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Ch. 23 - Parasitic Protozoa, Helminths, and Arthropod Vectors
Bauman - Microbiology with Diseases by Taxonomy 6th Edition
Bauman6th EditionMicrobiology with Diseases by TaxonomyISBN: 9780134832302Not the one you use?Change textbook
All textbooksBauman 6th EditionCh. 23 - Parasitic Protozoa, Helminths, and Arthropod VectorsProblem 10
Chapter 23, Problem 10

The immature fluke stages that infect snail intermediate hosts are called __________.


a. metacercariae
b. cercariae
c. cysticerci
d. miracidia

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1
Understand the life cycle of flukes (trematodes), which typically involves multiple stages including eggs, miracidia, sporocysts, rediae, cercariae, metacercariae, and adult flukes.
Identify the stage that specifically infects the snail intermediate host. Miracidia are the free-swimming larval stage that hatches from eggs and actively seeks out and penetrates the snail host.
Recall that cercariae are the next larval stage that emerges from the snail to infect the next host, and metacercariae are encysted forms that infect the definitive host, not the snail.
Note that cysticerci are larval forms of tapeworms, not flukes, so they are not relevant to this question.
Conclude that the immature fluke stage that infects the snail intermediate host is the miracidia.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Life Cycle of Flukes (Trematodes)

Flukes have complex life cycles involving multiple hosts, typically including a snail as an intermediate host. Understanding the stages—miracidia, sporocysts, rediae, cercariae, and metacercariae—is essential to identify which stage infects the snail and which infects the definitive host.
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Miracidia Stage

Miracidia are the free-swimming larval stage that hatches from eggs and actively seeks out and infects the snail intermediate host. This stage is crucial as it initiates the infection within the snail, leading to further development of the parasite.
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Cercariae Stage

Cercariae are the motile larval stage that emerges from the snail after development. They leave the snail to infect the next host, either directly or by encysting as metacercariae. Recognizing cercariae as the stage that exits the snail helps distinguish it from earlier stages like miracidia.
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Related Practice
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Both of the following parasites demonstrate nocturnal movement, which is important during diagnosis: __________ and _____________ .

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The beef tapeworm is known by what scientific name? 

a. Taenia solium

b. Taenia saginata

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Enterobius vermicularis is commonly called:

a. Hookworm

b. Pinworm

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