Parasitology Practice Questions

Q: Cysticercus cellulosae are pathogenic forms of which parasite?

Taenia solium. ***Taenia solium*** - **Cysticercus cellulosae** is the larval stage (metacestode form) of the **pork tapeworm**, *Taenia solium*. - Humans can acquire **cysticercosis** by ingesting *T. solium* eggs, leading to the development of these cysticerci in various tissues, including the muscles, subcutaneous tissue, and central nervous system. *Paragonimus westermani* - This is a **lung fluke**; its larval stage is a metacercaria, not a cysticercus. - It causes **paragonimiasis**, characterized by lung symptoms. *Enterobius vermicularis* - This is the **pinworm**, a nematode, which does not have a cysticercus stage. - It primarily causes **perianal itching** and does not form cysts in tissues. *Taenia saginata* - This is the **beef tapeworm**, and its larval stage is known as a **Cysticercus bovis**, not Cysticercus cellulosae. - Humans acquire *T. saginata* infection by consuming undercooked beef containing C. bovis.

Q: What is the most definitive method for diagnosing Ascaris lumbricoides infection?

Detection of eggs in stool. ***Detection of eggs in stool*** - The presence of **Ascaris eggs** in a **stool sample** under a microscope is the gold standard for diagnosing ascariasis. - This method directly identifies the parasite's reproductive stage, confirming an active infection. *Detection of adult worms in stool* - While the presence of **adult worms** in stool confirms infection, it is a less common and less reliable diagnostic method than egg detection. - Worm expulsion can occur spontaneously or after treatment, but their sporadic appearance makes it less definitive for initial diagnosis. *Antigen detection* - **Antigen detection tests** can be useful but are generally less accessible or specific than microscopic examination for Ascaris. - While they can indicate an active infection, they are not considered the primary definitive diagnostic method. *Antibody detection* - **Antibody detection tests** indicate exposure to Ascaris but do not necessarily reflect an ongoing or active infection. - Antibodies can persist for a long time after the infection has cleared, limiting their use in diagnosing current disease.

Q: A pregnant female in the first trimester has a 4-fold rise in IgG against toxoplasmosis. What does it indicate?

Acute infection in mother. ***Acute infection in mother*** - A **4-fold rise in IgG antibodies** between paired sera is the classic serological criterion for **acute or recent infection** with *Toxoplasma gondii*. - A **rising IgG titer** indicates active seroconversion and ongoing immune response to recent exposure, which is clinically significant in pregnancy due to risk of **congenital toxoplasmosis**. - While IgM typically appears first in acute infection, it can persist for months and is less specific; a documented **4-fold IgG rise** is more reliable for diagnosing recent infection. - In the first trimester, acute maternal infection carries approximately **10-25% risk of vertical transmission** and requires further evaluation with IgG avidity testing and consideration of spiramycin therapy. *Chronic infection in mother* - Chronic or past infection is characterized by **stable, unchanging IgG titers**, not rising ones. - A **4-fold rise** indicates an active immune response, which contradicts the definition of chronic/latent infection where antibody levels remain constant. - Women with pre-existing chronic toxoplasmosis (stable IgG, negative IgM) have minimal risk of transmitting infection to the fetus. *Protective antibodies* - While IgG antibodies do provide immunity against reinfection, the key finding here is the **rise in titer**, not just their presence. - **Stable protective antibodies** would show consistent titers on serial testing, not a 4-fold increase. - A rising titer indicates recent antigen exposure and active infection, not established immunity.

Q: A child from Bihar presents with fever, and blood examination reveals sheathed microfilaria with 2 nuclei in the tail tip. The diagnosis is:

B. malayi. ***B. malayi*** - *Brugia malayi* microfilariae are characterized by a **sheath** and **two distinct nuclei in the tail tip**, which is a key diagnostic feature differentiating it from other filarial species. - The disease caused by *B. malayi* is prevalent in certain parts of **Southeast Asia and India (including Bihar)**, making it a likely diagnosis in this geographical context. *W. bancrofti* - While *Wuchereria bancrofti* microfilariae are also **sheathed**, they typically have a **tapering tail tip without nuclei**. - *W. bancrofti* causes **lymphatic filariasis** and is also common in India, but the microscopic morphology described does not match. *Loa loa* - *Loa loa* microfilariae are **sheathed** but have a characteristic **body nuclei extending to the tip of the tail**. - This parasite is endemic to **West and Central Africa**, making it an unlikely finding in a child from Bihar. *Onchocerca volvulus* - *Onchocerca volvulus* microfilariae are typically **unsheathed** and have a **tail that is free of nuclei**. - This parasite is responsible for **onchocerciasis (river blindness)** and is primarily found in **Africa and parts of Latin America**, not in Bihar.

Q: Which of the following is detected in a peripheral blood smear?

