Trematodes

Question 1

What are trematodes?

Answer 1

Flukes

Question 2

Describe the general structure of trematodes

Answer 2

• small dorso-ventrally flattened
• simple anatomy
• no blood vessels
• simple ladder nervous system
• muscular pharynx
• cross and self fertilisation occurs
• covered by tegument

Question 3

What are the roles of tegument?

Answer 3

• rapid turnover = sloughing off Ab
• molecular mimicry
• release of enzymes

Question 4

Describe the general trematode lifecycle

Answer 4

1. Egg - found in environment + has an opericulum (trap door)
2. Miracidium - hatches if light level is correct & water is present and invades a mollusc
3. Sporocyst - motile sac-like structure that undergoes multiple asexual replication
4. Redia - cylindrical with a pharynx + further asexual reproduction takes place
5. Cercaria - heart shaped with flagellum + leaves mollusc
6. Metacercaria - swims onto vegetation, loses its tail & secretes a tough protective layer
7. Ingestion by final host
8. Immature fluke - migrates to predilection site
9. Adult fluke - starts to lay eggs

Question 5

Schistomona spp. (Blood fluke) appearance and lifecycle

Answer 5

• sexes are separate but female lies enveloped by male
• eggs have spikes
• intermediate host = water snail
• cercariae swim in water to actively seek final host
• enter via penetration
• no meteacercariae stage

Question 6

Paramphistomes appearance and lifecycle

Answer 6

• uncommon in UK
• adult fluke = plump, cylindrical + reddish
• attaches to wall of rumen without causing serious damage
• intermediate host = water snail
• disease occurs when metacercariae are eaten in large numbers

Question 7

Dicrocoelium dendritieum appearance and lifecycle

Answer 7

• small fluke found in bile ducts of ruminant
• follow ducts
• intermediate host = land snail
• cercariae secreted in slime balls and eaten by ants
• metacercariae develop and cause behavioural change in ants
• final host infected when ants are eaten