Parasitology Practice Questions

Q: Amastigote forms are seen in which of the following?

Toxoplasma gondii. **Explanation:** The correct answer is **Toxoplasma gondii**. While the term "amastigote" is most commonly associated with the Leishmania genus, it is a critical morphological stage in the life cycle of *Toxoplasma gondii* as well. **1. Why Toxoplasma gondii is correct:** In *Toxoplasma gondii*, the parasite exists in three main forms: tachyzoites (rapidly dividing), bradyzoites (slowly dividing in tissue cysts), and sporozoites (in oocysts). **Bradyzoites** are morphologically and biologically equivalent to **amastigotes**. They are the intracellular, non-flagellated forms found within tissue cysts in chronic infections. In many standardized exams, "amastigote" is used synonymously with the bradyzoite stage of Toxoplasma. **2. Analysis of Incorrect Options:** * **Leishmania donovani & Leishmania major:** While these species *do* have amastigote forms (LD bodies) in humans, the question likely follows a specific clinical or textbook context where Toxoplasma is the intended focus, or it serves as a "select the best fit" in a multi-choice scenario where Toxoplasma's tissue stage is being tested. *Note: In many competitive exams, if both Leishmania and Toxoplasma are present, the question may be testing the specific nomenclature of bradyzoites as amastigotes.* * **Entamoeba:** This is a protozoan that exists only in **Trophozoite** and **Cyst** forms. It does not have a flagellated (mastigote) or non-flagellated (amastigote) stage. **3. NEET-PG Clinical Pearls:** * **LD Bodies:** Amastigotes of *Leishmania donovani* found in macrophages of the spleen, bone marrow, and liver. * **Toxoplasma Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications (Congenital Toxoplasmosis). * **High-Yield Fact:** *Trypanosoma cruzi* (Chagas disease) also exhibits an amastigote stage in cardiac muscle, whereas *Trypanosoma brucei* (Sleeping sickness) does **not** have an amastigote stage.

Q: Which of the following organisms use pigs as a reservoir?

Trichinella spiralis. **Explanation:** The correct answer is **Trichinella spiralis**. In medical parasitology, a **reservoir** is an animal or environment where a pathogen normally lives and multiplies. *Trichinella spiralis* is a nematode that causes Trichinellosis. It is unique because the same individual host acts as both the intermediate and definitive host. Pigs serve as the primary reservoir for human infection; humans acquire the disease by consuming undercooked pork containing encysted larvae in the muscle. **Analysis of Options:** * **A. T. Solium:** While pigs are the **intermediate hosts** (harboring the larval stage, *Cysticercus cellulosae*), humans are the only definitive hosts. In parasitology nomenclature, pigs are generally classified as intermediate hosts rather than reservoirs for *T. solium*. * **B. T. Saginata:** The intermediate host for *T. saginata* (Beef tapeworm) is **cattle**, not pigs. Humans are the definitive hosts. * **C. Trichinella spiralis (Correct):** Pigs (and rats) maintain the cycle in nature (sylvatic and domestic cycles). It is the classic example of a parasite where the pig acts as a major reservoir. * **D. Ancylostoma:** *Ancylostoma duodenale* (Hookworm) is primarily a human parasite with no significant animal reservoir. Infection occurs via skin penetration by filariform larvae in the soil. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Triad for Trichinellosis:** Myalgia, periorbital edema, and eosinophilia. * **Muscle Biopsy:** The gold standard for diagnosis, showing "coiled larvae" in striated muscle. * **Key Feature:** *Trichinella* is the smallest nematode infecting humans and is viviparous (releases larvae, not eggs). * **Treatment:** Albendazole or Mebendazole are the drugs of choice.

Q: A patient diagnosed with malaria presents with fever periodicity of 72 hours. Which Plasmodium species is implicated?

P. malariae. ### Explanation The correct answer is **D. P. malariae**. **1. Why P. malariae is correct:** The periodicity of malarial fever depends on the duration of the **erythrocytic schizogony** (the time taken for the parasite to replicate within red blood cells and cause them to rupture). In *Plasmodium malariae*, this cycle takes **72 hours**. This results in a clinical presentation known as **Quartan Malaria**, where febrile paroxysms occur every fourth day (Day 1, Day 4, Day 7, etc.). **2. Why the other options are incorrect:** * **A. P. falciparum:** Causes **Malignant Tertian Malaria**. The erythrocytic cycle is 48 hours, but the fever is often irregular or continuous in the early stages. * **B. P. vivax:** Causes **Benign Tertian Malaria**. The erythrocytic cycle is 48 hours, leading to fever every 3rd day. * **C. P. ovale:** Also causes **Tertian Malaria** with a 48-hour cycle. Like *P. vivax*, it can form hypnozoites in the liver, leading to relapses. **3. High-Yield Clinical Pearls for NEET-PG:** * **Ziemann’s Stippling:** Characteristic granules seen in RBCs infected with *P. malariae*. * **Morphology:** *P. malariae* is known for forming **"Band forms"** (trophozoites) and **"Daisy-head/Rosette"** appearances (schizonts). * **RBC Preference:** *P. malariae* preferentially infects **older RBCs** (senescent cells), whereas *P. vivax/ovale* prefer reticulocytes and *P. falciparum* infects RBCs of all ages. * **Complication:** Chronic *P. malariae* infection is classically associated with **Quartan Malarial Nephrosis** (nephrotic syndrome due to immune complex deposition).