Malaria. ***Malaria*** - Malaria parasites, specifically **Plasmodium species**, infect **red blood cells** and can be directly observed in a **peripheral blood smear** using Giemsa stain. - Identification of different stages (ring forms, trophozoites, schizonts, gametocytes) within red blood cells helps in species identification and quantification of parasitemia. *Toxoplasma* - **Toxoplasma gondii** is an intracellular parasite primarily identified through **serological tests** (detecting antibodies) or **molecular methods** like PCR on tissue samples or body fluids. - It is not typically detected in a routine peripheral blood smear as it does not infect red blood cells or circulate freely in high numbers. *Leishmania* - **Leishmania parasites** are typically found within **macrophages** and **monocytes** in tissues such as bone marrow, spleen, liver, or skin biopsies. - While they can be observed in **bone marrow aspirates** or **tissue smears**, they are generally not seen in peripheral blood smears, except rarely in severe visceral leishmaniasis where heavily parasitized monocytes might be present. *Brucella* - **Brucella** is a **bacterium** that causes brucellosis, a systemic infection. - Diagnosis is primarily made through **blood cultures** (bacteremia) or **serological tests** to detect specific antibodies, not by direct visualization in a peripheral blood smear.

Q: Neurocysticercosis: Which of the following statements is false regarding its transmission?

Acquired by eating undercooked pork. ***Acquired by eating undercooked pork*** - This statement is **false** because consuming **undercooked pork** infected with **Taenia solium** leads to **taeniasis** (adult tapeworm in the intestine), not neurocysticercosis. - Neurocysticercosis results from ingesting **Taenia solium eggs**, not the larval cysts in pork. *Caused by ingestion of eggs from contaminated food or water* - This statement is **true** as neurocysticercosis is acquired by consuming **food or water contaminated with Taenia solium eggs**, typically from human feces. - The eggs hatch in the intestine, and the larvae migrate to the central nervous system, forming **cysts**. *Can occur through autoinfection in patients with intestinal taeniasis* - This statement is **true**; individuals with **intestinal taeniasis** (adult tapeworm) can develop neurocysticercosis through **autoinfection**. - This occurs via reverse peristalsis (eggs moving from intestine to stomach) or by ingesting eggs from their own fecal contamination. *Cannot be transmitted through person-to-person contact* - This statement is **true** in the direct sense; neurocysticercosis cannot be directly transmitted from one person to another through typical contact. - Transmission occurs indirectly via the **fecal-oral route** where an infected person sheds eggs that contaminate the environment, which are then ingested by another individual.

Q: The definitive host of ascariasis is

Human. ***Human*** - Humans are the **definitive host** for *Ascaris lumbricoides*, the causative agent of **ascariasis**, meaning the parasite reaches maturity and reproduces sexually within the human body. - Infection occurs when an individual **ingests embryonated *Ascaris* eggs** from contaminated soil or food. *Dog* - Dogs are hosts for **canine roundworms**, such as *Toxocara canis*, which can cause **visceral larva migrans** in humans, but they are not the definitive host for *Ascaris lumbricoides*. - While *Toxocara canis* is related, it is a distinct parasite with a different primary host. *Monkey* - Monkeys can be infected with various parasites, but they are generally not considered the primary or **definitive host** for *Ascaris lumbricoides*. - While some non-human primates might be susceptible to *Ascaris* species, humans are the main reservoir for the species causing human ascariasis. *Pig* - Pigs are the definitive host for *Ascaris suum*, a species closely related to *Ascaris lumbricoides*, but they are not the definitive host for the human-specific *Ascaris lumbricoides*. - Although **zoonotic transmission** of *Ascaris suum* to humans can occur, resulting in similar symptoms, *Ascaris lumbricoides* primarily cycles within human populations.

Q: Stage of P. falciparum not seen in peripheral blood is which of the following?

Schizont. ***Schizont*** - In *Plasmodium falciparum* infections, the **schizont stage** typically sequesters in the deep microvasculature of internal organs and is therefore rarely seen in peripheral blood smears. - This sequestration helps the parasite evade splenic clearance and contributes to the high pathogenicity of *P. falciparum*. *Gametocyte* - **Gametocytes** of *P. falciparum* have a characteristic **crescent or banana shape** and are readily observed in peripheral blood, as they are crucial for transmission to the mosquito vector. - They represent the sexual stages of the parasite cycle. *Ring form* - **Ring forms** are the earliest trophozoite stage observed in red blood cells and are commonly seen in peripheral blood smears of all *Plasmodium* species, especially *P. falciparum* due to high parasitemia. - *P. falciparum* infections often show **multiple rings per red blood cell** or rings adhering to the periphery of the red cell. *Double ring* - The presence of **multiple rings** or "double rings" within a single red blood cell is a distinctive morphological feature often observed in **heavy *P. falciparum* infections** and is easily detectable in peripheral blood. - This phenomenon is a diagnostic clue for *P. falciparum* on a peripheral blood smear.

