Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 681: Which of the following organisms exhibits a simple life cycle?

A. Ascaris (Correct Answer)
B. T. solium
C. Toxoplasma
D. Giardia

Explanation: **Explanation:** In parasitology, a **simple life cycle** (monoxenous) refers to an organism that requires only **one host** (usually human) to complete its entire development. A **complex life cycle** (heteroxenous) requires two or more hosts (definitive and intermediate). **Why Ascaris is Correct:** * ***Ascaris lumbricoides*** (Giant Roundworm) is a soil-transmitted helminth. It requires only humans to complete its life cycle. Eggs are passed in feces, embryonate in the soil, and are ingested by another human. There is no intermediate host involved. **Analysis of Incorrect Options:** * **B. *Taenia solium* (Pork Tapeworm):** Exhibits a complex life cycle requiring two hosts. Humans are the definitive host (adult worm), while pigs serve as the intermediate host (larval stage/Cysticercus cellulosae). * **C. *Toxoplasma gondii*:** Exhibits a complex life cycle. Cats (felids) are the definitive host, while humans and other mammals serve as intermediate hosts. * **D. *Giardia lamblia*:** While *Giardia* also has a simple life cycle (human-to-human via cysts), in the context of standard NEET-PG parasitology classifications, **Ascaris** is the classic textbook example of a nematode with a simple life cycle involving soil-mediated maturation. (Note: If this were a "multiple correct" scenario, Giardia would also qualify, but Ascaris is the primary academic focus for this concept). **High-Yield Clinical Pearls for NEET-PG:** * **Loeffler’s Syndrome:** Characterized by transient pulmonary infiltrates and eosinophilia, occurring during the heart-lung migration phase of *Ascaris* larvae. * **Infective Stage:** For *Ascaris*, it is the **embryonated egg** containing the Rhabditiform larva (L2). * **Rule of Thumb:** Most intestinal nematodes (*Ascaris, Enterobius, Trichuris, Ancylostoma*) have simple life cycles. Most Cestodes and Trematodes (except *Hymenolepis nana*) have complex life cycles.

Question 682: Which of the following causes malabsorption?

A. Giardiasis
B. Ascaris lumbricoides (Correct Answer)
C. Strongyloides
D. Capillaria phillipinesis

Explanation: **Explanation** The correct answer is **B. Ascaris lumbricoides**, based on the specific context of this question. While several parasites can cause malabsorption, *Ascaris lumbricoides* is a classic cause of protein-energy malnutrition and vitamin A/C deficiencies, especially in children with high worm burdens. **1. Why Ascaris lumbricoides is correct:** *Ascaris* resides in the lumen of the small intestine. Large numbers of worms compete with the host for nutrients and release anti-enzymes (like pepsin inhibitors) that interfere with protein digestion. This leads to **malabsorption of fats, proteins, and fat-soluble vitamins**, often manifesting as growth retardation in pediatric populations. **2. Analysis of other options:** * **Giardiasis (Option A):** *Giardia lamblia* is a notorious cause of malabsorption and steatorrhea by coating the duodenal mucosa (blunting villi). However, in many standardized exams, if *Ascaris* is the keyed answer, it refers to the massive nutritional drain seen in endemic areas. * **Strongyloides (Option C):** While *Strongyloides stercoralis* can cause malabsorption in heavy infections, it is more clinically significant for its "autoinfection" cycle and hyperinfection syndrome in immunocompromised patients. * **Capillaria philippinensis (Option D):** This parasite causes a severe "sprue-like" syndrome with profound malabsorption and protein-losing enteropathy, but it is much rarer than *Ascaris*. **Clinical Pearls for NEET-PG:** * **Most common cause of parasitic malabsorption:** *Giardia lamblia*. * **Ascaris complications:** Intestinal obstruction (most common), Loeffler’s syndrome (eosinophilic pneumonia), and biliary colic. * **Diagnosis:** *Ascaris* is diagnosed by finding bile-stained eggs (mammillated) in stool. * **Treatment:** Albendazole is the drug of choice. *Note: In clinical practice, Giardia, Strongyloides, and Capillaria all cause malabsorption. If this were a "Multiple Correct" type question, all could be considered; however, Ascaris is frequently highlighted in the context of global pediatric malnutrition.*

Question 683: A 30-year-old patient developed high fever of sudden onset. Peripheral blood smear showed crescent-shaped gametocytes. Malaria pigment was dark brown in color. Which of the following malarial parasites is the causative agent?

