Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 921: Unsegmented eggs are in which parasite?

A. Ancylostoma
B. Necator americanus
C. Dracunculus
D. Trichuris trichiura (Correct Answer)

Explanation: ***Trichuris trichiura*** - *Trichuris trichiura* (whipworm) eggs are typically **unembryonated** or **unsegmented** when passed in feces. - Upon defecation, the eggs require a period of **development in soil** to become infective. *Ancylostoma* - **Hookworm (Ancylostoma)** eggs are typically **segmented** (possessing a 2-8 cell stage) when passed in feces. - They develop into **rhabditiform larvae** in the soil. *Necator americanus* - **Hookworm (Necator americanus)** eggs are also typically **segmented** (possessing a 2-8 cell stage) when passed in feces. - Like *Ancylostoma*, they require further development in soil to become infective. *Dracunculus* - *Dracunculus medinensis* (Guinea worm) does not lay eggs; instead, it releases **larvae** from the skin blister of the host into water. - The larvae are then ingested by **cyclops** (copepods) to continue their life cycle.

Question 922: Congenital toxoplasmosis: False is

A. Diagnosed by detection of IgM in cord blood
B. Dye test is gold standard for IgG
C. IgA is more sensitive than IgM for detection (Correct Answer)
D. Avidity testing is used to date the time of maternal infection

Explanation: ***IgA is more sensitive than IgM for detection*** - This statement is **FALSE** - IgM and IgA have **similar sensitivity** (both around 20-30%) for detecting congenital toxoplasmosis - While IgA may persist longer than IgM, it is not definitively "more sensitive" for initial detection - Both tests are often used together to improve diagnostic accuracy in neonates *Diagnosed by detection of IgM in cord blood* - This is **TRUE** - detection of specific IgM antibodies in cord blood or neonatal serum is a standard diagnostic method - However, sensitivity is limited (20-30%), so negative IgM does not rule out infection - IgM does not cross the placenta, so its presence indicates fetal infection *Dye test is gold standard for IgG* - This is **TRUE** - the **Sabin-Feldman dye test** is the gold standard serological test for detecting IgG antibodies against *Toxoplasma gondii* - In newborns, maternal IgG crosses the placenta, so IgG alone cannot confirm congenital infection - Serial testing showing persistent or rising IgG titers beyond 12 months suggests congenital infection *Avidity testing is used to date the time of maternal infection* - This is **TRUE** - **IgG avidity testing** measures the binding strength of IgG antibodies - Low avidity indicates recent infection (within 3-4 months), high avidity suggests infection occurred >4 months ago - This helps assess the risk of congenital transmission by determining if maternal infection occurred during pregnancy

Question 923: Which organism is characterized by the Maltese cross formation?

A. Babesia microti (Correct Answer)
B. Penicillium marneffei
C. Cryptococcus neoformans
D. Blastomyces dermatitidis

Explanation: ***Babesia microti*** - The **Maltese cross formation** is a characteristic intraerythrocytic tetrad of merozoites, pathognomonic for *Babesia microti* infection in stained blood smears. - This formation is crucial for the microscopic diagnosis of **babesiosis**, a tick-borne parasitic disease. *Penicillium marneffei* - This is a **thermally dimorphic fungus** endemic to Southeast Asia, causing disseminated infections. - It is known for its intracellular yeast-like cells that reproduce by **fission**, not by forming Maltese crosses. *Cryptococcus neoformans* - This organism is a **yeast** known for its **polysaccharide capsule**, which is visualized with India ink stain. - It typically causes **meningitis** and pulmonary infections, especially in immunocompromised individuals, and does not form Maltese crosses. *Blastomyces dermatitidis* - This is a **dimorphic fungus** that causes **blastomycosis**, primarily affecting the lungs and skin. - It is characterized by relatively large, **broad-based budding yeast cells** in tissue samples and does not form Maltese crosses.

Question 924: Which infection is most commonly associated with causing blindness in adult men?

