Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 941: Adherence of E. histolytica to colonic mucosa is mediated by which of the following?

A. Fucose
B. Lectin (Correct Answer)
C. Fibronectin
D. Collagen

Explanation: ***Lectin*** - *Entamoeba histolytica* adherence to the colonic mucosa is primarily mediated by a **galactose- and N-acetylgalactosamine-specific adherence lectin** (Gal/GalNAc lectin). - This lectin binds to specific **carbohydrate residues** on host cell surfaces, facilitating initial attachment and subsequent invasion. *Fucose* - **Fucose** is a monosaccharide, and while it is present on host cell surface glycoproteins and glycolipids, it is **not the primary mediator** of *E. histolytica* adherence. - The lectin's specificity is predominantly for galactose and N-acetylgalactosamine, not fucose. *Fibronectin* - **Fibronectin** is an extracellular matrix protein that plays a role in cell adhesion and migration in many contexts, but it is **not the primary molecule** *E. histolytica* uses for initial adherence. - While *E. histolytica* may interact with extracellular matrix components later in the invasion process, it is not the initial adherence factor. *Collagen* - **Collagen** is a major structural protein in the extracellular matrix and connective tissues, providing structural support. - It is **not directly involved** in the initial adherence of *E. histolytica* to the intact colonic epithelial cells.

Question 942: Which organism is known to cause endemic hemoptysis?

A. Hymenolepis nana
B. Diphyllobothrium latum
C. Clonorchis sinensis
D. Paragonimus westermani (Correct Answer)

Explanation: ***Paragonimus westermani*** - This **lung fluke** is the classic cause of endemic hemoptysis, particularly in areas with consumption of undercooked crustaceans. - The adult worms reside in the lungs, causing inflammation and **fibrotic cysts**, leading to chronic cough and blood-tinged sputum. *Hymenolepis nana* - Known as the **dwarf tapeworm**, this organism primarily infects the small intestine causing gastrointestinal symptoms. - It does not involve the lungs or respiratory tract and therefore does not cause hemoptysis. *Diphyllobothrium latum* - This is the **fish tapeworm**, which establishes itself in the small intestine after ingestion of infected raw or undercooked fish. - Its main clinical manifestation is **megaloblastic anemia** due to vitamin B12 deficiency, not pulmonary symptoms. *Clonorchis sinensis* - Also known as the **Chinese liver fluke**, this parasite infects the bile ducts and liver. - It can cause **cholangitis**, cholelithiasis, and even cholangiocarcinoma, but it does not cause hemoptysis.

Question 943: What is the most common route of transmission for Toxoplasma gondii in adults?

A. Transmission through blood transfusion
B. Ingestion of undercooked meat containing tissue cysts (Correct Answer)
C. Congenital transmission from mother to fetus
D. Fecal-oral transmission via contaminated cat feces

Explanation: ***Ingestion of undercooked meat containing tissue cysts*** - Consuming **undercooked or raw meat** (especially pork and lamb) containing **tissue cysts (bradyzoites)** is the **most common route** of *Toxoplasma gondii* transmission in adults in most countries - These cysts are highly resistant and survive digestion, releasing bradyzoites that cause systemic infection - This accounts for **30-63%** of infections in various populations *Fecal-oral transmission via contaminated cat feces* - Contact with **oocysts** from cat feces (in litter boxes, contaminated soil/water) is an important route - However, it's less common than meat consumption in most developed countries - Oocysts require 1-5 days to sporulate and become infective *Transmission through blood transfusion* - **Rare route** - tachyzoites have short survival in stored blood - Modern screening practices have made this extremely uncommon - Not a significant transmission route in general populations *Congenital transmission from mother to fetus* - Occurs when **primary maternal infection** happens during pregnancy - Important clinically but represents a small proportion of total infections - Does not apply to adult acquisition of infection

Question 944: Route of transmission of toxoplasmosis is:

A. Oral (Correct Answer)
B. Blood
C. Urine
D. Respiratory

Explanation: ***Correct: Oral*** - **Primary route of transmission** for toxoplasmosis - Ingestion of **oocysts from cat feces** in contaminated soil, water, or food - Consumption of **undercooked meat** containing tissue cysts (especially pork, lamb, venison) - Ingestion of **contaminated unwashed vegetables or fruits** *Incorrect: Fecal* - Toxoplasmosis is not transmitted by fecal-oral route in the traditional sense (human-to-human) - Only **cat feces contain infective oocysts**, and transmission occurs through oral ingestion, not direct fecal contact *Incorrect: Blood* - Though rare, transmission via **blood transfusion** and **organ transplantation** is documented - Not a common route; screening helps prevent this - The question asks for the primary route *Incorrect: Urine* - Toxoplasma gondii is **not transmitted through urine** - Not a recognized route of transmission **Note:** **Congenital transmission** (transplacental) is another major route, causing severe disease in the fetus when primary maternal infection occurs during pregnancy.