A. Plasmodium vivax
B. Plasmodium malariae
C. Plasmodium falciparum (Correct Answer)
D. Plasmodium ovale

Explanation: ### Explanation The correct answer is **Plasmodium falciparum**. **1. Why Plasmodium falciparum is correct:** The diagnosis is based on two pathognomonic morphological features described in the peripheral blood smear: * **Crescent-shaped (Banana-shaped) Gametocytes:** This is the most characteristic diagnostic feature of *P. falciparum*. Other species have spherical or rounded gametocytes. * **Dark Brown Pigment:** Malarial pigment (hemozoin) in *P. falciparum* is typically dark brown to black. * **Clinical Presentation:** Sudden onset of high fever is consistent with the aggressive nature of falciparum malaria, which often causes "malignant tertian" malaria. **2. Why other options are incorrect:** * **P. vivax:** Gametocytes are large and **round/oval**. The pigment is yellowish-brown. It typically shows Schüffner’s dots and enlarged RBCs. * **P. malariae:** Gametocytes are **round** and smaller. A key feature is the "Ziemann’s dots" and the characteristic "Band form" trophozoites. The pigment is often dark brown but coarser. * **P. ovale:** Gametocytes are **round/oval**. RBCs are often oval with fimbriated (tufted) edges and contain James’ dots. **3. NEET-PG High-Yield Pearls:** * **Maurer’s Clefts:** Coarse granulations seen in RBCs infected with *P. falciparum*. * **Multiple Rings & Appole Forms:** *P. falciparum* often shows multiple ring forms per RBC and "appliqué" forms (parasite at the periphery of the RBC). * **Sequestration:** *P. falciparum* is the only species where mature trophozoites and schizonts are rarely seen in peripheral blood (except in severe cases) because they sequester in deep capillaries, leading to complications like Cerebral Malaria. * **Recrudescence** is seen in *P. falciparum* and *P. malariae*, whereas **Relapse** (due to hypnozoites) is seen in *P. vivax* and *P. ovale*.

Question 684: Ankylostoma duodenale commonly lives in which part of the small intestine?

A. Upper one-third of the duodenum
B. Lower one-third of the duodenum
C. Jejunum (Correct Answer)
D. Ileum

Explanation: **Explanation:** The correct answer is **Jejunum**. **1. Why Jejunum is Correct:** *Ankylostoma duodenale* (Old World Hookworm) primarily inhabits the **upper part of the small intestine**, specifically the **jejunum** (and occasionally the distal duodenum). While the name "duodenale" suggests the duodenum, the adult worms prefer the jejunum because its mucosal structure is ideal for attachment. The worms use their buccal capsule, equipped with two pairs of teeth, to hook onto the intestinal villi, where they suck blood and lymph. **2. Why Other Options are Incorrect:** * **Options A & B (Duodenum):** While the parasite passes through the duodenum and may occasionally attach to its distal portion, it is not the *primary* or most common site of residence. The jejunum provides a larger surface area and more favorable environment for the adult worm's survival. * **Option D (Ileum):** The ileum is the distal-most part of the small intestine. By the time contents reach the ileum, nutrient density is lower, and the environment is less optimal for hookworms. The ileum is more commonly associated with parasites like *Enterobius vermicularis* (near the ileocecal junction) or *Giardia* (though Giardia also prefers the duodenum/jejunum). **3. Clinical Pearls for NEET-PG:** * **Infective Stage:** Filariform larva (enters via skin penetration, often causing "Ground Itch"). * **Diagnostic Stage:** Non-bile stained, segmented eggs in feces. * **Pathogenesis:** The primary clinical manifestation is **Iron Deficiency Anemia** (Microcytic Hypochromic) due to chronic blood loss (approx. 0.15–0.2 ml per worm/day). * **Life Cycle:** Exhibits **Hepatopulmonary migration** (Loeffler’s syndrome can occur during the lung phase). * **Treatment:** Albendazole (Drug of choice).