A. Chlamydia trachomatis (Correct Answer)
B. Toxoplasma gondii
C. Onchocerca volvulus
D. Treponema pallidum

Explanation: ***Chlamydia trachomatis*** - *Chlamydia trachomatis* causes **trachoma**, which is the **leading infectious cause of preventable blindness worldwide** - Repeated childhood infections lead to chronic inflammation, **conjunctival scarring**, **trichiasis** (inturned eyelashes), and **corneal opacification** that manifests as **blindness in adulthood** - While initial infections occur in children, the blinding complications typically present in **adults**, particularly in endemic areas with poor sanitation - Approximately **1.9 million people are visually impaired or blind** due to trachoma globally *Toxoplasma gondii* - Causes **ocular toxoplasmosis** with chorioretinitis and can lead to retinal scarring - More common in **immunocompromised individuals** and congenital infections - While it causes significant ocular morbidity, it is **not the most common** infectious cause of blindness in adults globally - Usually presents as focal retinal lesions rather than causing complete blindness *Onchocerca volvulus* - Causes **onchocerciasis** (river blindness), the **second leading infectious cause** of blindness worldwide - Particularly affects **adult men** due to occupational exposure near fast-flowing rivers in endemic areas (sub-Saharan Africa, Yemen, Latin America) - Causes **keratitis**, **chorioretinitis**, and **optic atrophy** leading to irreversible blindness - While highly significant in endemic regions, trachoma has greater global prevalence *Treponema pallidum* - Causes **syphilis** with potential ocular manifestations including uveitis, retinitis, and optic neuritis - Ocular syphilis can cause vision loss if untreated - However, it is **much less common** as a cause of blindness compared to trachoma or onchocerciasis - With modern antibiotic treatment, syphilitic blindness is rare

Question 925: Which of the following is a trematode?

A. Diphyllobothrium latum
B. Taenia saginata
C. Echinococcus granulosus
D. Schistosoma mansoni (Correct Answer)

Explanation: ***Schistosoma mansoni*** - This is a genus of **trematodes**, commonly known as blood flukes, which cause **schistosomiasis**. - Trematodes are characterized by their **leaf-like body shape** and often complex life cycles involving intermediate hosts like snails. *Diphyllobothrium latum* - This is a **cestode**, or tapeworm, known as the broad fish tapeworm. - Cestodes are typically **segmented flatworms** with a scolex, distinct from the unsegmented body of a trematode. *Taenia saginata* - This is another example of a **cestode**, specifically the beef tapeworm. - Like other cestodes, it has a **scolex and proglottids**, which are absent in trematodes. *Echinococcus granulosus* - This is a **cestode** that causes **hydatid disease** in humans. - It is a small tapeworm, and its larval stage forms **hydatid cysts**, which is a characteristic feature of cestodes.

Question 926: Which of the following is NOT an intermediate host for Toxoplasma gondii?

A. Sheep
B. Human
C. Cat (Correct Answer)
D. Pig

Explanation: ***Correct: Cat*** - Cats are the **definitive hosts** for *Toxoplasma gondii*, not intermediate hosts - The parasite completes its **sexual life cycle** in cat intestines and produces oocysts - Oocysts are shed in cat feces and contaminate the environment - Definitive host = where sexual reproduction occurs *Incorrect: Human* - Humans are **intermediate hosts** for *Toxoplasma gondii* - Infection occurs by ingesting oocysts (from cat feces, contaminated soil/food) or tissue cysts (from undercooked meat) - The parasite forms **tissue cysts** in muscle and brain but does NOT undergo sexual reproduction *Incorrect: Sheep* - Sheep are common **intermediate hosts** for *Toxoplasma gondii* - They become infected by ingesting oocysts from contaminated environment - The parasite forms **tissue cysts** in their meat, which can transmit infection to humans or cats if consumed *Incorrect: Pig* - Pigs are **intermediate hosts** for *Toxoplasma gondii* - Infection acquired by ingesting oocysts from the environment - Parasite forms **tissue cysts** in muscle tissue, making undercooked pork a source of human infection

Question 927: Which organism is responsible for causing malignant hydatid cysts?

A. Echinococcus granulosus
B. E. multilocularis (Correct Answer)
C. E. vogeli
D. E. oligarthus

Explanation: ***E. multilocularis*** - This species causes **alveolar echinococcosis**, characterized by the formation of **multiloculated, infiltrative cysts** that behave like a malignant tumor. - The parasitic lesions have a highly invasive nature, often spreading to adjacent tissues and forming **metastatic foci**, primarily in the liver. *Echinococcus granulosus* - This species is responsible for **cystic echinococcosis**, which typically presents as **unilocular, slow-growing cysts**. - While cysts can be large and cause significant morbidity, they are generally **well-encapsulated** and do not exhibit the same infiltrative, malignant-like growth pattern as *E. multilocularis*. *E. vogeli* - This species causes **polycystic echinococcosis**, which involves the formation of multiple, interconnected cysts, primarily in the liver, but it lacks the infiltrative and metastatic potential seen with *E. multilocularis*. - Infections are rare and typically found in Central and South America. *E. oligarthus* - This species causes **polycystic echinococcosis** similar to *E. vogeli*, but it is even rarer and primarily affects wild felids as definitive hosts. - Human infections are extremely uncommon and do not typically present with malignant-like cystic growth.

