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  • 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