Parasitology Practice Questions

Q: All the following parasites cause malignancy except?

Onchocerca volvulus. **Explanation:** The association between parasitic infections and carcinogenesis is a high-yield topic in NEET-PG. Certain parasites are classified as **Group 1 Carcinogens** by the IARC because chronic inflammation and metabolic byproducts lead to DNA damage and malignant transformation. **Why Onchocerca volvulus is the correct answer:** *Onchocerca volvulus* is a nematode responsible for **River Blindness** (Onchocerciasis). While it causes severe pathology, including sclerosing keratitis and lichenified dermatitis ("lizard skin"), it has **no known association with malignancy**. **Analysis of Incorrect Options (Parasites that DO cause malignancy):** * **Schistosoma haematobium:** This trematode (blood fluke) inhabits the vesical venous plexus. Chronic irritation from eggs in the bladder wall leads to **Squamous Cell Carcinoma (SCC) of the urinary bladder** (Note: Not transitional cell carcinoma). * **Clonorchis sinensis (Chinese Liver Fluke):** Inhabits the bile ducts. Chronic infection causes biliary epithelial hyperplasia, which can progress to **Cholangiocarcinoma** (bile duct cancer). * **Opisthorchis viverrini (Southeast Asian Liver Fluke):** Similar to *Clonorchis*, it resides in the biliary tract and is a potent risk factor for **Cholangiocarcinoma**. **NEET-PG High-Yield Pearls:** 1. **Schistosoma mansoni/japonicum:** Associated with Hepatocellular Carcinoma (HCC) and Colorectal cancer, though the link is less definitive than *S. haematobium*. 2. **Strongyloides stercoralis:** Linked to Adult T-cell Leukemia/Lymphoma (ATLL) due to its co-infection synergy with HTLV-1. 3. **Key Distinction:** If a question asks for the most common bladder cancer worldwide, it is Transitional Cell Carcinoma; however, in **endemic areas** of Schistosomiasis (e.g., Egypt), **Squamous Cell Carcinoma** is more prevalent.

Q: Chronic dysentery, abdominal pain, and rectal prolapse in children is caused by which of the following parasites?

Trichuris trichura. **Explanation:** The correct answer is **Trichuris trichiura** (Whipworm). This parasite primarily inhabits the caecum and large intestine. In heavy infections, particularly in children, the worms can be found throughout the colon and rectum. **Why Trichuris trichiura is correct:** The hallmark clinical presentation of heavy Trichuriasis is **Trichuris Dysentery Syndrome**. The worms embed their slender anterior ends into the intestinal mucosa, causing chronic inflammation, mucosal friability, and blood loss. The constant irritation and straining (tenesmus) during defecation, combined with the weakening of the pelvic floor muscles and local inflammation, lead to the classic complication of **rectal prolapse**. **Analysis of Incorrect Options:** * **Enterobius vermicularis (Pinworm):** Primarily causes perianal pruritus (itching) at night. It does not cause dysentery or rectal prolapse. * **Ascaris lumbricoides (Roundworm):** Typically causes intestinal obstruction (bolus formation) or Loeffler’s syndrome (pulmonary phase). It does not typically cause chronic dysentery. * **Trichinella spiralis:** Known for causing muscle pain (myositis), periorbital edema, and eosinophilia after ingestion of undercooked pork. It does not inhabit the lower bowel to cause prolapse. **NEET-PG High-Yield Pearls:** * **Morphology:** Adult worm is whip-like (thick posterior, thin anterior). * **Egg:** Characteristic **barrel-shaped** (lemon-shaped) with **bipolar mucus plugs**. * **Treatment:** Mebendazole or Albendazole. * **Key Association:** Always link "Rectal Prolapse + Child + Dysentery" to *Trichuris trichiura*.

Q: Peripheral smear of malaria shows which of the following findings, EXCEPT?

Banana shaped gametocyte - Ovale. The correct answer is **D. Banana shaped gametocyte - Ovale**. ### **Explanation** The diagnosis of malaria via peripheral smear relies on identifying specific morphological features of the *Plasmodium* species within red blood cells (RBCs). 1. **Why Option D is correct:** Banana-shaped (crescentic) gametocytes are the pathognomonic hallmark of ***Plasmodium falciparum***, not *P. ovale*. In *P. ovale* infections, the gametocytes are typically round or oval, and the infected RBCs often show fimbriated (ragged) edges and an oval shape. 2. **Why Option A is incorrect:** *P. vivax* typically presents with a **single ring form** (trophozoite) per RBC. The infected RBC is usually enlarged and contains Schüffner’s dots. 3. **Why Option B is incorrect:** **Multiple ring forms** (multiple parasites infecting a single RBC) and the "Accole/Applique" position (rings at the periphery of the RBC) are characteristic features of ***P. falciparum*** due to its high parasitemia levels. 4. **Why Option C is incorrect:** ***P. malariae*** is known for its unique **"Band and Bar" forms**, where the growing trophozoite stretches across the diameter of the non-enlarged RBC. ### **High-Yield Clinical Pearls for NEET-PG** * **Maurer’s Dots:** Seen in *P. falciparum*. * **Schüffner’s Dots:** Seen in *P. vivax* and *P. ovale*. * **Ziemann’s Dots:** Seen in *P. malariae*. * **RBC Age Preference:** *P. vivax/ovale* prefer young RBCs (reticulocytes); *P. malariae* prefers old RBCs; *P. falciparum* is "indiscriminate" (infects RBCs of all ages), leading to severe anemia and high parasite load. * **Gold Standard Diagnosis:** Microscopy (Thick smear for detection, Thin smear for species identification).

