ISSN 2398-2977      



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


  • 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.


This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login


This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login


This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login


This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login

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.

Can’t find what you’re looking for?

We have an ever growing content library on Vetlexicon so if you ever find we haven't covered something that you need please fill in the form below and let us know!


To show you are not a Bot please can you enter the number showing adjacent to this field

 Security code