Onchocerciasis in Working Donkeys in Mali, Africa

The Oncocerca spp are parasitic filarioid nematodes found worldwide in humans and animals. Several species affect equids, of particular importance are Onchocerca reticulata (found in the flexor tendons and suspensory ligament), Onchocerca gutturosa and Onchocerca cervicalis which live in the ligamentum nuchae. Onchocerca cervicalis is a worldwide occurring parasite affecting the skin and ligaments of equids. The hair-like adult worms have a predilection for the ligamentum nuchae, where the females can grow to around 30cm long; the males being smaller at 5-8cm. The females produce microfilaria, which migrate through the dermis to sites including the ventral midline, face, neck, chest, withers and eyelids where they are ingested by feeding arthropods, mainly Culicoides spp. Maturation in the intermediate host takes 3-4 weeks, after which they are reintroduced to the equid by the biting vector during feeding. The microfilaria stages of O. cervicalis are susceptible to ivermectin, but the adults are resistant. In horses, disease can manifest as a type I and type III hypersensitivity reaction to the microfilaria, resulting in pruritis, alopecia, crusting, excoriation and depigmentation. […]