Parasitology Practice Questions

Q: What is the primary reservoir of protozoan infection caused by Toxoplasma gondii in relation to human infection?

Cats. ***Cats*** - **Cats** are the definitive host for *Toxoplasma gondii*, meaning the parasite can complete its sexual life cycle only within felines. - They shed **oocysts** in their feces, which are highly infectious and a primary source of human infection. *Dogs* - Dogs can become infected with *T. gondii* by eating infected tissues, but they do not excrete infectious **oocysts** and are therefore not significant in human transmission. - They are considered an intermediate host, similar to humans, not a primary reservoir. *Rats* - **Rats** (and other rodents) are intermediate hosts for *T. gondii*, typically getting infected by ingesting oocysts. - They can transmit the infection to cats when cats prey on them, but they do not directly transmit the parasite to humans as a primary reservoir. *Sheep* - **Sheep** are also intermediate hosts for *T. gondii*, often becoming infected by grazing on contaminated pastures. - Humans can acquire the infection by consuming undercooked meat from infected sheep, but sheep themselves do not shed oocysts and are not the primary reservoir.

Q: Kala azar is transmitted by:

Sandfly. ***Sandfly*** - **Kala azar**, also known as **visceral leishmaniasis**, is a severe parasitic disease caused by **Leishmania donovani**. - This parasite is transmitted to humans through the bite of an infected female **phlebotomine sandfly**. *Tse tse fly* - The **tse tse fly** is the vector for **African trypanosomiasis**, also known as **sleeping sickness**. - It transmits **Trypanosoma brucei**, a different parasitic organism than the one causing kala azar. *Hard tick* - **Hard ticks** are vectors for several diseases, including **Lyme disease** (Borrelia burgdorferi), **Rocky Mountain spotted fever** (Rickettsia rickettsii), and **anaplasmosis**. - They are not associated with the transmission of leishmaniasis. *Culex mosquito* - The **Culex mosquito** is a common vector for diseases such as **West Nile virus**, **Japanese encephalitis**, and **filariasis**. - It does not transmit the **Leishmania parasite** responsible for kala azar.

Q: Which Plasmodium species is known for causing severe malaria with rapid multiplication of infected red blood cells?

Plasmodium falciparum. ***Plasmodium falciparum*** - This species is responsible for the most severe forms of malaria, including **cerebral malaria**, due to its ability to infect red blood cells of all ages. - It exhibits **rapid asexual multiplication**, leading to a high parasitic load and significant erythrocyte destruction. *Plasmodium ovale* - This species typically causes a relatively **mild form of malaria** and can remain dormant in the liver as **hypnozoites**. - It primarily infects **young, enlarged red blood cells** and has a lower parasitic burden compared to *P. falciparum*. *Plasmodium vivax* - While it can also cause **recurrent infections** (due to hypnozoites), *P. vivax* usually leads to less severe disease than *P. falciparum*. - It predominantly infects **reticulocytes (young red blood cells)**, which limits the overall parasitic load. *Plasmodium malariae* - Known for causing **quartan malaria**, characterized by a 72-hour fever cycle, and can lead to **nephrotic syndrome**. - It primarily infects **older, senescent red blood cells** and has the lowest parasitic multiplication rate among the human *Plasmodium* species.

Q: What is the most common trophozoite infection transmitted by sexual intercourse?

Trichomonas vaginalis. ***Trichomonas vaginalis*** (Correct Answer) - *T. vaginalis* is a **flagellated protozoan** which exists only in the **trophozoite stage** and is the most common non-viral sexually transmitted infection globally. - It causes **trichomoniasis**, an infection of the urogenital tract, characterized by vaginitis in women and often asymptomatic urethritis in men. - As a trophozoite infection transmitted sexually, it perfectly fits the question criteria. *Entamoeba histolytica* (Incorrect) - This protozoan causes **amoebiasis**, an intestinal infection typically transmitted via the **fecal-oral route** through contaminated food or water, not sexual intercourse. - While it does exist as a **trophozoite**, it is not sexually transmitted. - It exists in both trophozoite and **cyst** forms, with cysts being the infectious stage. *Treponema pallidum* (Incorrect) - This is a **bacterium** (spirochete), not a trophozoite or protozoan, and it is the causative agent of **syphilis**. - While it is sexually transmitted, it does not fit the description of a trophozoite infection. *Giardia intestinalis* (Incorrect) - *Giardia intestinalis* (also known as **Giardia lamblia**) causes **giardiasis**, an intestinal infection typically transmitted via the **fecal-oral route** through contaminated water or food. - While it exists as **trophozoites** and cysts, it is not primarily a sexually transmitted infection. - Sexual transmission can rarely occur through oral-anal contact, but this is not the primary route.

