Oxyuriasis in Horses (Equis) | Vetlexicon
equis - Articles


ISSN 2398-2977

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  • Equine parastic disease causing perineal irritation via a sensitivity reaction.
  • CauseOxyuris equi  Oxyuris equi  - the equine pinworm.
  • Signs: tail rubbing, hair loss, irritation and restlessness   Oxyuris equi: hypersensitivity  .
  • Diagnosis: age, signs, identification ofOxyuriseggs on transparent adhesive tape imprint taken from perineal area (although this is prone to false negatives).
  • Treatment: susceptible to all common oral anti-parasiticides.
Print off the Owner factsheets on Pinworms - an unwanted irritation and Worm control to give to your clients.

Presenting signs

  • Perineal pruritus.
  • Tail rubbing.
  • Perineal alopecia.
  • Self-excoriation in perineal area.

Geographic incidence

  • Worldwide

Age predisposition

  • >3-6 months old.

Cost considerations

  • Cheap - easily treated with any of the commonly used anti-parasiticides, then control by hygiene when grooming.
  • Treatment of inflammation and secondary infection may also be necessary.




  • Adult female extends through anus to lay eggs along with cement on perineal skin.
  • Presence of cement causes pruritus   →   horse scratches area.
  • Ingested eggs develop to adulthood in colon.
  • Presence of cement on the perineum causes a local hypersensitivity reaction   →   inflammation and pruritus -> self excoriation -> alopecia and secondary infection.
  • Presence of L4 larvae cause slight mucosal ulcerations.


  • Egg develops to infective L3 larvae in 4-5 days, this is ingested, passes into the intestine and develops via L4 larvae to adult in 4-5 months.


  • Lifecycle involves development of adult in large and small colon. Females migrate to anus and lay eggs on perineum. Eggs stick to perineum or pass out in feces onto bedding or fall or are rubbed off onto bedding.


Presenting problems

  • Perineal pruritus.
  • Perineal and tail-base excoriation.
  • Alopecia of tail-base.
  • Presence of eggs on perineum.

Client history

  • Rubbing of tail-base.
  • 'Rat tailed' appearance due to loss of hair   Oxyuris equi: hypersensitivity  .
  • Hair loss, and broken hairs at tail base.

Clinical signs

  • Inflammation of skin around perineum and tail-base.
  • Excoriation and possibly secondary infection of skin around perineum and tail-base   Anus: proctitis - chronic  .
  • Visible grayish/yellow streaks of eggs on perineum.

Diagnostic investigation

Fecal analysis Microscopy
  • Apply transparent adhesive tape to perineal skin. Microscopic examination shows presence ofOxyuriseggs   Oxyuris equi: egg cluster  .
  • Run water between the tape and the slide to better outline the eggs.
  • Skin scrapes   Dermatology: scraping  .

Confirmation of diagnosis

Discriminatory diagnostic features

  • Perineal inflammation.
  • Perineal pruritus.
  • Loss of hair around tail base.
  • Secondary infection in perineal area.
  • Skin scrape.

Definitive diagnostic features

  • Presence ofOxyuriseggs on perineum, in feces or visualization of adult worms in feces.

Gross autopsy findings

  • Presence of adultOxyurisworms in colon/rectum.

Differential diagnosis

  • Lice   Pediculosis  , sucking lice in tail.
  • Atopy.


Standard treatment



  • Regular use of routine anthelmintics.
  • Hygiene by cleaning perineal area when grooming.



  • Very good.

Further Reading


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 Wiley.
  • 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.
  • Lyons E T et al (1987) Common internal parasites found in the stomach, large intestine and cranial mesenteric artery of thoroughbreds in Kentucky at necropsy (1985-1986). Am J Vet Res 48 (2), 268-273 PubMed.

Other sources of information

  • Urqhart G M, Armour J, Duncan J L et al (1988) Veterinary Parasitology.Longmann Scientific & Technical. ISBN 0 5824 0906 3.
  • Rose R J & Hodgson D R (1993) Manual of Equine Practice. Saunders. ISBN 0 7216 3739 6.