Parasitology Practice Questions

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

Round worm infestation. **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.

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

Rhabditiform larva. **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.

Q: What is the best preservative for protozoal cysts?

10% formalin. **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.

Q: 'Maltese Cross' is a characteristic feature of:

Babesia Microti. **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.

Q: Culex mosquito spreads all of the following diseases except?

Yellow fever. **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.

Q: Diphyllobothrium latum causes anemia by:

Competition with the host for vitamin B12. ### 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.

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

Filariasis. ### 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).

Q: Hookworm thrives on what component of blood?

Plasma. ### 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.

Question 1

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

Accepted Answer

Round worm infestation

Answer

Hook worm infestation

Answer

Tenia solium infestation

Answer

Hook worm and Round worm infestation

Question 2

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

Accepted Answer

Caudal end uniformly tapering to a delicate point, and no terminal nuclei present

Answer

Cephalic space twice as long as broad

Answer

Excretory pore prominent

Answer

Nuclear column smudged

Question 3

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

Accepted Answer

Rhabditiform larva

Answer

Eight blastomeres

Answer

Unsegmented ova

Answer

Ciliated embryo

Question 4

What is the best preservative for protozoal cysts?

Accepted Answer

10% formalin

Answer

Isopropyl alcohol

Answer

HCl solution

Answer

NaOH solution

Question 5

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

Accepted Answer

Balantidium coli

Answer

Entamoeba fragilis

Answer

Trichomonas vaginalis

Answer

Giardia intestinalis

Question 6

'Maltese Cross' is a characteristic feature of:

Accepted Answer

Babesia Microti

Answer

Cryptococcus Neoformans

Answer

Blastomycosis

Answer

Penicillium Marneffei

Question 7

Culex mosquito spreads all of the following diseases except?

Accepted Answer

Yellow fever

Answer

Viral arthritis

Answer

West Nile fever

Answer

Bancroftian filariasis

Question 8

Diphyllobothrium latum causes anemia by:

Accepted Answer

Competition with the host for vitamin B12

Answer

Its blood-sucking activities

Answer

The production of a toxin that affects hematopoiesis

Answer

Occlusion of the common bile duct

Question 9

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

Accepted Answer

Filariasis

Answer

Malaria

Answer

Dengue

Answer

Yellow Fever

Question 10

Hookworm thrives on what component of blood?

Accepted Answer

Plasma

Answer

Whole blood

Answer

Serum

Answer

Red blood cells

Parasitology — MCQs

Parasitology — MCQs

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