Medium:** NNN (Novy-MacNeal-Nicolle) medium. * **Gold Standard Diagnosis:** Splenic aspirate (highest sensitivity) showing LD bodies.

Q: In a case of Kala-azar, the aldehyde test becomes positive after what duration?

12 weeks. **Explanation:** The **Aldehyde Test (Napier’s Test)** is a non-specific biochemical test used in the diagnosis of Visceral Leishmaniasis (Kala-azar). Its positivity depends on a significant increase in serum **gamma globulins** (hypergammaglobulinemia), which is a hallmark of the body's immune response to *Leishmania donovani*. **Why 12 weeks is correct:** In Kala-azar, the rise in serum globulins occurs gradually. It takes approximately **3 months (12 weeks)** for the globulin levels to become sufficiently elevated to cause the "jellification" (solidification and opalescence) of serum when mixed with 40% formaldehyde. Therefore, the test is not useful for early diagnosis. **Analysis of incorrect options:** * **2 & 4 weeks:** These durations are too early in the disease course. During the first month, the immune system has not yet produced the massive quantity of globulins required to trigger a positive reaction. * **8 weeks:** While globulin levels are rising, they typically do not reach the threshold for a reliable aldehyde test result until the 12-week mark. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** The test detects a quantitative increase in globulins, not specific antibodies. * **Positive Result:** Serum turns into a stiff, white, opaque gel (resembling the white of a boiled egg) within 2–20 minutes. * **Chopra’s Antimony Test:** Another non-specific test for Kala-azar; it becomes positive earlier than the aldehyde test (around 4 weeks). * **Specific Tests:** For NEET-PG, remember that the **rk39 immunochromatographic test** is the rapid diagnostic test of choice, while **Amastigotes (LD bodies)** in bone marrow or splenic aspirates remain the gold standard for definitive diagnosis.

Q: Which of the following does NOT cause malabsorption?

Ascaris lumbricoides. **Explanation:** The correct answer is **B. Ascaris lumbricoides**. **1. Why Ascaris lumbricoides is the correct answer:** Malabsorption in parasitic infections typically occurs when the parasite causes significant structural damage to the intestinal mucosa (villous atrophy) or creates a physical barrier over the absorptive surface. *Ascaris lumbricoides* (Roundworm) resides in the lumen of the small intestine. While it competes with the host for nutrients (leading to protein-energy malnutrition and Vitamin A/C deficiency), it does **not** typically cause a malabsorption syndrome. Its primary complications are mechanical, such as intestinal obstruction (at the ileocecal valve) or migration into the biliary tract. **2. Analysis of Incorrect Options:** * **Giardia lamblia:** The classic cause of parasitic malabsorption. It causes "coating" of the intestinal mucosa, villous flattening, and brush border enzyme deficiency (especially lactase), leading to steatorrhea and fat-soluble vitamin deficiency. * **Strongyloides stercoralis:** In heavy infections, the larvae burrow into the duodenal and jejunal mucosa, causing significant inflammation, ulceration, and a secondary malabsorption syndrome. * **Capillaria philippinensis:** This parasite causes "sprue-like" symptoms. It leads to severe mucosal injury, resulting in a protein-losing enteropathy, electrolyte imbalance, and profound malabsorption. **3. NEET-PG High-Yield Pearls:** * **Most common parasite causing malabsorption:** *Giardia lamblia*. * **Parasites causing Autoinfection:** *Strongyloides stercoralis*, *Capillaria philippinensis*, *Enterobius vermicularis*, and *Hymenolepis nana*. * **Ascaris Clinical Sign:** "Loeffler’s Syndrome" (transient pulmonary infiltrates with eosinophilia) occurs during the lung migration phase. * **Diagnosis of Ascaris:** Stool microscopy for bile-stained eggs; "Spaghetti appearance" on Barium meal.

Q: Pernicious malaria is a complication seen in infection with which Plasmodium species?

Plasmodium falciparum. **Explanation:** **1. Why Plasmodium falciparum is correct:** Pernicious malaria refers to the life-threatening, severe clinical manifestations of malaria, which are almost exclusively caused by **Plasmodium falciparum**. The underlying pathophysiology is **cytoadherence** and **sequestration**. *P. falciparum* expresses a protein called **PfEMP-1** on the surface of infected RBCs, which forms "knobs." These knobs bind to endothelial receptors (like ICAM-1 and CD36) in deep capillaries. This leads to microvascular obstruction, tissue hypoxia, and organ dysfunction. Common presentations of pernicious malaria include: * **Cerebral malaria** (encephalopathy/coma) * **Algid malaria** (shock and peripheral circulatory failure) * **Blackwater fever** (hemoglobinuria due to massive intravascular hemolysis) * **Septicemic malaria** (high-grade fever with multiorgan failure) **2. Why the other options are incorrect:** * **P. vivax & P. ovale:** These species primarily cause "Benign Tertian Malaria." While *P. vivax* can occasionally cause severe disease (like splenic rupture), it does not typically exhibit the sequestration phenomenon required to be classified as "pernicious." They are known for forming **hypnozoites** in the liver, leading to relapses. * **P. malariae:** This species causes "Quartan Malaria." It is generally the most chronic but least severe form, though it is classically associated with **nephrotic syndrome** in children. **3. NEET-PG High-Yield Pearls:** * **Maurer’s dots:** Seen in RBCs infected with *P. falciparum*. * **Multiple rings and Crescent-shaped gametocytes:** Characteristic morphology of *P. falciparum*. * **Recrudescence:** Seen in *P. falciparum* (due to sub-therapeutic treatment), whereas **Relapse** is seen in *P. vivax/ovale* (due to hypnozoites). * **Drug of choice for Severe Malaria:** Intravenous **Artesunate**.

