Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 821: What type of life cycle does the malaria parasite exhibit?

A. None of the options
B. Cyclodevelopmental
C. Propagative
D. Cyclopropagative (Correct Answer)

Explanation: ***Cyclopropagative*** - The malaria parasite (Plasmodium) exhibits a **cyclopropagative life cycle** where it undergoes both **developmental changes** and **multiplication** within the mosquito vector. - In the mosquito, the parasite undergoes **sporogony**: gametocytes → gametes → zygote → ookinete → oocyst → **thousands of sporozoites**, demonstrating both morphological development and significant numerical increase. - This is the **standard classification** found in parasitology textbooks for arthropod-borne parasites that both develop and multiply in their vectors. *Cyclodevelopmental* - A **cyclodevelopmental life cycle** involves development and morphological changes within the vector but **without significant multiplication**. - Example: **Filarial worms** (Wuchereria bancrofti) develop through larval stages (L1→L2→L3) in mosquitoes but do not multiply significantly. - While malaria parasites do undergo developmental changes, they also undergo **massive multiplication** (one oocyst produces thousands of sporozoites), making cyclopropagative the correct term. *Propagative* - A **propagative life cycle** involves only **multiplication** within the vector without significant developmental or morphological changes. - Example: **Trypanosomes** multiply by binary fission in the tsetse fly without major morphological transformation. - This does not apply to malaria parasites, which undergo distinct **developmental stages** (sexual reproduction, ookinete formation, sporogony) in addition to multiplication. *None of the options* - This option is incorrect because the malaria parasite life cycle is accurately described as **cyclopropagative**. - The combination of both developmental stages and multiplication in the mosquito vector is a defining characteristic of the Plasmodium life cycle.

Question 822: A patient presents with a headache, high fever and meningismus. Within 3 days he becomes unconscious. Most probable causative agent?

A. Acanthamoeba castellanii
B. Trypanosoma cruzi
C. Naegleria fowleri (Correct Answer)
D. Entamoeba histolytica

Explanation: ***Naegleria fowleri*** - This protozoan causes **Primary Amebic Meningoencephalitis (PAM)**, characterized by rapid onset of headache, high fever, meningismus, and rapid progression to coma and death within days. - The disease is often acquired through **nasal insufflation of contaminated water**, allowing the amoeba to migrate to the brain. *Acanthamoeba castellanii* - This amoeba causes **Granulomatous Amebic Encephalitis (GAE)**, which is typically a chronic or subacute infection, progressing over weeks to months, unlike the rapid onset described. - GAE often occurs in **immunocompromised individuals** and can also cause keratitis or disseminated disease. *Trypanosoma cruzi* - This parasite causes **Chagas disease**, which can involve the central nervous system in acute or chronic stages, but does not typically present as acute fulminant meningoencephalitis with rapid progression to unconsciousness in days. - Neurological manifestations in Chagas disease are more varied and often associated with **cardiomyopathy** or gastrointestinal involvement. *Entamoeba histolytica* - This parasite is primarily known for causing **amebic dysentery** and **liver abscesses**. - While it can rarely cause brain abscesses, this is not the typical presentation of an acute, rapidly progressive meningoencephalitis with meningismus and high fever as described.

Question 823: A 24-year-old patient presents with redness, foreign body sensation, excessive tears in the eyes along with corneal ulcers following the use of contact lens. The saline mount preparation of the corneal scraping shows polygonal cysts. What would be the most probable cause?

A. Naegleria
B. Acanthamoeba (Correct Answer)
C. Giardia
D. Entamoeba

Explanation: ***Correct: Acanthamoeba*** - The presence of **corneal ulcers following contact lens use**, combined with the finding of **polygonal cysts** on saline mount of corneal scrapings, is highly suggestive of **Acanthamoeba keratitis** - *Acanthamoeba* is an opportunistic free-living amoeba commonly associated with **poor contact lens hygiene** and **contaminated water sources** - The polygonal double-walled cysts are **pathognomonic** for Acanthamoeba - Treatment involves topical biguanides (chlorhexidine) or diamidines (propamidine) *Incorrect: Naegleria* - *Naegleria fowleri* primarily causes **primary amoebic meningoencephalitis (PAM)**, a rapidly fatal brain infection - It is acquired by swimming in warm freshwater and the amoeba enters through the **nasal mucosa**, traveling to the brain via the olfactory nerve - Does not cause corneal ulcers or keratitis *Incorrect: Giardia* - *Giardia intestinalis* (lamblia) causes **giardiasis**, an intestinal infection characterized by **diarrhea, steatorrhea, and malabsorption** - This is an intestinal flagellate protozoan, not associated with eye infections - Does not produce cysts in corneal scrapings *Incorrect: Entamoeba* - *Entamoeba histolytica* causes **amoebic dysentery** and **liver abscesses** - While it is an amoeba, it is an intestinal pathogen and does not cause corneal infections - The cysts of *E. histolytica* are found in stool, not corneal tissue

Question 824: The removal of malarial parasites from the red blood cells is called:

