Equis ISSN 2398-2977

Infective nematode larvae - free living nematodes: key for differentiation

Contributor(s): Sheelagh Lloyd

Key for differentiation of infective nematode larvae and free living nematodes from horse feces

  • 1:
    • Without protective sheath    Free-living nematode 02: without protective sheath      →   2.
    • With protective sheath    Free-living nematode 03: with protective sheath      →   3.
  • 2:
    • Rhabditiform esophagus   Free-living nematode 01: rhabditiform esophagus  (dilated posteriorly into a bulb) = Free living nematode   Free-living nematodes  .
    • Not a rhabditiform esophagus. Esophagus is filariform and is nearly half the length of the body = Strongyloides westeri  Strongyloides westeri  .
  • 3:
    • Gut comprising 8 cells = Cyathostomins   Cyathostome 01: L3    Cyathostome 02: L3   ( Cyathostomum, Cylicocyclus, Cylicodontophorus, Cylicostephanus).
    • Gut comprising 12 cells, button on tail = Gyalocephalus*   Gyalocephalus spp: L3  .
    • Gut comprising 16 cells   →   4.
    • Gut comprising >16 cells   →   7.
  • 4:
    • Without long sheath tail = Trichostrongylus axei  Trichostrongylus axei 01: without protective sheath    Trichostrongylus axei 02: with protective sheath    Trichostrongylus axei 03: with protective sheath  .
    • With sheath tail   →   5.
  • 5:
    • Very large larva with large, well defined, triangular cells = Oesophagodontus*   Oesophagodontus spp: L3  .
    • Not large triangular cells   →   6.
  • 6:
    • Medium length larva with clearly defined slightly rectangular cells, sheath without long tail = A cyathostomin Poteriostomum.
    • Very long thin larva, ill-defined cells that are slightly rectangular. Small tri-lobed process on larval tail = Strongylus equinus.
  • 7:
    • Gut comprising 18-20 cells   →   8.
    • Gut comprising 28-32 well defined rectangular cells, very long broad larva, short esophagus = Strongylus vulgaris  Strongylus vulgaris 01: L3      Strongylus vulgaris 02: L3  .
  • 8:
    • Cells well defined and regular, broad larva of medium length = Triodontophorus.
    • Cells elongated and ill-defined, small thin larva, very blunt tail = Strongylus edentatus.

* Related to Triodontophorusspp   Triodontophorus spp  .

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