Parasitology Practice Questions

Q: Infestation with Clonorchis sinensis increases the risk of which of the following conditions?

Cholangiocarcinoma. **Explanation:** **Clonorchis sinensis** (the Chinese liver fluke) is a parasitic trematode acquired by consuming undercooked freshwater fish. It primarily inhabits the **intrahepatic bile ducts**. **1. Why Cholangiocarcinoma is correct:** Chronic infestation leads to mechanical irritation, localized obstruction, and the release of metabolic products that trigger chronic inflammation and adenomatous hyperplasia of the biliary epithelium. This persistent inflammatory state induces DNA damage and cellular proliferation, making *Clonorchis sinensis* (and *Opisthorchis viverrini*) a Group 1 carcinogen specifically for **Cholangiocarcinoma** (bile duct cancer). **2. Why other options are incorrect:** * **Gall bladder cancer:** While associated with gallstones (cholelithiasis) and "porcelain gallbladder," it is not classically linked to liver flukes, which prefer the bile ducts over the gallbladder. * **Hepatocellular carcinoma (HCC):** HCC is primarily associated with Hepatitis B and C, cirrhosis, and Aflatoxin B1. It arises from hepatocytes, not the biliary epithelium. * **Carcinoma of the head of the pancreas:** This is associated with smoking, chronic pancreatitis, and certain genetic syndromes (e.g., BRCA2, Peutz-Jeghers), but not parasitic fluke infections. **High-Yield Clinical Pearls for NEET-PG:** * **Key Parasites & Cancers:** * *Clonorchis sinensis/Opisthorchis:* Cholangiocarcinoma. * *Schistosoma haematobium:* Squamous cell carcinoma of the Urinary Bladder. * **Diagnostic Clue:** Look for a history of raw fish consumption and imaging showing "dilated intrahepatic bile ducts" with a normal common bile duct. * **Treatment:** **Praziquantel** is the drug of choice for liver fluke infestations.

Q: Duffy blood group antigen negativity confers protection against infection by which Plasmodium species?

Plasmodium vivax. ### Explanation **Correct Answer: C. Plasmodium vivax** **Mechanism of Protection:** *Plasmodium vivax* requires the **Duffy Antigen Receptor for Chemokines (DARC)**, located on the surface of red blood cells (RBCs), to act as a receptor for its **Duffy Binding Protein (DBP)**. This interaction is essential for the merozoite to invade the erythrocyte. Individuals who are **Duffy-negative** (genotype *Fy/Fy*) lack these receptors on their RBCs, making the cells resistant to invasion by *P. vivax*. This phenotype is highly prevalent in West African populations, explaining why *P. vivax* malaria is rare in that region. **Analysis of Incorrect Options:** * **A. Plasmodium falciparum:** Uses multiple alternative receptors (e.g., Glycophorins A, B, and C) for invasion. Protection against *P. falciparum* is instead associated with Sickle Cell Trait (HbAS), G6PD deficiency, and Thalassemia [1]. * **B. Plasmodium ovale:** Primarily uses different, less-defined pathways for entry and is common in West Africa, often "replacing" the niche left by *P. vivax* in Duffy-negative populations. * **D. Plasmodium malariae:** Does not utilize the Duffy antigen for RBC entry; its specific receptor mechanisms are distinct from those of *P. vivax* [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Duffy Status:** Duffy-negative individuals can still be infected by *P. vivax* in rare cases (recent reports from Ethiopia/Madagascar), but for exam purposes, it remains the classic protective factor. * **Reticulocyte Preference:** *P. vivax* and *P. ovale* selectively infect young RBCs (reticulocytes), whereas *P. falciparum* infects RBCs of all ages (leading to high parasitemia) [1]. * **Schüffner’s Dots:** Characteristically seen in RBCs infected with *P. vivax* and *P. ovale*. * **Hypnozoites:** Only *P. vivax* and *P. ovale* form dormant liver stages (hypnozoites), requiring **Primaquine** or **Tafenoquine** for a radical cure [1].

Q: What is the method for diagnosing Hydatid disease?

Serum examination. **Explanation:** Hydatid disease, caused by the larval stage of *Echinococcus granulosus*, is primarily diagnosed through a combination of imaging and serology. **1. Why Serum Examination is the Correct Answer:** Serology (Serum examination) is the mainstay of diagnosis. It detects specific antibodies (IgG) against hydatid antigens. The most commonly used tests include **ELISA** and **Indirect Hemagglutination (IHA)**. For confirmation, the **Immunoblot (Western Blot)** for the 'Arc 5' antigen is highly specific. Serology is preferred because it is non-invasive and carries no risk of anaphylaxis. **2. Why Other Options are Incorrect:** * **Biopsy (A):** This is strictly **contraindicated**. Aspiration or biopsy of a hydatid cyst can lead to the leakage of hydatid fluid, which contains highly antigenic protoscolices. This can trigger life-threatening **anaphylactic shock** or lead to secondary peritoneal hydatidosis (seeding). * **X-ray (B):** While X-rays may show a "water lily sign" or calcification of the cyst wall, they are non-specific and less sensitive than Ultrasound or CT scans. * **Casoni Test (C):** This is an immediate hypersensitivity skin test. While historically important, it is now **obsolete** due to low sensitivity, low specificity, and the risk of inducing sensitivity in the patient. **Clinical Pearls for NEET-PG:** * **Gold Standard Imaging:** Ultrasound is the first-line investigation (look for "Gharbi classification"). * **Treatment of Choice:** Surgical excision (PAIR technique: Puncture, Aspiration, Injection, Re-aspiration) combined with **Albendazole**. * **Microscopy:** Look for "Hydatid sand" (protoscolices, hooklets, and calcareous corpuscles) in the fluid. * **Eosinophilia:** Present in only about 20-25% of cases; its absence does not rule out the disease.