Q: Maltese cross appearance in peripheral blood smear is characteristic of which parasitic infection?

Babesia microti. **Explanation:** The **Maltese cross appearance** is the pathognomonic morphological feature of **Babesia microti**. This appearance occurs when the parasite undergoes asexual reproduction (merogony) within the host’s red blood cells, resulting in a **tetrad of four daughter merozoites** joined together at their bases. **Why the other options are incorrect:** * **Plasmodium falciparum:** While it also infects RBCs, it typically presents with delicate ring forms, "headphone" shaped trophozoites, and characteristic crescent or **banana-shaped gametocytes**. It does not form tetrads. * **Leishmania chagasi:** This is a tissue parasite. In a smear (usually bone marrow or splenic aspirate), it appears as **amastigotes** (Leishman-Donovan bodies) within macrophages, characterized by a nucleus and a kinetoplast. * **Trypanosoma cruzi:** In peripheral blood during the acute phase, it appears as C-shaped or U-shaped **trypomastigotes** with a prominent kinetoplast. It does not infect the interior of RBCs in a tetrad formation. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Babesia* is transmitted by the **Ixodes tick** (the same vector for Lyme disease and Anaplasmosis). * **Clinical Presentation:** Often presents as a malaria-like illness (fever, hemolytic anemia, jaundice). It is particularly severe or fatal in **asplenic patients**. * **Diagnosis:** Thick and thin peripheral blood smears (Giemsa stain). * **Treatment:** Combination of **Atovaquone + Azithromycin** (preferred) or Quinine + Clindamycin.

Q: Risk of transplacental transmission of Toxoplasma gondii is maximum when the mother is infected:

During the third trimester. 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.

Q: 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?

Opisthorchis viverni. ### 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.

Q: Which of the following statements about Entamoeba histolytica is true?

It is antigenically different from Entamoeba dispar.. **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).

Q: Which of the following is NOT true about Cryptosporidium?

Spores are larger than those of other protozoa.. **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 1

What is a highly specific and sensitive test for diagnosing kala-azar?

Accepted Answer

Immunofluorescent antibody test

Answer

Complement fixation test with WKK antigen

Answer

Napier's aldehyde test

Answer

Chopra's antimony test

Question 2

The amastigote form is seen in which of the following cell types?

Accepted Answer

Reticuloendothelial cells

Answer

Macrophages

Answer

Lymphocytes

Answer

Red blood cells

Question 3

In a case of Kala-azar, the aldehyde test becomes positive after what duration?

Accepted Answer

12 weeks

Answer

2 weeks

Answer

4 weeks

Answer

8 weeks

Question 4

Which of the following does NOT cause malabsorption?

Accepted Answer

Ascaris lumbricoides

Answer

Giardiasis

Answer

Strongyloides

Answer

Capillaria phillipinesis

Question 5

Pernicious malaria is a complication seen in infection with which Plasmodium species?

Accepted Answer

Plasmodium falciparum

Answer

Plasmodium vivax

Answer

Plasmodium malariae

Answer

Plasmodium ovale

Question 6

Maltese cross appearance in peripheral blood smear is characteristic of which parasitic infection?

Accepted Answer

Babesia microti

Answer

Plasmodium falciparum

Answer

Leishmania chagasi

Answer

Trypanosoma cruzi

Question 7

Risk of transplacental transmission of Toxoplasma gondii is maximum when the mother is infected:

Accepted Answer

During the third trimester

Answer

Prior to conception

Answer

During the first trimester

Answer

During the second trimester

Question 8

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?

Accepted Answer

Opisthorchis viverni

Answer

Fasciola gigantica

Answer

Echinostoma iliocanum

Answer

Gastrodiscoides hominis

Question 9

Which of the following statements about Entamoeba histolytica is true?

Accepted Answer

It is antigenically different from Entamoeba dispar.

Answer

It is mostly symptomatic.

Answer

It can be differentiated morphologically from Entamoeba dispar.

Answer

All of the above.

Question 10

Which of the following is NOT true about Cryptosporidium?

Accepted Answer

Spores are larger than those of other protozoa.

Answer

Spores are acid fast.

Answer

Spores are chlorine resistant.

Answer

The diagnostic form is the sporulated oocyst.

Parasitology — MCQs

Parasitology — MCQs

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