Parasitology Practice Questions

Q: Which of the following parasite eggs consists of polar filaments arising from either end of the ambryophore?

Hymenolepis nana. **Explanation:** The correct answer is **Hymenolepis nana** (Dwarf Tapeworm). **Why H. nana is correct:** The morphology of *Hymenolepis nana* eggs is a high-yield topic in parasitology. These eggs are characterized by an oval shape with a double membrane. The inner membrane (embryophore) encloses the oncosphere (hexacanth embryo) and possesses two distinct **polar thickenings**. From these thickenings, **4 to 8 polar filaments** arise and spread into the space between the inner and outer shells. This is a pathognomonic feature used to differentiate *H. nana* from *H. diminuta* (which lacks polar filaments). **Why other options are incorrect:** * **Taenia saginata & Taenia solium:** The eggs of both *Taenia* species are morphologically identical. They are spherical, brown, and have a thick, radially striated wall (embryophore) resembling a "wagon wheel." They do **not** possess polar filaments. * **Echinococcus granulosus:** The eggs of *Echinococcus* are morphologically indistinguishable from *Taenia* species (radially striated embryophore). Diagnosis is usually made via imaging or serology, as eggs are not typically found in human feces (humans are intermediate hosts). **NEET-PG High-Yield Pearls:** * **Smallest Cestode:** *H. nana* is the smallest intestinal cestode infecting humans. * **Direct Life Cycle:** It is unique among tapeworms because it does not require an intermediate host (though insects can act as optional ones). * **Autoinfection:** It is the only cestode capable of completing its entire life cycle in a single host, leading to internal autoinfection and heavy worm burdens. * **Treatment:** Praziquantel is the drug of choice.

Q: What is true about Plasmodium falciparum?

Crescentic macrogametocyte. **Explanation:** *Plasmodium falciparum* is the most virulent species of malaria, characterized by unique morphological features and a high parasite load. **Why Option C is Correct:** The hallmark of *P. falciparum* is the presence of **crescentic (banana-shaped) gametocytes**. These appear in the peripheral blood about 7–10 days after the initial asexual cycle. The macrogametocyte (female) is typically longer and more slender with central, compact chromatin, while the microgametocyte (male) is broader with diffuse chromatin. **Analysis of Incorrect Options:** * **A. Preferentially infects old erythrocytes:** This is incorrect. *P. falciparum* is unique because it **infects RBCs of all ages** (young and old), leading to very high levels of parasitemia. In contrast, *P. vivax* prefers reticulocytes (young RBCs), and *P. malariae* prefers senescent (old) RBCs. * **B. Schuffner's dots:** These are characteristic of *P. vivax* and *P. ovale*. In *P. falciparum*, the dots seen are called **Maurer’s clefts** (coarse granulations). * **D. Large schizonts:** While *P. falciparum* does form schizonts, they are **rarely seen in peripheral blood** because they sequester in deep capillaries (leading to cerebral malaria). When seen, they are smaller than those of *P. vivax*. **High-Yield Clinical Pearls for NEET-PG:** * **Multiple rings per RBC** and **Appole forms** (rings at the margin) are diagnostic of *P. falciparum*. * **Sequestration:** Mediated by **PfEMP-1** protein, causing cytoadherence to vascular endothelium (CD36/ICAM-1). * **Recrudescence** is seen in *P. falciparum* (due to sub-optimal treatment), whereas **Relapse** (hypnozoites) is seen in *P. vivax/ovale*.

Q: What condition is characterized by the occurrence of tetrads in red blood cells?

Babesiosis. **Explanation:** The correct answer is **Babesiosis**. This condition is caused by the protozoan parasite *Babesia microti*, which infects red blood cells (RBCs). The hallmark diagnostic feature on a Giemsa-stained peripheral blood smear is the presence of **merozoites arranged in a cross-like formation**, known as the **"Maltese Cross"** or **tetrad**. This occurs due to the parasite budding in pairs without producing pigment or gametocytes. **Analysis of Options:** * **Malaria:** While *Plasmodium falciparum* also infects RBCs and can show multiple ring forms, it typically presents with **crescent-shaped gametocytes** or Schüffner’s dots. It never forms tetrads. * **Lyme disease:** Caused by the spirochete *Borrelia burgdorferi*, it is a bacterial infection. While it shares the same vector (*Ixodes* tick) as Babesiosis, it is an extracellular pathogen and does not infect RBCs. * **Plague:** Caused by *Yersinia pestis*, it is a gram-negative coccobacillus. On microscopy, it shows a characteristic **"safety-pin" appearance** (bipolar staining) but does not involve intra-erythrocytic tetrads. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Ixodes scapularis* (deer tick). Co-infection with Lyme disease is common. * **Clinical Presentation:** Fever, hemolytic anemia, and hemoglobinuria. It is particularly severe or fatal in **asplenic patients**. * **Diagnosis:** Peripheral smear (Maltese cross) is the gold standard; PCR is more sensitive. * **Treatment:** Combination of **Atovaquone + Azithromycin** (preferred) or Quinine + Clindamycin.

Q: Sandfly acts as a vector to all of the following diseases, EXCEPT?

