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Parasitology lab notes



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  • 1. Lab 5: Trematodes! Flukes
  • 2. Trematodes: General Info
    • Phylum: Platyhelminthes – the flatworms
    • Unsegmented, leaf-like bodies
    • 2 subclasses: Monogenea (monogenetic trematodes) & Digenea (digenetic trematodes)
    • Monogenetics usually parasitize fish, reptiles & amphibians
    • Digenetic trematodes parasitize wild & domestic animals & humans
  • 3. Trematodes: Morphological Features
    • Mouth connects to pharynx, leads to esophagus, bifurcates into 2 ceca
    • No anus: releases cecal contents back through mouth into tissue it infects
    • Cecal contents can be seen in histopathologic section and are colloquially referred to as “fluke puke”
    • Also possess and acetabulum, or ventral sucker – holdfast organ not associated with feeding
    • Near anterior end, mouth
    • is surrounded by muscular
    • oral sucker
  • 4. Trematodes: Reproduction
    • With exception of schistosomes (blood flukes) all flukes are hermaphroditic
    • Each fluke possesses both sex organs
    • Self-fertilization usually takes place, but cross-fertalization can also occur
  • 5. Flukes: General Life Cycle Part 1
    • Operculated eggs pass in feces
    • Egg comes in contact w/ water – hatches and becomes motile miracidium
    • Miracidium seeks out and penetrates skin of aquatic snail (1 st intermediate host)
    • In snail, develops into sporocyst – sack in which next stage redia develops
    • Each sporocyst contains many redia, each redia many cercaria
    • Cercarial stage usually has a tail and will emerge from snail & swim in water.
  • 6. Flukes: General Life Cycle Part 2
    • Cercarial stage takes 1 of 3 paths:
      • Cercaria may directly penetrate the skin of definitive host
      • Cercaria may attach to vegetation, lose its tail, secrete a thick cyst wall around itself and develop into a metacercaria . Vegetation w/ attached metacercaria is ingested by definitive host
      • Cercaria may lose its tail, penetrate the 2 nd intermediate host, secrete thick cyst wall & become metacercaria in 2 nd intermediate host. In this case, the 2 nd intermediate host w/ encysted metacercaria is ingested by primary host
  • 7. Fluke: Life Cycle
  • 8. Identification of Trematode Ova
    • Singly operculated oval shaped eggs
    • Very distinctive
  • 9. Dicrocoelium dendriticum : Lancet Fluke
    • Definitive hosts: sheep, goats & cattle
    • Tiny ~ 6-10mm long
    • Live in the fine braches of bile duct – can produce biliary hyperplasia
    • Produces brown, embryonated, operculated ova
    • Intermediate hosts: snail then ant
    • Can be zoonotic if eat chocolate covered ants!
    • Found on fecal sedimentation or in bile ducts at necropsy
  • 10. Fasciola hepatica : Liver Fluke
    • Definitive hosts: ruminants, cattle
    • Most pathogenic fluke of cattle in US, very common
    • Lives in liver & bile ducts, causes liver rot
    • Eggs are large & heavy, should use fecal sedimentation to find
    • Intermediate host: snail – develops into metacercaria on vegetation
    • Can be zoonotic if eat fress watercress
    • Can be found as spurious eggs in dog & cat feces (coprophagy)
  • 11. Fascioloides magna: Deer Liver Fluke
    • Definitive host: White-tailed deer
    • May also use sheep, cattle & pigs as incidental hosts
    • Adults found in liver parenchyma
    • Adults are Unique in appearance
    • Eggs may be found on fecal flotation of deer feces, but not incidental hosts feces
  • 12. Platynosomum fastosum: Lizard-poisoning Fluke
    • Definitive host: cats
    • Intermediate hosts: snail then lizard
    • Seen frequently in Southeastern US (FL)
    • Adults found in liver, gall bladder, bile ducts
    • Signs: v/d, icterus, & anorexia, fever, death
  • 13. Nanophyetus salmincola: Salmon-poisoning fluke
    • Definitive hosts: dogs, cats, wild carnivores
    • Intermediate host: snail then fish (trout & salmon)
    • Signs begin 5-7 days after ingestion
    • Fluke causes minimal damage, severity is due to rickettsial parasite carried on fluke – causes damage to capillaries, rash, fever, fatal enteritis in dogs
    • Zoonotic potential if eat undercooked fish
  • 14. Paragonimus kellicotti: Lung fluke
    • Definitive hosts: dogs & cats
    • Intermediate host: snail, crayfish
    • #1 most common small animal fluke
    • Can be found in float of feces or sputum
    • Adults live in lung parenchyma but are known for getting “off track” – can end up in brain, other organs
    • Immature flukes encyst and penetrate intestinal wall, migrate to diaphragm & penetrate into pleural cavity – mature in lungs
  • 15. Schistosomes of wild birds: Swimmer’s Itch
    • Swimmer’s Itch or schistosome cercarial dermatitis caused by cercarial stage of schistosomes of migrating aquatic birds
    • Cercaria penetrate skin of human, causing severe pruritic dermatitis.
    • Only true zoonotic degenetic fluke