Equis ISSN 2398-2977

Gasterophilus

Contributor(s): Joseph DiPietro, Maggie Fisher, Sheelagh Lloyd

Introduction

Classification

Taxonomy

  • Phylum:Arthropoda.
  • Class:Insecta.
  • Family:Oestridae.
  • Genus:Gasterophilus.
  • Species:intestinalis,nasalisandhemorrhoidalis.

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Clinical Effects

Epidemiology

Lifecycle

  • Adults.
  • Eggs laid on horse's hair.
  • Larvae: 1st, 2nd and 3rd stage.
  • Pupate on ground.

Transmission

  • Adult fly on wing in the summer months   →   lays eggs on individual horses.
  • L1-L3 spend 9 months in the horse.
  • Pupa lasts about 6 weeks on the ground.

Pathological effects

  • Adult flies irritate horses. Most horses tolerate them.
  • Stomatitis may be seen as a result of larval migration in mouth - larvae very common but clinical symptoms uncommon.
  • Larvae attaching in stomach cause some inflammation. A circular fibrous crater with raised rim develops where larvae attach.
  • Rarely clinical signs associated with the presence of larvae are observed - gastritis, ulceration, perforation and even death.
  • Difficult to evaluate whether infection associated with any sub-clinical changes of significance, ie reduced performance.

Control

Control via animal

  • In the second half of summer, cut or pluck eggs off hairs around legs or mouth while grooming.
    50% of owners already do this
  • Treat host to kill larvae while in stomach and also mouth after first frost.

Control via chemotherapies

  • Treat bot larvae in stomach, ivermectin   Ivermectin  , moxidectin   Moxidectin  or haloxon   Haloxon  indicated for removal of bots.
    Ivermectin and moxidectin kill all stages of larvae. Haloxon only kills older larvae
  • Normally carried out in late autumn after first frost kills adults.
    Eggs ofG. intestinalismust be removed from the coat at treatment, if not, will infect horse over several months.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Lyons E T, Tolliver S C, Collins S S & Drudge J H (2001) Transmission of endoparasites in horse foals born on the same pasture on a farm in central Kentucky (1996-1999). Vet Parasitol 97 (2), 113-121 PubMed.
  • Coles G C & Pearson G R (2000) Gasterophilus nasalis infection: prevalence and pathological changes in equids in south-west England. Vet Rec 146 (8), 222-223 VetMedResource.
  • Lloyd S et al (2000) Parasite control methods used by horse owners: factors predisposing to the development of anthelmintic resistance in nematodes. Vet Rec 146, 487-492 PubMed.
  • Lyons E T et al (2000) Prevalence of selected species of internal parasites in equids at necropsy in central Kentucky (1995-1999). Vet Parasitol 92 (1), 51-62 PubMed.
  • Coles G C & Pearson G R (2000) Gasterophilus nasalis infection: prevalence and pathological changes in south-west England. Vet Rec 146 (8), 222-223 VetMedResource.
  • Reinemeyer C R, Scholl P J, Andrews F M & Rock D W (2000) Efficacy of moxidectin equine oral gel against endoscopically-confirmed Gasterophilus nasalis and Gasterophilus intestinalis (Diptera - Oestridae) infections in horses. Vet Parasitol 88 (3-4), 287-291 PubMed.
  • Cogley T P & Cogley M C (2000) Field observations of the host-parasite relationship associated with the common horse bot fly, Gasterophilus intestinalis. Vet Parasiotol 88 (1-2), 93-105 PubMed.

Other sources of information

  • Kettle D S (1997) Medical and Veterinary Entomology. 2nd edn. CAB International.

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