Q: Which statement is true regarding the trophozoites of E. histolytica?

Shows erythrophagocytosis. **Explanation:** *Entamoeba histolytica* is the causative agent of amoebiasis. Distinguishing it from the morphologically identical but non-pathogenic *E. dispar* is a common NEET-PG focus. **1. Why Option C is Correct:** The presence of **ingested Red Blood Cells (erythrophagocytosis)** within the cytoplasm of a trophozoite is the **pathognomonic** feature of *E. histolytica*. It indicates invasive disease, as the parasite actively destroys host tissue and consumes erythrocytes. This feature is never seen in *E. dispar* or *E. coli*. **2. Why Other Options are Incorrect:** * **Option A:** *E. histolytica* has a **central** karyosome (nucleolus). An **eccentric** (off-center) karyosome is a characteristic feature of *Entamoeba coli*, a non-pathogenic commensal. * **Option B:** The nuclear membrane of *E. histolytica* is lined with **fine, uniformly distributed peripheral chromatin**. A membrane "without chromatin" is not characteristic of this genus. * **Option D:** The presence of ingested bacteria is typical of **Entamoeba coli**. *E. histolytica* trophozoites in invasive disease usually contain RBCs but rarely contain bacteria, whereas commensal amoebae feed on intestinal flora. **High-Yield Clinical Pearls for NEET-PG:** * **Motility:** Trophozoites show unidirectional, purposeful movement using finger-like **pseudopodia**. * **Nuclear Structure:** Described as having a "Cartwheel appearance" due to the central karyosome and delicate chromatin. * **Stain of Choice:** Iron-hematoxylin or Trichrome stain. * **Quadrinucleate Cyst:** The infective stage; contains up to 4 nuclei, rounded chromatoid bars (cigar-shaped), and a glycogen mass.

Q: A specimen resected from a child with intestinal obstruction is shown. What is the most likely diagnosis?

Ascariasis. ***Ascariasis*** - The specimen shows a **bolus of large roundworms** (Ascaris lumbricoides) causing **mechanical intestinal obstruction**, which is pathognomonic for ascariasis. - This condition is **common in children** in endemic areas and typically presents with intestinal obstruction due to a **tangled mass of adult worms**. *Kala-azar* - This is a **systemic leishmaniasis** that causes hepatosplenomegaly, fever, and pancytopenia, not intestinal obstruction. - The pathology involves **reticuloendothelial system** involvement, not intestinal worm masses. *Meckel's diverticulum* - This congenital anomaly appears as a **small bowel outpouching** containing ectopic gastric or pancreatic tissue. - The specimen would show a **diverticular structure**, not a mass of parasitic worms. *Strongyloidiasis* - Caused by **Strongyloides stercoralis**, which are much **smaller threadlike worms** that don't form obstructing masses. - This parasite typically causes **duodenitis** and **malabsorption**, rarely mechanical obstruction.

Q: Lymphatic obstruction occurs with which of the following parasites?

Filarial worm. **Explanation:** **Correct Option: A. Filarial worm (*Wuchereria bancrofti* / *Brugia malayi*)** Lymphatic filariasis is primarily caused by *Wuchereria bancrofti*. The adult worms reside in the **afferent lymphatic vessels** and lymph nodes. The pathogenesis involves a combination of mechanical obstruction by the adult worms and a profound inflammatory response (Th2-mediated) to the parasite and its endosymbiont, *Wolbachia*. Over time, chronic inflammation leads to **lymphangiosclerosis** and fibrosis, resulting in permanent lymphatic obstruction, lymphoedema, and eventually **Elephantiasis**. **Incorrect Options:** * **B. Hookworm (*Ancylostoma duodenale*):** These reside in the small intestine and feed on blood. They are primarily associated with **Iron Deficiency Anemia** and ground itch, not lymphatic pathology. * **C. Guinea worm (*Dracunculus medinensis*):** The adult female migrates to the subcutaneous tissues (usually of the lower limbs) to create a blister and release larvae. It causes local ulcers and secondary infections but does not obstruct lymphatics. * **D. Pinworm (*Enterobius vermicularis*):** These inhabit the cecum and appendix. The hallmark clinical feature is **perianal pruritus** (nocturnal itching) as the female migrates to the perianal skin to lay eggs. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Culex quinquefasciatus* is the most common vector for *W. bancrofti* in India. * **Nocturnal Periodicity:** Microfilariae appear in the peripheral blood between **10 PM and 2 AM**. * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by nocturnal cough, wheezing, and high eosinophil counts. * **Drug of Choice:** Diethylcarbamazine (DEC). Note: DEC is contraindicated in Onchocerciasis due to the Mazzotti reaction. * **Diagnostic Gold Standard:** Demonstration of microfilariae in a peripheral blood smear (thick film).

