Trematodes

• Phylum of trematodes

  Platyhelminthes
• • Liver Fluke
  • Lung Fluke
  • Blood Fluke (blood vessel)
  • Intestinal Fluke
• Class: Trematoda / Digenea 

  Commonly known: Flukes / Flatworms

  Two groups: Hermaphroditic & Dioecious (no female or male worms; ovary and testes are present in one organism)
• Only organism that has separate sexes is the Schistosoma spp.
• Most trematodes have a complex life cycle with at least two hosts:

  • Definitive host: Humans and animals 
• • Intermediate host (asexual reproduction): F. buski
  • 1st intermediate host: Snails
  • 2nd intermediate host: Water plants, fish, and crabs 
• • Definitive host: Humans and animals 
  • Intermediate host (asexual reproduction):
  • 1st intermediate host: Snails

  2nd intermediate host: Water plants, fish, and crabs
• Additional sucker: gonotyl
• Has 2 suckers: Oral suckers and Ventral suckers

  • Additional sucker: gonotyl, only present in Heterophyids
• • Additional sucker: gonotyl, only present in Heterophyids attached in acetabulum
• Characteristics:

  • Dorso-ventrally flattened
  • Unsegmented
  • Leaf-like 
  • Hermaphroditic EXCEPT blood flukes
  • Two radially striated suckers
  • Incomplete digestive tract (no anus, through excretory duct or bladder or via regurgitation)
  • Adults are covered with spines
  • Most of the body is occupied by reproductive organs 
  • Oviparous - lays eggs
  • Infective stage is METACERCARIA (always present in 2nd intermediate host)
• Incomplete digestive tract (no anus, through excretory duct or bladder or via regurgitation)
• regurgitation - swallowed food bringing up again to the mouth
• Characteristics:

  • Adults are covered with spines
• Characteristics:

  • Most of the body is occupied by reproductive organs
• Characteristics:

  • Oviparous - lays eggs
• • Infective stage is METACERCARIA (always present in 2nd intermediate host)
  • Except Schistosoma spp: fork-tailed cercariae (no 2nd intermediate host) INFECTIVE STAGE
• Vitellaria: Responsible for secreting this material when it comes to the formation of egg cells of trematodes.
• Seminal receptacle: Helps when it comes to releasing fluids (e.g., semen).
• Testis: Branchy-looking.
• Three morphologic forms:

  1. Eggs 
  2. Larval stages
  3. Adult worms
• 1. Eggs 

  Operculated (presence of operculum, a lid-like structure; exit portal for hatching of miracidium which is the nonfeeding developing larva inside the egg shell)

  Abopercular knob - Clonorchis sinensis; functions as support for the egg and during hatching of embryonated egg

  Spines - Schistosoma; functions as an attachment and support 

  • Embryonated eggs
  • Unembryonated eggs
• 1. Eggs 

  Operculated (presence of operculum, a lid-like structure; exit portal for hatching of miracidium which is the nonfeeding developing larva inside the egg shell)
• operculum, a lid-like structure; exit portal for hatching of miracidium which is the nonfeeding developing larva inside the egg shell
• Abopercular knob - Clonorchis sinensis; functions as support for the egg and during hatching of embryonated egg
• Spines - Schistosoma; functions as an attachment and support 

  • Embryonated eggs
  • Unembryonated eggs
• miracidium - the nonfeeding developing larva inside the egg shell
• Larval Stages: Sporocysts, Rediae, Cercariae, and Metacercariae
• Larval Stages: Sporocysts, Rediae, Cercariae, and Metacercariae

  • Additional larval stage in Schistosoma spp. – Schistosomule
• • Rediae: Mother (R1) and daughter (R2) which transforms into cercariae and metacercariae
• • Cercariaes can continue to transform into Schistosomule

  unique in Schistosoma spp
• Adult Worms: Hermaphroditic and Dioecious (Schistosoma spp.)
• General DS and IS

  Diagnostic stage: Embryonated eggs or Unembryonated eggs

  Infective Stage: Metacercariae and Cercariae (Schistosoma spp.)
• LIFE CYCLE

  • Presence of eggs in the stool sample – majority of samples when it comes to diagnostic purposes are eggs in stool except in Paragonimus.
• Eggs hatch in water (embryonation usually happens in water as it requires different species that live in water – fish, crayfish, crabs, snails, and water plants).
• Eggs have miracidium, this miracidium will go into your first intermediate host (snail) and undergo different stages → sporocyst → R1 (Mother Rediae) → R2 (Daughter Rediae) → proceed into cercariae (can be present in bodies of water to find the second intermediate host – fish, crayfish, crab, or water plant to undergo encystation to transform into a metacercariae form which will then be injected in humans through the secondary intermediate host since we eat fishes, water plants).
• Encystation will transform cercariae into metacercarial cyst/form in the 2nd intermediate host
• Presence of eggs in stool sample except for Paragonimus (lung fluke)
• Intestinal Fluke

  1. Fasciolopsis buski
  2. Heterophyes heterophyes
  3. Metagonimus yokogawai
• Lung Fluke

  1. Paragonimus westermani