Question 685: Which of the following parasites most commonly causes malabsorption?

A. Giardia lamblia
B. Ascaris lumbricoides (Correct Answer)
C. Strongyloides stercoralis
D. Capillaria philippinensis

Explanation: **Explanation:** The correct answer is **Ascaris lumbricoides**. While several parasites can cause malabsorption, *Ascaris lumbricoides* is the most common cause globally due to its massive prevalence (infecting over 1 billion people). **1. Why Ascaris lumbricoides is correct:** In heavy infections, especially in children, *Ascaris* causes malabsorption by competing with the host for nutrients and inducing structural changes in the small intestine. It leads to **protein-energy malnutrition**, Vitamin A deficiency, and fat malabsorption. The sheer worm burden leads to "luminal competition" and mechanical interference with digestion and absorption. **2. Analysis of Incorrect Options:** * **Giardia lamblia:** This is a classic cause of malabsorption and steatorrhea (foul-smelling, fatty stools) due to the "carpeting" of the duodenal mucosa. However, in terms of global epidemiological scale and total cases of associated malnutrition, *Ascaris* is considered more common. * **Strongyloides stercoralis:** While it can cause a malabsorption syndrome (hyperinfection in immunocompromised hosts), it is significantly less common than *Ascaris*. * **Capillaria philippinensis:** This parasite causes a severe, life-threatening malabsorption syndrome known as "sprue-like" illness with profound protein-losing enteropathy, but it is geographically restricted (mainly Philippines/Thailand) and rare. **NEET-PG High-Yield Pearls:** * **Most common helminthic infection worldwide:** *Ascaris lumbricoides*. * **Loeffler’s Syndrome:** Transient pulmonary infiltrates with eosinophilia (caused by larval migration of *Ascaris*, *Strongyloides*, and Hookworms). * **Giardia:** Most common intestinal **protozoan** causing malabsorption; diagnosed by "falling leaf" motility on wet mount or the String Test (Entero-test). * **Drug of Choice:** Albendazole is the treatment for *Ascaris*, while Tinidazole/Metronidazole is preferred for *Giardia*.

Question 686: Arc-C-5 in countercurrent electrophoresis of serum is diagnostic of?

A. Cysticercosis
B. Cryptococcosis
C. Hydatidosis (Correct Answer)
D. Brucellosis

Explanation: **Explanation:** **Hydatidosis (Cystic Echinococcosis)** is caused by the larval stage of *Echinococcus granulosus*. The diagnosis relies heavily on imaging and serology. The **Arc-5 (or Arc-C-5)** is a specific precipitation line formed during immunoelectrophoresis or countercurrent immunoelectrophoresis (CIEP) when patient serum reacts with hydatid cyst fluid (antigen 5). 1. **Why Hydatidosis is correct:** Antigen 5 is a major lipoprotein found in the hydatid cyst fluid. When subjected to electrophoresis, it forms a characteristic "Arc-5" precipitation band. This finding is considered highly specific and **diagnostic** for *E. granulosus* infection, although cross-reactivity can rarely occur with *Taenia solium*. 2. **Why other options are incorrect:** * **Cysticercosis:** Diagnosis typically involves neuroimaging (MRI/CT) and Enzyme-linked Immunoelectrotransfer Blot (EITB) for detecting antibodies against glycoprotein antigens, not Arc-5. * **Cryptococcosis:** Diagnosis is confirmed by India ink preparation, CrAg (Cryptococcal Antigen) lateral flow assay, or culture. * **Brucellosis:** Diagnosis relies on blood culture (Castaneda medium) and serological tests like the Standard Agglutination Test (SAT) or Rose Bengal Plate Test. **Clinical Pearls for NEET-PG:** * **Antigen 5 and Antigen B** are the two most important immunogenic proteins in hydatid fluid. * **Casoni’s Test:** An immediate hypersensitivity skin test formerly used for Hydatidosis, now largely replaced by serology due to low sensitivity and specificity. * **PAIR technique:** (Puncture, Aspiration, Injection, Re-aspiration) is a minimally invasive treatment for hydatid cysts. * **Echinococcus multilocularis:** Causes Alveolar Hydatid Disease (more aggressive/malignant presentation).

