Parasitology Practice Questions

Q: Schistosomiasis is transmitted by?

Snail. ***Snail*** - **Snails** act as the **intermediate host** for all species of Schistosoma, where the parasite undergoes asexual reproduction. - Humans become infected when they come into contact with water contaminated with **cercariae**, which are released from infected snails. *Cyclops* - **Cyclops** (a type of freshwater crustacean) are the intermediate hosts for parasites like **Dracunculus medinensis** (guinea worm) and **Diphyllobothrium latum** (fish tapeworm). - They are not involved in the life cycle or transmission of Schistosoma. *Fish* - Various fish can be intermediate hosts for parasites such as **Clonorchis sinensis** (Chinese liver fluke) or **Diphyllobothrium latum**. - Fish do not play a role in the transmission of schistosomiasis. *Cattle* - **Cattle** can serve as definitive hosts for certain parasites, such as **Taenia saginata** (beef tapeworm), where the larval stage (cysticerci) is found in their muscle tissue. - They are not involved in the life cycle or transmission of Schistosoma.

Q: What is the correct sequence of the sexual cycle in malaria?

Gametocytes to sporozoites. ***Gametocytes to sporozoites*** - The sexual cycle begins when a mosquito ingests **gametocytes** during a blood meal. - These gametocytes develop into **gametes**, which fuse to form a **zygote**. The zygote matures into an **oocyst** and then releases **sporozoites**, which migrate to the mosquito's salivary glands, ready to infect a new human host. *Gametocytes to gametes* - This is an initial step within the sexual cycle where gametocytes differentiate into **male and female gametes**, respectively. - However, it's not the complete *sequence* of the sexual cycle, as it omits subsequent crucial stages like fertilization and sporozoite formation. *Sporozoites to gametocytes* - **Sporozoites** are injected into a human host and initiate the asexual cycle by infecting liver cells, then red blood cells. - **Gametocytes** are formed later during the asexual cycle in the human host, ready to be picked up by another mosquito; this sequence describes part of the human infection, not the sexual cycle in the mosquito. *Gametes to zygote* - This step represents **fertilization**, where male and female gametes fuse, forming a **zygote** in the mosquito gut. - While essential, it is only one part of the overall sexual cycle and doesn't encompass the full transformation from gametocytes to infective sporozoites.

Q: The Hanging Drop method is primarily used for studying which of the following microorganisms?

Trichomonas vaginalis. ***Trichomonas vaginalis*** - The **hanging drop method** is excellent for observing the **motility** of this parasite, which is crucial for its identification due to its characteristic jerky, tumbling movement. - This method helps differentiate it from other non-motile organisms in vaginal fluid samples. *Plasmodium falciparum* - This parasite is primarily identified through examination of **blood smears** (thick and thin films) for its characteristic **intraerythrocytic stages** (rings, trophozoites, schizonts, gametocytes). - It is an **intracellular parasite** and does not exhibit free motility in a hanging drop preparation. *Toxoplasma gondii* - Diagnosis typically involves **serological tests** for antibodies or **PCR** for detecting parasitic DNA, as well as histological examination of tissue biopsies. - While it can move, it's an **obligate intracellular parasite** and is not primarily identified by its motility in a simple hanging drop preparation from clinical samples. *Cryptosporidium parvum* - This parasite is diagnosed by detecting its **oocysts in stool samples** using specialized staining techniques like **acid-fast stain** or immunofluorescence assays. - The oocysts are non-motile and are not identified using the hanging drop method.

Q: Congenital toxoplasmosis: False is

IgA is more sensitive than IgM for detection. ***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

Q: A 5-year-old child presented with fever, fatigue, abdominal pain, and vomiting. On further history evaluation, he had a habit of eating dog feces. Investigations show visceral larva migrans. Which animal is the most likely source of this infection in this child?

Dogs. ***Dogs*** - The history of eating **dog feces** directly links to the transmission of **Toxocara canis** eggs, the primary cause of visceral larva migrans. - Humans, especially children, can get infected by ingesting infective eggs from contaminated soil or dog feces. *Pig* - While pigs can harbor parasites like **Taenia solium** (pork tapeworm) and **Trichinella spiralis**, these do not typically cause visceral larva migrans. - Transmission from pigs usually involves consumption of undercooked pork, not direct contact with feces in the context of visceral larva migrans. *Monkeys* - Monkeys are not a common source of parasites causing human visceral larva migrans. - Parasitic infections associated with monkeys in humans are generally rare and usually specific to certain geographical contexts or exotic pet exposure. *Cows* - Cows can be hosts for parasites such as **Taenia saginata** (beef tapeworm), but they are not associated with visceral larva migrans caused by *Toxocara* species. - Ingestion of raw or undercooked beef is the typical mode of transmission for cow-related parasitic infections.

Q: Which organism is characterized by the Maltese cross formation?

Babesia microti. ***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.

Q: Which of the following is a trematode?

Schistosoma mansoni. ***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.