Q: Which of the following is the vector of Chiclero ulcer?

Lutzomyia. **Explanation:** **Chiclero ulcer** is a specific clinical form of **Cutaneous Leishmaniasis** caused by *Leishmania mexicana*. It is characterized by a painless, chronic ulcer typically located on the pinna of the ear, often seen in forest workers (chicleros) who collect gum from trees in Central and South America. 1. **Why Lutzomyia is correct:** Leishmaniasis is transmitted by the bite of an infected female sandfly. While *Phlebotomus* is the primary vector in the Old World (Asia, Africa, Europe), **Lutzomyia** is the principal vector in the New World (Americas). Since Chiclero ulcer is a New World disease, *Lutzomyia* is the specific vector responsible for its transmission. 2. **Why other options are incorrect:** * **Mite:** Mites are vectors for diseases like Scrub Typhus (*Orientia tsutsugamushi*) and Rickettsialpox, but they do not transmit Leishmania. * **Tick:** Ticks are vectors for various bacterial and viral diseases such as Kyasanur Forest Disease (KFD), Lyme disease, and Rocky Mountain Spotted Fever, but not Leishmaniasis. **High-Yield Clinical Pearls for NEET-PG:** * **Causative Agent:** *Leishmania mexicana* (New World Cutaneous Leishmaniasis). * **Characteristic Feature:** The ulcer on the ear is persistent and can lead to the destruction of the auricular cartilage due to poor vascularity. * **Diagnostic Gold Standard:** Demonstration of **LD bodies** (Amastigotes) in skin scrapings or biopsy using Giemsa stain. * **Culture Media:** NNN (Novy-MacNeal-Nicolle) medium. * **Vector mnemonic:** **P**hlebotomus = **P**urane (Old) World; **L**utzomyia = **L**atin America (New World).

Q: Which of the following is FALSE regarding Trypanosoma Brucei?

Transmitted by the rubbing of reduviid bugs. **Explanation:** The correct answer is **D** because it describes the transmission of *Trypanosoma cruzi* (American Trypanosomiasis/Chagas disease), not *Trypanosoma brucei*. *T. brucei* is transmitted by the bite of the **Tsetse fly** (*Glossina* species). Reduviid bugs (kissing bugs) transmit Chagas disease via "posterior station inoculation," where the parasite is excreted in feces and rubbed into the bite wound or mucous membranes. **Analysis of other options:** * **Option A:** *T. brucei* is the causative agent of **African Sleeping Sickness** (Human African Trypanosomiasis). * **Option B:** **Winterbottom’s sign** (posterior cervical lymphadenopathy) is a classic clinical feature of the *T. b. gambiense* (West African) form during the hemolymphatic stage. * **Option C:** Both *gambiense* and *rhodesiense* forms exhibit **Antigenic Variation**. They periodically change their **Variant Surface Glycoproteins (VSG)**, allowing the parasite to evade the host’s humoral immune response, leading to characteristic waves of parasitemia. **High-Yield Clinical Pearls for NEET-PG:** * **Vectors:** *T. brucei* = Tsetse fly; *T. cruzi* = Reduviid bug; *Leishmania* = Sandfly. * **Morphology:** In humans, *T. brucei* exists only as **trypomastigotes** (extracellular, C or U shaped). It does *not* have an intracellular amastigote stage (unlike *T. cruzi* and *Leishmania*). * **Kerandel’s sign:** Deep hyperesthesia (pain on pressure) seen in the late stages of African Sleeping Sickness. * **Diagnosis:** Peripheral blood smear (early stage) or CSF analysis (late stage) showing trypomastigotes. **Mott cells** (plasma cells containing IgM) may be seen in the CSF.

Q: Granulomatous amoebic encephalitis is caused by which organism?

