Parasitology Practice Questions

Q: Visceral larva migrans is associated with which of the following?

Toxocara canis. **Explanation:** **Visceral Larva Migrans (VLM)** is a clinical syndrome caused by the migration of non-human nematode larvae through the internal organs of a human host. **Why Toxocara canis is correct:** *Toxocara canis* (dog roundworm) and *Toxocara cati* (cat roundworm) are the primary causative agents. Humans are accidental hosts who ingest embryonated eggs from soil contaminated with animal feces. Since humans are not the definitive hosts, the larvae cannot complete their life cycle to become adult worms. Instead, they penetrate the intestinal wall and migrate through the **liver, lungs, and eyes**, triggering a robust inflammatory response and marked **peripheral eosinophilia**. **Analysis of Incorrect Options:** * **Strongyloides stercoralis:** Causes **Hyperinfection syndrome** or "Larva currens" (a rapidly moving cutaneous track), but it is a human parasite that completes its life cycle in the human gut. * **Ancylostoma braziliense:** This is the primary cause of **Cutaneous Larva Migrans (CLM)** or "creeping eruption." The larvae penetrate the skin but lack the collagenases to penetrate the basement membrane, remaining confined to the epidermis. * **Visceral leishmaniasis (Kala-azar):** This is caused by a protozoan (*Leishmania donovani*), not a helminth. While it affects internal organs (spleen/liver), it does not involve larval migration. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Presentation:** A young child with a history of pica (eating dirt), hepatomegaly, wheezing, and extreme eosinophilia. * **Ocular Larva Migrans (OLM):** A variant where larvae migrate to the eye, often mimicking a retinoblastoma. * **Diagnosis:** Serology (ELISA) is the preferred method; stool examination is useless because the larvae never mature into egg-laying adults in humans. * **Treatment:** Albendazole or Mebendazole.

Q: Chyluria is due to:

Filaria. **Explanation:** **Chyluria** is the presence of chyle (a milky fluid consisting of lymph and emulsified fats) in the urine. It occurs due to a communication between the intestinal lymphatics and the urinary tract. **Why Filaria is correct:** The most common cause of chyluria worldwide is **Lymphatic Filariasis**, primarily caused by *Wuchereria bancrofti*. The adult worms reside in the lymphatic vessels, leading to chronic inflammation, fibrosis, and eventual **lymphatic obstruction**. This obstruction causes high pressure within the lymphatics (lymphatic hypertension), leading to the rupture of collateral lymphatic vessels into the renal pelvis, ureter, or bladder. The characteristic "milky white" appearance of urine is due to the presence of chylomicrons. **Why other options are incorrect:** * **Carcinoma:** While retroperitoneal tumors can occasionally cause lymphatic obstruction, they are a rare cause of chyluria compared to parasitic infections. * **Tuberculosis:** Renal TB typically presents with "sterile pyuria" (pus cells in urine without bacterial growth on standard media), not chyluria. * **Malaria:** Malaria causes hemolysis, which may lead to **hemoglobinuria** (Blackwater fever in *P. falciparum*), resulting in dark/cola-colored urine, but not milky chyluria. **NEET-PG High-Yield Pearls:** * **Diagnosis:** Chyluria can be confirmed by the **Ether test** (urine clears after adding ether) or by detecting high triglyceride levels in the urine. * **Microfilariae:** Usually show **nocturnal periodicity** (collected between 10 PM – 2 AM). * **Drug of Choice:** Diethylcarbamazine (DEC) is the mainstay for Filariasis, but it does not reverse established structural lymphatic damage. * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by nocturnal cough and high IgE levels.

Q: What is the most common site of extraintestinal amoebiasis?

Liver. **Explanation:** **Entamoeba histolytica** is primarily an intestinal parasite, but it can spread hematogenously to cause extraintestinal manifestations. **Why Liver is Correct:** The **Liver** is the most common site for extraintestinal amoebiasis. This occurs because trophozoites from the intestinal wall enter the **portal venous system**. Since the portal vein drains directly into the liver, it acts as the first major capillary filter for the parasite. The resulting **Amoebic Liver Abscess (ALA)** typically presents in the right lobe (due to the streamlining of portal blood flow) and is characterized by "anchovy sauce" pus. **Why Other Options are Incorrect:** * **Lungs (Option D):** This is the second most common site. It usually occurs via direct extension from a liver abscess through the diaphragm or, less commonly, through systemic circulation. * **Brain (Option A):** This is a rare, life-threatening complication resulting from hematogenous spread. It typically presents as sudden onset meningoencephalitis. * **Spleen (Option C):** Splenic involvement is extremely rare and usually occurs only in cases of widespread systemic dissemination. **High-Yield Clinical Pearls for NEET-PG:** * **Trophozoite Morphology:** Look for ingested RBCs (Erythrophagocytosis) in the cytoplasm—this is pathognomonic for *E. histolytica*. * **Anchovy Sauce Pus:** The abscess fluid is chocolate-brown, odorless, and sterile (contains no bacteria or trophozoites; trophozoites are found in the abscess wall). * **Treatment:** **Metronidazole** or Tinidazole is the drug of choice for the tissue stage, followed by a luminal amoebicide (e.g., Diloxanide furoate or Paromomycin) to eradicate cysts.