A. Binding
B. Pitting (Correct Answer)
C. Culling
D. Phagocytosis

Explanation: ***Pitting*** - **Pitting** is the process by which the spleen removes intraerythrocytic inclusions, such as malarial parasites, Howell-Jolly bodies, or Heinz bodies, from red blood cells while leaving the cell intact. - This function is critical in controlling **parasitemia** in malaria, as the spleen filters infected red blood cells and extracts the parasites, often resulting in uninfected, but slightly deformed, red blood cells returning to circulation. *Binding* - **Binding** refers to the adhesion of malarial parasites to red blood cells or endothelial cells, a process involved in parasite invasion or sequestration. - It does not describe the specific removal of the parasite from an already infected red blood cell. *Culling* - **Culling** is the process by which the spleen removes and destroys senescent (old) or damaged red blood cells from circulation. - While related to red blood cell removal, it specifically targets entire dysfunctional cells and doesn't describe the removal of an inclusion from an otherwise viable red blood cell. *Phagocytosis* - **Phagocytosis** is the process by which phagocytic cells (e.g., macrophages) engulf and digest foreign particles, microorganisms, or cellular debris. - While phagocytosis is crucial in clearing infected whole red blood cells, it is distinct from "pitting," where the parasite is "pitted out" of an intact red blood cell.

Question 825: Which of the following parasitic infections is characteristically associated with colitis?

A. Strongyloides
B. Clonorchis
C. Enterobius vermicularis
D. Trichuris trichiura (Correct Answer)

Explanation: ***Trichuris trichiura*** - Also known as **whipworm**, *Trichuris trichiura* primarily infects the **large intestine**, particularly the cecum and ascending colon. - Heavy infections can lead to **colitis**, characterized by bloody diarrhea, abdominal pain, and rectal prolapse in severe cases. *Strongyloides* - *Strongyloides stercoralis* infection (strongyloidiasis) primarily affects the **small intestine** and can cause symptoms like abdominal pain, diarrhea, and malabsorption. - While it can lead to gastrointestinal symptoms, it is not typically associated with prominent **colitis** as its primary manifestation. *Clonorchis* - *Clonorchis sinensis* (Chinese liver fluke) infects the **biliary ducts** of the liver, causing **cholangitis** and potentially cholangiocarcinoma. - It does not primarily cause **colitis** or involve the large intestine. *Enterobius vermicularis* - *Enterobius vermicularis* (pinworm) primarily resides in the **cecum and appendix**, causing perianal itching, especially at night. - While it can cause some localized irritation, it does not typically lead to **colitis** or significant inflammation of the large intestine.

Question 826: Prolonged parasitism in malaria is due to ?

A. Sequestration
B. Immunosuppression
C. Intracellularity of parasite
D. Antigenic variation (Correct Answer)

Explanation: ***Antigenic variation*** - **Antigenic variation** allows the parasite to continuously change its surface proteins, evading the host's immune response. - This immune evasion mechanism contributes to the **persistence of infection** and high parasite loads. *Sequestration* - **Sequestration** is the adherence of infected red blood cells to endothelial cells, primarily in organs, to avoid splenic clearance. - While it contributes to pathogenesis and organ damage, it does not directly explain **prolonged parasitism** in terms of immune evasion. *Immunosuppression* - While malaria can cause some degree of **immunosuppression**, making individuals susceptible to other infections, it's not the primary mechanism for the parasite's prolonged survival. - **Immunosuppression** often occurs as a consequence of chronic infection, rather than being the sole cause of its persistence. *Intracellularity of parasite* - The **intracellular lifestyle** of the parasite protects it from direct immune cell attack and antibodies. - However, the host immune system can still recognize and target infected cells, making **antigenic variation** a more direct mechanism for prolonged evasion.

Question 827: In the life cycle of malaria parasite, the definitive host is -

A. Mosquito (Correct Answer)
B. Man
C. Pig
D. Sandfly

Explanation: ***Mosquito*** - The **mosquito** is considered the **definitive host** because sexual reproduction of the *Plasmodium* parasite occurs within its gut. - Specifically, the *Anopheles* mosquito ingests gametocytes from an infected human, which then develop into mature gametes, fertilize, and form oocysts. *Man* - **Humans** are the **intermediate host** for the malaria parasite, where asexual reproduction (schizogony) occurs in the liver and red blood cells. - While humans experience the disease symptoms, the sexual phase of the parasite's life cycle does not take place in them. *Pig* - **Pigs** are not involved in the **life cycle of the human malaria parasite**. - They are known to host other parasites but are irrelevant to the transmission or development of *Plasmodium* species infecting humans. *Sandfly* - **Sandflies** are vectors for diseases like **leishmaniasis**, but they are not involved in the transmission of malaria. - Different insect species act as vectors for different parasitic diseases.

