Parasitology Practice Questions

Q: A 24-year-old patient with AIDS presents with chronic abdominal pain, low-grade fever, diarrhea, and malabsorption. Oocysts are demonstrated in the stool. What is the likely cause of his diarrhea?

Isospora belli. **Explanation:** The clinical presentation of chronic diarrhea, malabsorption, and fever in an HIV/AIDS patient, combined with the presence of **oocysts** in the stool, points directly to **Cystoisospora belli** (formerly *Isospora belli*). **1. Why Isospora belli is correct:** *Isospora belli* is an opportunistic protozoan that causes severe, watery, non-bloody diarrhea in immunocompromised individuals. It is unique among the common AIDS-related coccidia because it produces large, oval-shaped oocysts (approx. 25–30 µm) that are visible on modified acid-fast staining. It typically involves the small intestine, leading to malabsorption and weight loss. **2. Why other options are incorrect:** * **E. histolytica:** Causes amoebic dysentery (bloody diarrhea) and liver abscesses. It is identified by **cysts or trophozoites**, not oocysts. * **G. lamblia:** Causes foul-smelling, fatty stools (steatorrhea) but is not specifically an opportunistic infection of AIDS. It is identified by **cysts or pear-shaped trophozoites**. * **Microsporidia:** While a common cause of chronic diarrhea in AIDS, Microsporidia are **spores**, not oocysts. They are much smaller (1–2 µm) and usually require special stains like Chromotrope 2R. **High-Yield Clinical Pearls for NEET-PG:** * **Staining:** *Isospora*, *Cryptosporidium*, and *Cyclospora* are all **Acid-Fast positive**. * **Treatment:** Unlike *Cryptosporidium* (which is difficult to treat), *Isospora belli* responds excellently to **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. * **Morphology:** *Isospora* oocysts are the largest among the coccidia; *Cryptosporidium* oocysts are the smallest (4–5 µm) and spherical. * **Autofluorescence:** *Isospora* and *Cyclospora* oocysts exhibit blue-green autofluorescence under UV microscopy.

Q: Fish is a host for all of the following parasites except?

Paragonimus westermani. ### Explanation The correct answer is **Paragonimus westermani**. To answer this question correctly, one must distinguish between parasites that use **fish** as their second intermediate host versus those that use **crustaceans**. **1. Why Paragonimus westermani is the correct answer:** *Paragonimus westermani* (the Lung Fluke) follows a specific life cycle: the first intermediate host is a **snail**, but the second intermediate host is a **crustacean (crab or crayfish)**. Humans are infected by ingesting raw or undercooked crustacean meat containing metacercariae, not fish. **2. Analysis of Incorrect Options (Fish-borne Parasites):** * **Clonorchis sinensis (Chinese Liver Fluke):** Humans are infected by eating raw/undercooked **freshwater fish** containing metacercariae. * **Opisthorchis viverrini (Southeast Asian Liver Fluke):** Similar to *Clonorchis*, it utilizes **freshwater fish** (cyprinoid family) as the second intermediate host. * **Diphyllobothrium latum (Fish Tapeworm):** This is the longest tapeworm infecting humans. Its life cycle involves two intermediate hosts: a cyclops (crustacean) and then a **freshwater fish** (e.g., pike, perch). Humans get infected by eating raw fish containing plerocercoid larvae. **3. NEET-PG High-Yield Clinical Pearls:** * **Paragonimus westermani:** Classically presents with **hemoptysis** (mimicking Tuberculosis) and "rusty sputum." Look for a history of eating raw crabs. * **Diphyllobothrium latum:** Associated with **Vitamin B12 deficiency** and Megaloblastic anemia because the worm competes for B12 absorption in the jejunum. * **Clonorchis/Opisthorchis:** Chronic infection is a major risk factor for **Cholangiocarcinoma** (bile duct cancer). * **Heterophyes heterophyes** and **Metagonimus yokogawai** are other trematodes that also use fish as intermediate hosts.

Q: Which parasite causes periporal fibrosis of the liver?

Schistosoma mansoni. **Explanation:** **Schistosoma mansoni** is the primary cause of **Symmers’ pipestem fibrosis** (periportal fibrosis). The pathogenesis involves the deposition of eggs in the presinusoidal capillaries of the liver. These eggs secrete soluble antigens that trigger a chronic granulomatous inflammation. Over time, this leads to extensive collagen deposition around the portal veins (periportal fibrosis) without affecting the liver parenchyma itself. This results in portal hypertension, splenomegaly, and esophageal varices, while liver function tests often remain normal. **Analysis of Options:** * **Schistosoma mansoni (Correct):** Primarily inhabits the inferior mesenteric veins. Its eggs are frequently trapped in the liver, leading to the classic "pipestem" fibrosis. * **Schistosoma japonicum:** While it also causes liver fibrosis and inhabits the superior mesenteric veins, *S. mansoni* is the classic textbook association for Symmers' fibrosis in medical exams. *S. japonicum* often causes more severe, acute disease (Katayama fever). * **Schistosoma haematobium:** Primarily inhabits the vesical venous plexus. It is associated with urinary schistosomiasis, hematuria, and squamous cell carcinoma of the bladder, rather than liver fibrosis. * **Schistosoma mekongi:** Similar to *S. japonicum* but restricted to specific geographical areas (Mekong River basin); it is a less common cause of hepatosplenic disease compared to *S. mansoni*. **NEET-PG High-Yield Pearls:** * **Diagnostic feature:** *S. mansoni* eggs have a characteristic **lateral spine**. * **Intermediate host:** Biomphalaria snail. * **Infective stage:** Cercaria (enters via skin penetration). * **Drug of choice:** Praziquantel for all Schistosoma species.

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.

Question 1

A 24-year-old patient with AIDS presents with chronic abdominal pain, low-grade fever, diarrhea, and malabsorption. Oocysts are demonstrated in the stool. What is the likely cause of his diarrhea?

Accepted Answer

Isospora belli

Answer

E. histolytica

Answer

G. lamblia

Answer

Microsporidia

Question 2

Fish is a host for all of the following parasites except?

Accepted Answer

Paragonimus westermani

Answer

Clonorchis sinensis

Answer

Opisthorchis viverrini

Answer

Diphyllobothrium latum

Question 3

Which parasite causes periporal fibrosis of the liver?

Accepted Answer

Schistosoma mansoni

Answer

Schistosoma japonicum

Answer

Schistosoma haematobium

Answer

Schistosoma mekongi

Question 4

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 5

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 6

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 7

Which of the following does NOT cause malabsorption?

Accepted Answer

Ascaris lumbricoides

Answer

Giardiasis

Answer

Strongyloides

Answer

Capillaria phillipinesis

Question 8

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 9

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 10

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

Parasitology — MCQs

Parasitology — MCQs

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