Parasitology Practice Questions

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.

Q: An HIV patient presented with diarrhea. Stool examination revealed acid-fast organisms. What is the drug of choice for this patient?

Nitazoxanide. ### Explanation **1. Understanding the Diagnosis** In an HIV-positive patient presenting with diarrhea, the discovery of **acid-fast organisms** in the stool is a classic diagnostic marker for **Coccidian parasites**. The most common pathogens in this category include *Cryptosporidium hominis/parvum*, *Cyclospora cayetanensis*, and *Cystoisospora belli*. Among these, *Cryptosporidium* is the most frequent cause of chronic, watery diarrhea in immunocompromised individuals and is characterized by small (4–6 µm), spherical, acid-fast oocysts. **2. Why Nitazoxanide is Correct** **Nitazoxanide** is the FDA-approved drug of choice for treating diarrhea caused by *Cryptosporidium* and *Giardia*. It works by inhibiting the pyruvate:ferredoxin oxidoreductase (PFOR) enzyme pathway, essential for anaerobic energy metabolism. While its efficacy is higher in immunocompetent patients, it remains the primary treatment for HIV patients, often alongside the initiation of Highly Active Antiretroviral Therapy (HAART) to boost CD4 counts. **3. Why Other Options are Incorrect** * **Primaquine:** An antimalarial used for the radical cure of *P. vivax/ovale* and as a gametocide; it has no role in treating intestinal coccidiosis. * **Niclosamide:** The drug of choice for tapeworm infections (Cestodes) like *Taenia saginata* and *Diphyllobothrium latum*. * **TMP-SMX (Cotrimoxazole):** While this is the drug of choice for *Cystoisospora belli* and *Cyclospora*, the question points toward the most common acid-fast pathogen in HIV (*Cryptosporidium*), for which Nitazoxanide is the standard. **4. High-Yield Clinical Pearls for NEET-PG** * **Stain used:** Modified Kinyoun’s acid-fast stain. * **Size matters:** *Cryptosporidium* (4–6 µm), *Cyclospora* (8–10 µm), *Cystoisospora* (25 µm, oval). * **Key Management:** In HIV patients, the most effective long-term "treatment" for Cryptosporidiosis is **HAART** to restore immune function (CD4 >100 cells/mm³).

Q: What is the primary reservoir for hookworm infection?

Human beings. **Explanation:** The primary reservoir for hookworm infection (*Ancylostoma duodenale* and *Necator americanus*) is **human beings**. In medical parasitology, a reservoir is the host in which an infectious agent normally lives and multiplies, and on which it depends primarily for survival. Since adult hookworms reside exclusively in the human small intestine, where they produce thousands of eggs daily, humans are the only significant source of environmental contamination. **Analysis of Options:** * **Soil (Incorrect):** Soil is the **medium of development** and the **source of infection**, but not the reservoir. Hookworm eggs hatch in the soil to become rhabditiform larvae, which then transform into infective filariform larvae. * **Feces (Incorrect):** Feces serve as the **vehicle of transmission** for the eggs to reach the soil. They do not support the long-term survival or multiplication of the parasite. * **Monkeys (Incorrect):** While some parasites have zoonotic reservoirs, human hookworms are highly host-specific. Monkeys do not play a role in the transmission cycle of *A. duodenale* or *N. americanus*. **High-Yield Clinical Pearls for NEET-PG:** * **Infective Stage:** Third-stage filariform larva (L3). * **Mode of Entry:** Skin penetration (usually through bare feet), causing "Ground Itch." * **Classic Presentation:** Microcytic hypochromic anemia (Iron deficiency) due to chronic blood loss (approx. 0.15–0.2 ml/day for *A. duodenale*). * **Loeffler’s Syndrome:** May occur during the pulmonary migration phase of the larvae. * **Drug of Choice:** Albendazole (400 mg single dose).

Q: Which parasite is characterized by a cyst containing a scolex with hooks?

Taenia solium. **Explanation:** The question describes the characteristic morphology of the **Cysticercus cellulosae**, which is the larval stage of **Taenia solium** (Pork Tapeworm). 1. **Why Taenia solium is correct:** When humans ingest eggs of *T. solium* (via contaminated food/water), the oncospheres hatch and migrate to tissues (muscles, brain, subcutaneous tissue) to form cysts. This condition is called **Cysticercosis**. Microscopically, the cyst is fluid-filled and contains a single **invaginated scolex** equipped with four suckers and a **rostellum with hooks**. 2. **Why other options are incorrect:** * **Hymenolepis nana:** Known as the dwarf tapeworm. While it has a scolex with hooks, its larval stage (Cysticercoid) is microscopic and typically develops within the intestinal villi or insects, not as a distinct macroscopic tissue cyst in humans. * **Echinococcus granulosus:** Causes Hydatid disease. The hydatid cyst is much larger and more complex, containing multiple "brood capsules" and thousands of "protoscolices" (hydatid sand), rather than a single scolex within a simple cyst. * **Schistosoma:** These are trematodes (flukes). They do not form cysts with scolices; they exist as adult worms in the venous plexus and produce eggs that cause granulomatous inflammation. **High-Yield NEET-PG Pearls:** * **Neurocysticercosis (NCC):** The most common cause of adult-onset seizures in developing countries. On MRI/CT, it shows a "hole-with-dot" appearance (the dot is the scolex). * **Mode of Infection:** Ingesting **larvae** in undercooked pork leads to intestinal Taeniasis; ingesting **eggs** leads to Cysticercosis. * **Drug of Choice:** Albendazole is the preferred treatment for NCC, often administered with corticosteroids to reduce inflammation from dying larvae.

