Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 711: Which of the following will give Medusa head colony on x-ray?

A. Hook worm infestation
B. Round worm infestation (Correct Answer)
C. Tenia solium infestation
D. Hook worm and Round worm infestation

Explanation: **Explanation:** The "Medusa head" appearance on an X-ray (specifically on a Barium meal follow-through) is a classic radiological sign of **Ascariasis (Roundworm infestation)** caused by *Ascaris lumbricoides*. **Why Roundworm is correct:** *Ascaris lumbricoides* are large nematodes (20–35 cm) that reside in the small intestine. When a large number of worms are present, they tend to intertwine or clump together. On a contrast X-ray, the barium outlines the external surfaces of these tangled worms, while some barium may be ingested by the worms themselves (appearing as central longitudinal streaks). This mass of intertwined, elongated shadows resembles the snake-like hair of the mythical figure Medusa, hence the term **"Medusa head appearance."** **Why other options are incorrect:** * **Hookworm (Ancylostoma/Necator):** These are much smaller (approx. 1 cm). They do not form large visible masses on X-rays; their clinical hallmark is iron deficiency anemia due to blood-sucking. * **Taenia solium:** While these are long tapeworms, they usually present as single infestations and do not form the characteristic tangled "Medusa head" mass. Radiological findings are more common in *Cysticercosis* (calcified cysts in muscles/brain). **High-Yield Clinical Pearls for NEET-PG:** * **Whirlpool Sign:** Seen on Ultrasonography in cases of intestinal ascariasis. * **Loeffler’s Syndrome:** Transient pulmonary infiltrates with eosinophilia caused by the larval migration of *Ascaris* through the lungs. * **Bolus Obstruction:** *Ascaris* is the most common helminthic cause of mechanical bowel obstruction in children. * **Biliary Ascariasis:** Can lead to cholecystitis, pancreatitis, or cholangitis.

Question 712: Which one of the following is characteristic of microfilaria of W. bancrofti?

A. Cephalic space twice as long as broad
B. Excretory pore prominent
C. Nuclear column smudged
D. Caudal end uniformly tapering to a delicate point, and no terminal nuclei present (Correct Answer)

Explanation: ### Explanation The identification of microfilariae in peripheral blood smears is a high-yield topic for NEET-PG, primarily based on morphological features like the presence of a sheath and the distribution of nuclei in the tail. **Why Option D is Correct:** *Wuchereria bancrofti* microfilariae are characterized by a **sheath** (which stains pink with Giemsa) and a body that curves in smooth, graceful loops. A defining diagnostic feature is the **caudal end (tail)**, which tapers to a point and is **devoid of nuclei**. In contrast, other species like *Brugia malayi* have terminal nuclei at the tip of the tail. **Analysis of Incorrect Options:** * **Option A:** In *W. bancrofti*, the **cephalic space** (the clear space at the anterior end) is short, with a length-to-breadth ratio of **1:1**. A cephalic space that is twice as long as it is broad (2:1) is characteristic of *Brugia malayi*. * **Option B:** The **excretory pore** is relatively small and inconspicuous in *W. bancrofti*. It is much more prominent and distinct in *Brugia malayi*. * **Option C:** The **nuclear column** (the central row of nuclei) in *W. bancrofti* consists of discrete, well-separated nuclei that can be easily counted. A "smudged" or blurred nuclear column is a feature associated with *Brugia malayi*. **High-Yield Clinical Pearls for NEET-PG:** 1. **Periodicity:** *W. bancrofti* usually exhibits **nocturnal periodicity** (10 PM to 2 AM), coinciding with the feeding habits of the *Culex* mosquito. 2. **Diagnostic Test of Choice:** The **Membrane Filtration Method** is the most sensitive for detecting microfilariae. 3. **Drug of Choice:** **Diethylcarbamazine (DEC)** is the standard treatment; however, it is contraindicated in patients with heavy *Loa loa* co-infection due to the risk of encephalopathy. 4. **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to microfilarial antigens, characterized by nocturnal cough, wheezing, and high peripheral eosinophilia.

