Trematodes

• Digenetic - require at least two host organisms to complete its life cycle
• Schistosoma japonicum - only schistosome species considered to be zoonotic
• S. japonicum reservoir host

  Dogs and water buffaloes
• S. japonicum pathology

  • Granulomatous reaction to eggs deposited in the liver, intestines, lungs, CNS
  • Does not multiply in the definitive host
  • No. of cercariae that infect the host → severity of infection
  • Granuloma formation → obstruction of intrahepatic portal branches → splenomegaly and ascites
• Blood fluke - Schistosoma japonicum
• Intestinal fluke - Heterophyes heterophyes
• H. heterophyes mode of transmission

  Consumption of raw or undercooked freshwater/brackish water fish containing infective metacercariae
• H. heterophyes pathology

  • Abdominal pain and diarrhea
  • Inflammation at the site of attachment → damage to intestinal mucosa
  • Heart failure and intracerebral hemorrhage → presence of eggs in the heart and brain
  • Sensory and motor losses → eggs dislodged in the spinal cord
• H. heterophyes primary intermediate hosts

  Thiarid or Melaniid snails
• Family Thiaridae - high and turreted shell
• H. heterophyes secondary intermediate hosts

  Freshwater fish (tilapia, pait, dalag)
• Lung fluke - Paragonimus westermani
• Paragonimus westermani - main species that causes human paragonimiasis in PH
• Paragonimus siamensis - identified only in cats
• P. westermani primary intermediate host

  Antemelania asperata
• P. westermani secondary intermediate host

  Sundathelpusa philippina
• P. westermani reservoir hosts

  Dogs, cats, field rats
• P. westermani mode of transmission


  Ingestion of raw or undercooked crabs harboring metacercariae
• Cysteine protease - secreted by the excretory epithelium of metacercariae for excystment
• P. westermani pathology

  • Granulomatous reaction in the lungs → development of fibrotic encapsulation
  • Adult worms → found in pairs in fibrotic capsules OR cysts in the lungs
  • Serious complication: cerebral paragonimiasis
• Temperate liver fluke - Fasciola hepatica
• Tropical liver fluke - Fasciola gigantica
• F. hepatica/gigantica - found in the liver and biliary passages of humans and herbivorous mammals (ruminants)
• F. hepatica/gigantica mode of transmission

  Consumption of edible aquatic plants or drinking water with metacercariae
• F. hepatica/gigantica primary intermediate hosts


  Lymnaea sp. (L. philippinensis, L. auricularia rubiginosa)
• F. hepatica/gigantica secondary intermediate hosts


  • Aquatic plants (Nasturtium officinale, water cress; Ipomea obscura; Ipomea aquatica, kangkong)
• F. hepatica - two prominent shoulders
• F. gigantica - larger in size, less prominent shoulders
• F. hepatica/gigantica pathology

  • parasite burrows through the liver → necrotic lesions → hepatic fascioliasis (RUQ pain)
  • parasite can migrate in the lungs, brain, and orbit
• Chinese liver fluke - Clonorchis sinensis
• C. sinensis

  • parasite of man, dogs, and cats in SEA
  • found in China, Korea, Japan
  • resides in the bile duct and gallbladder of humans and fish-eating mammals
• C. sinensis egg - small protuberance at the abopercular end
• C. sinensis mode of transmission

  • ingestion of raw or undercooked fish infected with metacercariae
  • visible encysted metacercariae have been reported in salted, dried, or pickled freshwater fish
• C. sinensis metacercariae

  • excysts in the duodenum
  • moves through the ampulla of Vater → common bile duct → distal biliary capillaries → matures into an adult worm
• C. sinensis adult fluke

  • attaches itself to the mucosa of the bile duct by using its suckers and embedding itself in sticky mucus
  • can be found in the pancreatic duct and gallbladder
  • feeds on tissue fluids, RBCs, mucus
• C. sinensis egg

  • fully mature when released from the worm
  • passes with the bile to the intestine → passed out through feces
  • miracidium: hatches only after the egg is ingested by the first intermediate host
• C. sinensis first intermediate host

  Parafossarulus genera (P. manchoricus, P. anomaloispiralis, P. stratulus)