Parasitology Practice Questions

Q: Which parasite is associated with Charcot-Layden crystals but lacks pus cells in its stain?

E. histolytica. **Explanation:** The correct answer is **C. *Entamoeba histolytica***. The presence of **Charcot-Leyden crystals** in stool is a classic diagnostic marker for intestinal parasitosis. These diamond-shaped crystals are formed from the breakdown products of eosinophils (specifically the enzyme lysophospholipase). In **Amoebic dysentery** (*E. histolytica*), the stool is characterized by: 1. **Charcot-Leyden crystals:** Due to the eosinophilic response. 2. **Absence of Pus Cells (Neutrophils):** This is a high-yield distinction. *E. histolytica* produces a toxin called **amoebapore**, which lyses human neutrophils (pus cells) upon contact. Therefore, the microscopic examination shows "ghost cells" or cellular debris rather than intact pus cells, unlike bacillary dysentery (e.g., *Shigella*). **Analysis of Incorrect Options:** * **A. Giardia:** Causes malabsorption and steatorrhea (fatty stool). It is non-invasive and does not typically cause an eosinophilic or inflammatory response leading to these crystals. * **B. Taenia:** While helminthic infections can cause eosinophilia, *Taenia* (tapeworm) is usually diagnosed by identifying proglottids or eggs in stool; it does not typically present with the "no pus cell" dysenteric picture. * **D. Trichomonas:** This is a urogenital parasite. While it may cause discharge, it is not associated with stool findings or the specific crystal/pus cell paradox of amoebiasis. **NEET-PG High-Yield Pearls:** * **Amoebic Dysentery:** Stool is acidic, contains RBCs in clumps (rouleaux), and lacks pus cells. * **Bacillary Dysentery:** Stool is alkaline, contains numerous pus cells (neutrophils), and lacks Charcot-Leyden crystals. * **Trophozoite of *E. histolytica*:** Look for ingested RBCs (erythrophagocytosis), which is pathognomonic for invasive disease.

Q: A child presents with nocturnal perianal pruritus and adult worms in the stool. What is the most common intestinal infection in school-age children globally?

Enterobius vermicularis. **Explanation:** The clinical presentation of **nocturnal perianal pruritus** (itchy bottom at night) in a school-age child is the classic hallmark of **Enterobius vermicularis** (Pinworm/Threadworm) infection. **Why Enterobius vermicularis is correct:** Enterobius vermicularis is the **most common helminthic infection** worldwide, particularly among school-aged children. The pathogenesis involves the gravid female worm migrating out of the anus at night to deposit eggs on the perianal skin. This causes intense irritation (pruritus ani), leading to scratching and subsequent **autoinoculation** or transmission via contaminated fingers and fomites. Diagnosis is typically made using the **NIH swab** or **Scotch tape test** to detect eggs. **Why the other options are incorrect:** * **Plasmodium vivax:** This is a protozoan parasite causing malaria. It is a systemic infection transmitted by mosquitoes, not an intestinal infection presenting with perianal itching. * **Entamoeba histolytica:** This causes amoebic dysentery. While common, it typically presents with bloody diarrhea and abdominal pain rather than perianal pruritus. * **Strongyloides stercoralis:** Known for causing "larva currens" and autoinfection, it is less common than Enterobius in the general school-age population and usually presents with abdominal symptoms or respiratory signs (Loeffler’s syndrome). **High-Yield NEET-PG Pearls:** * **Drug of Choice:** Albendazole or Mebendazole (treat the **entire family** to prevent reinfection). * **Diagnostic Test of Choice:** Scotch tape test (performed early morning before bathing). * **Key Feature:** Eggs are non-bile stained and have a characteristic **D-shape** (flattened on one side). * **Retroinfection:** Occurs when larvae hatch on the perianal skin and migrate back into the colon.

Q: In which host is the adult worm of Echinococcus typically found?

