Onchocerciasis

• 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