Intro to Trema

• Helminths

  • Nemahelminthes
  • Platyhelminthes
• Class Trematoda

  • Fluke
  • Flat, unsegmented
• Cestode

  • Tapeworm
  • Flat, segmented

  
• Trematodes


  • Greek word trematos meaning pierced with holes
  • Resemble the shape of flounder fish or fluke fish
  • Fluke: flat end of an arm of an anchor
  • Oval- to lancet-shaped or leaf-shaped
  • Unsegmented, bilaterally symmetrical
  • Oviparous (all trematodes are egg-laying)
• Hosts

  • Definitive host: Humans
  • First intermediate host: Fresh water mollusk
  • Second intermediate host: Fish, crustacean, snail, plants
• Trematodes

  • Are dorsoventrally flattened
  • Are hermaphrodite (male and female parts are present in the same organism)
  • Have operculated ova
  • Operculum opens to release the embryo to the external environment or inside the first intermediate host depending on the species
  • EXCEPT Schistosoma
• Schistosoma spp.

  • The male is generally thicker to accommodate the female during copulation
  • The female is generally thin and long
• General Life Cycle of Trematodes

  1. Eggs are released from human via urine or feces in fresh water (can also be released via sputum depending on the species)

  2. Eggs hatch into first stage larvae (miracidium) that invade a snail as first intermediate host

  3. All trematodes EXCEPT Schistosoma spp. require second intermediate host which is mostly a water plant or animal

  4. The second larval stage (cercaria or metacercaria) comes out of the intermediate host

  5. Humans are infected through skin penetration of cercaria (infective stage of Schistosoma spp.) or ingestion of encysted metacercaria in water plant or animal (infective stage of other trematodes)

  
• Life Cycle of Other Trematodes (GENERALIZED)

  1. Egg is passed through the feces, urine, and sputum and is either embryonated or unembryonated

  2. If unembryonated, it is embryonated in the external environment

  3. The operculum of the egg opens, releasing the miracidium, the infective stage to the first intermediate host

  4. Inside the body of the first intermediate host, miracidium loses its cilia and becomes sporocyst

  5. Sporocyst matures to become redia

  6. Redia feeds on other trematodes inside the first intermediate host

  7. Redia matures to become cercaria

  8. Cercaria is the infective stage to the second intermediate host

  9. Inside the second intermediate host, cercaria loses its tail and encysts in the muscles to become metacercaria, the infective stage to the definitive host

  10. Ingested metacercaria matures into adults inside the definitive host and the cycle continues
• Life Cycle of Trematodes: Schistosoma spp.

  1. Schistosoma spp are dioecious and copulate to bear young (eggs)

  2. Like other trematodes, Schistosoma spp. have snails as the first intermediate host

  3. Eggs that are released to the external environment will hatch, releasing miracidium

  4. Miracidium penetrates the first intermediate host and matures to become sporocyst

  5. Sporocysts DOES NOT mature into redia, but immediately becomes cercaria

  6. Cercaria is released into the external environment and is the infective stage to the definitive host by means of skin penetration

  
• Classification of Ova

  • Unembryonated or Immature ova: Paragominus, Echinostoma, Fasciola, Fasciolopsis (undergoes embryonated in the external environment)
  • Embryonated or Mature ova: Schistosoma, Opisthorchis, Clonorchis, Heterophyid Group (ova is passed from the definitive host embryonated)
• Habitat

  • Portal Blood Stream of Vertebrates (Blood Flukes): Schistosoma japonicum, Schistosoma mansoni, Schistosoma haematobium
  • Liver of the Vertebrates (Liver Flukes): Fasciola hepatica, Fasciola gigantica, Clonorchis sinensis, Opisthorchis felineus, Opisthorchis viverrine
  • Small Intestine of Vertebrates (Intestinal Flukes): Fasciopolis buski, Echinostoma ilocanum, Heterophyid Group
  • Lungs of Vertebrates (Lung fluke): Paragonimus westermani
• Structures for Attachment