Q: Which of the following is not typically seen in the peripheral smear of Plasmodium falciparum infection?

Schizonts. ***Schizonts*** - While present in the life cycle, **mature schizonts** (containing merozoites) of *P. falciparum* are usually sequestered in **deep tissues** and are not commonly seen in large numbers in peripheral blood smears. - Their absence in a typical peripheral smear is a key diagnostic feature differentiating *P. falciparum* from other *Plasmodium* species. *Maurer's dots* - **Maurer's dots** (large, irregular clefts and stippling) are prominent diagnostic features observed in the red blood cells infected with **late trophozoites** and young schizonts of *Plasmodium falciparum*. - They represent rough endoplasmic reticulum and ribosomes modified by the parasite within the host red blood cell. *Accolé* - The **accolé** or **appliqué form** refers to rings of *P. falciparum* that appear flattened and closely applied to the periphery of the red blood cell. - This characteristic morphology is frequently observed in **young ring forms** of *P. falciparum* and is a useful diagnostic feature on peripheral smears. *Banana-shaped gametocytes* - **Banana-shaped** or **crescent-shaped gametocytes** are the hallmark diagnostic feature of *Plasmodium falciparum* on a peripheral blood smear. - These are the sexual stages of the parasite, and their unique morphology makes them easily identifiable.

Q: What is the investigation of choice for diagnosing amoebiasis?

Stool examination for cysts and trophozoites. **Stool examination for cysts and trophozoites** - **Direct microscopic examination** of fresh stool samples allows for the identification of *Entamoeba histolytica* **trophozoites** (in diarrheic stool) or **cysts** (in formed stool), which is crucial for diagnosis. - This method is **cost-effective** and readily available, making it the primary diagnostic approach for confirming the presence of the parasite. *Serological tests* - Serological tests like **ELISA** detect antibodies against *E. histolytica*, which can be helpful in diagnosing **extraintestinal amoebiasis** (e.g., amoebic liver abscess). - They are often not definitive for acute intestinal amoebiasis as antibodies may persist for a long time after infection or be absent in early stages. *Colonoscopy* - **Colonoscopy** with biopsy can visualize and sample **amoebic ulcers** in the colon, which can be useful in cases of severe dysentery or suspected colitis. - It is an **invasive procedure** and not the first-line investigation for routine diagnosis of amoebiasis, especially when stool examination is available. *Microscopy combined with serological tests* - While both can be used, **stool microscopy remains the gold standard** for diagnosing active intestinal infection. - The combination of **microscopy and serology** is generally employed in situations where intestinal amoebiasis is suspected but microscopy is repeatedly negative or when **extraintestinal amoebiasis** is suspected.

Q: What is the primary cause of malignant hydatid disease?

Infection with Echinococcus multilocularis. ***Infection with Echinococcus multilocularis*** - **Malignant hydatid disease** is specifically associated with *Echinococcus multilocularis*, which causes alveolar echinococcosis. - This parasite's larval stage grows in a highly **infiltrative** and **destructive** manner, resembling a malignant tumor, hence the term "malignant hydatid disease." *Malignant transformation of hydatid cysts* - Hydatid cysts themselves are parasitic structures and do not undergo **malignant transformation** in the conventional sense of human tissue developing cancer. - The term "malignant" in this context refers to the **aggressive growth pattern** of *E. multilocularis* rather than cellular anaplasia. *Hydatid disease in immunocompromised patients* - While immunocompromised individuals may experience more severe or disseminated hydatid disease, this does not directly cause the **"malignant" characteristic** of alveolar echinococcosis. - The inherent **aggressive growth** of *Echinococcus multilocularis* is the primary factor, regardless of host immune status. *Caused by Echinococcus granulosus* - *Echinococcus granulosus* causes **cystic echinococcosis** (CE), which typically forms unilocular cysts, often considered benign. - CE is generally less aggressive and does not exhibit the **infiltrative growth pattern** characteristic of "malignant hydatid disease" caused by *E. multilocularis*.

