Stomach Worms in Horses: Habronema and Draschia Infection
- Habronema and Draschia are stomach worms spread through flies. Adult worms usually live in the stomach with few obvious digestive signs, but larvae can cause nonhealing skin lesions called summer sores.
- Most horses with the gastric form have mild or no clear signs. Pet parents usually notice trouble when a wound, eye corner, lip, or genital area becomes itchy, ulcerated, proud-flesh-like, or slow to heal during fly season.
- Diagnosis may involve a physical exam, lesion evaluation, fecal testing with special flotation methods, and sometimes gastroscopy or biopsy if the lesion looks unusual or is not improving.
- Treatment is not one-size-fits-all. Your vet may recommend deworming, wound care, anti-inflammatory treatment, fly control, and in tougher cases debridement or biopsy-guided care.
- Typical 2025-2026 US cost range is about $150-$1,500+, depending on whether care stays at the exam-and-deworming level or progresses to biopsy, gastroscopy, repeated visits, or surgical wound management.
What Is Stomach Worms in Horses?
Habronema and Draschia are parasitic stomach worms of horses. The adult worms live in the stomach lining and are carried through part of their life cycle by flies. In many horses, the stomach stage causes little to no obvious illness, which is why these parasites can be easy to miss unless your vet is specifically looking for them.
The problem most pet parents recognize is cutaneous habronemiasis, often called summer sores. This happens when fly-borne larvae are deposited into a wound or onto moist tissues such as the lips, eyes, nostrils, or genital area instead of being swallowed. The larvae cannot complete their normal life cycle there, so they trigger a strong inflammatory reaction and a sore that may look raw, raised, itchy, or full of yellow gritty material.
Habronema species are still seen in horses, while Draschia megastoma appears to be much less common in domestic horses today. Even so, both are discussed together because they share a similar fly-associated life cycle and can contribute to the same type of chronic skin lesions.
This condition is often seasonal, with lesions showing up in spring and summer when flies are active. Some horses seem prone to recurrence, so long-term prevention usually focuses on fly control, wound protection, and a deworming plan tailored by your vet.
Symptoms of Stomach Worms in Horses
- Nonhealing skin wound or ulcer
- Yellow gritty material in the lesion
- Itching or rubbing
- Proud-flesh-like tissue
- Discharge from the sore
- Lesions at the lips, eye corner, penis/sheath, or other moist areas
- Few or no stomach-related signs
Call your vet sooner rather than later if a wound is getting larger, staying open, or returning every warm season. Summer sores can look like proud flesh, infection, or even some tumors, so it is worth getting the lesion checked instead of assuming it will heal on its own.
See your vet immediately if the sore is near the eye, interferes with urination, causes marked swelling, becomes very painful, or your horse seems systemically unwell. Those cases may need faster diagnostics and more intensive wound management.
What Causes Stomach Worms in Horses?
These parasites depend on both horses and flies. Adult Habronema or Draschia worms live in the horse's stomach and produce eggs or larvae that pass out in manure. Fly larvae develop in manure, pick up the parasite, and later become adult flies that carry infective larvae.
In the normal life cycle, flies deposit larvae around the horse's mouth, and the horse swallows them. The larvae then mature in the stomach over several weeks. In the abnormal life cycle that causes summer sores, flies deposit larvae into a wound or onto moist tissues such as the lips, eyes, nostrils, or genital area. Because the larvae cannot mature there, they trigger chronic inflammation instead.
Risk goes up during warm months with heavy fly pressure, especially where manure management is difficult or wounds are left exposed. Horses with recurring summer sores may also have individual susceptibility, although that is not fully understood.
Importantly, these sores are not directly contagious from horse to horse. The fly vector and the presence of a wound or moist tissue are what allow the problem to develop.
How Is Stomach Worms in Horses Diagnosed?