Question 828: The organism most commonly causing genital filariasis in most part of Bihar and eastern U.P. is -

A. Dirofilaria
B. Wuchereria bancrofti (Correct Answer)
C. Onchocerca volvulus
D. Brugia malayi

Explanation: ***Wuchereria bancrofti*** - This is the **most prevalent filarial parasite** causing lymphatic filariasis globally and in India, particularly in Bihar and Eastern U.P. - It specifically targets the **lymphatic system**, leading to conditions like **hydrocele**, **lymphedema**, and **lymphatic obstruction**, which are characteristic of genital filariasis. - Accounts for approximately **90% of lymphatic filariasis cases** worldwide and is the predominant species in the specified regions. *Dirofilaria* - This genus typically causes **zoonotic filariasis**, primarily known for **dog heartworm**, and is uncommon in humans. - When human infection occurs, it usually presents as **subcutaneous or pulmonary nodules**, not lymphatic or genital filariasis. - Not a significant cause of human lymphatic filariasis in India. *Onchocerca volvulus* - This parasite is the causative agent of **onchocerciasis** or **river blindness**, which mainly affects the **skin and eyes**. - It is predominantly found in parts of **sub-Saharan Africa** and the Americas (particularly Central and South America). - **Not endemic in India** and does not cause genital filariasis. *Brugia malayi* - While it does cause **lymphatic filariasis** similar to *Wuchereria bancrofti*, it is the **second most common** cause in India. - In India, it is endemic in **Kerala, Odisha, West Bengal**, parts of Andhra Pradesh, and some northeastern states. - However, in **Bihar and eastern U.P. specifically**, *Wuchereria bancrofti* is the **predominant species**, making it the correct answer for this geographical region. - Globally, B. malayi is more prevalent in Southeast Asian countries like Malaysia, Indonesia, and the Philippines.

Question 829: True regarding malaria is:

A. Schizonts are infective to mosquitoes
B. Trophozoites are infective to mosquitoes
C. Persistent tissue phase seen in P. falciparum
D. Persistent tissue phase seen in P. vivax (Correct Answer)

Explanation: ***Persistent tissue phase seen in P. vivax*** - The **persistent tissue phase** (or **exoerythrocytic phase**) is unique to *Plasmodium vivax* and *P. ovale*, where parasites infect **liver cells** (hepatocytes) and form **hypnozoites**. - **Hypnozoites** are **dormant forms** that can remain in the liver for weeks to months and cause **relapses** after the initial infection. - While all *Plasmodium* species have an initial liver phase, only *P. vivax* and *P. ovale* have this **persistent/dormant** tissue phase. *Schizonts are infective to mosquitoes* - **Schizonts** are a developmental stage found inside **human red blood cells** or **liver cells** during asexual reproduction. They are not infective to mosquitoes. - The stages infective to mosquitoes are the **gametocytes**, which are taken up by the female *Anopheles* mosquito during a blood meal. *Trophozoites are infective to mosquitoes* - **Trophozoites** are the feeding stage of the parasite within **human red blood cells** and consume hemoglobin. They are not infective to mosquitoes. - Only **gametocytes** (sexual forms) can continue the life cycle within the mosquito vector. *Persistent tissue phase seen in P. falciparum* - While *Plasmodium falciparum* does have an initial **exoerythrocytic (liver) phase**, it does **not** form **hypnozoites**. - Therefore, *P. falciparum* does **not** have a **persistent/dormant** liver stage and does not cause true relapses, unlike *P. vivax* and *P. ovale*.

Question 830: A 15-year-old boy returned from a vacation to his relatives' village. He developed a severe headache and purulent nasal discharge and was diagnosed with primary amebic meningoencephalitis (PAM). He died 5 days later. Which is the most likely etiological agent?

A. Plasmodium falciparum
B. Entamoeba histolytica
C. Naegleria fowleri (Correct Answer)
D. Toxoplasma

Explanation: ***Naegleria fowleri*** - This free-living amoeba is the causative agent of **Primary Amebic Meningoencephalitis (PAM)**, a rapidly fatal infection acquired through nasal exposure to contaminated warm freshwater. - The rapid progression from symptom onset (headache, purulent nasal discharge) to death within 5 days is characteristic of PAM caused by **_Naegleria fowleri_**. *Plasmodium falciparum* - This parasite causes **falciparum malaria**, which can lead to cerebral malaria, but its presentation involves cyclic fevers, chills, and typically a longer disease course and different diagnostic markers than PAM. - While it affects the brain, it does not cause purulent nasal discharge or the rapid, fulminant meningoencephalitis seen in PAM. *Entamoeba histolytica* - This amoeba causes **amebic dysentery** and, in rare cases, extraintestinal amebiasis like liver abscesses; it does not typically cause PAM. - Central nervous system involvement by _Entamoeba histolytica_ is usually secondary to systemic spread and manifests as abscesses, not a fulminant meningoencephalitis acquired via nasal passages. *Toxoplasma* - _Toxoplasma gondii_ causes toxoplasmosis, which can lead to toxoplasmic encephalitis, especially in immunocompromised individuals. - _Toxoplasma_ infection typically has a slower onset, different risk factors (e.g., raw meat, cat feces), and does not present with a rapid, purulent meningoencephalitis following swimming exposure.

Practice by Chapter

Classification of Parasites

Practice Questions

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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