Parasitology Practice Questions

Q: Diphyllobothrium latum is transmitted by which of the following modes?

Ingestion of plerocercoids through raw or undercooked fish. **Explanation:** *Diphyllobothrium latum* (the Fish Tapeworm) is the largest parasite infecting humans. Its complex life cycle involves two intermediate hosts: first, a **copepod** (crustacean), and second, a **freshwater fish**. **1. Why Option C is Correct:** The infective stage for humans is the **Plerocercoid larva** (also known as the sparganum). After a fish consumes an infected copepod, the larvae migrate into the fish's muscle. Humans acquire the infection by **ingesting raw or undercooked fish** containing these plerocercoids. Once inside the human intestine, they develop into adult worms. **2. Why the Other Options are Incorrect:** * **Options A & B:** **Cercariae** are the infective stages for Trematodes (Flukes), such as *Schistosoma*, not Cestodes (Tapeworms). In the *D. latum* cycle, the stage found in copepods is the *procercoid* larva, not cercariae. * **Option D:** **Metacercariae** are the infective stages for hermaphroditic flukes (e.g., *Fasciola hepatica*, *Clonorchis sinensis*). While copepods are involved in the life cycle of *D. latum*, they harbor *procercoids*, not metacercariae. **Clinical Pearls for NEET-PG:** * **Vitamin B12 Deficiency:** *D. latum* competes with the host for Vitamin B12 absorption in the jejunum, leading to **Megaloblastic Anemia** and subacute combined degeneration of the spinal cord. * **Operculated Eggs:** It is the only human tapeworm that produces operculated eggs (similar to fluke eggs) and has a ciliated larval stage called **Coracidium**. * **Treatment:** Praziquantel is the drug of choice.

Q: What is the basis for the 'Dipstick Test' used for the rapid diagnosis of Plasmodium falciparum?

Histidine-rich protein. ### Explanation The correct answer is **D. Histidine-rich protein (HRP-2)**. **1. Why Histidine-rich protein is correct:** Rapid Diagnostic Tests (RDTs) for Malaria, often called the 'Dipstick Test', utilize immunochromatographic methods to detect specific circulating antigens. **Histidine-rich protein 2 (HRP-2)** is a water-soluble protein produced specifically by the asexual stages and young gametocytes of ***Plasmodium falciparum***. Because HRP-2 is secreted into the host’s bloodstream, it serves as a highly sensitive biomarker for diagnosing *P. falciparum* infections, even when parasite density is low. **2. Why the other options are incorrect:** * **Arginine, Serine, and Tyrosine-rich proteins:** While *Plasmodium* species do possess various proteins rich in these amino acids (e.g., Serine-repeat antigen), they are not utilized in commercial rapid diagnostic dipsticks. HRP-2 is uniquely targeted because of its high expression levels and specificity to the *falciparum* species. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Target Antigens:** * **HRP-2:** Specific for *P. falciparum* only. * **pLDH (Parasite Lactate Dehydrogenase):** Produced by all four species (*P. falciparum, P. vivax, P. ovale, P. malariae*). It indicates the presence of **viable** parasites. * **Persistence:** HRP-2 can persist in the blood for **2–4 weeks** even after successful treatment. Therefore, a positive dipstick test immediately after treatment may represent a "false positive" for active infection. * **Prozone Effect:** Very high parasitemia can sometimes lead to a false-negative result in RDTs due to the prozone phenomenon. * **Gold Standard:** Despite the convenience of RDTs, **Microscopy** (Peripheral Smear) remains the gold standard for malaria diagnosis.

Q: Which of the following is false about Echinococcus granulosus?

Hydatid fluid is secreted by the ectocyst. **Explanation:** The correct answer is **D**. In *Echinococcus granulosus* (Hydatid disease), the cyst wall consists of three layers. The **ectocyst** is the outermost, thick, fibrous layer formed by the **host’s inflammatory response**. It is not a part of the parasite itself and does not secrete fluid. The hydatid fluid is actually secreted by the **endocyst** (germinal layer), which is the innermost, metabolically active layer of the parasite. **Analysis of Options:** * **A. Man is the dead-end host:** True. Humans act as accidental intermediate hosts. Since the life cycle is broken (human-to-dog transmission does not occur), they are considered dead-end hosts. * **B. It causes hydatid disease:** True. *E. granulosus* is the causative agent of cystic echinococcosis, commonly known as hydatid disease, primarily affecting the liver and lungs. * **C. Casoni's test is sensitive:** True. This is an immediate hypersensitivity skin test. While it has high sensitivity (approx. 90%), it is rarely used today due to low specificity and the risk of anaphylaxis; it has been replaced by serology (ELISA) and imaging. **High-Yield Clinical Pearls for NEET-PG:** * **Definitive Host:** Dog (adult worm lives in the intestine). * **Intermediate Host:** Sheep (natural) and Man (accidental). * **Infective Stage:** Embryonated eggs (found in dog feces). * **Hydatid Sand:** Consists of free scolices, daughter cysts, and hooklets found within the fluid. * **Water Lily Sign:** Seen on imaging when the endocyst ruptures and floats within the ectocyst. * **Treatment:** PAIR (Puncture, Aspiration, Injection, Re-aspiration) technique and Albendazole. Avoid cyst rupture to prevent life-threatening **anaphylactic shock**.