Dog. ### Explanation **Correct Option: A (Dog)** *Echinococcus granulosus* (the dog tapeworm) follows a life cycle involving a **definitive host** and an **intermediate host**. By definition, the **adult worm** resides in the small intestine of the definitive host, which is the **Dog** (or other canines like wolves and foxes). The adult worm is small (3–6 mm) and does not cause significant disease in the dog. **Why Incorrect Options are Wrong:** * **B. Human:** Humans serve as **accidental intermediate hosts**. In humans, the parasite exists only in the **larval stage** (metacestode), which develops into a **Hydatid cyst**, typically in the liver or lungs. Humans are a "dead-end" for the parasite. * **C. Domestic animals:** Animals like sheep, cattle, and goats are the **natural intermediate hosts**. Like humans, they harbor the **larval stage** (Hydatid cyst) after ingesting eggs. The cycle is completed when a dog eats the viscera of these animals containing the cysts. * **D. Feline:** Cats are generally refractory to infection with *E. granulosus* and do not play a significant role in its life cycle. **NEET-PG High-Yield Pearls:** 1. **Infective Stage for Humans:** Embryonated eggs (found in dog feces). 2. **Diagnostic Feature:** "Hydatid sand" (contains brood capsules and protoscolices) found within the cyst fluid. 3. **Casoni Test:** An immediate hypersensitivity skin test (now largely replaced by ELISA and imaging). 4. **Radiology:** Look for the **"Water Lily Sign"** (collapsed germinal membrane) on ultrasound/CT. 5. **Treatment:** PAIR (Puncture, Aspiration, Injection, Re-aspiration) technique and Albendazole. Never biopsy a suspected cyst due to the risk of **anaphylaxis** from fluid leakage.

Q: Cysticercosis cellulosae causes infection with which of the following?

Taenia solium. **Explanation:** **Cysticercosis cellulosae** is the larval stage of **_Taenia solium_** (Pork tapeworm). In the normal life cycle, humans are the definitive hosts (harboring the adult worm) and pigs are the intermediate hosts (harboring the larvae). However, humans can become accidental intermediate hosts by ingesting _T. solium_ eggs through contaminated food/water or autoinfection. Once ingested, the oncospheres hatch, penetrate the intestinal wall, and disseminate to various tissues (brain, muscles, eyes) to form **Cysticercus cellulosae**. **Analysis of Options:** * **Taenia saginata (Beef tapeworm):** Its larval stage is called *Cysticercus bovis*, found in cattle. Importantly, *T. saginata* does **not** cause cysticercosis in humans because the eggs are not infectious to man. * **Echinococcus granulosus (Dog tapeworm):** This parasite causes **Hydatid disease**. The larval stage is the Hydatid cyst, typically found in the liver or lungs. * **Diphyllobothrium latum (Fish tapeworm):** The larval stages are the procercoid and plerocercoid (sparganum). It is clinically associated with Vitamin B12 deficiency and megaloblastic anemia. **NEET-PG High-Yield Pearls:** * **Neurocysticercosis (NCC):** The most common cause of adult-onset seizures in developing countries. On CT/MRI, it presents with "starry sky" appearance (multiple calcified cysts) or a "hole-with-dot" appearance (scolex inside the cyst). * **Infective Stage:** For intestinal taeniasis, it is the *Cysticercus cellulosae* (in undercooked pork); for cysticercosis, it is the **egg** of _T. solium_. * **Drug of Choice:** Albendazole is the preferred cysticidal agent; Praziquantel is an alternative. Steroids are added to manage inflammation caused by dying larvae.

Q: A 15-year-old boy presented with fever and chills for the last 3 days. A peripheral blood smear revealed the following. Which of the following is the most probable causative agent?

