Characteristics of Phylum Platyhelminthes

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Parasitology Exam 3

What is the layman's term for the Phylum Platyhelminthes?

flatworms

What are the two major groups in Platyhelminthes?

Class trematoda or flukes
Class Cestoda or tapeworms

Describe generally what an adult flatworm looks like?

Dorsoventrally flattened, bilaterally symmetrical, w/out a true body cavity

Flatworms have a living _ and their internal body spaces are fill with what?

Living tegument
Filled with parenchyma, a gel-liked matrix in which the body organs are embedded
No cuticle

What kind of body systems do flatworms have?

No circulatory or respiratory systems
Digestive system may be incomplete/blind sac (trematoda) or absent (cestoda)

What kind of reproductive system do flatworms have?

Most are hemaphroditic, w/both male and female reproductive organs in same individual or segment

What do flatworms use the anterior sucker for and what is it called?

Oral sucker
Used in feeding

What do flatworms use the posterior sucker for and what is it called?

Ventral sucker or acetabulum
Used for hanging on and maintaining position

Where will adult flukes live in the body?

Any organ!
But prefer digestive tract or related ducts, lungs, vasculature, urinary bladder

What kind of flukes are we most concerned with?

Lung flukes, GI and liver flukes, blood flukes

What kind of life cycle do digenetic trematodes have?

Indirect!
1 or more IH and alternation of sexual and asexual generations

What is ALWAYS the first IH for digenetic trematodes and what happens in the it?

Mollusc (snail or clam)
Several larval stages occur and asexual multiplication

What happens when the eggs are passed into the environment?

Eggs passed to outside develop to first stage larva inside

What is the first stage larva called?

Miracidium

What kind of environment does the trematodes need to complete the life cycle?

An aquatic environment

What happens to the miracidium/egg?

Miracidium either hatches, swims and penetrates a snail or the egg and miracidium are eaten by the snail

In snail, miracidium gives rise to other larval stages, the _ and _

Sporocytes
Rediae

Describe the differences between sporocytes and rediae.

Sporocytes- immobile, non-feeding sacs
Rediae- move around and feed

What occurs within the sporocyst and rediae stages?

Asexual reproduction

What do the sporocyst/rediae eventually give rise to?

Cercariae

What does the cercariae do?

Leaves the snail
Then either penetrate the DH (man, dog, etc) or penetrate another IH and encyst there as metacercariae
Metacercariae may also encyst on vegetation

What is the name of the larval form in the 2nd IH?

Metacercariae

How does a flatworm eventually enter the body

Metacercariae encysted either on plants or in/on 2nd IH are eaten by DH.
Also cercariae can penetrate the DH directly

How are trematode infections diagnosed?

Finding eggs in feces, urine or sputum

What kind of fecal test needs to be done to recover trematode eggs?

Sedimentation or direct smear because the eggs are heavy

What do trematode eggs look like?

Oval, golden to dark brown in color
Also all have an operculum
Some may or may not contain a miracidium

Flukes usually cause damage by _, by direct _, and _ trauma, by _ duct systems, by stimulating large space-occupying _ in the lungs, and by depositing their _ in organs and tissues causing _ and _ formation

Migration
Irritation
Mechanical
Obstructing
Cysts
Eggs
Inflammation and granuloma

True/False: Humans can be directly infected by handling the infected animal

FALSE

What must occur first before an infection with flatworms?

Passage thru snail, followed by cercarial shedding and formation & ingestion of metacercariae

Cercariae from bird or mammalian blood flukes will penetrate man from infested bodies of water and cause a penetration dermatitis called what?

Cercarial Dermatitis
Swimmer's itch
Clam digger's itch

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