Q: A patient presents with features of biliary obstruction and a history of consuming raw fish during a recent trip. Which of the following is the most probable etiology?

Clonorchis sinensis. ### Explanation **Correct Option: A. *Clonorchis sinensis*** *Clonorchis sinensis*, also known as the **Chinese Liver Fluke**, is a trematode primarily found in East Asia. The infection is acquired by ingesting undercooked or **raw freshwater fish** containing encysted metacercariae. Once ingested, the larvae migrate to the **biliary tract**, where they mature into adults. Chronic infection causes mechanical obstruction, inflammation, and hyperplasia of the bile duct epithelium. This leads to clinical features of **biliary obstruction** (jaundice, right upper quadrant pain) and is a well-known risk factor for **cholangiocarcinoma**. **Why Incorrect Options are Wrong:** * **B. *Ancylostoma* (Hookworm):** Infection occurs via larval skin penetration (filariform larvae). It primarily causes iron-deficiency anemia and GI symptoms, not biliary obstruction. * **C. *Strongyloides stercoralis*:** Also enters via skin penetration. It causes autoinfection and "larva currens." While it can cause malabsorption, it does not typically involve the biliary tree. * **D. *Enterobius vermicularis* (Pinworm):** Transmitted via the feco-oral route. It resides in the cecum and causes perianal pruritus; it is not associated with fish consumption or biliary pathology. **High-Yield Clinical Pearls for NEET-PG:** * **Intermediate Hosts:** 1st host is the Snail (*Parafossarulus*); 2nd host is the Fish (Cyprinidae family). * **Drug of Choice:** Praziquantel. * **Diagnostic Stage:** Ovoid, "operculated" eggs with a small knob at the posterior end, found in feces. * **Key Association:** Always link *Clonorchis sinensis* and *Opisthorchis viverrini* with **Cholangiocarcinoma** (Bile duct cancer).

Q: Infection with which organism during pregnancy can cause congenital hydrocephalus?

Toxoplasma gondii. **Explanation:** **Toxoplasma gondii** is the correct answer because it is a classic member of the **TORCH** group of infections [1]. When a pregnant woman acquires a primary infection (often via cat feces or undercooked meat), the parasite can cross the placenta. The hallmark of Congenital Toxoplasmosis is the **Classic Triad of Sabin**: 1. **Hydrocephalus** (due to aqueductal stenosis caused by periventricular inflammation) [1]. 2. **Chorioretinitis** (the most common finding) [1]. 3. **Diffuse Intracranial Calcifications** (scattered throughout the brain parenchyma). **Analysis of Incorrect Options:** * **Clostridium tetani:** Causes Neonatal Tetanus (usually due to unsterile cord cutting), characterized by muscle rigidity and spasms, not congenital malformations or hydrocephalus. * **Treponema pallidum:** Causes Congenital Syphilis. While it affects multiple systems, its classic signs include **Hutchinson’s triad** (interstitial keratitis, sensorineural deafness, and notched incisors), snuffles, and periostitis, rather than hydrocephalus. * **Streptococcus species:** Group B Streptococcus (GBS) is a leading cause of neonatal sepsis and meningitis, but it is an acute postnatal or intrapartum infection rather than a cause of congenital hydrocephalus. **NEET-PG High-Yield Pearls:** * **Calcification Pattern:** Toxoplasmosis causes **diffuse** calcifications, whereas CMV (the most common TORCH infection) causes **periventricular** calcifications. * **Treatment:** Maternal infection is treated with **Spiramycin**; fetal infection is treated with **Pyrimethamine, Sulfadiazine, and Folinic acid**. * **Diagnosis:** Best initial test is serology (IgM/IgG); PCR of amniotic fluid is the gold standard for fetal diagnosis.

Q: Which of the following parasitic infections predisposes to malignancies?