Q: Cutaneous larva currens is a feature of which of the following?

Strongyloides stercoralis. **Explanation:** **Larva currens** is a pathognomonic clinical sign of **Strongyloides stercoralis** infection. It occurs during the autoinfection cycle when filariform larvae penetrate the perianal skin and migrate rapidly through the dermis. The term "currens" (Latin for "running") refers to the exceptionally high speed of migration—up to **5–10 cm per hour**—resulting in a rapidly advancing, pruritic, erythematous, serpiginous wheal. **Analysis of Options:** * **Strongyloides stercoralis (Correct):** Causes Larva currens. It typically presents in the perianal region, buttocks, or trunk. Due to its speed, the lesion changes position visibly within a short period. * **Ancylostoma braziliense & A. caninum (Incorrect):** These are the most common causes of **Cutaneous Larva Migrans (CLM)** or "creeping eruption." Unlike larva currens, CLM moves much slower (about **1–2 cm per day**) and is caused by non-human hookworms that cannot complete their life cycle in humans. * **Loa loa (Incorrect):** This filarial nematode causes **Calabar swellings** (transient localized angioedema) and can be seen migrating across the subconjunctiva of the eye. **High-Yield NEET-PG Pearls:** 1. **Speed is the Key:** Larva currens (cm/hour) vs. Larva migrans (cm/day). 2. **Autoinfection:** *S. stercoralis* is unique because it can complete its entire life cycle within the human host, leading to persistent infections for decades. 3. **Hyperinfection Syndrome:** In immunocompromised patients (especially those on steroids), *S. stercoralis* can lead to fatal disseminated disease. 4. **Treatment:** Ivermectin is the drug of choice for Strongyloidiasis.

Question 1

All the following parasites cause malignancy except?

Accepted Answer

Onchocerca volvulus

Answer

Schistosoma haematobium

Answer

Clonorchis sinensis

Answer

Opisthrochis viverrini

Question 2

Chronic dysentery, abdominal pain, and rectal prolapse in children is caused by which of the following parasites?

Accepted Answer

Trichuris trichura

Answer

Enterobius vermicularis

Answer

Ascariasis

Answer

Trichinella spiralis

Question 3

Recurrent giardiasis is associated with which of the following conditions?

Accepted Answer

Common variable immunodeficiency

Answer

Severe combined immunodeficiency

Answer

DiGeorge syndrome

Answer

C8 deficiency

Question 4

Peripheral smear of malaria shows which of the following findings, EXCEPT?

Accepted Answer

Banana shaped gametocyte - Ovale

Answer

Single ring form - Vivax

Answer

Multiple ring form - Falciparum

Answer

Bar and band forms - Malariae

Question 5

A 23-year-old man undergoing chemotherapy for acute lymphoblastic leukemia has developed a fever and abdominal pain within the past week. He now has a severe cough. On physical examination, his temperature is 38.4°C. On auscultation, crackles are heard over all lung fields. Laboratory studies show hemoglobin, 12.8 g/dL; hematocrit, 39%; MCV, 90 mm³; platelet count, 221,000/mm³; and WBC count, 16,475/mm³ with 51% segmented neutrophils, 5% bands, 18% lymphocytes, 8% monocytes, and 18% eosinophils. Infection with which of the following organisms is most likely to be complicating the course of this patient's disease?

Accepted Answer

Strongyloides stercoralis

Answer

Cryptococcus neoformans

Answer

Cytomegalovirus

Answer

Pseudomonas aeruginosa

Question 6

Which statement is true regarding the trophozoites of E. histolytica?

Accepted Answer

Shows erythrophagocytosis

Answer

Has an eccentric karyosome

Answer

Nuclear membrane is without chromatin

Answer

Presence of bacteria inside the cell

Question 7

All of the following statements about toxoplasmosis are true except?

Accepted Answer

Arthralgia, sore throat and abdominal pain are the most common manifestations

Answer

May spread by organ transplantation

Answer

Maternal infection acquired after 6 months has high risk of transmission

Answer

Oocyst in freshly passed cat's faeces is infective

Question 8

A specimen resected from a child with intestinal obstruction is shown. What is the most likely diagnosis?

Accepted Answer

Ascariasis

Answer

Kala-azar

Answer

Meckel's diverticulum

Answer

Strongyloidiasis

Question 9

Lymphatic obstruction occurs with which of the following parasites?

Accepted Answer

Filarial worm

Answer

Hook worm

Answer

Guinea worm

Answer

Pin worm

Question 10

Cutaneous larva currens is a feature of which of the following?

Accepted Answer

Strongyloides stercoralis

Answer

Ancylostoma braziliense

Answer

Ancylostoma caninum

Answer

Loa loa

Parasitology — MCQs

Parasitology — MCQs

On this page

Practice by Chapter

Want unlimited practice?