  • Oral Sucker: Found in the most anterior portion of the parasite
  • Ventral sucker: Found in the anterior portion of the parasite
  • Thick integument with spines and sensory papillae
• Genital Sucker or Gonotyl

  • Present in Heterophyes spp, the only group that has genital sucker
  • Used for the release of ova
  • Located adjacent to the ventral sucker
• Gynecophoric Canal

  • Present in male Schistosoma spp
  • Used to house and hold the female parasite in place during copulation
  • Transient - female parasite can leave the gynecophoric canal when they release eggs, but then return to it
• Digestive System

  1. Oral Sucker: Major part that takes in nutrients and other material that the parasite ingests, skin/tegument can also absorb nutrients

  2. Pharynx: Appears as a bulbous part after the oral sucker

  3. Esophagus is very short and leads to bifurcating intestine

  4. Intestine or Cecum: Inverted letter "Y" in shape, with blind end, NO ANUS (fecal material is vomited out through the oral sucker)

  5. Types: Branching (Fasciola spp.) or Unbranching (Other trematodes)
• Gynecophoric canal


  Structure that females return to after releasing eggs, as Schistosoma are always in copulation
• Egg release


  1. Females leave the gynecophoric canal

  2. Females return to the gynecophoric canal
• Parts of the Digestive System

  • Oral Sucker
  • Pharynx
  • Esophagus
  • Intestine/Cecum
• Oral Sucker


  Major part that takes in nutrients and other material that the parasite ingests, skin/tegument can also absorb nutrients
• Pharynx


  Appears as a bulbous part after the oral sucker
• Esophagus


  Very short and leads to bifurcating intestine
• Intestine/Cecum


  Inverted letter "Y" in shape, with blind end, no anus, waste vomited out through oral sucker
• Types of Intestine

  • Branching: Fasciola spp.
  • Unbranched: Other trematodes
• Digestive System of Schistosoma spp.

  With bifurcated intestine plus fused intestine at the distal end
• Excretory System (Protonephridium)


  Equivalent to human's urinary system, with flame cells, collecting ducts, excretory bladder, and excretory pore
• Nervous System


  • Ladder-type system with anterior ganglionic mass (brain), lateral nerve trunks, and connecting commissures
• Male Reproductive System (Other Trematodes)


  • Paired testes at the posterior end, globular/branched/lobated in shape
• Male Reproductive System (Schistosoma spp.)


  Testes found behind the ventral sucker, in the anterior portion of the parasite
• Female Reproductive System (Other Trematodes)


  • Single ovary found anterior to the testes, globular/branched/lobate in shape

  
• Female Reproductive System (Schistosoma spp.)

  Oviduct, seminal receptacle, ootype, vitellaria, and Mehlis gland

  
• Ovary of Schistosoma spp. is at the midline, with a darkly staining gravid uterus anterior to it
• Life Cycle Stages


  • Ova
  • Miracidium
  • Sporocyst
  • Redia
  • Cercaria
  • Metacercaria
  • Adult
• Ova


  Can be unembryonated (PEFF) or embryonated (SOCH)
• Miracidium


  Motile, ciliated, infective stage to the first intermediate host

  
• Sporocyst


  Miracidium loses cilia and becomes sporocyst in the first intermediate host
• Redia


  Sporocysts mature to develop oral sucker and become the feeding stage in the first intermediate host, absent in Schistosoma spp.
• Cercaria


  Motile, free-swimming stage that is the infective stage to the second intermediate host (other trematodes) or definitive host (Schistosoma spp.)

  
• Metacercaria


  Encysted stage in the second intermediate host, infective to the definitive host (absent in Schistosoma spp.)

  
• Life Cycle Summary


  1. Egg

  2. Miracidium

  3. Sporocyst

  4. Redia

  5. Cercaria

  6. Metacercaria

  7. Adult