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Oxyuris equi

ISSN 2398-2977

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Introduction

Classification

Taxonomy

  • Phylum: Nematoda.
  • Superfamily: Oxyuroidea.
  • Family: Oxyuridae.
  • Genus:Oxyuris.
  • Species:equi.

Distribution

  • Worldwide - though should be controlled by anthelmintics in regularly wormed horses or by hygiene while grooming.
  • 36% of horses infected in survey in Poland, 7% in Victoria, Australia and 26% in Queensland, Australia.
  • Number of worms in individuals ranged from 20-3770.

Significance

  • Adult female worms lay eggs with cement around anus causing irritation   Oxyuriasis  .

Active Forms

Active Form 1

Morphology

  • Female large worm: up to 10 cm long   Oxyuris equi: adult - female  .
  • Long tapering tail (hence name pinworms).
  • Males about 1 cm in length, one spicule.

Taxonomy

  • Long tapering tail in female.

Color

  • White.

Tolerances

Other
  • In vivoonly.
  • Feed on intestinal contents.

Development

Reproduction
  • Pre-patent period 5 months.
  • Gravid female migrates down intestine from colon   Oxyuris equi: adult - female  and protrudes through anus to lay her eggs on skin round anus   Oxyuris equi: egg cluster  .
  • Egg masses are surrounded by sticky gray/yellow fluid.
  • Eggs develop to infective stage in 4-5 days when fluid cracks into flakes that contaminate the environment.
  • Flakes may be rubbed off onto fences, etc.
  • Infective material then ingested by horses.

Active Form 2

Morphology

  • Appear like carpet tacks (5-10 mm), tapering tail   Oxyuris equi  .

Tolerances

Other
  • In vivoonly.
  • Feed on intestinal wall - cause small erosions of mucosa.

Development

Growth
  • Develop from L3 larvae approximately 10 days after infection.

Resting Forms

Resting Form 1

Morphology

  • Oval shaped (approximately 90 x 45 um) with a mucoid plug at one end.
  • One side flattened   Oxyuris equi: egg  .
  • L3 larvae develops inside egg.

Color

  • Yellow.

Tolerances

Temperature
  • Develops to infective stage close to skin around anus.

Development

  • Develops to infective stage in 4-5 days.

Clinical Effects

Epidemiology

Lifecycle

  • Adult worms in intestine.
  • Eggs laid around anus.
  • L3 larvae develops within egg.
  • Egg ingested.
  • Larvae hatches in intestine.
  • L4.

Transmission

  • By ingestion of infective eggs off contaminated fomites.
  • Eggs remain stuck to the perineal area for several days before dropping or being rubbed off onto fomites or bedding.
  • Eggs are very susceptible to dessication and so those outdoors usually die.
  • Heavy infections can occur in stabled horses where eggs are at high concentrations in damp areas such as mangers or bedding.

Pathological effects

  • Adult worms cause pruritus during egg-laying.
  • Horses rub tail area causing damage to hairs of tail head, 'rat-tailed' appearance.
  • L4 larvae may cause inflammation of intestinal mucosa as erosions caused by feeding (rare).

Control

Control via animal

  • Local irritation around anus can be controlled by sponging anal area to remove eggs.

Control via chemotherapies

  • Oxyuris equiis susceptible to most anthelmintics, therefore should be controlled by routine anthelmintic treatments.

USA

UK

Diagnosis

Useful samples

  • Sticky tape, eg sellotape, cellophane tape, strip applied around anus.
  • Freshly passed fecal sample (not rectal feces).
  • Both may give false negatives.

Specimen storage

  • Attach strip to microscope slide.

Transport of samples

  • In slide holder/box.
  • In sealed container.

Field diagnosis

  • Rubbed tail hairs in tail head   Oxyuris equi: hypersensitivity  .
  • Egg masses can be seen as yellowish-gray streaks on perineum.
  • Worms can be seen in feces following anthelmintic treatment.

Laboratory diagnosis

  • Examine sticky tape strip, run water between slide and tape to better outline eggs .
  • Eggs have distinctive morphology   Oxyuris equi  .

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Reinemeyer C R & Nielsen M K (2014) Review of the biology and control of Oxyuris equiEquine Vet Educ 46 (11), 584-591 VetMedResource. 
  • Stephenson R (2010) Oxyuris equi a resurgent problem? UK Vet 15 (5), 8-10 VetMedResource.
  • Costa A J et al (1998) Comparative efficacy evaluation of moxidectin gel and ivermectin paste against internal parasites of equines in Brazil. Vet Parasitol 80 (1), 29-36 PubMed.
  • Gawor J J (1995) The prevalence and abundance of intestinal parasites in working horses autopsied in Poland. Vet Parasitol 58 (1-2), 99-108 PubMed.