Q: Which tick-borne fever is characterized by an organism that attacks red blood cells?

Babesiosis. **Explanation:** **Babesiosis** is the correct answer because it is a tick-borne zoonosis caused by protozoan parasites of the genus *Babesia* (most commonly *B. microti*). The organism is transmitted by the **Ixodes tick** (the same vector for Lyme disease). Once in the bloodstream, the sporozoites invade **Red Blood Cells (RBCs)**, where they replicate asexually. A hallmark diagnostic feature on a peripheral blood smear is the **"Maltese Cross" appearance** (tetrads of merozoites), which confirms its intra-erythrocytic nature. **Why other options are incorrect:** * **Typhus:** While some forms (like Endemic or Epidemic Typhus) are vector-borne (fleas/lice), **Scrub Typhus** is mite-borne. However, *Rickettsia* species primarily infect **vascular endothelial cells**, not RBCs. * **Dengue:** This is a viral infection transmitted by the **Aedes mosquito**, not ticks. It primarily affects platelets and causes plasma leakage. * **Malaria:** While *Plasmodium* does attack RBCs, it is transmitted by the **Anopheles mosquito**, not ticks. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Ixodes scapularis* (Deer tick). * **Morphology:** Look for "Maltese Cross" or ring forms (often confused with *P. falciparum*, but Babesia lacks hemozoin pigment). * **Clinical Presentation:** Fever, hemolytic anemia, and hemoglobinuria. It can be fatal in asplenic patients. * **Treatment:** Combination of **Atovaquone + Azithromycin** (preferred) or Clindamycin + Quinine.

Q: Which Entamoeba species is morphologically identical to E. histolytica?

E. dispar. ### Explanation **Correct Answer: B. E. dispar** **Why it is correct:** *Entamoeba dispar* is a non-pathogenic commensal that is **morphologically identical** to *E. histolytica* in both its trophozoite and cyst stages. Under a light microscope, they cannot be distinguished by size, nuclear structure, or number of nuclei (both have 1–4 nuclei in the cyst stage). The only definitive way to differentiate them is through **isoenzyme analysis (zymodemes)**, molecular methods (PCR), or by observing ingested RBCs (erythrophagocytosis), which is a feature unique to the pathogenic *E. histolytica*. **Why the other options are incorrect:** * **A. E. coli:** This is a non-pathogenic commensal but is morphologically distinct. The mature cyst has **8 nuclei** (compared to 4 in *E. histolytica*), and the trophozoite has a sluggish motility with a coarse, eccentric karyosome. * **C. E. hartmanni:** Known as the "small race" of *E. histolytica*, it is morphologically similar but significantly **smaller** in size (cysts are <10 µm, whereas *E. histolytica* cysts are 10–15 µm). * **D. E. gingivalis:** This species is found in the oral cavity (gingival pockets). It **does not have a cyst stage** and is the only *Entamoeba* known to ingest White Blood Cells (WBCs). **High-Yield Clinical Pearls for NEET-PG:** * **E. moshkovskii:** Another species morphologically identical to *E. histolytica* and *E. dispar*, usually found in sewage but occasionally in human stools. * **Pathognomonic Feature:** The presence of **ingested RBCs** in a trophozoite is the gold standard for diagnosing invasive amoebiasis caused by *E. histolytica*. * **Treatment Note:** Since *E. dispar* is non-pathogenic, its identification in an asymptomatic patient does not require treatment.

Q: All of the following can cause obstruction of the hepatobiliary system EXCEPT?

