Parasitology Practice Questions

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.

Q: A 30-year-old man presents with subcutaneous itchy nodules over the left iliac crest. On examination, the nodules are firm, non-tender, and mobile. Skin scrapings contain microfilariae and adult worms. Which parasite is most likely responsible?

Onchocerca volvulus. ### Explanation The clinical presentation of firm, non-tender, mobile subcutaneous nodules (known as **Onchocercomata**) containing both adult worms and microfilariae is pathognomonic for **_Onchocerca volvulus_**. **1. Why the Correct Answer is Right:** _Onchocerca volvulus_ (the causative agent of River Blindness) typically presents with subcutaneous nodules over bony prominences (like the iliac crest or skull). The adult worms reside within these fibrous nodules, where they mate and release microfilariae. Diagnosis is confirmed by identifying microfilariae in **skin snips** (scrapings) or by finding adult worms in an excised nodule. **2. Why the Incorrect Options are Wrong:** * **_Loa loa_ (African Eye Worm):** Characterized by transient, localized subcutaneous swellings called **Calabar swellings**. Adult worms migrate through the subconjunctiva of the eye. Microfilariae are found in the **blood**, not skin scrapings. * **_Brugia malayi_:** A cause of lymphatic filariasis. It primarily affects the lymphatic system, leading to lymphadenitis and elephantiasis of the lower limbs. Microfilariae are found in the **blood** (nocturnal periodicity). * **_Mansonella streptocerca_:** While it can cause itchy skin rashes and hypopigmented macules, it rarely forms the distinct, firm, mobile nodules (onchocercomata) characteristic of _O. volvulus_. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Blackfly (_Simulium_). * **Mazzotti Reaction:** A severe inflammatory response (fever, rash, tachycardia) occurring after treatment with Diethylcarbamazine (DEC) due to the rapid killing of microfilariae. * **Drug of Choice:** **Ivermectin** (Note: DEC is contraindicated in Onchocerciasis as it can worsen ocular damage). * **Ocular Complication:** "Snowflake" opacities leading to Sclerosing Keratitis (River Blindness).

Q: Man is the definitive host for which of the following parasites?

Filaria. ### Explanation In medical parasitology, the **Definitive Host (DH)** is defined as the host in which the parasite undergoes its **sexual cycle** or reaches adult maturity. An **Intermediate Host (IH)** is one where the parasite undergoes asexual reproduction or larval development. **Correct Option: B. Filaria** In the life cycle of *Wuchereria bancrofti* and *Brugia malayi*, **humans are the definitive host** because they harbor the adult worms in the lymphatic system, where sexual reproduction occurs. The mosquito (Culex, Anopheles, or Aedes) serves as the intermediate host, harboring the larval stages (L1 to L3). **Incorrect Options:** * **A. Malaria (*Plasmodium*):** In malaria, the **Female Anopheles mosquito is the definitive host** because the sexual cycle (sporogony) occurs within the mosquito. Humans are the **intermediate host** because only asexual reproduction (schizogony) occurs in human liver and red blood cells. * **C. Measles:** This is a viral infection, not a parasitic one. Viruses do not follow the "definitive/intermediate host" classification used for parasites; humans are the natural reservoir and only host. * **D. All:** Incorrect, as the host status differs between Malaria and Filaria. **High-Yield Clinical Pearls for NEET-PG:** * **Exception to the Rule:** For most helminths (like Filaria, *Taenia solium*, *Ascaris*), man is the DH. The major exception is **Hydatid disease (*Echinococcus granulosus*)**, where the dog is the DH and man is the **accidental intermediate host** (dead-end host). * **Toxoplasmosis:** Cats are the DH; humans are IH. * **Diagnostic Stage of Filaria:** Microfilariae (detected in peripheral blood, usually with nocturnal periodicity). * **Drug of Choice for Filariasis:** Diethylcarbamazine (DEC).

Question 1

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 2

What is the primary reservoir for hookworm infection?

Accepted Answer

Human beings

Answer

Soil

Answer

Feces

Answer

Monkeys

Question 3

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

Accepted Answer

Taenia solium

Answer

Hymenolepis nana

Answer

Echinococcus

Answer

Schistosoma

Question 4

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 5

Infection with which organism during pregnancy can cause congenital hydrocephalus?

Accepted Answer

Toxoplasma gondii

Answer

Clostridium tetani

Answer

Treponema pallidum

Answer

Streptococcus species

Question 6

Which of the following parasitic infections predisposes to malignancies?

Accepted Answer

Clonorchiasis

Answer

Paragonimus westermani

Answer

Guinea worm infection

Answer

Ancyclostoma

Question 7

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.

Question 8

A 30-year-old man presents with subcutaneous itchy nodules over the left iliac crest. On examination, the nodules are firm, non-tender, and mobile. Skin scrapings contain microfilariae and adult worms. Which parasite is most likely responsible?

Accepted Answer

Onchocerca volvulus

Answer

Loa Loa

Answer

Brugia malayi

Answer

Mansonella streptocerca

Question 9

Which of the following is a neuropathogenic amoeba?

Accepted Answer

Acanthamoeba

Answer

Entamoeba coli

Answer

Naegleria

Answer

Entamoeba histolytica

Question 10

Man is the definitive host for which of the following parasites?

Accepted Answer

Filaria

Answer

Malaria

Answer

Measles

Answer

All

Parasitology — MCQs

Parasitology — MCQs

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