Parasitology Practice Questions

Q: Rhabditiform larvae are seen in which of the following?

Strongyloides stercoralis. ***Strongyloides stercoralis*** - *Strongyloides stercoralis* is unique among intestinal nematodes in that it can produce **rhabditiform larvae** in the stool. These larvae can then mature into infective **filariform larvae** either in the soil or within the host. - The presence of **rhabditiform larvae in fresh stool samples** is a key diagnostic feature differentiating *Strongyloides* from other parasitic infections that typically shed eggs. *Taenia solium* - *Taenia solium* (pork tapeworm) is transmitted by **ingesting undercooked pork** containing cysticerci. - The parasite is diagnosed by finding **eggs or proglottids in stool**, not rhabditiform larvae. *Diphyllobothrium latum* - *Diphyllobothrium latum* (fish tapeworm) infects humans upon consumption of **undercooked or raw freshwater fish**. - Diagnosis is made by identifying characteristic **operculated eggs in stool samples**, which do not contain rhabditiform larvae. *Trichinella spiralis* - *Trichinella spiralis* causes trichinosis, usually acquired by eating **undercooked meat infected with encysted larvae**. - This parasite is typically diagnosed by **muscle biopsy** showing encysted larvae or serological tests, as it does not produce rhabditiform larvae in stool.

Q: Which of the following statements is true regarding Diphyllobothrium?

The operculated egg is a diagnostic feature. ***The operculated egg is a diagnostic feature*** - *Diphyllobothrium latum*, also known as the **fish tapeworm**, produces characteristic **operculated eggs** that are oval-shaped with an operculum (cap) at one end and a small knob at the other. - The presence of these **unembryonated eggs** in stool samples is the primary diagnostic method for diphyllobothriasis. *Humans are the only definitive host* - While humans are common definitive hosts, other **fish-eating mammals** such as bears, dogs, and cats can also serve as definitive hosts for *Diphyllobothrium latum*. - The definitive host is where the **adult worm resides** and reproduces sexually. *Vitamin B12 deficiency always occurs in infection* - **Vitamin B12 deficiency (megaloblastic anemia)** is a known complication of *Diphyllobothrium latum* infection, as the worm competes for B12 in the host's intestine. - However, it does **not occur in all infected individuals**; it is estimated to affect a significant minority, typically those with heavy worm burdens or prolonged infection, and can be influenced by dietary intake. *Fish are definitive hosts* - Fish (specifically freshwater fish like pike, perch, and salmon) act as **second intermediate hosts** for *Diphyllobothrium latum*, carrying the **plerocercoid larvae**. - **Humans and other fish-eating mammals** are the definitive hosts, where the plerocercoid larvae mature into adult tapeworms in the small intestine.

Q: What is the most common protozoan associated with keratitis?

Acanthamoeba. ***Acanthamoeba*** - **Acanthamoeba keratitis** is a serious and painful infection of the eye's cornea, most commonly associated with **contact lens wearers** who do not properly disinfect their lenses. - The organism is a **free-living protozoan** found in soil and water. *Plasmodium* - **Plasmodium** species are the causative agents of **malaria**, a disease that primarily affects **red blood cells** and the liver. - While it can manifest with ocular symptoms like **retinopathy**, it does not typically cause **keratitis**. *Toxoplasma* - **Toxoplasma gondii** causes **toxoplasmosis**, an infection that can lead to **chorioretinitis** (inflammation of the retina and choroid), especially in immunocompromised individuals or congenitally infected infants. - It does not directly cause **keratitis** as its primary ocular manifestation. *Entamoeba histolytica* - **Entamoeba histolytica** is the protozoan responsible for **amebiasis**, particularly **amoebic dysentery** and **liver abscesses**. - Ocular involvement with *Entamoeba histolytica* is extremely rare and typically involves **metastatic lesions** to the orbit or eyelids, not directly primary keratitis.

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: 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 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

Rhabditiform larvae are seen in which of the following?

Accepted Answer

Strongyloides stercoralis

Answer

Taenia solium

Answer

Diphyllobothrium latum

Answer

Trichinella spiralis

Question 2

Which of the following statements is true regarding Diphyllobothrium?

Accepted Answer

The operculated egg is a diagnostic feature

Answer

Humans are the only definitive host

Answer

Vitamin B12 deficiency always occurs in infection

Answer

Fish are definitive hosts

Question 3

What is the most common protozoan associated with keratitis?

Accepted Answer

Acanthamoeba

Answer

Plasmodium

Answer

Toxoplasma

Answer

Entamoeba histolytica

Question 4

Schistosomiasis is transmitted by?

Accepted Answer

Snail

Answer

Fish

Answer

Cattle

Answer

Cyclops

Question 5

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 6

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 7

Which organism is characterized by the Maltese cross formation?

Accepted Answer

Babesia microti

Answer

Penicillium marneffei

Answer

Cryptococcus neoformans

Answer

Blastomyces dermatitidis

Question 8

Which of the following is a trematode?

Accepted Answer

Schistosoma mansoni

Answer

Diphyllobothrium latum

Answer

Taenia saginata

Answer

Echinococcus granulosus

Question 9

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 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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