Summer Sores Around a Horse’s Eye – Vet Guide 2025 ☀️🐴

By Dr Duncan Houston, BVSc

Introduction

Also called habronemiasis, summer sores are wound‑like lesions caused by parasitic larvae (from Habronema or Draschia worms) deposited by flies, around the eye and other areas. These itchy sores bleed easily, contain yellow “granules,” and stubbornly resist healing. In this comprehensive 2025 guide, Dr Duncan Houston explains causes, diagnostics, treatment options, and prevention—designed to help horse owners protect their equine companions.

What Are Summer Sores?

Summer sores are granulomatous reactions to parasite larvae deposited by house and stable flies. These larvae fail to develop fully on the skin but incite intense allergic inflammation, causing ulcerated, non-healing lesions festooned with yellow debris—a hallmark of habronemiasis .

Why They Form Around the Eye

• Flies are drawn to moisture—eyes, nostrils, sheath—making these areas prime deposition sites.
• The eye region is sensitive; even small lesions cause intense itching and tear staining.
• Persistent rubbing aggravates lesions, allowing fly exposure to continue and lesions to worsen.

Signs to Watch For

• Red, ulcerated mass near eyelids or surrounding skin.
• Yellow “sulfur” granules within the lesion.
• Chronic, non-healing despite standard wound care.
• Severe itching, head shaking, tear staining.
• Bleeding, discharge, or raw appearance.

Diagnosing Summer Sores

• **Clinical exam**: look for classic appearance and location.
• **Biopsy**: essential to rule out look-alikes like sarcoids or squamous cell carcinoma .
• **Larval detection**: occasionally larvae are visible in tissue.
• **History**: lesion seasonality, fly exposure, existing parasitic control protocols.

Treatment Options

1. Debulking or Surgical Removal

• Excise large lesions to reduce parasite load and inflammatory tissue.
• Allows easier access for topical or injected medication.

2. Anti-inflammatory Steroids

Corticosteroids help calm hypersensitive responses:

• Systemic (oral or injected) or topical use.
• Injected directly into the lesion to inhibit inflammation locally.
• Often dramatically reduces lesion size within days .

3. Topical Treatments

• Combine antibiotics and larvicidal agents to treat secondary infection and kill larvae.
• Apply directly to the cleaned lesion site; frequency as directed by vet.

4. Deworming with Ivermectin

All horses with summer sores should receive ivermectin, which eliminates Habronema larvae and adult stomach worms. Routine deworming has led to significant reductions in cases over the past decades .

5. Fly Control

• Essential: masks, sprays, physical barriers.
• Reduces new larvae deposition and supports healing.
• Barn hygiene—waste removal to minimize fly breeding sites.

Why Prompt Treatment Matters

• Lesions worsen without intervention—itching, bleeding, secondary infection.
• Ocular regions are sensitive—a sore can impair vision if close to the eye.
• Misdiagnosis may lead to unnecessary procedures or delay appropriate care.

Preventive Approaches

• Maintain consistent, vet-approved deworming schedule.
• Strengthen fly control—especially during fly season.
• Inspect skin daily for early signs of lesions.
• Clean lesion sites promptly to reduce fly attraction.
• Life-cycle awareness: Habronema larvae deposited May–September in temperate zones.

Case Study: Eyelid Summer Sore

1. Day 0: Owner notices ulcerated mass with yellow granules near eyelid.
2. Day 2: Vet performs biopsy, removes part of lesion, injects steroids, begins topical treatment.
3. Day 3: Administer ivermectin, implement fly masks and sprays.
4. Week 1: Lesion shrinks noticeably; itching reduced.
5. Week 4: Lesion essentially healed—no discharge, normal eyelid appearance.
6. Follow-up: Owner given schedule for continued deworming and fly control through summer.

When to Call the Vet

• Persistent ulcers near the eye that don’t heal.
• Presence of yellow granules.
• Lesions that bleed or become infected.
• Sarcoid- or cancer-like appearance—biopsy is needed.

Conclusion

Summer sores (habronemiasis) around the eye are treatable—and often prevented—with targeted intervention: diagnosis by biopsy, lesion removal, steroids, ivermectin, and robust fly control. Quick action at the first sign protects your horse’s eye and speedier recovery.

See a suspicious sore? Reach out to Ask A Vet via AskAVet.com or our app for expert triage, photo review, and tailored treatment plans. 🩺📱