Parasitology Practice Questions

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.

Q: Trichomoniasis is transmitted through which stage?

Trophozoite. ### Explanation **Correct Answer: D. Trophozoite** **Medical Concept:** *Trichomonas vaginalis* is a flagellated protozoan that is unique because it **exists only in the trophozoite stage**. Unlike most intestinal protozoa (like *Entamoeba* or *Giardia*), it does not possess a cyst stage in its life cycle. Since there is no cyst to protect the organism from environmental stress, it is primarily transmitted through direct mucosal contact—most commonly via sexual intercourse. The pear-shaped, motile trophozoite is both the **infective stage** and the **diagnostic stage**. **Why the other options are incorrect:** * **A. Cyst:** While cysts are the infective stage for many protozoa (e.g., *E. histolytica*), *Trichomonas* does not form cysts. This is why it cannot survive long outside the human host. * **B. Oocyst:** This stage is characteristic of Apicomplexan parasites like *Cryptosporidium*, *Cyclospora*, and *Toxoplasma*. * **C. Sporozoite:** This is the infective stage for *Plasmodium* (Malaria), transmitted via the bite of an infected female Anopheles mosquito. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Causes a foul-smelling, **frothy, yellowish-green vaginal discharge** and vulvar irritation. * **Strawberry Cervix:** Colposcopy may reveal punctate hemorrhages on the cervix (Cervicitis emphysematosa), a classic board-exam finding. * **Diagnosis:** The gold standard is **Whiff test** (KOH) and **Wet mount microscopy**, which shows "jerky, twitching motility." Culture (Diamond’s medium) is the most sensitive method. * **Treatment:** The drug of choice is **Metronidazole**. It is crucial to **treat both partners** to prevent "ping-pong" reinfection.

Q: Which of the following filarial worms is not found in the blood?

Onchocerca volvulus. ### Explanation The diagnostic hallmark of filarial infections is the detection of **microfilariae** (embryonic larvae). The location of these microfilariae determines the diagnostic specimen required. **Why Onchocerca volvulus is the correct answer:** Unlike most filarial nematodes, the microfilariae of *Onchocerca volvulus* (the causative agent of River Blindness) do not circulate in the peripheral blood. Instead, they reside in the **subcutaneous lymphatics and the dermis**. Therefore, the diagnosis is made via **skin snips** rather than blood films. **Analysis of Incorrect Options:** * **Wuchereria bancrofti & Brugia malayi:** These are lymphatic filarial worms. Their microfilariae circulate in the peripheral blood, typically exhibiting **nocturnal periodicity** (peak density between 10 PM and 2 AM). * **Loa loa:** Also known as the African eye worm, its microfilariae circulate in the blood with **diurnal periodicity** (peak density during the day). **NEET-PG High-Yield Pearls:** 1. **Specimen of Choice:** * Blood: *W. bancrofti, B. malayi, Loa loa, Mansonella* species. * Skin Snip: *Onchocerca volvulus, Mansonella streptocerca*. 2. **Vector Mnemonic:** * *W. bancrofti*: *Culex* (urban), *Anopheles* (rural), *Aedes*. * *Onchocerca*: *Simulium* (Blackfly). * *Loa loa*: *Chrysops* (Deerfly/Mango fly). 3. **Clinical Signs:** *Onchocerca* is associated with **Mazzotti reaction** (severe immune response to dying microfilariae after treatment) and "hanging groin." 4. **Drug of Choice:** **Ivermectin** is the treatment of choice for *Onchocerca*, whereas **Diethylcarbamazine (DEC)** is used for *W. bancrofti*. (Note: DEC is contraindicated in Onchocerciasis due to the risk of severe ocular damage).

Q: Which of the following is NOT a usual feature of Ascariasis?

Anemia. **Explanation:** The correct answer is **Anemia (Option C)** because *Ascaris lumbricoides* (Giant Roundworm) does not feed on host blood. Unlike hookworms (*Ancylostoma duodenale* and *Necator americanus*), which attach to the intestinal mucosa and cause chronic blood loss leading to Iron Deficiency Anemia, *Ascaris* lives freely in the intestinal lumen and competes with the host for nutrients, leading to malnutrition and Vitamin A deficiency rather than anemia. **Analysis of other options:** * **Abdominal pain (Option A):** This is a common symptom. Large burdens of adult worms can cause mechanical irritation, vague abdominal discomfort, or even intestinal obstruction (the most common complication in children). * **Urticaria (Option B):** During the life cycle, *Ascaris* larvae migrate through various tissues. This migration triggers a Type I hypersensitivity reaction, often manifesting as allergic symptoms like urticaria (hives) or angioedema. * **Loeffler’s syndrome (Option D):** This is a classic feature occurring during the pulmonary phase of larval migration. It is characterized by transient pulmonary infiltrates on X-ray, cough, dyspnea, and peripheral eosinophilia. **High-Yield Clinical Pearls for NEET-PG:** * **Most common helminthic infection** worldwide: *Ascaris lumbricoides*. * **Infective stage:** Embryonated egg; **Diagnostic stage:** Bile-stained eggs in stool. * **Complications:** Biliary ascariasis (causing cholangitis or pancreatitis) and intestinal bolus obstruction at the ileocecal valve. * **Drug of choice:** Albendazole or Mebendazole.

Question 1

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 2

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 3

Duffy antigen is associated with which Plasmodium species?

Accepted Answer

Plasmodium vivax

Answer

Plasmodium falciparum

Answer

Plasmodium ovale

Answer

Plasmodium malariae

Question 4

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 5

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 6

Malaria affects all the following organs except?

Accepted Answer

Heart

Answer

Brain

Answer

Liver

Answer

Spleen

Question 7

Which of the following helminths produces bile-stained eggs?

Accepted Answer

Taenia solium

Answer

Ancylostoma duodenale

Answer

Enterobius vermicularis

Answer

Necator americanus

Question 8

Trichomoniasis is transmitted through which stage?

Accepted Answer

Trophozoite

Answer

Cyst

Answer

Oocyst

Answer

Sporozoite

Question 9

Which of the following filarial worms is not found in the blood?

Accepted Answer

Onchocerca volvulus

Answer

Wuchereria bancrofti

Answer

Brugia malayi

Answer

Loa loa

Question 10

Which of the following is NOT a usual feature of Ascariasis?

Accepted Answer

Anemia

Answer

Abdominal pain

Answer

Urticaria

Answer

Loeffler's syndrome

Parasitology — MCQs

Parasitology — MCQs

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