Plasmodium falciparum. ***Plasmodium falciparum*** - **Multiple ring forms per RBC** and **appliqué/accolé forms** (rings positioned at the periphery of RBCs) are pathognomonic for P. falciparum on peripheral smear. - **Small delicate rings** with **crescent/banana-shaped gametocytes** and absence of enlarged RBCs distinguish it from other species, making it the most dangerous malaria parasite causing **cerebral malaria**. *Plasmodium malariae* - Shows **thick band forms** and **rosette schizonts** with 6-12 merozoites arranged around central pigment, not multiple rings per RBC. - Has a **72-hour fever cycle** (quartan malaria) and typically shows **single ring forms** per infected RBC. *Plasmodium ovale* - Characterized by **oval-shaped infected RBCs** with **fimbriated edges** and **Schüffner's dots** in the cytoplasm. - Shows **enlarged RBCs** and **compact ring forms**, unlike the small delicate rings seen in P. falciparum. *Plasmodium vivax* - Distinguished by **enlarged pale RBCs** with **Schüffner's dots** and **amoeboid trophozoites** that fill most of the RBC. - Shows **single ring forms** per RBC and **round gametocytes**, contrasting with P. falciparum's multiple rings and crescent gametocytes.

Q: A 3-year-old child presents with weakness and a hemoglobin level of <5 gm/100 ml. There is a history of joint swelling and bleeding spots. What is the most likely causative organism?

Hookworm. **Explanation:** The clinical presentation of severe anemia (Hb <5 gm/dl) in a child, coupled with signs of nutritional deficiency and potential occult blood loss, points toward **Hookworm infestation** (*Ancylostoma duodenale* or *Necator americanus*). **Why Hookworm is correct:** Hookworms are the most common helminthic cause of **iron deficiency anemia**. They attach to the small intestinal mucosa using buccal capsules (teeth or cutting plates) and suck host blood. A single *A. duodenale* can cause up to 0.2 ml of blood loss per day. Chronic infection leads to profound microcytic hypochromic anemia, which can manifest as weakness, pallor, and in severe cases, congestive heart failure. The "joint swelling and bleeding spots" mentioned in the history often refer to the associated malnutrition and potential Vitamin C/K deficiencies secondary to malabsorption or chronic illness. **Why other options are incorrect:** * **Roundworm (*Ascaris lumbricoides*):** Primarily causes intestinal obstruction, Loeffler’s syndrome (pneumonitis), or biliary colic. It does not cause significant blood loss. * **Whipworm (*Trichuris trichiura*):** While heavy infections can cause "Trichuris dysentery syndrome" and rectal prolapse, the degree of anemia is significantly less than that seen in hookworm. * **Pinworm (*Enterobius vermicularis*):** Causes perianal pruritus (worse at night) but does not cause anemia or systemic bleeding. **NEET-PG High-Yield Pearls:** * **Route of entry:** Filariform larvae penetrate intact skin (usually feet), leading to **Ground Itch**. * **Diagnosis:** Presence of non-bile stained, oval, segmented eggs in stool. * **Treatment of choice:** Albendazole (400 mg single dose) or Mebendazole. * **Public Health:** Hookworm is a major cause of "Anemic Heart Failure" in tropical pediatric populations.

Q: A 35-year-old lady presents with vaginal discharge. What is the likely causative organism seen on vaginal smears?

Trichomonas. ***Trichomonas*** - **Trichomonas vaginalis** is a common cause of **vaginal discharge** and can be directly visualized on **wet mount vaginal smears** as motile, pear-shaped organisms. - It appears as **flagellated protozoa** with jerky motility and is easily identified in fresh vaginal discharge specimens under microscopy. *Entamoeba Histolytica* - This parasite primarily causes **intestinal amebiasis** and **liver abscesses**, not vaginal infections. - It is found in **stool samples** as trophozoites or cysts, not in vaginal discharge specimens. *Toxoplasma* - **Toxoplasma gondii** is an intracellular parasite that causes **systemic toxoplasmosis**, particularly dangerous in immunocompromised patients and pregnancy. - It does not cause vaginal discharge and is not visualized on routine **vaginal smears** but requires specialized testing like serology or tissue biopsy. *Giardia* - **Giardia lamblia** is a **gastrointestinal parasite** causing diarrhea and malabsorption, not vaginal symptoms. - It is identified in **stool samples** as trophozoites or cysts with characteristic **binucleate** appearance, not in vaginal specimens.