Q: Cysticercosis is caused by which of the following parasites?

Taenia solium. **Explanation:** **Cysticercosis** is a systemic parasitic infection caused by the larval stage (*Cysticercus cellulosae*) of the pork tapeworm, **Taenia solium**. 1. **Why Taenia solium is correct:** In the normal life cycle, humans are definitive hosts (harboring the adult worm) by eating undercooked pork containing cysticerci. However, if a human accidentally ingests **T. solium eggs** (via contaminated food/water or autoinfection), the human acts as an **accidental intermediate host**. The eggs hatch in the intestine, and oncospheres penetrate the gut wall to migrate to muscles, eyes, and the brain, forming cysticerci. **Neurocysticercosis** is the most common cause of acquired epilepsy worldwide. 2. **Why other options are incorrect:** * **Taenia saginata (Beef tapeworm):** Humans are only definitive hosts. Ingesting *T. saginata* eggs does **not** cause cysticercosis in humans because the eggs do not hatch in the human gut. * **Ancylostoma duodenale (Hookworm):** This is a nematode that causes iron-deficiency anemia; it does not form cysts in tissues. * **Echinococcus granulosus (Dog tapeworm):** This causes **Hydatid disease**, characterized by slow-growing unilocular cysts, typically in the liver or lungs. **High-Yield Clinical Pearls for NEET-PG:** * **Mode of Infection:** Cysticercosis is caused by ingesting **eggs**; Taeniasis (intestinal) is caused by ingesting **larvae** (cysticerci). * **Diagnosis:** MRI/CT shows "starry sky appearance" (multiple calcified cysts) or a cyst with a **scolex (dot sign)**. * **Treatment:** Albendazole is the drug of choice; steroids are added to manage inflammation from dying larvae.

Q: A pregnant woman in her first trimester is diagnosed with an infection. Her baby is born with hydrocephalus. Which pathogen is the most likely cause of this infection?

Toxoplasma gondii. **Explanation:** The correct answer is **Toxoplasma gondii**. This protozoan infection is a classic member of the TORCH group. When a mother acquires a primary infection during pregnancy, the parasite can cross the placenta. The classic **Sabine’s Triad** of Congenital Toxoplasmosis includes: 1. **Hydrocephalus** (due to aqueductal stenosis) 2. **Intracranial calcifications** (typically diffuse/scattered) 3. **Chorioretinitis** **Why the other options are incorrect:** * **Herpes Simplex Virus (HSV):** Neonatal HSV is usually acquired during delivery (birth canal). It typically presents with skin-eye-mouth (SEM) vesicles, encephalitis, or disseminated multi-organ failure, rather than congenital hydrocephalus. * **Treponema pallidum (Syphilis):** Congenital syphilis is characterized by "Hutchinson’s Triad" (interstitial keratitis, sensorineural hearing loss, and notched incisors), along with hepatosplenomegaly, snuffles, and skeletal abnormalities (e.g., Sabre shin). * **Cytomegalovirus (CMV):** While CMV is the most common congenital infection and can cause ventriculomegaly, its hallmark finding is **periventricular calcifications** and microcephaly, rather than macrocephaly/hydrocephalus. **High-Yield Pearls for NEET-PG:** * **Toxoplasmosis:** Look for "Diffuse calcifications" and "Hydrocephalus." Treatment for the mother is **Spiramycin**; for the fetus/neonate, it is **Pyrimethamine and Sulfadiazine**. * **CMV:** Look for "Periventricular calcifications" and "Sensorineural hearing loss" (the most common sequela). * **Rule of Thumb:** If the head is large (hydrocephalus), think Toxoplasma. If the head is small (microcephaly), think CMV or Zika.

Q: An 8-year-old child presents with perianal itching. Perianal scraping/swab shows the following bile non-stained eggs. What is the causative parasite?