Question 928: Which of the following parasites passes through three hosts?

A. Fasciola hepatica
B. Schistosoma haematobium
C. Clonorchis sinensis (Correct Answer)
D. Fasciolopsis buski

Explanation: ***Clonorchis sinensis*** - *Clonorchis sinensis* (the Chinese liver fluke) requires **three hosts** to complete its life cycle: a **snail** (first intermediate host), a **freshwater fish** (second intermediate host), and a **mammalian definitive host** (e.g., humans). - Humans acquire the infection by consuming undercooked infected fish, where the **metacercariae** excyst in the duodenum and migrate to the biliary ducts. *Fasciola hepatica* - *Fasciola hepatica* (the common liver fluke) is a **two-host parasite**, requiring a **snail** as the intermediate host and a **mammalian herbivore** (or human) as the definitive host. - Humans are infected by ingesting **metacercariae** on contaminated aquatic vegetation. *Fasciolopsis buski* - *Fasciolopsis buski* (the giant intestinal fluke) is a **two-host parasite**, with freshwater **snails** acting as the intermediate host and **pigs and humans** as definitive hosts. - Infection occurs when humans consume raw or undercooked aquatic plants contaminated with **metacercariae**. *Schistosoma haematobium* - *Schistosoma haematobium* (the urinary blood fluke) is a **two-host parasite**, requiring an aquatic **snail** as the intermediate host and **humans** as the definitive host. - Infection is acquired through contact with fresh water containing **cercariae**, which penetrate the skin.

Question 929: Which of the following organisms produces acid-fast oocysts that exhibit autofluorescence under UV light?

A. Cryptosporidium
B. Isospora
C. Cyclospora (Correct Answer)
D. Giardia

Explanation: ***Cyclospora*** - **Cyclospora cayetanensis** oocysts are **acid-fast** and exhibit characteristic **blue autofluorescence under UV light (365 nm)**, which is a distinctive diagnostic feature. - They are spherical, 8-10 µm in diameter, and contain two sporocysts (visible after sporulation). - The autofluorescence property is unique to Cyclospora and helps differentiate it from other acid-fast coccidian parasites. *Cryptosporidium* - **Cryptosporidium parvum** produces **acid-fast oocysts** (4-6 µm), but they **do not exhibit autofluorescence**. - These smaller oocysts stain uniformly with modified acid-fast stain (pink-red) but lack the UV fluorescence characteristic of Cyclospora. *Isospora* - **Isospora (Cystoisospora) belli** produces large, ellipsoidal **acid-fast oocysts** (20-30 µm), but they **do not show autofluorescence**. - Their characteristic elongated shape and larger size help differentiate them, but UV fluorescence is absent. *Giardia* - **Giardia lamblia** produces cysts that are **not acid-fast** and do not exhibit autofluorescence. - Giardia cysts are identified using iodine staining, showing their characteristic oval shape with internal nuclei and median bodies.

Question 930: Which of the following is the most characteristic diagnostic feature of the trophozoites of Entamoeba histolytica?

A. Shows erythrophagocytosis (Correct Answer)
B. Has a central karyosome
C. Nuclear membrane with chromatin
D. Presence of bacteria outside the cell

Explanation: ***Shows erythrophagocytosis*** - The presence of **engulfed red blood cells** within the cytoplasm (**erythrophagocytosis**) is the **pathognomonic and most diagnostic feature** of **Entamoeba histolytica** trophozoites. - This indicates the amoeba's invasive nature and its ability to damage host tissues, leading to symptoms like **dysentery**. - This feature distinguishes it from non-pathogenic amoebae like *E. dispar* and *E. coli*. *Has a central karyosome* - **Entamoeba histolytica** does have a **small, dot-like, centrally located karyosome** within its nucleus. - However, this feature alone is **not diagnostic** as it is shared with *E. dispar*, which is morphologically identical but non-pathogenic. - Differentiation requires molecular methods or identification of erythrophagocytosis. *Nuclear membrane with chromatin* - **Entamoeba histolytica** trophozoites do have **fine, uniform peripheral chromatin** along the nuclear membrane. - While this is a correct morphological feature, it is **not pathognomonic** and is also present in *E. dispar*. - This helps differentiate from *E. coli* (which has coarse, clumped chromatin) but not from other *Entamoeba* species. *Presence of bacteria outside the cell* - The presence of bacteria outside the cell is an **environmental factor**, not a morphological feature of the trophozoite. - **Entamoeba histolytica** rarely ingests bacteria, preferring red blood cells and host tissue. - In contrast, non-pathogenic *E. coli* commonly ingests bacteria, which can be a distinguishing feature.

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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