- Caused by Onchocerca spp.
- Affects horses, cattle, donkeys, mules, sheep, goats
- Transmitted by Simulidae and Ceratopogonidae
- Hypersensitivity varies with individuals, may occur without any inflammation
- Grossly:
- Adult parasites within connective tissue nodules
- Microfilaria in dermis, especially ventral midline
- Patchy alopecia, erythema, scaling, crusting, change in pigmentation
- Circular areas of dermatitis on forehead appears in some horses
- May also involve keratitis, uveitis and conjunctivitis
- Microscopically:
- Normal to superficial to deep perivascular dermatitis
- Eosinophils, lymphocytes, microfilariae