Q: Toxoplasmosis in the fetus can be best confirmed by:

IgM antibodies against toxoplasmosis in the fetus. ***IgM antibodies against toxoplasmosis in the fetus*** - The presence of **IgM antibodies** in the fetus indicates an **active fetal immune response** to *Toxoplasma gondii*, meaning the fetus is currently infected. - Maternal IgM does not cross the placenta, so fetal IgM is a reliable marker of **congenital infection**. *IgG antibodies against toxoplasmosis in the mother* - Maternal **IgG antibodies** indicate either current or past exposure to *Toxoplasma gondii* in the mother. - These antibodies **cross the placenta** and can be present in the fetal circulation without indicating an active fetal infection. *IgG antibodies against toxoplasmosis in the fetus* - Fetal **IgG antibodies** are usually of maternal origin, having crossed the placenta, and therefore do not confirm an active fetal infection. - A positive IgG in the fetus only confirms maternal exposure, not necessarily fetal infection, unless there is a **rising titer** or specific patterns suggesting production by the fetal immune system. *IgM antibodies against toxoplasmosis in the mother* - Maternal **IgM antibodies** suggest a recent primary *Toxoplasma* infection in the mother. - While this indicates a risk of congenital transmission, it does not directly confirm the presence of **fetal infection**.

Q: Which among the following statements about congenital toxoplasmosis is false?

IgG is diagnostic. ***IgG is diagnostic*** - **IgG antibodies** against *Toxoplasma gondii* cross the placenta from mother to fetus, so their presence in a neonate merely reflects maternal immunity rather than confirming congenital infection. - Therefore, the presence of IgG alone in a neonate is **NOT diagnostic** of congenital toxoplasmosis; specific tests like **IgG avidity testing** or demonstrating rising IgG titers over months are needed. - **This statement is FALSE.** *IgA is better than IgM for detection in neonates* - This statement is **TRUE** because **IgA antibodies** have superior sensitivity and specificity compared to IgM for diagnosing congenital toxoplasmosis. - IgA testing has fewer false positives and better diagnostic accuracy in neonates. - Both IgA and IgM can be used, but IgA is generally more reliable. *Congenital toxoplasmosis is diagnosed using serological tests* - This statement is **TRUE** as **serological testing** (IgM, IgA, IgG avidity) forms the cornerstone of diagnosis. - Combined with **PCR testing** of amniotic fluid or other specimens and clinical/radiological findings, serology provides crucial diagnostic information. *IgM detection in cord blood is not diagnostic* - This statement is **TRUE** because while **IgM antibodies** don't cross the placenta (making their presence suggestive of infection), they have significant limitations. - IgM can give **false positives** (rheumatoid factor, maternal blood contamination) and **false negatives** (up to 25% of infected infants may be IgM-negative at birth). - Therefore, IgM alone cannot be relied upon as a standalone diagnostic marker.

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

Cat. ***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 1

Schistosomiasis is transmitted by?

Accepted Answer

Snail

Answer

Fish

Answer

Cattle

Answer

Cyclops

Question 2

What is the correct sequence of the sexual cycle in malaria?

Accepted Answer

Gametocytes to sporozoites

Answer

Sporozoites to gametocytes

Answer

Gametocytes to gametes

Answer

Gametes to zygote

Question 3

The Hanging Drop method is primarily used for studying which of the following microorganisms?

Accepted Answer

Trichomonas vaginalis

Answer

Plasmodium falciparum

Answer

Toxoplasma gondii

Answer

Cryptosporidium parvum

Question 4

Congenital toxoplasmosis: False is

Accepted Answer

IgA is more sensitive than IgM for detection

Answer

Diagnosed by detection of IgM in cord blood

Answer

Dye test is gold standard for IgG

Answer

Avidity testing is used to date the time of maternal infection

Question 5

A 5-year-old child presented with fever, fatigue, abdominal pain, and vomiting. On further history evaluation, he had a habit of eating dog feces. Investigations show visceral larva migrans. Which animal is the most likely source of this infection in this child?

Accepted Answer

Dogs

Answer

Pig

Answer

Monkeys

Answer

Cows

Question 6

Which organism is characterized by the Maltese cross formation?

Accepted Answer

Babesia microti

Answer

Penicillium marneffei

Answer

Cryptococcus neoformans

Answer

Blastomyces dermatitidis

Question 7

Which of the following is a trematode?

Accepted Answer

Schistosoma mansoni

Answer

Diphyllobothrium latum

Answer

Taenia saginata

Answer

Echinococcus granulosus

Question 8

Toxoplasmosis in the fetus can be best confirmed by:

Accepted Answer

IgM antibodies against toxoplasmosis in the fetus

Answer

IgG antibodies against toxoplasmosis in the mother

Answer

IgG antibodies against toxoplasmosis in the fetus

Answer

IgM antibodies against toxoplasmosis in the mother

Question 9

Which among the following statements about congenital toxoplasmosis is false?

Accepted Answer

IgG is diagnostic

Answer

Congenital toxoplasmosis is diagnosed using serological tests.

Answer

IgM detection in cord blood is not diagnostic

Answer

IgA is better than IgM for detection in neonates

Question 10

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

Accepted Answer

Cat

Answer

Sheep

Answer

Human

Answer

Pig

Parasitology — MCQs

Parasitology — MCQs

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