Question 687: Where does Schistosoma Japonicum reside?

A. Vesical Plexus
B. Ileocecal plexus (Correct Answer)
C. Systemic Circulation
D. Gallbladder

Explanation: **Explanation:** *Schistosoma japonicum* is a blood fluke that primarily inhabits the **superior mesenteric veins**, which drain the small intestine and the ascending/transverse colon. The **ileocecal plexus** is the specific anatomical site within this drainage system where the adult worms reside and deposit their eggs. **Why the other options are incorrect:** * **Vesical Plexus:** This is the primary habitat for ***Schistosoma haematobium***. It leads to urinary schistosomiasis, characterized by terminal hematuria and an increased risk of squamous cell carcinoma of the bladder. * **Systemic Circulation:** While cercariae travel through the blood to reach the liver (where they mature), the adult worms do not reside in the general systemic circulation. They live specifically in the portal venous system. * **Gallbladder:** This is a common site for liver flukes like *Clonorchis sinensis* or *Fasciola hepatica*, but not for Schistosomes. **High-Yield NEET-PG Pearls:** 1. **Habitat Mnemonic:** * *S. haematobium*: **H**ematobium = **H**ole (Bladder/Vesical plexus). * *S. mansoni*: **M**ansoni = **M**inferior (Inferior mesenteric veins/Sigmoid-rectal area). * *S. japonicum*: **J**aponicum = **J**uperior (Superior mesenteric veins/Ileocecal area). 2. **Egg Morphology:** *S. japonicum* eggs are unique for being **rounded/oval with a rudimentary lateral knob** (often difficult to see), unlike the prominent terminal spine of *S. haematobium* or the large lateral spine of *S. mansoni*. 3. **Pathology:** *S. japonicum* is associated with "Katayama Fever" and has the highest egg output, often leading to severe hepatic fibrosis and portal hypertension.

Question 688: Splenic rupture is most commonly associated with infection by which of the following Plasmodium species?

A. Plasmodium vivax (Correct Answer)
B. Plasmodium ovale
C. Plasmodium malariae
D. Plasmodium falciparum

Explanation: ### Explanation **Correct Answer: A. Plasmodium vivax** **1. Why Plasmodium vivax is correct:** While *Plasmodium falciparum* is responsible for the highest overall mortality in malaria, **spontaneous splenic rupture** is most frequently associated with **non-falciparum malaria**, specifically ***Plasmodium vivax***. The underlying mechanism involves rapid splenic enlargement (splenomegaly) during the acute phase of infection. In *P. vivax*, the spleen becomes congested, soft, and friable. Sudden increases in intra-abdominal pressure or minor trauma can lead to subcapsular hematoma formation and subsequent rupture. It is a rare but life-threatening complication, typically occurring during the primary infection rather than chronic relapses. **2. Why other options are incorrect:** * **B & C (P. ovale & P. malariae):** While these species cause splenomegaly, they are significantly less common globally and have a lower incidence of splenic complications compared to *P. vivax*. * **D (P. falciparum):** Although *P. falciparum* causes severe systemic disease (cerebral malaria, ARDS, renal failure), it is less commonly associated with acute splenic rupture. In endemic areas, chronic *P. falciparum* exposure leads to "Tropical Splenomegaly Syndrome" (Hyperreactive Malarial Splenomegaly), where the spleen becomes massive but fibrotic (firm), making it more resistant to acute rupture than the "soft" spleen of acute *P. vivax*. **3. High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of Malarial Splenic Rupture:** *P. vivax*. * **Most common cause of Cerebral Malaria:** *P. falciparum*. * **Schüffner’s dots:** Seen in *P. vivax* and *P. ovale*. * **Maurer’s clefts:** Seen in *P. falciparum*. * **Ziemann’s dots:** Seen in *P. malariae*. * **Recurrence vs. Relapse:** Relapse (due to hypnozoites in the liver) is a feature of *P. vivax* and *P. ovale*.