Onchocerciasis. **Explanation:** The correct answer is **D. Onchocerciasis**. The **Sandfly** (*Phlebotomus* species in the Old World and *Lutzomyia* in the New World) is a significant medical vector. However, **Onchocerciasis** (River Blindness), caused by the nematode *Onchocerca volvulus*, is transmitted by the bite of the **Blackfly** (*Simulium* species). **Analysis of Options:** * **Oriental Sore (A):** This is a form of Old World Cutaneous Leishmaniasis caused by *Leishmania tropica*. It is transmitted by the bite of the female Sandfly. * **Oraya Fever (B):** Also known as Carrion’s disease (caused by *Bartonella bacilliformis*), this bacterial infection is transmitted by the *Lutzomyia* sandfly, primarily in the Andes region of South America. * **Kala-azar (C):** Visceral Leishmaniasis, caused by *Leishmania donovani*, is the most clinically significant disease transmitted by the *Phlebotomus argentipes* sandfly in the Indian subcontinent. **Clinical Pearls for NEET-PG:** 1. **Sandfly Characteristics:** They are small, fuzzy, and fly in short hops. Only the **females** bite as they require a blood meal for egg production. 2. **Leishmaniasis Life Cycle:** The sandfly injects the **promastigote** stage into the human host; inside the host, these transform into **amastigotes** within macrophages. 3. **Vector Mnemonic:** * **Sandfly:** Leishmaniasis, Sandfly fever (Pappataci fever), Chandipura virus, and Bartonellosis. * **Blackfly:** Onchocerciasis (Remember: **B**lackfly = **B**lindness). * **Tsetse fly:** Sleeping Sickness (Trypanosomiasis).

Q: Duffy antigen is associated with which Plasmodium species?

Plasmodium vivax. ### Explanation **Correct Answer: C. Plasmodium vivax** **Mechanism and Pathophysiology:** *Plasmodium vivax* requires the **Duffy Antigen Receptor for Chemokines (DARC)**, located on the surface of red blood cells (RBCs), to act as a receptor for its attachment and subsequent invasion. Specifically, the parasite uses the **Duffy Binding Protein (DBP)** to bind to these receptors. Individuals who are **Duffy-negative** (genotype *Fy/Fy*, common in West African populations) are naturally resistant to *P. vivax* infection because the merozoites cannot penetrate the RBCs. **Analysis of Incorrect Options:** * **A. Plasmodium falciparum:** Uses multiple alternative receptors (like Glycophorin A, B, and C) to invade RBCs of all ages. It is not dependent on the Duffy antigen, which is why it remains the dominant species in Africa. * **B. Plasmodium ovale:** Primarily infects young RBCs (reticulocytes) but uses different, less clearly defined receptors. It is often found in Duffy-negative individuals where *P. vivax* cannot survive. * **D. Plasmodium malariae:** Prefers older RBCs (senescent cells) and does not utilize the Duffy antigen for entry. **NEET-PG High-Yield Pearls:** 1. **Selectivity:** *P. vivax* and *P. ovale* selectively infect **reticulocytes** (young RBCs), whereas *P. malariae* infects **old RBCs**, and *P. falciparum* infects **RBCs of all ages** (leading to high parasitemia). 2. **Relapse:** Both *P. vivax* and *P. ovale* form **hypnozoites** in the liver, which can cause clinical relapse months or years later. 3. **Schuffner’s Dots:** These are characteristic stippling seen on peripheral smears in *P. vivax* and *P. ovale* infections. 4. **Sickle Cell Trait:** Provides protection specifically against severe *P. falciparum* malaria, whereas **Duffy negativity** protects against *P. vivax*.

Q: Malaria affects all the following organs except?

Heart. **Explanation:** Malaria, caused by *Plasmodium* species, is a systemic protozoal infection characterized by an intra-erythrocytic life cycle. The pathophysiology primarily involves the destruction of Red Blood Cells (RBCs) and the sequestration of parasitized RBCs in the microvasculature of specific organs. **Why the Heart is the correct answer:** While severe malaria can lead to secondary hemodynamic changes (like tachycardia due to fever or anemia), the heart is **not** a primary target organ for the malarial parasite. Unlike the brain or kidneys, the heart does not typically show specific histopathological changes or primary organ failure directly caused by *Plasmodium* sequestration in routine clinical presentations. **Analysis of Incorrect Options:** * **Brain:** *P. falciparum* causes **Cerebral Malaria**. Parasitized RBCs express PfEMP-1, leading to cytoadherence in cerebral capillaries, causing microvascular obstruction, hypoxia, and coma. * **Liver:** The liver is the site of the **Exo-erythrocytic cycle**. Sporozoites infect hepatocytes to multiply (Schizogony). In *P. vivax* and *P. ovale*, dormant forms called **hypnozoites** persist here, causing relapses. * **Spleen:** The spleen is the primary organ for filtering damaged RBCs. Malaria typically causes **Splenomegaly** due to congestion and hyperplasia of the Reticuloendothelial system (RE system). **NEET-PG Clinical Pearls:** * **Blackwater Fever:** Intravascular hemolysis leading to hemoglobinuria, often associated with *P. falciparum* and quinine use. * **Tropical Splenomegaly Syndrome (HMS):** An abnormal immunologic response to malaria. * **Recrudescence:** Seen in *P. falciparum* (due to sub-optimal treatment); **Relapse:** Seen in *P. vivax/ovale* (due to hypnozoites).