Clonorchiasis. **Explanation:** The association between parasitic infections and malignancy is a high-yield topic in NEET-PG. **Clonorchiasis**, caused by the Chinese liver fluke (*Clonorchis sinensis*), is a well-established risk factor for **Cholangiocarcinoma** (cancer of the bile duct epithelium). **Why Clonorchiasis is correct:** Chronic infection leads to mechanical irritation and the release of excretory-secretory products by the flukes residing in the bile ducts. This triggers chronic inflammation, epithelial hyperplasia, and periductal fibrosis. The International Agency for Research on Cancer (IARC) classifies *Clonorchis sinensis* and *Opisthorchis viverrini* as Group 1 carcinogens because this prolonged inflammatory state promotes DNA damage and malignant transformation of the biliary epithelium. **Analysis of Incorrect Options:** * **Paragonimus westermani:** Known as the lung fluke; it causes pulmonary symptoms mimicking tuberculosis (hemoptysis, cavitary lesions) but is not typically associated with malignancy. * **Guinea worm (Dracunculus medinensis):** Causes cutaneous ulcers and local inflammation upon emergence; it does not have oncogenic potential. * **Ancylostoma (Hookworm):** Primarily causes iron-deficiency anemia and ground itch; it is not linked to cancer. **High-Yield Clinical Pearls for NEET-PG:** 1. **Schistosoma haematobium:** Associated with **Squamous Cell Carcinoma of the Urinary Bladder** (not transitional cell). 2. **Opisthorchis viverrini:** Similar to *Clonorchis*, it is a major cause of Cholangiocarcinoma in Southeast Asia. 3. **Intermediate Host:** For *Clonorchis*, the first intermediate host is a snail, and the second is **freshwater fish**. 4. **Drug of Choice:** Praziquantel is the treatment for most trematode infections, including Clonorchiasis.

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

Stool trophozoites are essential for diagnosis.. **Explanation:** **1. Why Option A is Incorrect (The Correct Answer):** While finding trophozoites in stool (especially those containing ingested RBCs or "erythrophagocytosis") is diagnostic of invasive amoebiasis, they are **not essential** for diagnosis. Trophozoites are labile and often disintegrate rapidly outside the body. In clinical practice, diagnosis frequently relies on the detection of **cysts** in formed stools, stool antigen assays (ELISA for Gal/GalNAc lectin), or PCR. Furthermore, in extra-intestinal cases like Amoebic Liver Abscess (ALA), stool microscopy is negative in 60-90% of patients, necessitating serology or imaging. **2. Analysis of Other Options:** * **Option B:** Correct statement. Approximately **90%** of *E. histolytica* infections are asymptomatic (luminal amoebiasis), where the parasite remains a commensal in the gut. * **Option C:** Correct statement. The liver is the most common site for extra-intestinal amoebiasis. Trophozoites travel via the portal circulation to cause **"Anchovy sauce"** appearance abscesses. * **Option D:** Correct statement. Infection with *E. histolytica* does **not** confer long-term protective immunity. Recurrent infections are common in endemic areas because the immune response (humoral and cellular) is insufficient to prevent reinfection. **High-Yield NEET-PG Pearls:** * **Infective Stage:** Quadrinucleate cyst. * **Pathognomonic Feature:** Trophozoites with ingested RBCs (indicates tissue invasion). * **Culture Media:** Robinson’s medium and NIH polyxenic medium. * **Drug of Choice:** Metronidazole (for invasive disease) followed by a luminal amoebicide (e.g., Paromomycin or Diloxanide furoate) to clear cysts.

Question 1

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 2

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 3

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

Question 4

An HIV patient presented with diarrhea. Stool examination revealed acid-fast organisms. What is the drug of choice for this patient?

Accepted Answer

Nitazoxanide

Answer

Primaquine

Answer

Niclosamide

Answer

TMP-SMX

Question 5

What is the primary reservoir for hookworm infection?

Accepted Answer

Human beings

Answer

Soil

Answer

Feces

Answer

Monkeys

Question 6

Which parasite is characterized by a cyst containing a scolex with hooks?

Accepted Answer

Taenia solium

Answer

Hymenolepis nana

Answer

Echinococcus

Answer

Schistosoma

Question 7

A patient presents with features of biliary obstruction and a history of consuming raw fish during a recent trip. Which of the following is the most probable etiology?

Accepted Answer

Clonorchis sinensis

Answer

Ancylostoma

Answer

Strongyloides

Answer

Enterobius

Question 8

Infection with which organism during pregnancy can cause congenital hydrocephalus?

Accepted Answer

Toxoplasma gondii

Answer

Clostridium tetani

Answer

Treponema pallidum

Answer

Streptococcus species

Question 9

Which of the following parasitic infections predisposes to malignancies?

Accepted Answer

Clonorchiasis

Answer

Paragonimus westermani

Answer

Guinea worm infection

Answer

Ancyclostoma

Question 10

Which of the following statements about Entamoeba histolytica is incorrect?

Accepted Answer

Stool trophozoites are essential for diagnosis.

Answer

The infection is mostly asymptomatic.

Answer

It can cause disease in the liver.

Answer

Infection does not provide immunity.

Parasitology — MCQs

Parasitology — MCQs

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