Question 689: 'rK 39 antigen' is useful for the diagnosis of which condition?

A. Diphtheria
B. Tuberculosis
C. Leprosy
D. Kala azar (Correct Answer)

Explanation: **Explanation:** The **rK39 antigen** is a recombinant protein derived from a 39-amino acid repeat unit found in the kinesin-like protein of ***Leishmania donovani***. It is the gold standard for the rapid serological diagnosis of **Visceral Leishmaniasis (Kala-azar)**. 1. **Why Kala-azar is correct:** The rK39 immunochromatographic test (ICT) detects circulating antibodies against this specific antigen. It is highly sensitive (>95%) and specific, especially in the Indian subcontinent. It is a point-of-care test that provides results within minutes, making it ideal for field diagnosis in endemic areas like Bihar and West Bengal. 2. **Why other options are incorrect:** * **Diphtheria:** Diagnosis is primarily clinical, confirmed by **Elek’s gel precipitation test** or culture on Löffler's serum slope/Potassium tellurite agar. * **Tuberculosis:** Diagnosis relies on Sputum microscopy (AFB), **CBNAAT (GeneXpert)**, or culture on LJ medium. Serological tests are not recommended for TB diagnosis. * **Leprosy:** Diagnosis is clinical (skin patches with sensory loss) and confirmed by **Slit-skin smears** (Z-N stain) or histopathology. **High-Yield Clinical Pearls for NEET-PG:** * **rK39 Limitations:** It remains positive for several months even after a successful cure; therefore, it **cannot** be used to diagnose relapse or monitor treatment response. * **PKDL:** rK39 is also positive in cases of Post-Kala-azar Dermal Leishmaniasis. * **Definitive Diagnosis:** The "Gold Standard" for Kala-azar remains the demonstration of **LD bodies** (Amastigotes) in splenic or bone marrow aspirates. * **Drug of Choice:** Liposomal Amphotericin B is currently the preferred treatment for Kala-azar in India.

Question 690: What is true about Diphyllobothrium?

A. Man is the single intermediate host
B. Iron deficiency anemia is a clinical manifestation
C. An operculated egg is diagnostic (Correct Answer)
D. Fish is the definitive host

Explanation: ### Explanation **Diphyllobothrium latum** (Fish Tapeworm) is the largest tapeworm infecting humans. The correct answer is **Option C** because the diagnosis is primarily made by identifying characteristic **operculated eggs** (possessing a lid-like structure at one end) and an abopercular knob in the stool. Unlike most other cestodes, *Diphyllobothrium* eggs are unembryonated when passed. #### Analysis of Options: * **Option A (Incorrect):** Man is the **definitive host**, not the intermediate host. Humans harbor the adult worm in the small intestine after consuming undercooked fish. * **Option B (Incorrect):** It causes **Megaloblastic anemia (Vitamin B12 deficiency)**, not iron deficiency anemia. The parasite competes with the host for B12 absorption in the jejunum, leading to Pernicious-like anemia. * **Option D (Incorrect):** Fish (specifically freshwater fish) act as the **second intermediate host** (containing the infective *plerocercoid* larva). The definitive hosts are humans and fish-eating mammals. #### High-Yield NEET-PG Pearls: * **Life Cycle:** Requires two intermediate hosts: 1st is **Cyclops** (contains procercoid larva); 2nd is **Freshwater fish** (contains plerocercoid larva). * **Infective Stage:** Plerocercoid larva. * **Clinical Feature:** Most infections are asymptomatic, but heavy loads cause Vitamin B12 deficiency and subacute combined degeneration of the spinal cord. * **Morphology:** The adult worm has a **spatulate (almond-shaped) scolex** with two longitudinal sucking grooves called **bothria**. * **Treatment:** Praziquantel is the drug of choice.

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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