Your vet will usually start with the horse's history, the season, and the appearance of the lesion. A nonhealing wound in fly season, especially one with yellow gritty material or proud-flesh-like tissue, raises suspicion for cutaneous habronemiasis. Because several other conditions can look similar, diagnosis often involves ruling out other causes at the same time.
For suspected gastric infection, fecal testing can help, but standard fecal flotation may miss Habronema eggs. Merck notes that low-specific-gravity zinc sulfate flotation is more reliable for these eggs. In some cases, your vet may recommend gastroscopy to directly look for adult worms on the stomach lining.
For suspected summer sores, your vet may diagnose based on the lesion's appearance and response to treatment. If the sore is severe, unusual, near the eye, or not improving as expected, your vet may collect skin scrapings or recommend a biopsy to look for larvae and to rule out other problems such as exuberant granulation tissue, infection, or neoplasia.
Because there is no single perfect test for every case, diagnosis is often practical and stepwise. That is one reason Spectrum of Care planning matters here: some horses do well with exam-based treatment, while others need biopsy, gastroscopy, or repeat follow-up to reach a confident answer.
Treatment Options for Stomach Worms in Horses
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Farm call or clinic exam
- Targeted deworming plan prescribed by your vet, often using a macrocyclic lactone such as ivermectin or moxidectin when appropriate
- Basic wound cleaning and protection guidance
- Fly-control plan for the horse and environment
- Short-term recheck by phone or photo when appropriate
Recommended Standard Treatment
- Full veterinary exam and lesion assessment
- Deworming treatment selected by your vet
- Topical and/or systemic anti-inflammatory care when indicated
- Bandaging or wound-management plan
- Fecal egg count or targeted fecal testing when useful
- Sedated wound evaluation, lesion scraping, or follow-up recheck as needed
Advanced / Critical Care
- Biopsy and histopathology for nonhealing or suspicious lesions
- Gastroscopy if gastric infection is a concern or diagnosis remains unclear
- Standing sedation and debridement of exuberant granulation tissue when needed
- Advanced wound management for lesions near the eye, genitalia, or other high-motion areas
- Repeat rechecks and referral-level care if the lesion is severe or recurrent
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Stomach Worms in Horses
Bring these questions to your vet appointment to get the most out of your visit.
- Does this lesion look most consistent with a summer sore, or are there other conditions you want to rule out?
- Would a fecal egg count help in this case, and if so, do you use a method that can better detect Habronema eggs?
- Is this a case where exam-based treatment is reasonable, or do you recommend biopsy or gastroscopy now?
- Which deworming medication fits my horse's history, age, and parasite-control plan?
- What wound-care steps should I do at home, and what products should I avoid unless you recommend them?
- How should I change fly control around the barn, manure pile, and turnout areas to reduce recurrence?
- What signs would mean the sore is worsening or needs a faster recheck, especially if it is near the eye or genital area?
- Based on my horse's case, what is the expected cost range for conservative, standard, and advanced care?
How to Prevent Stomach Worms in Horses
Prevention focuses on breaking the parasite life cycle and reducing fly contact with wounds and moist tissues. Good manure management matters because flies develop in manure and help spread infective larvae. Removing manure, disposing of soiled bedding and wet feed, and reducing fly breeding areas can make a real difference.
Daily fly control on the horse also helps. Depending on your horse and setup, your vet may suggest a combination of fly masks, fly sheets, repellents, stabling during peak fly activity, and careful wound coverage. Promptly cleaning and protecting even small cuts is important, especially in spring and summer.
Deworming should be strategic, not automatic. Current equine parasite guidance supports using fecal egg counts and the horse's age and risk profile to guide treatment frequency, rather than rotating products on a fixed schedule without testing. Your vet can help build a plan that addresses common parasites while also considering horses with a history of summer sores.
If your horse has had summer sores before, stay alert for recurrence each warm season. Early treatment of new lesions is usually easier than trying to manage a large chronic sore later.