Habronemiasis (Summer Sores)
Learn what the condition is, how it may be detected early, how it is treated or managed, and which breeds or species are linked to it.
Condition snapshot
A concise guide to the condition’s pattern, detection, management and urgency.
This snapshot is a general guide, not a diagnosis or treatment plan. New, severe or worsening signs require veterinary assessment.
About the condition
Cutaneous habronemiasis, or a summer sore, is a granulomatous skin reaction to larvae of Habronema or Draschia stomach worms. Muscid flies pick up larvae around horse manure and deposit them while feeding on moisture at wounds, eyes, lips or genital tissue. Larvae placed on skin cannot complete their life cycle, but they provoke intense inflammation and persistent exuberant tissue.
Lesions are itchy, ulcerated, reddish-brown and greasy, often enlarging during warm fly season instead of healing. Yellow gritty granules resembling rice grains can be embedded in the tissue. Common sites include limb wounds, the inner corner of the eye, mouth corners, sheath and urethral process. Rubbing, bleeding and proud flesh can become severe.
Summer sores resemble sarcoids, squamous cell carcinoma, fungal granulomas and ordinary exuberant granulation tissue. Season and appearance support suspicion but should not justify repeated deworming without sampling. Gastric Habronema infection is usually clinically silent, and routine faecal egg counts often miss the delicate eggs.
The condition is not spread directly horse to horse; flies connect the stomach-worm life cycle with wounds. Healing requires control of larvae, inflammation, contaminated tissue and fly access. Prognosis is good for early lesions but recurrence is common when proud flesh remains or the next fly season finds an unprotected wound. Ocular and genital sites demand specialist care because aggressive home treatment can damage the globe or urethra.
Habronema larvae deposited by flies in wounds or moist mucocutaneous sites cannot mature normally and provoke exuberant granulomatous inflammation. Lesions enlarge during warm fly seasons, itch intensely and contain yellow gritty foci. They can mimic proud flesh or tumour, while gastric adult worms in the same horse may cause no obvious digestive signs.
Ocular lesions add a separate risk to sight and require urgent examination.
Screening & Early Detection
A non-healing seasonal wound is examined for gritty yellow foci, exuberant granulation and typical fly-access sites. Deep scraping or biopsy may reveal larvae and the eosinophilic granulomatous reaction. Biopsy is particularly important for nodular, recurrent or atypical lesions to exclude sarcoid, SCC, pythiosis and other fungal or oomycete infection.
Ocular examination includes fluorescein staining and eyelid eversion; genital lesions require careful inspection of the penis, urethral process and sheath. Cytology and bacterial culture identify secondary infection but do not prove habronemiasis. Standard faecal flotation is insensitive and a negative result does not exclude cutaneous disease.
The property’s manure handling, fly burden and deworming efficacy are reviewed. Lesion photographs and measurements document response. Rapid growth, deep invasion, severe ocular pain, urinary difficulty or failure to regress outside fly season are reasons for prompt biopsy and diagnostic reconsideration rather than another empirical antiparasitic dose.
Biopsy distinguishes larval granulomas from sarcoid, squamous-cell carcinoma and exuberant granulation tissue. Season and fly exposure are recorded with any previous response to deworming.
Treatment & Management
Ivermectin or moxidectin is administered at an appropriate equine dose to kill susceptible larvae and gastric stages, considering the farm’s parasite-control history. Inflammation can briefly worsen as larvae die. Topical or systemic corticosteroid is often required to suppress the marked hypersensitivity response, but only after infection and tumour differentials are considered and laminitis risk assessed.
Exuberant or mineralised tissue may need surgical excision, cryotherapy or careful cautery. Ocular lesions are treated by a veterinarian experienced with the eye; caustic chemicals and unlabelled organophosphates near the globe or genitalia are unsafe. Secondary bacterial infection receives targeted treatment. The wound is covered where feasible and protected with repellent and a fly mask.
Prevention breaks fly access: manure is removed and managed regularly, feed areas kept clean, wounds bandaged, periocular discharge treated and effective fly control maintained. Strategic anthelmintic decisions consider resistance and the whole parasite programme rather than frequent blind dosing. Treatment continues until healthy epithelialisation occurs, because a smaller mound of proud flesh can seed recurrence.
Reducing manure and stable-fly breeding sites lowers reinoculation of the healing wound. Ocular cases receive specialist-directed therapy to protect the cornea and vision.
Breeds or species affected
Akhal-Teke
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Anglo-Arabian
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Arabian
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Barb
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Caspian
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Kathiawari
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Marwari
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Shagya Arabian
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Thoroughbred
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American Quarter Horse
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American Paint Horse
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Appaloosa
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Australian Stock Horse
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Brumby
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Waler
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Morgan
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Standardbred
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American Saddlebred
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Tennessee Walking Horse
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Missouri Fox Trotter
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Rocky Mountain Horse
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Peruvian Paso
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Criollo
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Mustang
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Canadian Horse
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Andalusian
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Lusitano
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Lipizzaner
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Friesian
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Dutch Warmblood
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Hanoverian
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Holsteiner
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Oldenburg
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Westphalian
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Trakehner
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Selle Français
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Belgian Warmblood
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Danish Warmblood
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Swedish Warmblood
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Swiss Warmblood
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Australian Warmblood
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Irish Sport Horse
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Cleveland Bay
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Württemberger
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Zangersheide
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Knabstrupper
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Orlov Trotter
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Camargue
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Icelandic Horse
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Pony of the Americas
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Quarter Pony
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Miniature Horse
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Clydesdale
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Shire
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Percheron
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Belgian Draft
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Suffolk Punch
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American Cream Draft
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Ardennes
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Breton
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Boulonnais
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Comtois
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Dutch Draft
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North Swedish Horse
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Norwegian Fjord
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Haflinger
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Gypsy Cob
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Irish Draught
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Welsh Pony and Cob
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Connemara Pony
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New Forest Pony
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Dartmoor Pony
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Exmoor Pony
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Shetland Pony
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Highland Pony
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Fell Pony
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Dales Pony
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Australian Pony
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Finnhorse
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Black Forest Horse
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