Question 713: A fully embryonated egg of Trichuris trichiura contains which of the following?

A. Eight blastomeres
B. Unsegmented ova
C. Rhabditiform larva (Correct Answer)
D. Ciliated embryo

Explanation: **Explanation:** The correct answer is **C. Rhabditiform larva.** *Trichuris trichiura* (Whipworm) follows a direct life cycle. When eggs are passed in the feces, they are unsegmented and non-infective. For these eggs to become infective, they must undergo development in the soil (embryonation). During this process, the zygote matures into a **first-stage rhabditiform larva** within the eggshell. Therefore, a **fully embryonated egg** is the infective stage and contains a mature larva. **Analysis of Incorrect Options:** * **A. Eight blastomeres:** This represents an early stage of cleavage. While some helminths (like *Ancylostoma duodenale*) are passed in the 4-to-8 cell stage, *Trichuris* eggs are passed unsegmented. * **B. Unsegmented ova:** This is the state of the egg when it is **freshly passed** in the feces. It is not yet embryonated and is not infective to humans. * **D. Ciliated embryo:** This refers to a **Miracidium**, which is the larval stage found in the eggs of Trematodes (flukes), not Nematodes like *Trichuris*. **High-Yield NEET-PG Pearls:** * **Morphology:** *Trichuris* eggs are characteristically **barrel-shaped** (bile-stained) with **bipolar mucus plugs**. * **Infective Stage:** Embryonated egg containing rhabditiform larva (ingested via contaminated food/water). * **Clinical Presentation:** Heavy infections in children can lead to **rectal prolapse** due to increased peristalsis and mucosal edema. * **Diagnosis:** Stool microscopy for characteristic eggs; "Whip-like" adult worms may be seen on colonoscopy.

Question 714: What is the best preservative for protozoal cysts?

A. 10% formalin (Correct Answer)
B. Isopropyl alcohol
C. HCl solution
D. NaOH solution

Explanation: **Explanation:** In diagnostic parasitology, the primary goal of preservation is to maintain the morphology of protozoa and helminth eggs for microscopic examination. **Why 10% Formalin is the Correct Answer:** 10% Formalin (a 1:10 dilution of commercial formaldehyde) is the "gold standard" and most widely used preservative for fecal specimens. It acts as a chemical fixative that preserves the internal structures of **protozoal cysts**, helminth eggs, and larvae for long periods. It is particularly valued because it is compatible with various concentration techniques (like the Formalin-Ether sedimentation method) and permanent stained smears. **Analysis of Incorrect Options:** * **Isopropyl alcohol:** While alcohols are used as fixatives in cytology and for preserving adult worms/arthropods, they are not ideal for fecal protozoa as they can cause significant shrinkage and distortion of delicate cyst walls. * **HCl and NaOH solutions:** These are caustic agents. NaOH is typically used in microbiology for the decontamination of sputum (Petroff’s method) to kill commensal flora while preserving Mycobacteria. These chemicals would destroy or severely distort the morphology of protozoal cysts, making diagnosis impossible. **High-Yield Clinical Pearls for NEET-PG:** * **Two-Vial System:** Standard protocol often involves one vial of **10% Formalin** (for concentration/wet mounts) and one vial of **PVA (Polyvinyl Alcohol)** (for permanent staining like Trichrome). * **MIF (Merthiolate-Iodine-Formalin):** Another common preservative that both stains and preserves, though it is less effective for permanent smears. * **Trophozoites vs. Cysts:** While 10% formalin preserves cysts well, **trophozoites** usually require immediate examination or specialized fixatives like PVA or SAF (Sodium acetate-acetic acid-formalin) because they disintegrate rapidly.

Question 715: Which of the following protozoa is typically found in a cyst form?