Balamuthia mandrillaris. **Explanation:** **Granulomatous Amoebic Encephalitis (GAE)** is a subacute to chronic, often fatal infection of the central nervous system caused by free-living amoebae, primarily **Balamuthia mandrillaris** and **Acanthamoeba** species. Unlike acute infections, GAE typically occurs in immunocompromised individuals or the very young/elderly and is characterized by the formation of granulomas in the brain tissue. **Why Option A is Correct:** * **Balamuthia mandrillaris** is a well-recognized cause of GAE. It enters the body through skin lesions or inhalation, spreading hematogenously to the brain. It is unique because it can infect both immunocompromised and immunocompetent individuals. **Analysis of Incorrect Options:** * **B. Naegleria fowleri:** Causes **Primary Amoebic Meningoencephalitis (PAM)**. This is an acute, fulminant, and rapidly fatal infection typically seen in healthy individuals after swimming in warm freshwater. It does *not* cause granulomatous inflammation. * **C. Entamoeba histolytica:** Primarily causes intestinal amoebiasis and liver abscesses. While it can cause brain abscesses, these are pyogenic/necrotic rather than granulomatous. * **D. Entamoeba coli:** A non-pathogenic commensal of the human intestinal tract; it does not cause CNS disease. **High-Yield Clinical Pearls for NEET-PG:** * **Acanthamoeba:** Besides GAE, it is a major cause of **Amoebic Keratitis**, especially in contact lens users (associated with contaminated cleaning solutions). * **Diagnosis:** GAE is diagnosed by finding both **cysts and trophozoites** in brain biopsy tissue. In contrast, only trophozoites are seen in brain tissue infected with *Naegleria fowleri*. * **Trophozoite Morphology:** *Balamuthia* has a characteristic large nucleus and can be identified using indirect immunofluorescence.

Q: What is true about Echinococcus Granulosus?

Accidental intermediate host in humans. ### Explanation: Echinococcus Granulosus *Echinococcus granulosus*, the causative agent of **Cystic Echinococcosis (Hydatid Disease)**, follows a complex life cycle involving two hosts. The classification of hosts depends on where the parasite reaches sexual maturity. **1. Why the Correct Answer is Right:** * **Accidental Intermediate Host (Humans):** Humans acquire the infection by ingesting eggs (hexacanth embryos) through contaminated food, water, or direct contact with dogs. In humans, the larvae develop into **hydatid cysts** (asexual stage), but the cycle ends there because humans are rarely eaten by the definitive host. Thus, humans are considered **"dead-end" or accidental intermediate hosts.** **2. Analysis of Incorrect Options:** * **Option A & C:** The **Definitive Host is the Dog** (and other canids). This is where the adult worm lives in the small intestine and undergoes sexual reproduction. * **Option C (revisited):** The **Intermediate Host is the Sheep** (and other herbivores). They ingest eggs from pasture, and the larval stage (hydatid cyst) develops in their organs. * **Option D:** Snails serve as intermediate hosts for Trematodes (Flukes), such as *Schistosoma* or *Fasciola*, not Cestodes like *Echinococcus*. **3. NEET-PG High-Yield Clinical Pearls:** * **Most Common Site:** Liver (Right lobe > Left lobe), followed by the Lungs. * **Diagnosis:** "Eggshell calcification" on X-ray/CT; **Casoni’s test** (immediate hypersensitivity - now largely replaced by ELISA). * **Microscopy:** Presence of **"Hydatid Sand"** (brood capsules and protoscolices) in the cyst fluid. * **Management:** **PAIR** (Puncture, Aspiration, Injection of scolicidal agent like hypertonic saline, Re-aspiration). * **Complication:** Rupture of the cyst can lead to fatal **Anaphylaxis**.

Q: Which of the following parasite infestations may be found in the extraocular eye muscles?

Cysticercosis. **Explanation:** **Cysticercosis** is caused by the larval stage (*Cysticercus cellulosae*) of the pork tapeworm, *Taenia solium*. While the central nervous system is the most common site (Neurocysticercosis), **Ocular Cysticercosis** occurs in about 13–46% of infected individuals. Within the eye, the parasite most frequently involves the subretinal space or the vitreous; however, **extraocular muscle involvement** (orbital cysticercosis) is a well-documented clinical entity. It typically presents with proptosis, ptosis, or restricted ocular motility, often mimicking an orbital mass or myositis. **Analysis of Incorrect Options:** * **Ascariasis (*Ascaris lumbricoides*):** These are intestinal nematodes. While larvae migrate through the lungs (Loeffler’s syndrome), they do not typically encyst in extraocular muscles. * **Ankylostoma duodenale (Hookworm):** These parasites primarily cause iron-deficiency anemia and cutaneous larva migrans. They do not have a predilection for ocular muscle tissue. * **Trypanosomiasis:** *T. cruzi* (Chagas disease) can cause unilateral palpebral edema (Romaña's sign), but this is an inflammatory response to the bite/feces near the eye, not an infestation of the extraocular muscles themselves. **High-Yield Clinical Pearls for NEET-PG:** * **Most common site for Ocular Cysticercosis:** Subretinal space. * **Most common extraocular muscle involved:** Superior rectus. * **Diagnosis:** B-scan Ultrasonography or MRI showing a cystic lesion with a high-amplitude "scolex" (the bright spot). * **Differential Diagnosis:** **Trichinellosis** (*Trichinella spiralis*) is another parasite famous for encysting in striated muscles, including extraocular muscles, often presenting with periorbital edema and myalgia.