Ascaris lumbricoides. **Explanation:** The correct answer is **A. *Ankylostoma duodenale***. The question asks for the organism that does **NOT** typically cause hepatobiliary obstruction. While *Ascaris lumbricoides* is often associated with this condition, the provided key indicates a focus on the primary habitat of these parasites. 1. **Why *Ankylostoma duodenale* is the correct answer:** *Ankylostoma duodenale* (Hookworm) resides primarily in the **upper small intestine (jejunum)**, where it attaches to the mucosa to suck blood. It does not migrate into the biliary tree. Its clinical manifestations are primarily related to iron-deficiency anemia and ground itch, not mechanical obstruction of the liver or bile ducts. 2. **Analysis of other options:** * **B. *Ascaris lumbricoides*:** This is the most common cause of biliary ascariasis. Adult worms are highly motile and can migrate from the duodenum through the Ampulla of Vater into the common bile duct, causing obstructive jaundice, cholangitis, or cholecystitis. * **C. *Clonorchis sinensis* (Chinese Liver Fluke):** These parasites reside directly within the distal bile ducts. Chronic infection leads to mechanical obstruction, inflammatory hyperplasia, and is a major risk factor for **cholangiocarcinoma**. * **D. *Fasciola hepatica* (Sheep Liver Fluke):** After ingestion, the larvae penetrate the liver parenchyma and settle in the bile ducts to mature into adults, causing "liver rot" and biliary obstruction. **High-Yield Clinical Pearls for NEET-PG:** * **Most common helminth causing biliary obstruction:** *Ascaris lumbricoides*. * **Parasite associated with Cholangiocarcinoma:** *Clonorchis sinensis* and *Opisthorchis viverrini*. * **Hookworm (Ankylostoma):** Key association is **Microcytic Hypochromic Anemia** and **Loffler’s Syndrome** (during pulmonary migration). * **Fasciola hepatica:** Acquired by eating contaminated **watercress**.

Q: A terminally ill HIV infected patient develops focal neurologic signs, dementia, and coma. Amoebic parasites are demonstrated in CSF. Which of the following organisms is most likely to be the causative agent?

Acanthamoeba sp. **Explanation:** The clinical presentation of focal neurological signs, dementia, and coma in an immunocompromised (HIV-infected) patient, combined with the presence of amoebae in the CSF, points toward **Granulomatous Amoebic Encephalitis (GAE)** caused by **Acanthamoeba species**. **1. Why Acanthamoeba is correct:** Acanthamoeba is an opportunistic free-living amoeba. In immunocompromised individuals, it causes GAE, a subacute to chronic infection characterized by a slow onset (weeks to months) involving dementia, personality changes, and focal deficits. It typically spreads hematogenously from a primary site in the skin or lungs to the CNS. **2. Why other options are incorrect:** * **Naegleria fowleri:** Causes **Primary Amoebic Meningoencephalitis (PAM)**. Unlike GAE, PAM is an acute, rapidly fatal infection (death within 5–10 days) that occurs in previously healthy individuals (not necessarily immunocompromised) following exposure to contaminated warm freshwater. * **Entamoeba histolytica:** While it can cause brain abscesses, it is primarily an intestinal pathogen. Brain involvement is rare, secondary to liver abscesses, and presents as an acute abscess rather than the granulomatous encephalitis described. * **Giardia lamblia:** This is a flagellated protozoan that causes intestinal malabsorption and diarrhea; it does not invade the CNS. **Clinical Pearls for NEET-PG:** * **Acanthamoeba:** Also causes **Amoebic Keratitis** (associated with contact lens use) and skin ulcers. Diagnosis is made by finding **both cysts and trophozoites** in tissue/CSF. * **Naegleria fowleri:** Enters via the **cribriform plate**. Diagnosis shows **only trophozoites** in CSF. * **Drug of Choice for GAE:** No standard regimen, but often includes Miltefosine, Fluconazole, or Pentamidine.

Q: Significant titres of indirect hemagglutination (IHA) are seen in all types of amoebiasis except:

Cyst passers. **Explanation:** The Indirect Hemagglutination (IHA) test is a serological assay used to detect circulating antibodies against *Entamoeba histolytica*. The fundamental principle governing its positivity is **tissue invasion**. **Why "Cyst Passers" is the correct answer:** Cyst passers (asymptomatic carriers) harbor the parasite only within the intestinal lumen. Since there is no invasion of the intestinal wall or deeper tissues, the parasite does not come into contact with the host’s immune system to trigger a systemic humoral response. Consequently, antibody titers remain insignificant or undetectable in these individuals. **Analysis of Incorrect Options:** * **Acute Amoebic Dysentery:** This involves mucosal invasion and ulceration of the colon. The breach of the intestinal barrier allows for antibody production, leading to significant IHA titers in approximately 60-70% of cases. * **Liver Abscess:** This is the most common form of extra-intestinal amoebiasis. Because it involves deep tissue invasion and a robust systemic immune response, IHA titers are highly sensitive (positive in >95% of cases) and usually reach very high levels. * **Brain Abscess:** Similar to liver abscesses, this represents a severe extra-intestinal spread where tissue destruction is significant, leading to high antibody titers. **High-Yield Clinical Pearls for NEET-PG:** * **Serology vs. Microscopy:** Serology (IHA, ELISA) is the gold standard for diagnosing **extra-intestinal** amoebiasis, whereas stool microscopy is preferred for **intestinal** amoebiasis. * **Persistence:** IHA titers can remain positive for several years even after successful treatment; thus, a single positive test may not always indicate an active infection in endemic areas. * **E. dispar vs. E. histolytica:** Serology helps differentiate these two; *E. dispar* (non-pathogenic) does not cause a rise in antibody titers.