A. Entamoeba fragilis
B. Balantidium coli (Correct Answer)
C. Trichomonas vaginalis
D. Giardia intestinalis

Explanation: ### Explanation **Correct Answer: B. Balantidium coli** **Why it is correct:** *Balantidium coli* is the largest protozoan and the only ciliate that infects humans. Its life cycle consists of two distinct stages: the **trophozoite** (motile, feeding stage) and the **cyst** (infective, resistant stage). The cyst is the form typically found in formed stools and is responsible for transmission via the feco-oral route, usually associated with pig contact. **Analysis of Incorrect Options:** * **A. Dientamoeba fragilis:** Despite its name, this is a flagellate. A key high-yield characteristic is that it **lacks a cyst stage**. It exists only as a trophozoite, and transmission is hypothesized to occur via the eggs of *Enterobius vermicularis*. * **C. Trichomonas vaginalis:** This urogenital parasite exists **only in the trophozoite stage**. Because it lacks a resistant cyst form, it cannot survive long outside the host, necessitating direct sexual contact for transmission. * **D. Giardia intestinalis:** While *Giardia* **does** have a cyst form, the question asks which is "typically found" in a cyst form among the choices provided. However, in many competitive exams like NEET-PG, when *D. fragilis* and *T. vaginalis* (which strictly lack cysts) are options, the focus shifts to identifying which organisms *possess* a cyst. In this specific question context, *B. coli* is highlighted as the classic example of a cyst-forming intestinal protozoan. *(Note: If this were a "multiple correct" scenario, Giardia would also be correct; however, in single-best-response, B. coli is often the intended answer in specific parasitology modules focusing on ciliates).* **NEET-PG High-Yield Pearls:** * **No Cyst Stage:** *Trichomonas vaginalis*, *Dientamoeba fragilis*, and *Entamoeba gingivalis*. * **Balantidium coli:** Look for "pig farmers" or "ciliates" in the clinical stem. It causes "balantidial dysentery" with ulcers similar to *E. histolytica* but larger. * **Staining:** *B. coli* cysts are easily identified by a large, kidney-shaped (reniform) macronucleus.

Question 716: 'Maltese Cross' is a characteristic feature of:

A. Cryptococcus Neoformans
B. Babesia Microti (Correct Answer)
C. Blastomycosis
D. Penicillium Marneffei

Explanation: **Explanation:** The **'Maltese Cross'** appearance is a pathognomonic finding in **Babesia microti** infections. This characteristic feature occurs during the intra-erythrocytic stage of the parasite's life cycle, where the trophozoites undergo asexual reproduction (budding) to form a **tetrad of four daughter merozoites** connected at their bases. This arrangement resembles the heraldic Maltese Cross and is best visualized on Giemsa or Wright-stained peripheral blood smears. **Analysis of Options:** * **Babesia microti (Correct):** A protozoan parasite transmitted by the *Ixodes* tick. It infects RBCs, mimicking Malaria, but is distinguished by the absence of hemozoin pigment and the presence of the tetrad (Maltese Cross) form. * **Cryptococcus neoformans:** While it does not show a tetrad in RBCs, its polysaccharide capsule exhibits a "Maltese Cross" pattern only under **polarized light** (birefringence), not on standard smears. * **Blastomycosis:** Characterized by large, thick-walled yeast cells with **broad-based budding**. * **Penicillium marneffei (Talaromyces):** A dimorphic fungus characterized by intracellular yeast cells that divide by **fission** (forming a transverse septum), not budding or tetrad formation. **NEET-PG High-Yield Pearls:** 1. **Vector:** *Ixodes scapularis* (same as Lyme disease and Anaplasmosis). 2. **Clinical Presentation:** Fever, hemolytic anemia, and hemoglobinuria; severe in asplenic patients. 3. **Drug of Choice:** Atovaquone + Azithromycin (Mild); Quinine + Clindamycin (Severe). 4. **Differential Diagnosis:** Often confused with *Plasmodium falciparum* (ring forms), but Babesia lacks gametocytes and intracellular pigment.

