Veterinary Parasitology CH7 - Trematodes

Study material for Chapter 7 of Diagnostic Parasitology for Veterinary Technicians. For class BIO225 at MWCC.

What shape are trematodes/flukes?

Dorsoventrally flattened​, unsegmented​, leaf-like

What are the two subclasses of trematodes/flukes?

• Monogenea: Ectoparasites of fish, amphibians and reptiles​

• Digenea: Associated with wild and domestic animals and humans

Subclass Monogenea

• Attach to gills, skin, fins or mouth​

• Posterior adhesive organ: suckers, hooks or clamps​

• Usually only diagnosed in specialty practices that do saltwater or freshwater fish or fish farming

Subclass Digenea

• Flukes are endoparasites of domestic and wild animals and sometimes humans​

• Most are flat and broad, although a few are thicker and fleshier like Fascioloides magna​

• Schistosomas can be long thin and wormlike, more resembling nematodes

Trematode/fluke morphology

• Near anterior end is oral sucker, used to eat​

• Connects to pharynx and esophagus, bifurcates into two blind ceca​

• No anus; regurgitate contents of ceca into tissues or organs of host animal they infect​

• Can be seen in histological sections as fluke puke​

• Also contain an acetabulum or ventral sucker used to attach to host​

• Most flukes are hermaphrataditic​ (Exception is blood flukes or Schistosomes that have male and female​)

• Self-fertilization is most common but cross-fertilization between two adult flukes can happen

Trematode/fluke lifecycle

• Female produces operculated eggs stored in the uterus​

• Pass out the genital pore to external environment, usually in host feces​

• Eggs embryonate in external environment and hatch into motile ciliated miracidium​

• Swims in aquatic environment, penetrates skin of snail 1st intermediate host ​

• Develops into sporocyst. Inside sporocyst, many rediae develop.​

• Within each redia, many cercariae develop, often with a tail

List the three possible fates of the cercariae

1. Penetrate skin of definitive host​

2. Attach to vegetation, lose tail, encyst and develop into metacercaria — definitive host eats vegetation​

3. Lose tail, penetrate 2nd intermediate host, encyst and develop into metacercaria—definitive host ingests 2nd intermediate host

Most trematodes/flukes migrate to…

The digestive system

Which trematodes/flukes don’t migrate to the digestive system?

Paragonimus kellicotti (lung fluke) and Schistosomes (blood flukes)

List the stages of trematodes/flukes in order

1. Egg

2. Miracidium

3. Sporocyst

4. Rediae

5. Cercaria

6. Metacercaria