Equis ISSN 2398-2977


Synonym(s): Summer sores, cutaneous habronemiasis, habronemiosis

Contributor(s): Dawn Logas, Rosanna Marsella, Reginald Pascoe, Sue Paterson, David Senter, Vetstream Ltd


  • A seasonal condition characterized by mildly pruritic, reddish-brown granulomatous lesions.
  • Cause: aberrant intradermal migration of larvae of stomach worms:Habronema muscae,Habronema majusandDraschia megastoma.
  • Signs: granulomatous lesions occur in medial canthus of eye, around male genitalia and on uncovered wounds.
  • Diagnosis: history and clinical signs are suggestive. Confirmation is by skin biopsy.
  • Treatment: debulk lesion (may involve amputation of urethral process), anti-inflammatories, parasiticides to reduce size of lesion, reduce inflammation and to prevent re-infestation.
  • Prognosis: strict adherence to fly control measures and wound control for life in hypersensitive animals.
  • See also:



  • Larvae of stomach worms:Habronema muscae,Habronema majusandDraschia megastoma  Habronema spp  .
  • Musca domestica(house fly) is host toHabronema muscaeandDraschia megastoma,Stomoxys calcitrans(stable fly) is host toHabronema microstoma.

Predisposing factors

  • Poor fly control.
  • Poor manure disposal.
  • Uncovered wounds on distal limbs.


  • Exposure to relevant species of biting flies (Musca domesticaandStomoxys calcitrans).
  • Previous exposure to the disease and development of hypersensitivity to migrating larvae.


  • Adult worms in stomach   →   larvae in feces   →   ingested by host fly   →   fly bites horse transmitting larvae to horse   →   migrate to stomach where a mild chronic gastritis may occur due to reaction to presence of worms in stomach.
  • Flies land and deposit larvae at aberrant sites where skin is moist   →   aberrant intra-dermal migration of worms   →   granulomatous response   →   lesions to skin, ocular area   Skin: habronemiasis 01 - face   and male genitalia.
  • Larval death may be part of the allergic pathogenesis.
  • Migration of larvae within the skin causes granulomatous reaction. This occurs particularly at sites that preferentially attract flies such as open wounds   Skin: habronemiasis 03 - jaw    Skin: habronemiasis 04 - jaw (close-up)      Skin: habronemiasis 05 - face    Skin: habronemiasis 06 - face  .

Male genitalia

  • Flies are attracted to this area, larvae burrow into prepuce and urethral process causing granulomatous reaction, preputial swelling and discharge.

Ocular lesions

  • Flies are attracted to the eyes, particularly the medial canthus of the eye, larvae burrow into conjunctivae and eyelids causing lesions   Eye: habronemiasis  .


  • Gastritis occurs due to local inflammatory response to presence of large numbers of worms in the stomach.
  • Rarely causes overt disease, but may be seen at necropsy.
  • Habronema megastomacan provoke formation of large fibrous nodules in the stomach but these are well tolerated unless they occur close to the pylorus.


  • Life cycle 2 months.
  • Local reaction and development of the lesions occurs within hours to days of the flies biting and transmitting larvae, particularly in hypersensitive (previously exposed) horses.


  • Adult worms live in the stomach   →   larvae in feces (D. megastoma, H. musce)   →   ingested by larvae of intermediate host flies, house fly (Musca domestica)   Musca domestica   and the stable fly (Stomoxys calcitrans)   Stomoxys calcitrans   (H. majus).
  • The larval worms develop inside the maggot, becoming infective third-stage larvae at about the time that the adult fly emerges from its pupa.
  • Fly feeds around horse's mouth and larvae (or whole fly) are swallowed and complete their development in the glandular area of the stomach.
  • Larvae deposited onto skin wound or around the eyes invade the tissues   Skin: habronemiasis 01 - face  , but do not complete their development.
  • Another method of infection is by ingestion of infected flies with the water or feed.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Down S S, Hughes I & Henson F M D (2009) Cutaneous habronemiasis in a 9-year old Arab gelding in the United Kingdom. Equine Vet Educ 21 (1), 4-8 VetMedResource.
  • Paterson S (2009) Cutaneous habronemiasis. Equine Vet Educ 21 (1), 9-10 VetMedResource.
  • Smith M A, Levine  D G, Getman L M et al (2009) Vulvar squamous cell carcinoma in situ within viral papillomas in an aged Quarter horse mare. Equine Vet Educ 21 (1), 11-16 VetMedResource.
  • Giangaspero A, Traversa D & Otranto D (2005) A new tool for the diagnosisin vivoof habronemosis in horses. Equine Vet J 37 (3), 263-264 PubMed.
  • Gasthuys F M R, van Heerden M & Vercruysse J (2004)Conjunctival habronemiosis in a horse in Belgium.Vet Rec154(24), 757-758 PubMed.
  • Pascoe R R (1991) Equine nodular and erosive skin conditions - the common and the not so common. Equine Vet Educ (3), 153-159 Wiley Online Library.
  • Mohammed F H et al (1990) Cutaneous habronemiasis in horses and domestic donkeys (Equus asinus asinus). Rev Elev Med Vet Pays Trop 42 (4), 535-540 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 to 1986). Am J Vet Res 48 (2), 268-273 PubMed.
  • Foil L et al (1986) Parasitic skin diseases. Vet Clin North Am Equine Pract (2), 403-437 PubMed.
  • Trees A J et al (1984) Apparent case of equine cutaneous habronemiasis. Vet Rec 115 (1), 14-15 PubMed.
  • Reinemeyer C R et al (1984) The prevalence and intensity of internal parasites of horses in the USA. Vet Parasitol 15 (1), 75-83 PubMed.
  • Fadok V A (1984) Parasitic skin diseases of large animals. Vet Clin North Am Large An Pract (1), 3-26 PubMed.
  • Miller R I et al (1982) A survey of granulomatous and neoplastic diseases of equine skin in north Queensland. Aust Vet J 59 (2), 33-37 VetMedResource.

Other sources of information

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