Parasitology Lec- Trematodes

• GENERAL LIFE CYCLE: TREMATODES

  1. Fertilized egg

  2. Embryonation takes place in water

  3. L5 (Metacercaria) is the infective stage

  4. L1 (Miracidium), L2 (Sporocyst), and L3 (Cercaria) are found in dioecious flukes

  5. L3 (Cercaria) is the infective stage for dioecious flukes
• Trematodes


  • Bodies are non-segmented, dorsoventrally flattened (leaf-like), and bilaterally symmetrical (cylindrical)
  • With a digestive tract, and two acetabula (suckers located in dorsal, but H. heterophyes has three) as opposed to four of cestodes
  • Heteroxenous
  • Never use humans as intermediate hosts. Humans are accidental hosts
• According to reproduction


  • Monoecious – complete set of male and female organs (vulva, testes)
  • Dioecious – separate sexes (male/ female sexes), blood flukes are only dioecious
• According to habitat


  • Lungs
  • Liver
  • Intestine
  • Blood
• Monoecious Flukes: Leaf-like, non-segmented bodies, hermaphroditic (Males possess gynecophoral canal, while females possess vulva)
• Monoecious Flukes: Eggs


  Have distinct feature (Operculated)
• Monoecious Flukes: Host requirement


  3 hosts (1st: Snail, 2nd: Fishes, Plants, Crustaceans, Snails, 3rd: Humans/ Animals)
• Paragonimus westermani


  • Oriental Lung Fluke, Causative agent of Paragonimiasis, Pulmonary distomiasis
  • 2nd Intermediate Host: Fresh Water crab, Crayfish
  • Clinical manifestations: Coffee-colored, blood-tinged colored, rusty-colored sputum (hemoptysis), Pulmonary discomfort (mimic tuberculosis), Fibrosis in lung tissue, Migrates to the brain
  • Treatment: PRAZIQUANTEL
• Fasciola hepatica


  • Ship Liver Fluke, Temperate Liver Fluke, Causative agent of Fasioliasis, Sheep Liver Rot
  • 2nd Intermediate Host: Water plants (Ipomoea obscura (Kangkong), Nasturtium officinale (Watercress))
  • Clinical manifestations: Acute/Invasive stage: Diagnostic triad (Fever, Hepatomegaly, Marked Eosinophilia), Chronic/Latent stage: Biliary obstruction, Fibrosis in tissues, Tongue Syndrome (Halzoun, Marrara Syndrome, it can also cause Hemorrhagic Nasopharyngitis)
  • Treatment: TRICLABENDAZOLE (not available in US), BITHIONOL (not available to certain countries)
• Clonorchis sinensis


  • Chinese Liver Fluke, Oriental Liver Fluke, Causative agent of Clonorchiasis
  • 2nd Intermediate Host: Fish
  • Clinical manifestations: Cholangiocarcinoma, Hepatocellular carcinoma
  • Treatment: PRAZIQUANTEL (MOST EFFECTIVE), ALBENDAZOLE (LOW COST), or combination of two drugs (LIGHT INFECTION)
• Opisthorchis felineus


  • Cat Liver Fluke, Causative agent of OPistorchiasis
  • 2nd Intermediate Host: Fish
  • Clinical manifestations: Cholangiocarcinoma, Hepatocellular carcinoma
  • Treatment: PRAZIQUANTEL (MOST EFFECTIVE), ALBENDAZOLE (LOW COST), or combination of two drugs (LIGHT INFECTION)
• Heterophyes heterophyes


  • Dwarf Fluke, Heterophyid Fluke, considered as the smallest intestinal fluke, Causative agent of Heterophyiasis
  • 2nd Intermediate Host: Fish
  • Clinical manifestations: Peptic Ulcer Disease or Acid Peptic Disease, Colicky abdominal pain- sharp and tender pain, Mucoid diarrhea, Cardiac and neural tendencies- migrates to heart, brain (H. heterophyes is the only fluke that can migrate to heart and brain due to its size)
  • Treatment: PRAZIQUANTEL
• Metagonimus yokogawai