Q: How do hookworms infect humans?

Contaminated soil. ***Contaminated soil*** - Hookworm larvae (filariform larvae) present in **contaminated soil** can penetrate unbroken human skin, typically through the feet. - This penetration is the primary mode of infection for humans in endemic areas. *Water* - While some parasitic protozoa are transmitted through contaminated water, hookworms primarily infect via **skin penetration** from soil. - Ingestion of contaminated water is not a common or direct route for hookworm infection. *Food* - Hookworm infection is generally not acquired through the ingestion of **contaminated food**. - Infections spread via food usually involve other parasitic organisms like *Taenia* species or *Ascaris lumbricoides* eggs. *Human feces* - Human feces contain hookworm eggs, which hatch into rhabditiform larvae and then mature into infectious filariform larvae in the soil. - However, direct contact with **feces** itself is not the immediate infective route; the larvae in the soil are the infective stage.

Q: An HIV patient is admitted with malabsorption, fever, chronic diarrhea, and acid-fast positive organism. What is the likely causative agent?

Isospora. ***Isospora (Cystoisospora belli)*** - **Cystoisospora belli** (formerly *Isospora belli*) is a coccidian parasite common in HIV patients, causing **chronic watery diarrhea**, fever, and malabsorption, especially when the CD4 count is low. - The diagnosis is confirmed by identifying **acid-fast oocysts** in stool samples, which is the key distinguishing feature in this case. - The **acid-fast positive** property makes this the definitive answer among the given options. *Giardia* - **Giardia lamblia** causes malabsorption and chronic diarrhea but is typically characterized by **fatty, foul-smelling stools** and abdominal cramping. - While it can be diagnosed with stool examination, its cysts and trophozoites are **not acid-fast**, which excludes it based on the clinical description. *Microsporidia* - Microsporidia species like **Enterocytozoon bieneusi** can cause chronic diarrhea and malabsorption in HIV patients. - However, they are **intracellular obligate parasites** detected using specialized stains (modified trichrome or calcofluor white) rather than acid-fast staining, making them inconsistent with the **acid-fast positive** finding. *E. histolytica* - **Entamoeba histolytica** causes amebiasis, which can manifest as **amebic dysentery** with bloody stools or chronic non-bloody diarrhea. - Its trophozoites and cysts are **not acid-fast**, and the malabsorption syndrome is less prominent than with Cystoisospora, excluding it from consideration.

Question 1

Cysticercus cellulosae are pathogenic forms of which parasite?

Accepted Answer

Taenia solium

Answer

Paragonimus westermani

Answer

Enterobius vermicularis

Answer

Taenia saginata

Question 2

What is the most definitive method for diagnosing Ascaris lumbricoides infection?

Accepted Answer

Detection of eggs in stool

Answer

Detection of adult worms in stool

Answer

Antigen detection

Answer

Antibody detection

Question 3

A pregnant female in the first trimester has a 4-fold rise in IgG against toxoplasmosis. What does it indicate?

Accepted Answer

Acute infection in mother

Answer

Chronic infection in mother

Answer

Protective antibodies

Answer

None of the above

Question 4

A child from Bihar presents with fever, and blood examination reveals sheathed microfilaria with 2 nuclei in the tail tip. The diagnosis is:

Accepted Answer

B. malayi

Answer

W. bancrofti

Answer

Loa loa

Answer

Onchocerca volvulus

Question 5

Which of the following is detected in a peripheral blood smear?

Accepted Answer

Malaria

Answer

Brucella

Answer

Leishmania

Answer

Toxoplasma

Question 6

Neurocysticercosis: Which of the following statements is false regarding its transmission?

Accepted Answer

Acquired by eating undercooked pork

Answer

Caused by ingestion of eggs from contaminated food or water

Answer

Cannot be transmitted through person-to-person contact

Answer

Can occur through autoinfection in patients with intestinal taeniasis

Question 7

The definitive host of ascariasis is

Accepted Answer

Human

Answer

Monkey

Answer

Dog

Answer

Pig

Question 8

Stage of P. falciparum not seen in peripheral blood is which of the following?

Accepted Answer

Schizont

Answer

Ring form

Answer

Double ring

Answer

Gametocyte

Question 9

How do hookworms infect humans?

Accepted Answer

Contaminated soil

Answer

Water

Answer

Food

Answer

Human feces

Question 10

An HIV patient is admitted with malabsorption, fever, chronic diarrhea, and acid-fast positive organism. What is the likely causative agent?

Accepted Answer

Isospora

Answer

Giardia

Answer

Microsporidia

Answer

E. histolytica

Parasitology — MCQs

Parasitology — MCQs

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