Q: A patient diagnosed with malaria has a peripheral blood smear showing all stages of schizonts with 14-20 merozoites and yellowish-brown pigment. What is the most likely type of malaria?

Plasmodium vivax. ### Explanation The correct answer is **Plasmodium vivax**. The diagnosis of malaria species via peripheral blood smear relies on specific morphological characteristics of the parasite and the infected Red Blood Cells (RBCs). **Why Plasmodium vivax is correct:** * **Schizont Morphology:** *P. vivax* schizonts are large and typically contain **12–24 merozoites** (matching the 14–20 range in the question). * **Pigment:** It characteristically shows **yellowish-brown (golden-brown)** hemozoin pigment. * **RBC Appearance:** *P. vivax* infects young RBCs (reticulocytes), causing the cells to become **enlarged/hypertrophied** and often showing Schüffner’s dots. * **Stages Present:** Unlike *P. falciparum*, all stages (trophozoites, schizonts, and gametocytes) are commonly seen in the peripheral blood. **Why the other options are incorrect:** * **P. falciparum:** Typically, only ring forms and crescent-shaped gametocytes are seen in peripheral blood. Schizonts are rarely seen as they are sequestered in deep capillaries. When present, they contain 8–36 merozoites and dark black pigment. * **P. malariae:** Schizonts typically show a **"Rosette appearance"** with only **6–12 merozoites**. The pigment is usually dark brown/black. It infects older RBCs, so the cells are not enlarged. * **P. ovale:** While it also shows Schüffner’s dots and 6–12 merozoites, the infected RBCs are typically **oval-shaped with fimbriated (tufted) edges**. **High-Yield NEET-PG Pearls:** * **P. vivax & P. ovale:** Associated with **Hypnozoites** (latent liver stages) causing relapses; treated with Primaquine. * **P. falciparum:** Associated with **Maurer’s dots** and multiple rings per RBC (Accole/Applique forms). * **P. malariae:** Associated with **Ziemann’s dots** and "Band forms." * **P. knowlesi:** A zoonotic malaria showing a 24-hour erythrocytic cycle (quotidian fever).

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: 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).

Question 1

Diphyllobothrium latum is transmitted by which of the following modes?

Accepted Answer

Ingestion of plerocercoids through raw or undercooked fish

Answer

Ingestion of cercariae through copepods

Answer

Ingestion of cercariae through fish meal

Answer

Ingestion of metacercariae in copepods

Question 2

What is the basis for the 'Dipstick Test' used for the rapid diagnosis of Plasmodium falciparum?

Accepted Answer

Histidine-rich protein

Answer

Arginine-rich protein

Answer

Serine-rich protein

Answer

Tyrosine-rich protein

Question 3

Which of the following is false about Echinococcus granulosus?

Accepted Answer

Hydatid fluid is secreted by the ectocyst

Answer

Man is the dead-end host

Answer

It causes hydatid disease

Answer

Casoni's test is sensitive

Question 4

A patient diagnosed with malaria has a peripheral blood smear showing all stages of schizonts with 14-20 merozoites and yellowish-brown pigment. What is the most likely type of malaria?

Accepted Answer

Plasmodium vivax

Answer

Plasmodium falciparum

Answer

Plasmodium malariae

Answer

Plasmodium ovale

Question 5

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 6

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 7

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 8

A 20-year-old man presents with swelling of the left lower limb and hydrocele. Which of the following is NOT a causative agent for these symptoms?

Accepted Answer

Onchocerca volvulus

Answer

Brugia malayi

Answer

Brugia timori

Answer

Wuchereria bancrofti

Question 9

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 10

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

Parasitology — MCQs

Parasitology — MCQs

On this page

Practice by Chapter

Want unlimited practice?