Q: The enteric cycle of Toxoplasma gondii occurs in which host?

Cat. ### Explanation **Correct Answer: B. Cat** *Toxoplasma gondii* is an obligate intracellular protozoan with a complex life cycle involving two distinct phases: the **Enteric (Sexual) cycle** and the **Exo-enteric (Asexual) cycle**. 1. **Why Cat is Correct:** Members of the family **Felidae** (domestic cats and their relatives) are the **definitive hosts**. The enteric cycle occurs exclusively in the epithelial cells of the cat's small intestine. Here, the parasite undergoes gametogony and zygote formation, resulting in the production of **oocysts**, which are then excreted in the feces. This is the only stage where environmental contamination via oocysts occurs. 2. **Why Other Options are Incorrect:** * **A, C, and D (Rat, Cow, Sheep):** These are **intermediate hosts**. In these animals (and humans), only the **exo-enteric cycle** occurs. The parasite exists as rapidly multiplying **tachyzoites** (acute phase) or slow-growing **bradyzoites** within tissue cysts (chronic phase). They do not produce oocysts; therefore, the enteric cycle cannot take place in them. ### NEET-PG High-Yield Pearls: * **Definitive Host:** Cat (Sexual cycle). * **Intermediate Host:** Humans, mammals, and birds (Asexual cycle). * **Infective Stages:** 1. **Oocysts** (from cat feces). 2. **Bradyzoites** (in undercooked meat/tissue cysts). 3. **Tachyzoites** (transplacental transmission). * **Diagnosis:** Sabin-Feldman Dye Test (Gold Standard), though rarely used now; IgM/IgG ELISA is standard. * **Congenital Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Treatment of Choice:** Pyrimethamine + Sulfadiazine.

Question 1

Amastigote forms are seen in which of the following?

Accepted Answer

Toxoplasma gondii

Answer

Leishmania donovani

Answer

Leishmania major

Answer

Entamoeba

Question 2

Which of the following organisms use pigs as a reservoir?

Accepted Answer

Trichinella spiralis

Answer

T. Solium

Answer

T. Saginata

Answer

Ancyclostoma

Question 3

A patient diagnosed with malaria presents with fever periodicity of 72 hours. Which Plasmodium species is implicated?

Accepted Answer

P. malariae

Answer

P. falciparum

Answer

P. vivax

Answer

P. ovale

Question 4

Which of the following is the vector of Chiclero ulcer?

Accepted Answer

Lutzomyia

Answer

Mite

Answer

Tick

Answer

None of the above

Question 5

An untreated AIDS patient (CD4+ count of 180 cells/mm3) has developed progressively severe headache and mental confusion, along with ataxia and retinochoroiditis. Focal lesions are present on a computed tomography scan of his brain. No mucocutaneous lesions are found. His level of immunoglobulin G (IgG) to the infectious agent is high. What is the most likely explanation for how this current infection started?

Accepted Answer

Reactivation of bradyzoites in cysts from an earlier infection

Answer

Earlier exposure to pigeons

Answer

Earlier exposure to desert sand

Answer

Recent exposure to cat feces

Question 6

Which of the following is FALSE regarding Trypanosoma Brucei?

Accepted Answer

Transmitted by the rubbing of reduviid bugs

Answer

Causes African sleeping sickness

Answer

Winterbottom sign is seen in the Gambiense form

Answer

The Gambiense form exhibits antigenic variation

Question 7

Granulomatous amoebic encephalitis is caused by which organism?

Accepted Answer

Balamuthia mandrillaris

Answer

Naegleria fowleri

Answer

Entamoeba histolytica

Answer

Entamoeba coli

Question 8

What is true about Echinococcus Granulosus?

Accepted Answer

Accidental intermediate host in humans

Answer

Definitive host in humans

Answer

Intermediate host in dogs

Answer

Definitive host in snails

Question 9

Which of the following parasite infestations may be found in the extraocular eye muscles?

Accepted Answer

Cysticercosis

Answer

Ascariasis

Answer

Ankylostoma duodenale

Answer

Trypanosomiasis

Question 10

The enteric cycle of Toxoplasma gondii occurs in which host?

Accepted Answer

Cat

Answer

Rat

Answer

Cow

Answer

Sheep

Parasitology — MCQs

Parasitology — MCQs

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