Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 951: Chyluria is due to which of the following?

A. Filaria (Correct Answer)
B. Carcinoma
C. Tuberculosis
D. Malaria

Explanation: ***Filaria*** - **Filarial infections**, specifically **lymphatic filariasis** caused by parasites like *Wuchereria bancrofti* and *Brugia malayi*, are the most common cause of chyluria worldwide. - These parasites obstruct lymphatic vessels, leading to leakage of **lymphatic fluid (chyle)** into the urinary tract. *Carcinoma* - While tumors can cause lymphatic obstruction, chyluria due to carcinoma is **less common** than filariasis and typically associated with advanced malignancy directly invading or compressing lymphatic drainage. - The primary presentation would likely involve symptoms related to the **underlying cancer**, rather than chyluria as the initial or sole symptom. *Tuberculosis* - **Tuberculosis (TB)** can affect various organ systems, including the lymphatic system, but it is a **rare cause of chyluria**. - If TB were to cause chyluria, it would often be part of a broader presentation of **disseminated TB** or **tuberculous lymphadenitis** involving significant lymphatic obstruction. *Malaria* - **Malaria** is a parasitic disease caused by *Plasmodium* species transmitted by mosquitoes, primarily affecting red blood cells and the liver. - It does **not directly cause chyluria** and is not associated with lymphatic obstruction or leakage of chyle into the urine.

Question 952: What is the most definitive method for diagnosing Ascaris lumbricoides infection?

A. Detection of adult worms in stool
B. Antigen detection
C. Antibody detection
D. Detection of eggs in stool (Correct Answer)

Explanation: ***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.

Question 953: Cysticercus cellulosae are pathogenic forms of which parasite?

A. Taenia solium (Correct Answer)
B. Paragonimus westermani
C. Enterobius vermicularis
D. Taenia saginata

Explanation: ***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.

Question 954: A child from Bihar presents with fever, and blood examination reveals sheathed microfilaria with 2 nuclei in the tail tip. The diagnosis is:

A. B. malayi (Correct Answer)
B. W. bancrofti
C. Loa loa
D. Onchocerca volvulus

Explanation: ***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.

Question 955: Which of the following is detected in a peripheral blood smear?

A. Malaria (Correct Answer)
B. Brucella
C. Leishmania
D. Toxoplasma

Explanation: ***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.

Question 956: Neurocysticercosis: Which of the following statements is false regarding its transmission?

A. Acquired by eating undercooked pork (Correct Answer)
B. Caused by ingestion of eggs from contaminated food or water
C. Cannot be transmitted through person-to-person contact
D. Can occur through autoinfection in patients with intestinal taeniasis

Explanation: ***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.

Question 957: Stage of P. falciparum not seen in peripheral blood is which of the following?

A. Ring form
B. Double ring
C. Gametocyte
D. Schizont (Correct Answer)

Explanation: ***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.

Question 958: The definitive host of ascariasis is

A. Human (Correct Answer)
B. Monkey
C. Dog
D. Pig

Explanation: ***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.

Question 959: An HIV patient is admitted with malabsorption, fever, chronic diarrhea, and acid-fast positive organism. What is the likely causative agent?

A. Giardia
B. Microsporidia
C. Isospora (Correct Answer)
D. E. histolytica

Explanation: ***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 960: Which of the following statements is true regarding Wuchereria bancrofti?

A. Unsheathed
B. Tail tip free from nuclei (Correct Answer)
C. Non-periodic
D. None of the options

Explanation: ***Tail tip free from nuclei*** - The **microfilariae** of *Wuchereria bancrofti* are characterized by a **clean tail tip**, meaning there are no nuclei extending into the very end of the tail. - This feature is crucial for differentiating it from other microfilariae like *Brugia malayi*, which has two distinct nuclei in its tail tip. *Unsheathed* - *Wuchereria bancrofti* microfilariae are **sheathed**, meaning they retain an egg envelope as a loose covering. - An unsheathed microfilaria, like that of *Onchocerca volvulus*, lacks this outer covering. *Non-periodic* - *Wuchereria bancrofti* exhibits **nocturnal periodicity**, meaning its microfilariae are most abundant in the peripheral blood during the night. - Non-periodic microfilariae are found in the blood at any time of day, as seen with *Loa loa*. *None of the options* - This statement is incorrect because "Tail tip free from nuclei" is a true characteristic of *Wuchereria bancrofti* microfilariae.

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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