Q: Which of the following produces bile-stained eggs?

Ascaris. **Explanation:** The correct answer is **Ascaris lumbricoides**. In parasitology, eggs are classified as "bile-stained" if they absorb the golden-brown pigment of bile while passing through the human intestine. **1. Why Ascaris is correct:** *Ascaris lumbricoides* (Roundworm) eggs are characterized by a thick, translucent shell surrounded by a coarse, wavy, or mammillated albuminous coat. This outer layer is highly permeable to bile pigments, giving the eggs their characteristic **golden-brown color**. Both fertilized and unfertilized eggs of Ascaris are bile-stained. **2. Why the other options are incorrect:** * **Ancylostoma duodenale & Necator americanus (Hookworms):** These parasites produce eggs that are colorless (non-bile stained), oval, and surrounded by a thin, transparent hyaline membrane. They are typically seen in the 4-to-8-cell cleavage stage. * **Enterobius vermicularis (Pinworm):** These eggs are also non-bile stained. They have a characteristic plano-convex shape (one side flat, one side convex) and are surrounded by a thin, double-layered transparent shell. **3. NEET-PG High-Yield Pearls:** * **Bile-stained eggs (Mnemonic: "TAFT"):** **T**richuris trichiura, **A**scaris lumbricoides, **F**asciola hepatica, **T**aenia species. * **Non-bile stained eggs:** Hookworms (*Ancylostoma, Necator*), *Enterobius vermicularis*, and *Hymenolepis nana*. * **Ascaris Clinical Note:** It is the most common helminthic infection worldwide. Heavy infestations can lead to **Loeffler’s syndrome** (eosinophilic pneumonia) during the larval migratory phase.

Question 1

Visceral larva migrans is associated with which of the following?

Accepted Answer

Toxocara canis

Answer

Strongyloides stercoralis

Answer

Ancylostoma braziliense

Answer

Visceral leishmaniasis

Question 2

Chyluria is due to:

Accepted Answer

Filaria

Answer

Carcinoma

Answer

Tuberculosis

Answer

Malaria

Question 3

What is the most common site of extraintestinal amoebiasis?

Accepted Answer

Liver

Answer

Brain

Answer

Spleen

Answer

Lungs

Question 4

Which tick-borne fever is characterized by an organism that attacks red blood cells?

Accepted Answer

Babesiosis

Answer

Typhus

Answer

Dengue

Answer

Malaria

Question 5

Which Entamoeba species is morphologically identical to E. histolytica?

Accepted Answer

E. dispar

Answer

E. coli

Answer

E. hartmanni

Answer

E. gingivalis

Question 6

All of the following can cause obstruction of the hepatobiliary system EXCEPT?

Accepted Answer

Ascaris lumbricoides

Answer

Ankylostoma duodenale

Answer

Clonorchis sinensis

Answer

Fasciola hepatica

Question 7

Most West Africans and people with origins in that region carry the Duffy-negative FyFy phenotype and are therefore resistant to______ malaria?

Accepted Answer

P. vivax

Answer

P. ovale

Answer

P. malariae

Answer

P. falciparum

Question 8

A terminally ill HIV infected patient develops focal neurologic signs, dementia, and coma. Amoebic parasites are demonstrated in CSF. Which of the following organisms is most likely to be the causative agent?

Accepted Answer

Acanthamoeba sp

Answer

Entamoeba histolytica

Answer

Giardia lamblia

Answer

Naegleria fowleri

Question 9

Significant titres of indirect hemagglutination (IHA) are seen in all types of amoebiasis except:

Accepted Answer

Cyst passers

Answer

Acute amoebic dysentery

Answer

Brain abscess

Answer

Liver abscess

Question 10

Which of the following produces bile-stained eggs?

Accepted Answer

Ascaris

Answer

Ancylostoma duodenale

Answer

Enterobius vermicularis

Answer

Necator americanus

Parasitology — MCQs

Parasitology — MCQs

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