Question 945: Tsetse fly transmits:

A. Trypanosoma brucei (Correct Answer)
B. T. cruzi
C. Leishmania donovani
D. Leishmania tropica

Explanation: ***Trypanosoma brucei*** - The **tsetse fly** (genus *Glossina*) is the biological vector for **African trypanosomiasis**, caused by *Trypanosoma brucei*. - This parasite is responsible for **sleeping sickness** in humans and **nagana** in livestock. *T. cruzi* - *Trypanosoma cruzi* is the causative agent of **Chagas disease** (American trypanosomiasis). - It is primarily transmitted by **reduviid bugs** (also known as kissing bugs or assassin bugs), not tsetse flies. *Leishmania donovani* - *Leishmania donovani* causes **visceral leishmaniasis** (kala-azar), a severe systemic infection. - Its transmission occurs through the bite of infected **sandflies**, specifically of the genus *Phlebotomus*. *Leishmania tropica* - *Leishmania tropica* causes **cutaneous leishmaniasis** (oriental sore), a localized skin infection. - Like *L. donovani*, it is transmitted by the bite of infected **sandflies**.

Question 946: Man is a definitive host of which parasite?

A. Taenia solium
B. Plasmodium
C. Wuchereria bancrofti (Correct Answer)
D. Taenia saginata

Explanation: ***Wuchereria bancrofti*** - Humans are the **only definitive host** for *Wuchereria bancrofti*, where adult worms reside in the **lymphatic system** and undergo **sexual reproduction**. - The parasite causes **lymphatic filariasis**, leading to conditions like **elephantiasis** and **hydrocele**. - The **microfilariae** (larval stage) circulate in blood and are transmitted by mosquito vectors (intermediate hosts). *Plasmodium* - Humans are the **intermediate host** for *Plasmodium* species that cause malaria. - The **sexual reproductive cycle** (definitive host stage) occurs in the **Anopheles mosquito**, not in humans. - Humans harbor the **asexual stages** (liver schizonts and blood-stage merozoites). *Taenia solium* - Humans can be **either** the definitive host (harboring adult tapeworms in the intestine) **or** an intermediate host (developing **cysticercosis** from ingesting eggs). - This dual role makes it less representative of a parasite where humans are exclusively the definitive host. *Taenia saginata* - Humans are the **definitive host** for *Taenia saginata* (beef tapeworm) in the small intestine. - However, unlike *Wuchereria bancrofti*, cattle serve as the intermediate host in the life cycle. - *Wuchereria bancrofti* is the more commonly cited example in parasitology for human definitive host status.

Question 947: Which larvae infect humans by penetrating through the skin?

A. Ancylostoma duodenale (Correct Answer)
B. Ascaris lumbricoides
C. Trichinella spiralis
D. Enterobius vermicularis

Explanation: ***Ancylostoma duodenale*** - The **filariform larvae** (L3) of *Ancylostoma duodenale*, a **hookworm**, are capable of penetrating intact **human skin**, typically through the feet. - This penetration is how the infection initially establishes in the host, leading to a migratory phase through the circulatory and respiratory systems. *Ascaris lumbricoides* - Humans become infected with *Ascaris lumbricoides* by ingesting **embryonated eggs**, usually through contaminated food or water. - The larvae hatch in the small intestine and then embark on a **lung migration phase**, but they do not penetrate the skin to initiate infection. *Trichinella spiralis* - Infection with *Trichinella spiralis* occurs by consuming undercooked meat, particularly **pork**, containing infectious cysts. - The larvae are released in the stomach and small intestine, then migrate throughout the body to encyst in muscle tissue, without a skin penetration stage. *Enterobius vermicularis* - Humans acquire *Enterobius vermicularis* (pinworm) infection by ingesting the **embryonated eggs**, often through **self-ingestion** due to perianal itching or contact with contaminated surfaces. - The life cycle is direct and does not involve larval penetration of the skin.