Q: Granulomatous reactions caused by ova or products of schistosomes at their primary sites of egg deposition can lead to various clinical manifestations. Which of the following is NOT among these manifestations?

Cardiac abnormalities. **Explanation:** The clinical manifestations of Schistosomiasis are primarily driven by the host's **granulomatous immune response** to the eggs trapped in tissues, rather than the adult worms themselves. **Why "Cardiac abnormalities" is the correct answer:** While Schistosomiasis can cause pulmonary hypertension (due to eggs reaching the lungs via portosystemic shunts), it does not typically cause primary cardiac abnormalities or direct granulomatous reactions in the heart. Cardiac involvement is extremely rare and is not a recognized classic manifestation of the disease. **Analysis of incorrect options:** * **Bladder wall hyperplasia:** In *S. haematobium* infections, eggs are deposited in the vesical venous plexus. The resulting chronic inflammation and granuloma formation lead to bladder wall thickening, hyperplasia, polypoid lesions, and eventually an increased risk of **Squamous Cell Carcinoma** of the bladder. * **Portal hypertension:** In *S. mansoni* and *S. japonicum*, eggs are deposited in the mesenteric veins and travel to the liver. They lodge in the presinusoidal capillaries, causing **Symmers' pipe-stem fibrosis**. This leads to portal hypertension without affecting the liver parenchyma (non-cirrhotic portal hypertension). * **Splenomegaly:** This is a direct consequence of portal hypertension (congestive splenomegaly) and is a hallmark of hepatosplenic schistosomiasis. **High-Yield Clinical Pearls for NEET-PG:** * **Intermediate Host:** Freshwater snails (*Biomphalaria* for *S. mansoni*, *Bulinus* for *S. haematobium*). * **Infective Stage:** Cercaria (penetrates unbroken skin). * **Diagnostic Feature:** *S. haematobium* (Terminal spine), *S. mansoni* (Lateral spine), *S. japonicum* (Rudimentary spine). * **Drug of Choice:** Praziquantel. * **Katayama Fever:** An acute serum sickness-like reaction occurring weeks after infection.

Q: In which of the following parasites does a fish act as an intermediate host?

Clonorchis sinensis. **Explanation:** The correct answer is **Clonorchis sinensis** (the Chinese Liver Fluke). In its complex life cycle, this parasite requires two intermediate hosts: 1. **First Intermediate Host:** Freshwater snails (e.g., *Parafossarulus*). 2. **Second Intermediate Host:** Freshwater **fish** (specifically of the Cyprinidae family). Humans become infected by ingesting undercooked or raw fish containing **metacercariae**. **Analysis of Options:** * **Diphyllobothrium latum:** While this parasite (the Fish Tapeworm) also involves fish, it was likely excluded or ranked lower depending on the specific question context. However, in standard parasitology, *D. latum* uses a crustacean (Cyclops) as the first and fish as the second intermediate host. If this were a "multiple correct" scenario, both A and B would apply, but *Clonorchis* is a classic textbook example for trematodes. * **Hymenolepis diminuta:** This is the Rat Tapeworm. It requires an **arthropod** (like a grain beetle or flea) as an intermediate host. * **Hymenolepis nana:** This is the Dwarf Tapeworm. It is unique because it **does not require an intermediate host** (direct life cycle), though insects can occasionally serve as optional intermediate hosts. **NEET-PG Clinical Pearls:** * **Clonorchis sinensis** is strongly associated with **Cholangiocarcinoma** (bile duct cancer) due to chronic irritation of the biliary epithelium. * **Diphyllobothrium latum** is high-yield for causing **Vitamin B12 deficiency**, leading to Megaloblastic Anemia. * **H. nana** is the most common cause of all cestode infections and is the only tapeworm that can complete its entire life cycle in a single host.

Q: What is the most common cause of an amoebic lung abscess?

