Parasitology Practice Questions

Q: Steatorrhea associated with Giardia infection is seen in which immunoglobulin deficiency?

IgA. **Explanation:** **1. Why IgA is the correct answer:** Secretory IgA (sIgA) is the primary immunoglobulin responsible for mucosal immunity. It acts as the first line of defense in the gastrointestinal tract by preventing the attachment of pathogens to the intestinal epithelium. In patients with **Selective IgA Deficiency** or **Common Variable Immunodeficiency (CVID)**, the lack of mucosal IgA allows *Giardia lamblia* trophozoites to adhere extensively to the duodenal and jejunal mucosa. This leads to villous atrophy and malabsorption, manifesting clinically as chronic diarrhea and **steatorrhea** (fatty stools). **2. Why other options are incorrect:** * **IgE:** Primarily involved in Type I hypersensitivity reactions and defense against helminths (multicellular parasites). It does not play a significant role in preventing protozoal adhesion. * **IgG:** The most abundant systemic antibody, crucial for opsonization and neutralizing toxins in the blood and tissues, but it is not the dominant antibody on mucosal surfaces. * **IgM:** The first antibody produced during a primary immune response. While it can be secreted onto mucosa in small amounts (especially as a compensatory mechanism in IgA deficiency), it is not the primary diagnostic association for Giardia-induced steatorrhea. **3. NEET-PG High-Yield Pearls:** * **Selective IgA Deficiency** is the most common primary immunodeficiency. * **Clinical Association:** Patients are often asymptomatic but have an increased risk of respiratory infections, GI infections (*Giardia*), and **Anaphylaxis during blood transfusions** (due to anti-IgA antibodies). * **Giardia Diagnosis:** Stool microscopy (cysts/trophozoites) is standard, but the **Entero-test (String test)** or duodenal aspiration may be used if stool samples are negative. * **Drug of Choice:** Metronidazole or Tinidazole.

Q: A patient with prolonged diarrhea undergoes esophagogastroduodenoscopy. Biopsy of the small intestine demonstrates numerous crescent-shaped protozoa adjacent to the epithelial brush border. Which of the following organisms is the most likely pathogen?

Giardia lamblia. ### Explanation **Correct Answer: C. Giardia lamblia** The clinical presentation and histopathological findings are classic for **Giardiasis**. * **Mechanism:** *Giardia lamblia* (or *G. duodenalis*) trophozoites are pear-shaped or **crescent-shaped** (when viewed laterally) and possess a ventral sucking disc. They attach to the **brush border of the duodenal and jejunal enterocytes** but do not invade the mucosa. * **Pathology:** This attachment leads to the blunting of villi and malabsorption, resulting in foul-smelling, non-bloody, fatty diarrhea (steatorrhea). The biopsy finding of crescentic organisms "falling off" or "clinging to" the epithelial surface is a high-yield diagnostic feature. **Analysis of Incorrect Options:** * **A. Entamoeba histolytica:** Primarily affects the **colon** (not the small intestine). Histology shows "flask-shaped ulcers" and trophozoites with ingested RBCs (erythrophagocytosis). * **B. Escherichia coli:** This is a bacterium, not a protozoan. While ETEC/EPEC cause diarrhea, they would not appear as large crescent-shaped protozoa on biopsy. * **D. Naegleria fowleri:** This is a free-living amoeba that causes **Primary Amoebic Meningoencephalitis (PAM)**. It enters through the cribriform plate via nasal inhalation and does not cause intestinal disease. **High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** Duodenum and upper jejunum (acidic pH favors excystation). * **Diagnosis:** Stool microscopy (cysts/trophozoites), String test (Entero-test), or biopsy. * **Morphology:** Trophozoite has a "Monkey face" or "Owl's eye" appearance (2 nuclei, 4 pairs of flagella). * **Risk Factors:** IgA deficiency (predisposes to chronic giardiasis). * **Treatment:** Metronidazole or Tinidazole.

Q: Persistent diarrhea in AIDS is caused by which of the following?

