Trematodes

• Phylum Platyhelminthes


  Multi-cellular worms, flattened dorsoventrally, incomplete (or no) digestive system, excretion by flame cells, tegument unique to the phylum (syncitium), body is not truly segmented, ectoderm and endoderm with cells filling in area between the two layers (no mesoderm), no coelom
• Traditional classes of Phylum Platyhelminthes


  • Turbellaria (mostly free-living)
  • Monogenea
  • Trematoda (a.k.a. Digenea)
  • Cestodea
• Molecular genetics suggests these groups may not be monophyletic, especially turbellaria and trematoda
• We will keep the traditional divisions because it helps us organize the parasitic groups
• Subclass Digenea


  Part of the Class Trematoda of the Phylum Platyhelminthes, all have two suckers (one around mouth and one middle of body), acetabulum (sucker not around mouth), muscular pharynx pulls host tissues into mouth, most are very flat and leaf-shaped (except Schistosoma sp.), most are hermaphroditic (except Schistosoma sp.)
• Digenean Life Cycle


  Complex life cycles with at least two hosts and several life cycle stages, first intermediate host is almost always a snail, some have another aquatic animal or plant as a second intermediate host, definitive host usually eats the second intermediate host (except Schistosoma sp.)

  
• Digenea Egg


  Not an ovum but a developing embryo, already fertilized and developing into a new organism, most digene eggs have an operculum (except Schistosoma)
• Digenea Miracidium


  Covered in cilia, slipper shaped, leaves the egg, swims around looking for first intermediate host (a snail), burrows into the first intermediate host and loses the cilia, turns into a sporocyst or redia
• Digenea Sporocyst


  When miracidium finds a snail, it penetrates its mantle and turns into a sporocyst, "sac" of embryos, releases embryos into the snail, embryos can become sporocyst, redia, or cercaria
• Digenea Redia


  Similar to a sporocyst but has a pharynx and small digestive system, more mobile than sporocyst, makes embryos which can turn into redia or cercaria
• Digenea Cercaria


  Leaves the snail to find next host, looks like a miniature adult with a tail, tail for swimming, loses tail as it penetrates next host, Schistosoma cercaria have forked-tails
• Digenea Metacercaria


  "Resting" stage of the life cycle, miniature adult curled up in a tissue cyst, waiting for intermediate host to be eaten by definitive host

  
• Digenea Adult


  Typical digene adults are flat, leaf-shaped, male and female organs in same individual, adult Schistosoma are round, sexes are separate, males are larger than females
• Digenean Life Cycle


  1. Egg

  2. Miracidium

  3. Sporocyst

  4. Cercaria

  5. Redia

  6. Daughter sporocyst

  7. Daughter Redia

  8. Metacercaria

  9. Adult

  
• Superfamily Schistosomatidea


  • Very different from most digenea (sexes are separate, adults are round not flat, eggs have no operculum, cercaria have forked tail, only one intermediate host), but have some characteristics of digenea (two suckers, same integument, incomplete digestive tract, snail intermediate host, same life cycle stages except no metacercaria or redia)

  
• Schistosoma japonicum


  Definitive hosts: humans, wild mammals including dogs, cats, deer, primates, horses, swine, cattle, first intermediate host: Oncomelania hupensis quadrasi (Phils), no second intermediate host, geographic distribution: South East Asia
• Schistosoma japonicum Transmission


  Cercaria burrow into the skin
• Schistosoma japonicum Location


  Veins of the small intestine
• Schistosoma japonicum Pathology


  Most pathology is due to the body's inflammatory response to the eggs, eggs lack sharp spine for anchorage so they are transported by blood easier than the other Schisto species
• Schistosoma japonicum Symptoms


  Causes Schistosomiasis, three phases: migratory (usually asymptomatic), acute (fever, chills, fatigue, headache, malaise, muscle aches, gastrointestinal discomfort), chronic (ascites, enlargement of spleen and liver, dwarfism, eggs may lodge in brain causing neurological damage)
• Schistosoma japonicum Diagnosis


  Eggs in a fecalysis, biopsies of liver granulomas may reveal eggs (ovoid with small lateral knob), ELISA tests (rapid testing) more reliable than fecalysis but not very sensitive and cannot detect active infection, molecular detection (PCR) most sensitive test
• Schistosoma japonicum Prevention


  Proper sanitation, killing snail host, staying out of water
• Schistosoma japonicum is more pathogenic than S. mansoni and S. haematobium
• Schistosoma japonicum Life Cycle

  1. Adults in veins of the sm. intestine

  2. Eggs go out in feces

  3. Eggs hatch in water

  4. Miracidium

  5. Penetrates snail

  6. Sporocyst

  7. Daughter Sporocyst

  8. Cercaria

  9. Leaves snail

  10. Penetrates skin of D.H.

  11. Goes to peripheral blood vessels

  12. Heart, lungs back to heart

  13. Liver

  14. Small Intestines

  15. Mature

  
• Schistosomiasis Control Targets


  • DOH target (<1% prevalence)
  • WHO target (<1% HI infection)
  • WHO target (≥75% MDA coverage)
  • DOH-IHCP target (≥85% MDA coverage)
  • DOH target (100% sanitary toilet coverage)
• Prevalence of SCH in Humans


  • Kato-Katz Method
  • qPCR
• SCH Animal Prevalence


  • Kato-Katz Method
  • qPCR
• Schistosoma mansoni


  Definitive hosts: humans, and many wild mammals including monkeys and rodents, first intermediate host: aquatic snails, no second intermediate host, geographic distribution: Africa and South America (spread to South America with the slave trade)
• Schistosoma mansoni Transmission


  Cercaria burrow into the skin
• Schistosoma mansoni Location


  Portal veins of the large intestine
• Schistosoma mansoni Pathology


  Most pathology is due to the body's inflammatory response to the eggs, eggs have a sharp lateral spine so they tend to lodge in the liver, the body walls them off in granulomas, reducing liver function
• Schistosoma mansoni Symptoms


  Causes Schistosomiasis, same symptoms as S. japonicum except that the eggs rarely get to the brain so less lethal
• Schistosoma mansoni Diagnosis


  Fecalysis, eggs with lateral spine (diagnostic feature), ELISA test (same problems as S. japonicum), PCR test
• Schistosoma mansoni Prevention


  Same as S. japonicum
• Recent studies suggest immune cells pick up S. mansoni eggs and transport them to the lumen of the intestine, people with AIDS lack those cells so people with AIDS and Schistosomiasis shed fewer eggs that people without AIDS
• Schistosoma mansoni Life Cycle


  1. Adults in veins of the large intestine

  2. Eggs go out in feces

  3. Eggs hatch in water

  4. Miracidium

  5. Penetrates snail

  6. Sporocyst

  7. Daughter Sporocyst

  8. Cercaria

  9. Leaves snail

  10. Penetrates skin of D.H.

  11. Goes to peripheral blood vessels

  12. Large Intestines

  13. Heart, lungs back to heart

  14. Liver

  15. Mature

  
• Schistosoma haematobium


  Definitive hosts: humans, very host specific with no known reservoir hosts, first intermediate host: aquatic snails, no second intermediate host, geographic distribution: northern Africa and small area of Middle East

  
• Schistosoma haematobium Transmission


  Cercaria burrow into the skin
• Schistosoma haematobium Location


  Veins of the urinary plexus (ureters, bladder, urethra)
• Schistosoma haematobium Pathology


  Most pathology is due to the body's inflammatory response to the eggs, eggs have a sharp terminal spine, they lodge in walls of the urinary bladder, causing calcification of the bladder, seminal vesicles, urethra, and ureters, may also block the ureters