Q: Which of the following helminths produces bile-stained eggs?

Taenia solium. **Explanation:** In parasitology, the presence or absence of **bile staining** is a crucial morphological feature used to identify helminth eggs in stool samples. Bile-stained eggs absorb bile pigments in the intestine, giving them a characteristic golden-brown or yellowish color. **1. Why Taenia solium is correct:** The eggs of *Taenia* species (both *T. solium* and *T. saginata*) are characterized by a thick, radially striated embryophore that is **bile-stained**. Inside the egg is a hexacanth embryo (oncosphere) with three pairs of hooklets. Because these eggs are exposed to bile in the small intestine, they consistently appear brown. **2. Why the other options are incorrect:** * **Ancylostoma duodenale & Necator americanus (Hookworms):** Both produce eggs that are **non-bile stained**. They are characterized by a thin, transparent hyaline shell and are usually seen in the 4-to-8-cell cleavage stage. * **Enterobius vermicularis (Pinworm):** These eggs are also **non-bile stained**. They have a unique "D-shape" (one side flattened) and a double-layered translucent shell. They are rarely found in feces as they are typically deposited on the perianal skin. **Clinical Pearls for NEET-PG:** * **Mnemonic for Bile-Stained Eggs:** Remember **"ABC of Bile"** — **A**scaris lumbricoides (Fertilized), **B**ile-stained (General), **C**lonorchis, and **T**aenia/**T**richuris. * **Non-Bile Stained Eggs:** Hookworms (*Ancylostoma, Necator*), *Enterobius*, and *Hymenolepis nana* (the only bile-stained exception in the Cestode group is *Taenia*; *H. nana* is colorless). * **High-Yield Fact:** *Taenia solium* eggs are indistinguishable from *Taenia saginata* eggs; species differentiation requires examining the gravid proglottid or the scolex.

Question 1

Which of the following parasite eggs consists of polar filaments arising from either end of the ambryophore?

Accepted Answer

Hymenolepis nana

Answer

Taenia saginata

Answer

Taenia solium

Answer

Echinococcus granulosus

Question 2

What is true about Plasmodium falciparum?

Accepted Answer

Crescentic macrogametocyte

Answer

Preferentially infects old erythrocytes only

Answer

Schuffner's dots are characteristic

Answer

Large schizonts

Question 3

What condition is characterized by the occurrence of tetrads in red blood cells?

Accepted Answer

Babesiosis

Answer

Malaria

Answer

Lyme disease

Answer

Plague

Question 4

Which is the most sensitive method for detecting low-density microfilaraemia?

Accepted Answer

Membrane filter concentration method

Answer

Mass blood survey

Answer

DEC Provocation test

Answer

Xenodiagnosis

Question 5

Sandfly acts as a vector to all of the following diseases, EXCEPT?

Accepted Answer

Onchocerciasis

Answer

Oriental sore

Answer

Oraya fever

Answer

Kala-azar

Question 6

Duffy antigen is associated with which Plasmodium species?

Accepted Answer

Plasmodium vivax

Answer

Plasmodium falciparum

Answer

Plasmodium ovale

Answer

Plasmodium malariae

Question 7

A 25-year-old man is exposed to Ascaris but does not develop clinical signs of infection. Which of the following mechanisms is likely to be responsible for his resistance to infection?

Accepted Answer

IgE-mediated type I hypersensitivity disrupting worm attachment

Answer

Antibody-mediated destruction of worm-infected host cells

Answer

Cytotoxic T-lymphocyte (CTL) induced apoptosis of worm-infected host cells

Answer

Complement-mediated lysis of worms attached to host tissues

Question 8

A 20-year-old female presents with complaints of vaginal itching, discharge, pain with intercourse, and discomfort with urination. She has had 3 different sexual partners over the past 2 years. A wet mount of vaginal secretions reveals a flagellated organism, approximately the size of a white blood cell, with "twitching motility", suggestive of Trichomonas vaginalis. Which of the following statements regarding Trichomonas vaginalis is FALSE?

Accepted Answer

The cyst form of the life cycle is the most common method of transmission.

Answer

Men are most likely asymptomatic but efficient transmitters of this organism.

Answer

Simultaneous treatment of the patient and her sexual contacts will decrease the chance of recurrences.

Answer

In severe cases, the regional mucosa may be red with petechial lesions, and the cervix has been described as a "strawberry cervix".

Question 9

Malaria affects all the following organs except?

Accepted Answer

Heart

Answer

Brain

Answer

Liver

Answer

Spleen

Question 10

Which of the following helminths produces bile-stained eggs?

Accepted Answer

Taenia solium

Answer

Ancylostoma duodenale

Answer

Enterobius vermicularis

Answer

Necator americanus

Parasitology — MCQs

Parasitology — MCQs

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