Cryptosporidia. **Explanation:** **Cryptosporidium parvum** is the most common cause of chronic, persistent, and life-threatening watery diarrhea in patients with AIDS, particularly when CD4 counts drop below 100 cells/mm³. It is an acid-fast obligate intracellular protozoan that infects the intestinal epithelium, leading to malabsorption and severe dehydration. **Analysis of Options:** * **Cryptosporidium (Correct):** It is the classic "high-yield" pathogen associated with intractable diarrhea in HIV/AIDS. Diagnosis is typically made via **Modified Acid-Fast staining** (showing red oocysts) or Enzyme Immunoassay (EIA). * **Microspora:** While *Enterocytozoon bieneusi* causes diarrhea in AIDS, it is less common than Cryptosporidium. It requires specialized stains like Chromotrope 2R or electron microscopy for detection. * **Isospora belli (Cystoisospora):** This also causes diarrhea in AIDS, but it is less frequent globally than Cryptosporidium. A key differentiator is that *Isospora* responds well to **Trimethoprim-Sulfamethoxazole (TMP-SMX)**, whereas Cryptosporidium is often refractory to treatment until HAART improves the CD4 count. * **Cryptococcus:** *Cryptococcus neoformans* is a fungus primarily associated with **meningitis** and pulmonary infections in AIDS patients, not primary diarrheal disease. **NEET-PG High-Yield Pearls:** 1. **Staining:** Cryptosporidium, Isospora, and Cyclospora are all **Acid-Fast**. Cryptosporidium oocysts are small (4-6 µm), while Isospora oocysts are larger (20-30 µm) and oval. 2. **Treatment:** The drug of choice for Cryptosporidiosis in immunocompetent patients is **Nitazoxanide**, but in AIDS patients, the definitive treatment is **HAART** to restore immunity. 3. **Transmission:** Often associated with contaminated water supplies (oocysts are resistant to chlorination).

Q: A patient presented with subcutaneous nodules over the Iliac Crest and snowflake opacity in the eye. Skin scraping contains microfilaria and adult worms. Which parasite is likely responsible?

Onchocerca volvulus. ### Explanation The correct answer is **Onchocerca volvulus**. This parasite is the causative agent of **Onchocerciasis (River Blindness)**. #### Why Onchocerca volvulus is correct: The clinical presentation is classic for Onchocerciasis. * **Subcutaneous Nodules:** Known as **Onchocercomas**, these contain both adult worms and microfilariae. They typically occur over bony prominences like the iliac crest or skull. * **Ocular Involvement:** Microfilariae migrating to the eye cause **Snowflake Opacities** (punctate keratitis), which are reversible inflammatory lesions. Chronic infection leads to sclerosing keratitis and blindness. * **Diagnosis:** Unlike other filarial worms, *O. volvulus* microfilariae are found in **skin snips/scrapings**, not in the blood. #### Why other options are incorrect: * **Loa loa (African Eye Worm):** Characterized by transient **Calabar swellings** and the visible migration of the adult worm across the subconjunctiva. Microfilariae are found in the **blood** (diurnal periodicity). * **Brugia timori:** Causes lymphatic filariasis (elephantiasis) primarily in the lower limbs. Microfilariae are found in the **blood** and have a nocturnal periodicity. * **Mansonella ozzardi:** Generally asymptomatic or causes mild skin rashes/joint pain. Microfilariae are found in the **blood** and lack a sheath. #### High-Yield Clinical Pearls for NEET-PG: * **Vector:** *Simulium* fly (Blackfly), which breeds in fast-flowing rivers. * **Skin Changes:** "Leopard skin" (patchy depigmentation) and "Lizard skin" (atrophy/thickening). * **Hanging Groin:** Loss of elasticity in the inguinal skin leading to pendulous lymph nodes. * **Drug of Choice:** **Ivermectin** (Note: Diethylcarbamazine is contraindicated as it can trigger a severe Mazzotti reaction). * **Wolbachia:** An endosymbiotic bacteria required for the fertility of the adult worm; targeting it with Doxycycline can sterilize the parasite.

Q: Which one of the following is NOT a neuroparasite?

