Module 7- Trematodes AKA Flukes

Trematode’s Phylum

Platyhelminthes (Flatworm)

Class name

Trematode (Flukes)

What species is always the first IH host?

Snails

What type of lifecycle do Trematodes (Flukes) have?

Indirect

Trematodes/ Flukes transmission type?

Ingestion is most common

Skin Penetration possible in some

What type of reproduction do trematodes have?

Sexual and Asexual

What type of reproduction happens in the DH (definitive host) ?

Sexual

What type of reproduction happens in the IH?

Asexual reproduction (leads to dramatically increasing numbers)

How many immature stages do trematodes have?

5

Five immature stages

What are the 6 stages of trematodes lifecycle

1. Adult fluke pass eggs into the external environment within the hosts feces

2. When egg contacts water it will hatch and produce a motile stage called miracidium

3. The miracidium is covered with tiny hairs called cilia. Movement of the cilia allows the miracidium to seek out an aquatic snail (1st IH) and penetrate the skin of the snail and develop to the next stage (Sporocyst)

4. Sporocyst is a sack in which the next stage, the redia develops

5. . Many redia develop within one sporocyst. Within each redia many cercariae develop.

6. The cercarial stage often has a tail and will emerge from the snail and will do one of the following 3 paths…

List the 3 paths Cercaria can take?

1. Directly penetrates DH – heads to its preferred site in DH and develops to adult

2. Attaches to vegetation, loses its tail, secretes thick cyst wall around itself, and develops to metacercaria – in DH juvenile fluke released and migrates to predilection site and develops to adult

3. Loses tail, penetrates second IH, secretes thick cyst wall around itself, develops to metacercaria – second IH with metacercaria ingested - after ingestion juvenile fluke released and migrates to predilection site, develops to adult

What type of species do monogenic flukes usually parasitize?

Fish, amphibians and reptiles

What species do digenetic trematodes usually effect?

Wild and domestic animals and humans

What are the 2 sucker’s functions at the anterior end of flukes?

1. Used for attachment

2. Used as a mouth

What are the two subclasses of trematodes?

1. Monogenic

2. Digenetic

Monogenetic flukes usually ecto or endo parasites?

Ectoparasites mainly on fish

Digenetic trematodes usually endo or ecto parasites?

Endoparasites

Difference between cercaria and metacercaria?

Cercaria- larval form of trematode

Metacercaria- One of the three pathways a cercaria can turn into. Cercaria can develop into a metacercaria in the second intermediate host

What characteristic ovum do digenetic flukes have that is almost unique to their subclass?

Operculated egg- looks like a door on one side (pole) of the egg

 Operculum

Door or cap at one end, or pole, of the trematode egg

Hermaphroditic 

Simultaneously possessing both male and female reproductive organs

Sporocyst

Developmental stage after penetration of the miracidium into a

snail (first intermediate host)

Operculum

Door or cap at one end, or pole, of the trematode egg

 Monogenetic trematodes

Ectoparasites of fish, amphibians, and reptiles

Metacercaria

Encysted stage in the life cycle of the trematode usually found on

vegetation or within the second intermediate host

Cercaria

Stage that follows the redia; stage that emerges from the second

intermediate host

Miracidium 

Motile stage emerging from the operculated fluke egg

Acetabulum

Ventral sucker that is used as a holdfast organ of attachment for

digenetic flukes

Redia 

Stage that develops on the inside of the sporocyst

Nanophyetus salmincola

Salmon-poisoning fluke of dogs

Heterobilharzia americana

Canine schistosomes (blood flukes)

Fasciola hepatica

Liver fluke of cattle

Dicrocoelium dendriticum

The lancet fluke of ruminants

Paramphistomum and Cotylophoron

Rumen flukes

Black spot

Melanin deposition in response to the presence of

metacercariae

Swimmer’s itch

Schistosome cercarial dermatitis

Fascioloides magna

Liver fluke of white-tailed deer

Platynosomum fastosum

Liver fluke of white-tailed deer

Paragonimus kellicotti

Lung fluke of dogs and cats