Parasitology — MCQs
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Which of the following does not penetrate the skin?
Which worm can reach the longest length?
Which of the following is seen encysted in skeletal muscle of humans?
Cerebral malaria is primarily caused by which of the following?
Which parasite is most characteristically known for its larval forms residing primarily in muscle tissue?
Parasitology Indian Medical PG Practice Questions and MCQs
Question 961: Which of the following does not penetrate the skin?
- A. Necator americanus
- B. Strongyloides stercoralis
- C. Taenia saginata (Correct Answer)
- D. Ancylostoma duodenale
Explanation: ***Taenia saginata*** - *Taenia saginata*, the **beef tapeworm**, is acquired by consuming **undercooked beef** containing infective cysts (cysticerci). - Its life cycle does not involve larval penetration of the skin; instead, infection occurs via the **oral route**. *Necator americanus* - *Necator americanus*, also known as the **New World hookworm**, typically infects humans through **skin penetration** by filariform larvae. - The larvae are often found in **contaminated soil** and penetrate the skin, usually of the feet. *Strongyloides stercoralis* - *Strongyloides stercoralis* larvae can penetrate unbroken skin, establishing infection through this route. - It is unique among intestinal nematodes for its ability to cause **autoinfection**, where larvae mature within the host and reinfect without leaving the host. *Ancylostoma duodenale* - *Ancylostoma duodenale*, the **Old World hookworm**, also infects humans when its **filariform larvae** penetrate intact skin, primarily from contact with contaminated soil. - These larvae then migrate through the bloodstream to the lungs and are eventually swallowed to mature in the intestines.
Question 962: Which worm can reach the longest length?
- A. T. Saginata (Correct Answer)
- B. Hookworm
- C. A. Lumbricoides
- D. T. solium
Explanation: ***T. Saginata*** - The **beef tapeworm**, *Taenia saginata*, can reach impressive lengths of up to **25 meters** in the human intestine. - Its long, ribbon-like body consists of thousands of proglottids, each containing reproductive organs, allowing for extensive growth. *Hookworm* - Hookworms, such as *Ancylostoma duodenale* and *Necator americanus*, are relatively small, typically measuring only **0.8 to 1.3 cm**. - They are known for causing **iron deficiency anemia** due to chronic blood loss. *A. Lumbricoides* - *Ascaris lumbricoides*, the **giant intestinal roundworm**, is the largest intestinal nematode, but its maximum length is around **35-40 cm**. - While significant, this is considerably shorter than the tapeworm *T. saginata*. *T. solium* - *Taenia solium*, the **pork tapeworm**, typically reaches lengths of **2 to 8 meters**. - While long, it is generally **shorter than *T. saginata*** and is medically significant due to the risk of **neurocysticercosis**.
Question 963: Which of the following is seen encysted in skeletal muscle of humans?
- A. Trichinella spiralis (Correct Answer)
- B. Entamoeba histolytica
- C. Leishmania spp.
- D. Toxoplasma gondii
Explanation: ***Trichinella spiralis*** - This nematode causes **trichinellosis**, with its larvae forming the **classic encysted form** in **skeletal muscle** of humans. - The larvae form a distinctive **nurse cell-larva complex** in striated muscle, which is the **pathognomonic feature** of trichinellosis. - Ingestion of undercooked meat (especially pork) containing these **encysted larvae** is the primary mode of transmission. - This is the **textbook example** of skeletal muscle encystation in parasitology. *Entamoeba histolytica* - This is an **intestinal amoeba** that causes **amoebiasis**, affecting the colon and potentially leading to liver abscesses. - It does not encyst in skeletal muscle but forms **cysts** in the intestinal lumen for fecal-oral transmission. *Leishmania spp.* - These are **intracellular parasites** transmitted by **sandflies**, causing various forms of **leishmaniasis**. - They primarily infect **macrophages** in skin, mucous membranes, or visceral organs (liver, spleen), not skeletal muscle. *Toxoplasma gondii* - While this parasite can form **tissue cysts** containing bradyzoites in skeletal muscle, brain, and heart, skeletal muscle is **not its characteristic location**. - The **classic site** for *Toxoplasma* cysts is the **brain** (causing encephalitis in immunocompromised patients). - Unlike *Trichinella*, *Toxoplasma* muscle cysts are not the primary diagnostic or clinical feature of the infection.
Question 964: Cerebral malaria is primarily caused by which of the following?
- A. P. falciparum (Correct Answer)
- B. P. vivax
- C. P. ovale
- D. P. malariae
Explanation: ***P. falciparum*** - **P. falciparum** is the most virulent species of malaria parasites and is responsible for almost all cases of **severe malaria**, including cerebral malaria. - Its ability to cause **sequestration** of infected red blood cells in the microvasculature of the brain leads to impaired blood flow and neurological complications. - Accounts for **>90% of cerebral malaria cases** worldwide. *P. vivax* - While *P. vivax* can cause severe disease, it is generally **less virulent** than *P. falciparum* and rarely causes cerebral malaria. - *P. vivax* primarily causes benign tertian malaria and is known for its ability to form **hypnozoites** in the liver, leading to relapses. *P. ovale* - *P. ovale* is the **least common** form of human malaria and causes a mild form of the disease with symptoms similar to *P. vivax*. - It is **not associated** with severe complications like cerebral malaria. - Also forms **hypnozoites** and can cause relapses. *P. malariae* - *P. malariae* causes **quartan malaria** (72-hour fever cycle) and is the mildest form of human malaria. - It is **not associated** with cerebral malaria but can cause chronic infection and **nephrotic syndrome** in long-standing cases.
Question 965: Which parasite is most characteristically known for its larval forms residing primarily in muscle tissue?
- A. Taenia solium
- B. Echinococcus granulosus
- C. Trichinella spiralis (Correct Answer)
- D. All of the options
Explanation: ***Trichinella spiralis*** - This parasite is renowned for its **larval forms** that encyst primarily in **striated muscle tissue** of its hosts, causing trichinosis. - Humans typically acquire the infection by consuming **undercooked meat**, especially pork and wild game, containing these encysted larvae. *Taenia solium* - While *Taenia solium* can cause **cysticercosis** in humans, where larvae (cysticerci) encyst in tissues, their primary target is often the **central nervous system**, eyes, and subcutaneous tissue, rather than muscle as the predominant site. - Infection occurs by ingesting *T. solium* **eggs**, not larvae in meat, and pigs serve as the intermediate host for muscle cyst formation. *Echinococcus granulosus* - This parasite causes **hydatid disease** where large cysts (hydatid cysts) develop, most commonly in the **liver** and **lungs**, although they can occur in other organs. - The disease is acquired by ingesting **eggs** from dog feces, and the larval stage does not primarily reside in muscle tissue. *All of the options* - This option is incorrect because while *Taenia solium* and *Echinococcus granulosus* have larval stages that can reside in various tissues, only **Trichinella spiralis** is primarily characterized by its larvae encysting in muscle tissue.
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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