  • Heterophid Fluke, Yokogawa's Fluke, Causative agent of Metagonomiasis
  • 2nd Intermediate Host: Fish
  • Clinical manifestations: Peptic Ulcer Disease or Acid Peptic Disease, Colicky abdominal pain- sharp and tender pain, Mucoid diarrhea
  • Treatment: PRAZIQUANTEL
• Fasciolopsis buski


  • Giant Intestinal Fluke, Large Intestinal Fluke, "Largest intestinal Fluke", Causative agent of Fasciolopsiasis
  • 2nd Intermediate Host: Aquatic plants, Chestnuts, Bamboo Shots
  • Clinical manifestations: Abdominal discomfort, Intestinal obstruction
  • Treatment: PRAZIQUANTEL
• Echinostoma ilocanum


  • Garrison's Fluke, found in Ilocos Norte in the Philippines, Causative agent of Echinostomiasis
  • 2nd Intermediate Host: Snail (Kuhol)
  • Clinical manifestations: Inflammation, Ulceration, Bloody diarrhea
  • Treatment: PRAZIQUANTEL
• Dioecious Flukes: Cylindrical bodies, non-hermaphroditic, male has distinct feature (Gynecophoral canal)
• Dioecious Flukes: Eggs


  Have distinct feature (Non-operculated, spines)
• Dioecious Flukes: Mode of transmission


  Skin penetration of cercaria
• Dioecious Flukes: Host requirement


  2 hosts (1st: Snail, 2nd: Human)
• Schistosoma spp. (Romantic Parasites)


  • Schistosoma mansoni (Manson's Blood Fluke, Causative agent of Intestinal Schistosomiasis), Schistosoma haematobium (Vesical Blood Fluke, Causative agent of Urinary Schistosomiasis), Schistosoma japonicum (Oriental Blood Fluke, Causative agent of Oriental Schistosomiasis)
  • Laboratory Diagnosis: DFS, Liver, and Rectal Biopsy (S. mansoni), Urinalysis (S. haematobium), DFS, Liver and Rectal Biopsy, MIFC (S. japonicum)
  • Intermediate hosts: Biomphalaria, Planorbis, Tropicorbis (S. mansoni), Bulinus, Physopsis (S. haematobium), Oncomelania quadrasi (S. japonicum)
  • Habitat: Mesenteric Vein of Rectum (S. mansoni), Venous plexuses of Urinary Bladder (S. haematobium), Mesenteric vein of Intestine (S. japonicum)
• Schistosoma spp.: Eggs


  S. mansoni: Anterior: tapered, slightly curved, Posterior: prominent lateral spine

  S. haematobium: Anterior: round, Posterior: terminal spine

  S. japonicum: Anterior: rounder, Posterior: small lateral spine
• Schistosoma spp.: Adults


  S. mansoni: Tegument: coarsely tuberculated, Ovary and Uterus: in anterior half, short

  S. haematobium: Tegument: finely tuberculated, Ovary and Uterus: in posterior half, long

  S. japonicum: Tegument: smooth (non-tuberculated), Ovary and Uterus: median, long
• Clinical manifestations of Schistosomiasis: Hemozoin (found in macrophages and neutrophils. They are brown insoluble hematin pigments due to degradation of hemoglobin), Cercarial Dermatitis (Swimmer's itch), Fatigue, respiratory symptoms, arthralgias, myalgias, malaise, eosinophilia, fever, and abdominal pain (Snail Fever, Katayama fever, Katayama syndrome if no fever), Hepatomegaly (Oriental Schistosomiasis from S. japonicum), Granulomatous inflammatory reaction caused by egg (Hoeppli's reaction)
• Treatment for Schistosomiasis: PRAZIQUANTEL
• Larval Stages of Monoecious Flukes

  L1: Miracidium

  L2: Sporocysts

  L3: Redia

  L4: Cercaria

  L5: Metacercaria (Infective Stage)
• Larval Stages of Monoecious Flukes

  L1: Miracidium

  L2: Sporocysts

  L3: Cercaria (Infective Stage)
• Lung Flukes

  Paragonimus westermani
• Intestinal Flukes

  Fasciolopsis buski

  Echinostoma ilocanum
• Liver Flukes

  Fasciola hepatica

  Chlonorchis sinensis

  Opistorchis felineus
• Heterophyid Flukes:

  Heterophyes heterophyes

  Metagonimus yokogawai