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Also Known As

Summer sores


Habronema, often referred to as stomach worms, are a nematode worm that is attracted to moist mucous membranes of the horse's anatomy, including the eyes, lips, mouth, wounds, and prepuce.

These larvae are so small that they can only be seen through a microscope, so a skin biopsy is a good method of diagnosing cutaneous habronemiasas.

Most active during warm summer months, habronema cause "summer sores" that are itchy, may become infected, and may assume a growth-like appearance resembling a sacroid or squamous cell carcinoma, especially around the eyes or on the sheath of the penis of the horse. The intense itchiness often prompts the horse to chew and bite at the area, causing additional damage to the skin.

Habronema nematodes produce eggs in the horse's stomach, and the larvae move through the gastrointestinal tract and out in the horse's feces where maggots of stable or house flies can pick up the larvae. The habronema larvae migrate to the mouth parts of the fly where they can be spread to other horses.

If the larvae migrate to the lungs, they can become trapped and form cysts, which are usually harmless. If they migrate through the skin, they cause cutaneous irritation and ulceration.


  • Ulceration of moist areas around eyes, mouth, nostrils, foreskin, and wounds
  • Intense itching
  • Open sores that are messy and moist with pus
  • An open wound that enlarges, ulcerates, and becomes covered with reddish-yellow tissue that bleeds easily
  • Growth-like (granulomatous) appearance resembling a sacroid or squamous cell carcinoma


Summer sores are caused by larval habronema deposited by stable and horseflies as they feed around moist areas on the body, especially the sheath of the penis and corners of the eye, or in open wounds. .


Fly control is the best prevention. Keeping stable and pasture areas clean and free of manure will discourage the fly population. Using misting systems in stalls and barns, spraying barn and stable areas with appropriate fly killers, and using fly repellents specifically made for horses in the form of sprays or skin products that are dabbed on and spread around the eyes, will minimize exposure to the larvae which is carried by flies.

In some cases, face masks and other protective coverings will help keep the horse comfortable and limit exposure.


A skin biopsy is the best way to diagnose cutaneous habronemiasis. Once diagnosed, orally administered de-worming medications to rid the horse of stomach worms, along with oral and/or topical steroids, help reduce exposure, inflammation, and irritation. .

Veterinarians often recommend Ivermectin paste, which is effective against both the adult worms in the stomach and the larvae in wounds and sores. Skin preparations, wettable powders, and antibiotics can be applied with dressings or massaged into large open sores to prevent further infestation and infection. .

Large masses of infected tissue may require surgical removal with proper care afterward to prevent further infection. A veterinarian can recommend the best course of treatment and write prescriptions for appropriate medications.

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EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.