Direct spread from the liver. **Explanation:** Amoebic lung abscess is almost always a secondary complication of intestinal amoebiasis [1], caused by the protozoan *Entamoeba histolytica*. **Why Option B is Correct:** The most common route of pulmonary involvement is **direct extension (transdiaphragmatic spread)** from an Amoebic Liver Abscess (ALA). Because the liver is situated immediately below the diaphragm, an abscess in the superior surface of the right lobe can cause inflammatory adhesion to the diaphragm [1]. The abscess then ruptures through the diaphragm into the pleural space (causing empyema) or directly into the lung parenchyma, leading to a lung abscess [2]. This typically involves the lower lobe of the right lung. **Why Other Options are Incorrect:** * **Option A (Aspiration):** This is the most common cause of *pyogenic* lung abscesses (usually involving anaerobes), but it is not the mechanism for amoebic infections. * **Option C & D (Hematogenous spread):** While *E. histolytica* can rarely travel via the bloodstream (portal circulation to the liver or systemic circulation to the lungs/brain), this is a significantly less common route for pulmonary involvement compared to direct local extension. **NEET-PG High-Yield Pearls:** * **Sputum Appearance:** Classically described as **"Anchovy sauce"** [1] or "Chocolate" colored sputum. * **Location:** Most common in the **Right Lower Lobe** (due to the proximity of the right lobe of the liver). * **Hepatobronchial Fistula:** If the abscess ruptures into a bronchus, the patient may expectorate large amounts of "anchovy sauce" pus. * **Treatment:** The drug of choice is **Metronidazole** [2] (or Tinidazole), followed by a luminal amoebicide (e.g., Diloxanide furoate) to eradicate the intestinal cyst stage.

Question 1

Which parasite is associated with Charcot-Layden crystals but lacks pus cells in its stain?

Accepted Answer

E. histolytica

Answer

Giardia

Answer

Taenia

Answer

Trichomonas

Question 2

A child presents with nocturnal perianal pruritus and adult worms in the stool. What is the most common intestinal infection in school-age children globally?

Accepted Answer

Enterobius vermicularis

Answer

Plasmodium vivax

Answer

Entamoeba histolytica

Answer

Strongyloides stercoralis

Question 3

In which host is the adult worm of Echinococcus typically found?

Accepted Answer

Dog

Answer

Human

Answer

Domestic animals

Answer

Feline

Question 4

Cysticercosis cellulosae causes infection with which of the following?

Accepted Answer

Taenia solium

Answer

Taenia saginata

Answer

Echinococcus granulosus

Answer

Diphyllobothrium latum

Question 5

A 15-year-old boy presented with fever and chills for the last 3 days. A peripheral blood smear revealed the following. Which of the following is the most probable causative agent?

Accepted Answer

Plasmodium falciparum

Answer

Plasmodium malariae

Answer

Plasmodium ovale

Answer

Plasmodium vivax

Question 6

A 3-year-old child presents with weakness and a hemoglobin level of <5 gm/100 ml. There is a history of joint swelling and bleeding spots. What is the most likely causative organism?

Accepted Answer

Hookworm

Answer

Roundworm

Answer

Whipworm

Answer

Pinworm

Question 7

A 35-year-old lady presents with vaginal discharge. What is the likely causative organism seen on vaginal smears?

Accepted Answer

Trichomonas

Answer

Entamoeba Histolytica

Answer

Toxoplasma

Answer

Giardia

Question 8

Granulomatous reactions caused by ova or products of schistosomes at their primary sites of egg deposition can lead to various clinical manifestations. Which of the following is NOT among these manifestations?

Accepted Answer

Cardiac abnormalities

Answer

Bladder wall hyperplasia

Answer

Portal hypertension

Answer

Splenomegaly

Question 9

In which of the following parasites does a fish act as an intermediate host?

Accepted Answer

Clonorchis sinensis

Answer

Diphyllobothrium latum

Answer

Hymenolepis diminuta

Answer

Hymenolepis nana

Question 10

What is the most common cause of an amoebic lung abscess?

Accepted Answer

Direct spread from the liver

Answer

Aspiration

Answer

Hematogenous spread from the liver

Answer

Hematogenous spread from the gut

Parasitology — MCQs

Parasitology — MCQs

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