Trematodes

• Types of trematodes


  • Blood trematodes
  • Lung trematode
  • Liver trematodes
  • Intestinal trematodes
  • Heterophyid trematodes
• Paragonimus westermani


  Also known as the "ORIENTAL LUNG FLUKE"

  
• P. westermani causes 90% of paragonimiasis in Asia

  
• In the Philippines, P. westermani is the major species that causes paragonimiasis in humans

  
• P. siamensis is the only other species in the Philippines, but has only been identified in cats
• Paragonimiasis


  Caused by Paragonimus species
• There are 40 known species of Paragonimus, and 6 are reported to cause infections in humans

  
• Coenrad Kerbert first described the infection in Bengal Tigers


  1878
• Ringer discovered the P. westermani in the lungs


  1879
• Manson & Erwin von Baelz recognized P. westermani eggs in the sputum


  1880

  
• Manson proposed the snail Semisulcospira as intermediate host


  1916 & 1922
• Musgrave described the first case of human paragonimiasis in the Philippines

  1907

  
• Nakagawa discovered that crabs act as a 2nd intermediate host


  1915
• Nakagawa succeeded in infecting the snail Melania libertine with Paragonimus miracidia


  1917
• Paragonimus westermani eggs


  80-120um length, 45-70um wide, yellow brown, ovoid or elongate, operculum clearly visible at large end, opposite end thickened

  
• Diphylobothrium latum eggs


  Similar morphology to P. westermani but lack opercular shoulders and are more rounded in shape

  
• Paragonimus westermani eggs


  • Thick shell often asymmetrical with one end slightly flattened, bile-stained, can go out of the body through sputum or feces, embryonates in water

  
• Metacercaria


  Infective stage, encysted in tissue, exterior spined, has 2 suckers

  
• Adult Paragonimus westermani


  • Reddish-brown & ovoid, resembles a coffee bean, 7-16mm by 4-8mm, hermaphrodite with 2 deeply lobed testes situated opposite each other, has oral & ventral suckers

  
• Hosts of Paragonimus westermani

  • 1st intermediate host (snails): Antemelania asperata, Antemelania dactylus
  • 2nd intermediate host: Sundathelphusa philippina (cray fish or crabs)
  • Definitive host: Humans
  • Paratenic host: Wild Pigs

  
• Life cycle of Paragonimus westermani

  1. Ingestion of infected crustacean tissue by host

  2. Metacercariae excyst in duodenum

  3. Immature worm traverses intestinal wall into peritoneal cavity, wanders and embeds in abdominal wall

  4. Parasite migrates through diaphragm into pleural cavity

  5. Juvenile diploid worm wanders in pleural spaces until it finds another, then migrates into lung parenchyma to develop into adults in about 6 weeks, where they mate and lay eggs

  
• Clinical manifestations of Paragonimus westermani infection

  • Parasite activates peritoneal macrophages, causing increased IgE and decreased eosinophil-associated tissue inflammation due to proteases
  • Primary infection: fever, cough, chest pain
  • Secondary infection: hemoptysis, pulmonary paragonimiasis, cerebral paragonimiasis (most serious complication)

  
• Chronic cough and hemoptysis are the most common symptoms of paragonimiasis
• Cutaneous and cerebral paragonimiasis are classic known forms of ectopic infection
• Diagnostic methods for Paragonimus westermani

  • Microscopy: detection of characteristic eggs in stool/sputum
  • Intradermal test: simple, rapid, cheap and highly sensitive
  • ELISA: detects Paragonimus-specific IgG antibody
  • CT scan or MRI: for cerebral paragonimiasis

  
• Drugs used to treat Paragonimus westermani infection

  • Praziquantel: drug of choice
  • Triclabendazole: binds to B-tubulins of trematodes
  • Bithionol: alternative drug
• Paragonimiasis is endemic in certain regions of the Philippines
• Fasciola hepatica


  "TEMPERATE LIVER FLUKE", "SHEEP LIVER FLUKE"

  
• Fasciola gigantica


  "TROPICAL LIVER FLUKE", "GIANT LIVER FLUKE"

  
• Fasciola hepatica eggs


  • Large, ovoidal, operculated & yellowish-brownish, 140-180um by 63-90um, immature, containing large unsegmented mass of vitelline cells

  
• Fasciola gigantica eggs


  • Slightly larger than F. hepatica, 160-190um by 70-90um
• Adult Fasciola hepatica


  • Marked widening at base of cone ("shoulder")
• Adult Fasciola gigantica


  • Less developed shoulder (no shoulder)
• Snail hosts for Fasciola hepatica


  • Lymnaea truncatula (Europe and North Asia)
  • Lymnaea bulmoides (North America)
  • Lymnaea tomentosa (Australia)

  
• Snail hosts for Fasciola gigantica

  • Lymnaea auricularia (Asia)
  • Lymnaea acuminata (Indian Subcontinent)
  • Lymnaea natalensis (Africa)
• 2nd intermediate hosts for Fasciola spp.

  • Ipomea obscura (morning glory or kangkong)
  • Nasturtium officinale (watercress)

  
• Planorbidae snails also act as an intermediate host of F. hepatica sporadically

  
• In the Philippines, the snail hosts of Fasciola spp. are L. philippinensis and L. auricularia rubiginosa

  
• General life cycle of trematodes (except blood trematodes)

  1. Miracidium (for 1st intermediate host)

  2. Cercariae (for 2nd intermediate host)

  3. Metacercariae (for definitive host)

  
• Human fascioliasis


  • Has 2 clinical stages: acute/invasive phase (larval migration & worm maturation) and chronic/latent phase (persistence of Fasciola worms in the biliary ducts)