Trichinella spiralis. **Explanation:** The term **neuroparasite** refers to parasites that have a predilection for the Central Nervous System (CNS) or cause significant clinical disease by invading brain tissue. **Why Trichinella spiralis is the correct answer:** *Trichinella spiralis* is primarily a **tissue nematode** that causes trichinellosis. While the larvae migrate through various organs (including the brain, where they can cause transient encephalitis), they **cannot encyst in the CNS**. They have a specific tropism for **striated skeletal muscle** (e.g., diaphragm, deltoid, extraocular muscles), where they form characteristic calcified cysts. Therefore, it is classified as a muscle parasite rather than a neuroparasite. **Analysis of Incorrect Options:** * **Taenia solium:** The larval stage (*Cysticercus cellulosae*) has a high affinity for the brain, causing **Neurocysticercosis (NCC)**, the most common cause of adult-onset seizures worldwide. * **Naegleria fowleri:** Known as the "brain-eating amoeba," it enters via the olfactory neuroepithelium to cause **Primary Amoebic Meningoencephalitis (PAM)**, which is rapidly fatal. * **Acanthamoeba:** An opportunistic free-living amoeba that causes **Granulomatous Amoebic Encephalitis (GAE)**, particularly in immunocompromised individuals. **High-Yield Clinical Pearls for NEET-PG:** * **Most common CNS parasite:** *Taenia solium* (Neurocysticercosis). * **Drug of choice for NCC:** Albendazole (Praziquantel is an alternative). * **Diagnostic feature of Trichinella:** Muscle biopsy showing "coiled larvae" and elevated serum **creatine kinase (CK)** levels. * **Free-living amoebae:** *Naegleria* (freshwater history), *Acanthamoeba* (contact lens use/keratitis), and *Balamuthia mandrillaris* are all neuroparasites.

Q: The number of pairs of flagella in the depicted organism is:

4. ***4*** - **Giardia lamblia** trophozoites possess **4 pairs of flagella** (8 flagella total), which is a key diagnostic feature for identification. - The **trophozoite** has a characteristic **pear-shaped** morphology with **two nuclei** giving it a "face-like" appearance under microscopy. *1* - **Leishmania** species have only **1 flagellum** in their promastigote form, not pairs of flagella. - This count is too low for **Giardia lamblia**, which requires multiple flagella for its characteristic tumbling motility. *2* - **Trichomonas vaginalis** has **1 pair of flagella** (4 flagella total) plus an **undulating membrane**. - This number is insufficient for **Giardia**, which needs more flagella for its complex swimming pattern. *3* - No major **flagellated parasite** of clinical significance possesses exactly **3 pairs of flagella**. - This count falls short of **Giardia's** requirement for **4 pairs** to maintain its characteristic motility and adherence mechanisms.

Q: A biology graduate student who recently visited a tropical region of Africa presents with new visual impairment and the sensation that something is moving in her eye. She is concerned because she was warned about an eye disease transmitted by black flies. While in Africa, she was in a river area and received numerous black fly bites. She also has some subcutaneous nodules. If her infection was acquired by black fly bite, what is the most likely causative agent?

Onchocerca volvulus. **Explanation** The correct answer is **D. Onchocerca volvulus**. The clinical presentation describes **Onchocerciasis (River Blindness)**. The diagnosis is confirmed by the classic triad: history of exposure in an endemic region (Africa), transmission via the **Black fly (*Simulium* species)**, and clinical features including subcutaneous nodules (**Onchocercomas**) and visual impairment. The "moving sensation" in the eye refers to the migration of microfilariae into the ocular tissues, leading to sclerosing keratitis—the second leading infectious cause of blindness worldwide. **Why other options are incorrect:** * **A. Ancylostoma braziliense:** Causes Cutaneous Larva Migrans (creeping eruption). It is transmitted by direct skin contact with soil contaminated by hookworm larvae from cats/dogs, not by black flies. * **B. Trichinella spiralis:** Acquired by consuming undercooked meat (pork) containing encysted larvae. It presents with periorbital edema, myalgia, and eosinophilia, but does not involve black fly transmission. * **C. Dracunculus medinensis:** Causes Guinea worm disease. It is transmitted by drinking water containing infected *Cyclops* (copepods). It presents with a painful skin blister, usually on the lower limb, through which the adult worm emerges. **High-Yield NEET-PG Pearls:** * **Vector:** *Simulium* (Black fly) breeds in fast-flowing rivers (hence "River Blindness"). * **Infective stage:** Third-stage larvae (L3). * **Diagnosis:** **Skin snip preparation** to demonstrate microfilariae (they do not have a periodic presence in the blood). * **Treatment:** **Ivermectin** is the drug of choice (kills microfilariae). Doxycycline is used to target *Wolbachia*, an endosymbiont essential for the worm's survival. * **Mazzotti Reaction:** A severe inflammatory response (fever, rash, hypotension) that can occur after treating Onchocerciasis with diethylcarbamazine (DEC).

Q: All of the following are true about Trichinella spiralis EXCEPT?