Question 717: Culex mosquito spreads all of the following diseases except?

A. Viral arthritis
B. West Nile fever
C. Yellow fever (Correct Answer)
D. Bancroftian filariasis

Explanation: **Explanation:** The correct answer is **Yellow fever** because it is primarily transmitted by the **Aedes aegypti** mosquito (and *Haemagogus* species in jungle cycles), not by the *Culex* mosquito. **Why Yellow Fever is the correct answer:** Yellow fever is a viral hemorrhagic fever caused by a Flavivirus. Its transmission cycle involves *Aedes* mosquitoes in urban settings. *Culex* mosquitoes are not biological vectors for this specific virus. **Analysis of other options:** * **Viral arthritis:** Several viruses causing arthritis, most notably the **Ross River virus** and **Sindbis virus**, are transmitted by *Culex* species. * **West Nile fever:** The *Culex* mosquito (specifically *C. pipiens*) is the primary vector for West Nile Virus, maintaining the transmission cycle between birds and humans. * **Bancroftian filariasis:** In many parts of the world, especially in urban and semi-urban areas of India, **Culex quinquefasciatus** is the classic vector for *Wuchereria bancrofti*. **High-Yield Clinical Pearls for NEET-PG:** 1. **Culex Characteristics:** They are "night-biters," breed in stagnant polluted water (like sewage), and fly with the body parallel to the surface. 2. **Diseases transmitted by Culex:** * **J**apanese Encephalitis (Vector: *Culex tritaeniorhynchus*) * **B**ancroftian Filariasis (*Culex quinquefasciatus*) * **W**est Nile Fever * **V**iral Arthritis (Ross River/Sindbis) 3. **Aedes vs. Culex:** Remember that *Aedes* transmits the "Big Three": Dengue, Chikungunya, and Yellow Fever, along with Zika. 4. **Japanese Encephalitis (JE):** This is the most important viral encephalitis transmitted by *Culex* in India; the mosquito acts as a bridge vector between pigs/herons and humans.

Question 718: Diphyllobothrium latum causes anemia by:

A. Its blood-sucking activities
B. The production of a toxin that affects hematopoiesis
C. Competition with the host for vitamin B12 (Correct Answer)
D. Occlusion of the common bile duct

Explanation: ### Explanation **Correct Answer: C. Competition with the host for vitamin B12** *Diphyllobothrium latum* (the Fish Tapeworm) is the largest tapeworm infecting humans. The primary mechanism for anemia is **nutritional competition**. The adult worm has a high affinity for Vitamin B12 and can absorb up to 80-100% of the host’s dietary intake. This leads to a Vitamin B12 deficiency, resulting in **Megaloblastic Anemia** (also known as Bothriocephalus anemia), which is clinically indistinguishable from Pernicious Anemia. **Why the other options are incorrect:** * **A. Blood-sucking activities:** This is the mechanism for *Ancylostoma duodenale* and *Necator americanus* (Hookworms), which cause Iron Deficiency Anemia. * **B. Production of a toxin:** While some parasites cause pathology via metabolic byproducts, *D. latum* does not produce a specific hematopoiesis-inhibiting toxin. * **D. Occlusion of the common bile duct:** This is a classic complication of *Ascaris lumbricoides* (migration) or *Clonorchis sinensis* (liver fluke), but it is not a feature of *D. latum* or a cause of its associated anemia. **High-Yield Clinical Pearls for NEET-PG:** * **Infective Stage:** Plerocercoid larva (found in undercooked freshwater fish). * **Diagnostic Stage:** Operculated eggs in stool (unembryonated). * **Morphology:** Scolex has two slit-like sucking grooves called **Bothria**. * **Key Association:** It is the only parasite classically associated with **Vitamin B12 deficiency** and megaloblastic changes. * **Treatment:** Praziquantel is the drug of choice.

Question 719: Which of the following diseases worldwide is transmitted by the mosquito genera Culex, Anopheles, and Aedes?