Q: A child is brought to you because of perianal itching, which has been disturbing the child's sleep. Examination reveals scaly skin in the perianal region. You instruct the parents to place transparent tape on the perianal region the next morning, and then return to you. Next day, the tape is transferred to a microscope slide, and low-power examination of the tape reveals oval eggs that are flattened along one side. What is the most likely cause?

Enterobius vermicularis (pinworm). ***Enterobius vermicularis (pinworm)*** - The classic presentation of **perianal itching**, especially disrupting sleep, combined with the finding of **oval eggs flattened on one side** via the **tape test**, is pathognomonic for *Enterobius vermicularis* infection. - Female pinworms migrate to the **perianal region at night** to lay eggs, causing intense pruritus. *Ancylostoma duodenale (hookworm)* - Hookworm infections typically cause **gastrointestinal symptoms** and **iron-deficiency anemia**, not primarily perianal itching. - Hookworm eggs are usually **oval**, thin-shelled, and contain **developing larvae**, but are not flattened on one side and are found in stool samples, not perianal tape tests. *Ascaris lumbricoides (roundworm)* - *Ascaris lumbricoides* infection often presents with **gastrointestinal and pulmonary symptoms** (due to larval migration). - Its eggs are typically **mammillated** (roughened outer shell) or smooth (decorticated) and are detected in **stool samples**, not through a perianal tape test. *Necator americanus (hookworm)* - Similar to *Ancylostoma duodenale*, *Necator americanus* causes **anemia** and **gastrointestinal issues** and is acquired through skin penetration. - Its eggs are morphologically similar to *Ancylostoma duodenale* eggs (thin-shelled, containing developing larvae), found in **stool**, and do not cause perianal itching or show the flattened morphology seen in pinworm.

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

Lectin. ***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 1

What is the primary reservoir of protozoan infection caused by Toxoplasma gondii in relation to human infection?

Accepted Answer

Cats

Answer

Dogs

Answer

Rats

Answer

Sheep

Question 2

Which one of the following statements is false?

Accepted Answer

A low iron content in the diet predisposes to invasive amoebiasis

Answer

Young adult males of low socioeconomic status are most commonly affected by invasive amoebiasis

Answer

The presence of ingested RBC is seen only in E. histolytica

Answer

The pathogenic and non-pathogenic strains of E. histolytica can be differentiated by the electrophoretic study of zymodemes

Question 3

Kala azar is transmitted by:

Accepted Answer

Sandfly

Answer

Tse tse fly

Answer

Hard tick

Answer

Culex mosquito

Question 4

Which Plasmodium species is known for causing severe malaria with rapid multiplication of infected red blood cells?

Accepted Answer

Plasmodium falciparum

Answer

Plasmodium ovale

Answer

Plasmodium vivax

Answer

Plasmodium malariae

Question 5

What is the most common trophozoite infection transmitted by sexual intercourse?

Accepted Answer

Trichomonas vaginalis

Answer

Entamoeba histolytica

Answer

Treponema pallidum

Answer

Giardia intestinalis

Question 6

Which of the following is not typically seen in the peripheral smear of Plasmodium falciparum infection?

Accepted Answer

Schizonts

Answer

Maurer's dot

Answer

Accole

Answer

Banana-shaped gametocytes

Question 7

What is the investigation of choice for diagnosing amoebiasis?

Accepted Answer

Stool examination for cysts and trophozoites

Answer

Serological tests

Answer

Colonoscopy

Answer

Microscopy combined with serological tests

Question 8

What is the primary cause of malignant hydatid disease?

Accepted Answer

Infection with Echinococcus multilocularis

Answer

Malignant transformation of hydatid cysts

Answer

Hydatid disease in immunocompromised patients

Answer

Caused by Echinococcus granulosus

Question 9

A child is brought to you because of perianal itching, which has been disturbing the child's sleep. Examination reveals scaly skin in the perianal region. You instruct the parents to place transparent tape on the perianal region the next morning, and then return to you. Next day, the tape is transferred to a microscope slide, and low-power examination of the tape reveals oval eggs that are flattened along one side. What is the most likely cause?

Accepted Answer

Enterobius vermicularis (pinworm)

Answer

Ancylostoma duodenale (hookworm)

Answer

Ascaris lumbricoides (roundworm)

Answer

Necator americanus (hookworm)

Question 10

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

Accepted Answer

Lectin

Answer

Fucose

Answer

Fibronectin

Answer

Collagen

Parasitology — MCQs

Parasitology — MCQs

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