Fairey's test is the intradermal test done.. **Explanation:** *Trichinella spiralis* is a tissue nematode that causes Trichinellosis. Understanding its unique life cycle and diagnostic tests is crucial for NEET-PG. **Why Option D is the Correct Answer (The "Except" statement):** The intradermal test used for the diagnosis of Trichinellosis is the **Bachman intradermal test**, not Fairey’s test. **Fairey’s test** is an intradermal test historically associated with **Schistosomiasis**. Therefore, statement D is factually incorrect regarding *Trichinella*. **Analysis of Other Options:** * **Option A:** Humans are indeed **accidental hosts**. While both the adult and larval stages occur in the same host, humans act as a **dead-end** because the larvae encysted in human muscle are unlikely to be consumed by another host. * **Option B:** The primary mode of transmission is the **ingestion of raw or undercooked meat** (most commonly pork) containing the infective encysted larvae. * **Option C:** Larvae have a predilection for highly active muscles with high oxygen content. The **extraocular muscles** are the most frequently involved, followed by the tongue, diaphragm, and intercostal muscles. **Clinical Pearls for NEET-PG:** * **Clinical Triad:** Look for a history of pork ingestion followed by **fever, periorbital edema, and myalgia**. * **Lab Findings:** Marked **Eosinophilia** and elevated **Creatine Phosphokinase (CPK)** due to muscle damage. * **Diagnosis:** Muscle biopsy (showing coiled larvae) is the gold standard. * **Treatment:** Albendazole or Mebendazole are the drugs of choice.

Question 1

Steatorrhea associated with Giardia infection is seen in which immunoglobulin deficiency?

Accepted Answer

IgA

Answer

IgE

Answer

IgG

Answer

IgM

Question 2

A patient with prolonged diarrhea undergoes esophagogastroduodenoscopy. Biopsy of the small intestine demonstrates numerous crescent-shaped protozoa adjacent to the epithelial brush border. Which of the following organisms is the most likely pathogen?

Accepted Answer

Giardia lamblia

Answer

Entamoeba histolytica

Answer

Escherichia coli

Answer

Naegleria fowleri

Question 3

Which of the following is NOT true of Giardiasis?

Accepted Answer

Complement fixation test is diagnostic

Answer

Stool contains only cysts

Answer

Habitat is the colon

Answer

Trophozoites and cysts are found in the duodenum

Question 4

Persistent diarrhea in AIDS is caused by which of the following?

Accepted Answer

Cryptosporidia

Answer

Microspora

Answer

Cryptococcus

Answer

Isospora belli

Question 5

A patient presented with subcutaneous nodules over the Iliac Crest and snowflake opacity in the eye. Skin scraping contains microfilaria and adult worms. Which parasite is likely responsible?

Accepted Answer

Onchocerca volvulus

Answer

Loa loa

Answer

Brugia timori

Answer

Mansonella ozzardi

Question 6

Which one of the following is NOT a neuroparasite?

Accepted Answer

Trichinella spiralis

Answer

Taenia solium

Answer

Acanthamoeba

Answer

Naegleria

Question 7

The number of pairs of flagella in the depicted organism is:

Accepted Answer

4

Answer

1

Answer

2

Answer

3

Question 8

A biology graduate student who recently visited a tropical region of Africa presents with new visual impairment and the sensation that something is moving in her eye. She is concerned because she was warned about an eye disease transmitted by black flies. While in Africa, she was in a river area and received numerous black fly bites. She also has some subcutaneous nodules. If her infection was acquired by black fly bite, what is the most likely causative agent?

Accepted Answer

Onchocerca volvulus

Answer

Ancylostoma braziliense

Answer

Trichinella spiralis

Answer

Dracunculus medinensis

Question 9

A 30-year-old farmer, treated initially with chloroquine for uncomplicated malaria, now has an episode of relapse. What could be the reason for relapse?

Accepted Answer

P. vivax has a persistent exoerythrocytic stage (hypnozoite).

Answer

P. vivax has a significant level of chloroquine resistance.

Answer

P. vivax has a persistent erythrocytic stage.

Answer

Chloroquine is not one of the drugs of choice.

Question 10

All of the following are true about Trichinella spiralis EXCEPT?

Accepted Answer

Fairey's test is the intradermal test done.

Answer

Man is an accidental host and acts as a dead-end.

Answer

Transmitted by ingestion of raw or undercooked pork.

Answer

Most common muscle involved is extraocular muscles.

Parasitology — MCQs

Parasitology — MCQs

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