Enterobius. ***Enterobius*** - **Perianal itching** in children is the classic presentation of **pinworm infection** (Enterobius vermicularis), especially at night when female worms migrate to lay eggs. - The **non-bile-stained, D-shaped, colorless eggs** found on perianal scraping are pathognomonic for Enterobius vermicularis. *Ascaris* - Eggs are **bile-stained, thick-walled, and oval-shaped** with a distinctive **mammillated outer coat**, unlike the description given. - Typically causes **pulmonary symptoms** during larval migration and **intestinal obstruction** in heavy infections, not perianal itching. *Strongyloides* - **Rhabditiform larvae** are typically found in stool samples, not eggs on perianal scraping. - Causes **duodenal ulceration**, **malabsorption**, and **hyperinfection syndrome** in immunocompromised patients, not perianal itching. *Trichuris* - Eggs have a characteristic **barrel-shape with bipolar plugs** and are found in stool, not on perianal scraping. - Causes **chronic diarrhea**, **rectal prolapse**, and **growth retardation** in heavy infections, not the described symptoms.

Q: All of the following are true of Neurocysticercosis EXCEPT?

More common in vegetarians. **Explanation:** Neurocysticercosis (NCC) is caused by the larval stage (*Cysticercus cellulosae*) of the pork tapeworm, **_Taenia solium_**. **Why Option B is the correct answer (False statement):** A common misconception is that NCC only occurs in pork eaters. In reality, NCC is acquired through the **fecal-oral route** by ingesting **eggs** of *T. solium* (via contaminated water or food handled by a person with intestinal taeniasis). Since eggs are shed in human feces, vegetarians are at equal or even higher risk if hygiene is poor. Eating undercooked pork leads to intestinal taeniasis (adult worm), not cysticercosis. **Analysis of other options:** * **Option A:** **Albendazole** is the drug of choice for NCC (often combined with corticosteroids to reduce inflammation caused by dying larvae). Praziquantel is an alternative. * **Option C:** The "Starry Sky" appearance on CT/MRI is a classic finding. As the larvae die, they undergo **dystrophic calcification**, appearing as hyperdense punctate lesions. * **Option D:** In the life cycle of *T. solium*, **Man is the definitive host** (harbors the adult worm). However, in cysticercosis, man acts as an **accidental intermediate host** (harbors the larvae). **High-Yield Clinical Pearls for NEET-PG:** * **Most common clinical presentation:** New-onset seizures (focal or generalized). * **Pathognomonic finding on Imaging:** Presence of a **scolex** (seen as a "hole-with-dot" appearance) within a cyst. * **Staging:** Vesicular → Colloidal vesicular → Granular nodular → Calcified nodular. * **Note:** In *T. saginata* (beef tapeworm), cysticercosis does **not** occur in humans.

Question 1

Infestation with Clonorchis sinensis increases the risk of which of the following conditions?

Accepted Answer

Cholangiocarcinoma

Answer

Gall bladder cancer

Answer

Hepatocellular carcinoma

Answer

Carcinoma of the head of the pancreas

Question 2

Duffy blood group antigen negativity confers protection against infection by which Plasmodium species?

Accepted Answer

Plasmodium vivax

Answer

Plasmodium falciparum

Answer

Plasmodium ovale

Answer

Plasmodium malariae

Question 3

Which of the following is NOT true about toxoplasmosis?

Accepted Answer

IgG antibodies are diagnostic in congenital toxoplasmosis.

Answer

In adults, toxoplasmosis is usually asymptomatic.

Answer

It is an antroponotic disease.

Answer

Encephalitis is uncommon (rare) in immunocompetent individuals.

Question 4

Which statement is true regarding malaria?

Accepted Answer

Red blood cell size is increased in Plasmodium vivax infections

Answer

Rods forms are seen in Plasmodium malariae

Answer

Relapse is seen in Plasmodium falciparum infections

Answer

Both male and female Anopheles mosquitoes transmit the disease

Question 5

What is the method for diagnosing Hydatid disease?

Accepted Answer

Serum examination

Answer

Biopsy

Answer

X-ray

Answer

Casoni test

Question 6

Cysticercosis is caused by which of the following parasites?

Accepted Answer

Taenia solium

Answer

Taenia saginata

Answer

Ancylostoma duodenale

Answer

Echinococcus granulosus

Question 7

A pregnant woman in her first trimester is diagnosed with an infection. Her baby is born with hydrocephalus. Which pathogen is the most likely cause of this infection?

Accepted Answer

Toxoplasma gondii

Answer

Herpes Simplex Virus (HSV)

Answer

Treponema pallidum

Answer

Cytomegalovirus (CMV)

Question 8

An 8-year-old child presents with perianal itching. Perianal scraping/swab shows the following bile non-stained eggs. What is the causative parasite?

Accepted Answer

Enterobius

Answer

Ascaris

Answer

Strongyloides

Answer

Trichuris

Question 9

All of the following are true of Neurocysticercosis EXCEPT?

Accepted Answer

More common in vegetarians

Answer

Albendazole is the drug of choice

Answer

Produces intracerebral calcification

Answer

Man is the definitive host

Question 10

Why are schizont and late trophozoite stages of Plasmodium falciparum not observed in peripheral blood smears?

Accepted Answer

Due to adherence to the capillary endothelium, they are not seen in peripheral blood

Answer

They are sequestered in the spleen

Answer

Due to antigen-antibody reaction and removal

Answer

They are seen in mosquito blood

Parasitology — MCQs

Parasitology — MCQs

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