A. Malaria
B. Dengue
C. Filariasis (Correct Answer)
D. Yellow Fever

Explanation: ### Explanation **Correct Answer: C. Filariasis** **Why Filariasis is Correct:** Lymphatic Filariasis (caused primarily by *Wuchereria bancrofti* and *Brugia malayi*) is unique because it can be transmitted by multiple genera of mosquitoes depending on the geographical location and the species of the parasite. * **Culex:** The most common vector worldwide (especially *Culex quinquefasciatus* in urban/semi-urban areas). * **Anopheles:** A major vector in rural areas, particularly in Africa. * **Aedes:** Transmits the sub-periodic form in the Pacific islands. * **Mansonia:** The primary vector for *Brugia malayi* (often found near water plants like *Pistia*). **Why Other Options are Incorrect:** * **A. Malaria:** Exclusively transmitted by the female **Anopheles** mosquito. * **B. Dengue:** Transmitted primarily by **Aedes aegypti** and occasionally *Aedes albopictus*. * **D. Yellow Fever:** Also transmitted by the **Aedes** genus (specifically *Aedes aegypti* in urban cycles and *Haemagogus* in jungle cycles). **NEET-PG High-Yield Pearls:** 1. **Vector for Brugia malayi:** Specifically **Mansonia** mosquitoes. Control involves the removal of aquatic plants (*Pistia stratiotes*). 2. **Nocturnal Periodicity:** Microfilariae of *W. bancrofti* appear in peripheral blood between **10 PM and 2 AM**, coinciding with the biting habits of the Culex vector. 3. **Drug of Choice:** **Diethylcarbamazine (DEC)** is the standard treatment; however, it is contraindicated in Onchocerciasis (due to Mazzotti reaction). 4. **National Health Goal:** India aims for the **Elimination of Lymphatic Filariasis (ELF)** using Mass Drug Administration (MDA) with DEC + Albendazole (and recently, Ivermectin/IDA triple therapy).

Question 720: Hookworm thrives on what component of blood?

A. Whole blood
B. Plasma (Correct Answer)
C. Serum
D. Red blood cells

Explanation: ### Explanation The correct answer is **Plasma**. **Underlying Medical Concept:** Hookworms (*Ancylostoma duodenale* and *Necator americanus*) are hematophagous nematodes that attach to the mucosal villi of the small intestine using their buccal capsules. While it is a common misconception that they consume whole blood for nutrition, they primarily ingest blood to extract **plasma proteins and glucose**. The hookworm’s digestive tract is inefficient at processing solid cellular components. Once the worm draws blood, it rapidly passes the red blood cells (RBCs) through its intestine relatively intact and unutilized. The worm primarily utilizes the liquid portion—**plasma**—as its main source of nourishment. The iron deficiency anemia associated with hookworm infestation is actually a result of the **accidental loss of RBCs** (hemorrhage) caused by the worm's anticoagulant (ancylostomin) and its inability to digest the iron-rich hemoglobin it ingests. **Analysis of Incorrect Options:** * **A. Whole blood:** Although the worm ingests whole blood, it does not "thrive" on it entirely; it selectively utilizes plasma components and discards the rest. * **C. Serum:** Serum is plasma minus clotting factors. Since the worm ingests circulating blood (which contains fibrinogen), it is consuming plasma, not serum. * **D. Red blood cells:** Hookworms cannot effectively digest the hemoglobin within RBCs. The RBCs are excreted in the host's feces, leading to the characteristic occult blood loss. **NEET-PG High-Yield Pearls:** * **Daily blood loss:** *A. duodenale* (0.15–0.2 ml/day) causes more blood loss than *N. americanus* (0.03 ml/day). * **Clinical Presentation:** Microcytic hypochromic anemia (Iron deficiency) and Ground itch (at the site of larval entry). * **Infective Stage:** Filariform larva (L3). * **Diagnostic Feature:** Non-bile stained, segmented eggs with a clear space between the shell and the embryo.

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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