Question 948: Which of the following stages of the life cycle of Plasmodium is seen in humans?

A. Sporogonic phase (mosquito stage)
B. Oocyst stage (mosquito stage)
C. Asexual reproduction (Schizogony in humans) (Correct Answer)
D. Sexual reproduction (occurs in humans)

Explanation: ***Asexual reproduction (Schizogony in humans)*** - The **human host** experiences the asexual reproductive cycle of Plasmodium, which involves the formation of **merozoites** through schizogony in both liver cells and red blood cells. - This stage is responsible for the clinical manifestations of **malaria** as red blood cells are lysed, releasing new merozoites and toxins. *Sporogonic phase (mosquito stage)* - The sporogonic phase is a **sexual reproductive stage** that occurs exclusively within the **Anopheles mosquito**, the definitive host. - During this phase, **sporozoites** develop within the oocysts in the mosquito's gut, which are then transmitted to humans. *Oocyst stage (mosquito stage)* - **Oocysts** are formed in the midgut of the **Anopheles mosquito** after the fertilization of male and female gametes. - This stage is crucial for the development of **sporozoites** but does not occur within the human body. *Sexual reproduction (occurs in humans)* - Sexual reproduction, involving the fusion of gametes, takes place in the **mosquito's gut**, not in humans. - In humans, **gametocytes** are formed, which are then ingested by the mosquito to continue the sexual cycle.

Question 949: Which form of the malarial parasite is present in the saliva of an infective mosquito?

A. Ring form
B. Schizont
C. Gametocyte
D. Sporozoite (Correct Answer)

Explanation: ***Sporozoite*** - **Sporozoites** are the infective stage of the malarial parasite that reside in the **salivary glands** of the *Anopheles* mosquito. - When an infected mosquito bites a human, these **sporozoites** are injected into the bloodstream, initiating the infection. *Ring form* - The **ring form** is an early **trophozoite stage** found within **red blood cells** in the human host, typically seen after the exoerythrocytic cycle. - This stage is not present in the mosquito's saliva. *Schizont* - A **schizont** is a stage of asexual reproduction where the parasite multiplies inside a host cell, such as **liver cells** or **red blood cells**, forming many merozoites. - This stage is part of the human infection cycle, not present in the mosquito's saliva. *Gametocyte* - **Gametocytes** are the sexual stages of the parasite that develop in **human red blood cells** and are ingested by a mosquito during a blood meal. - These forms develop into gametes within the mosquito gut, but gametocytes themselves are not the infective form transmitted to humans.

Question 950: Romana's sign is seen in:

A. Trypanosoma brucei
B. Loa loa
C. Wuchereria
D. Trypanosoma cruzi (Correct Answer)

Explanation: ***Trypanosoma cruzi*** - **Romana's sign** is a characteristic unilateral painless **periorbital swelling** (oedema) that occurs in the acute phase of **Chagas disease**, caused by **Trypanosoma cruzi**. - It is a classic clinical manifestation indicating an **inoculation chagoma** (a localized inflammatory response) due to the parasite entering the body through the conjunctiva, often after being deposited by the **reduviid bug's feces**. *Trypanosoma brucei* - **Trypanosoma brucei** is the causative agent of **African sleeping sickness**, and its bite causes a **tsetse chancre**, not Romana's sign. - The illness is characterized by **fever**, **headaches**, joint pains, and eventually **neurological symptoms** (sleeping sickness) as the parasite invades the central nervous system. *Loa loa* - **Loa loa** causes **loiasis**, characterized by **Calabar swellings** (transient subcutaneous oedema) and the migration of adult worms across the **conjunctiva** (eye worm). - It is transmitted by **deerflies** (Chrysops species) and does not present with Romana's sign. *Wuchereria* - **Wuchereria bancrofti** and **Brugia malayi** cause **lymphatic filariasis**, leading to **lymphoedema** and **elephantiasis**. - These parasites are transmitted by mosquitoes and do not cause Romana's sign.

Practice by Chapter

Classification of Parasites

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Intestinal Protozoa

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Blood and Tissue Protozoa

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Malaria Parasites

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Leishmaniasis

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Intestinal Helminths: Nematodes

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Tissue Nematodes

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Trematodes

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Cestodes

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Ectoparasites

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Antiparasitic Drugs

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Laboratory Diagnosis of Parasitic Infections

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