Suspensory Ligament Desmitis Caused by Onchocerca sp. in Three Donkeys

Abstract

Three donkeys were presented with progressive lameness and distal suspensory ligament breakdown in multiple limbs. Treatment with nonsteroidal anti-inflammatory drugs was only partially effective and eventually the donkeys were euthanized due to further progression of the lameness and concerns for their welfare. At necropsy, the distal part of the suspensory ligaments in multiple limbs, including the suspensory ligament branches, was markedly thickened, enlarged, and mottled white and brown on cut section. In one case, adult Onchocerca sp. nematodes were grossly identified embedded within the suspensory ligaments. Histopathologic examination revealed chronic, multifocal to coalescing, moderate to severe, lymphoplasmacytic, eosinophilic, and fibrosing desmitis and tendinitis with intralesional, coiled adult nematodes of Onchocerca sp., accompanied by osseous and cartilaginous metaplasia. To the authors’ knowledge, this is the first histopathologic description of suspensory ligament desmitis and tendinitis associated with Onchocerca sp. in donkeys.

Onchocerca sp. in an imported Zangersheide gelding causing suspensory ligament desmitis

“…Microfilariae might have been identified to species, but no microfilariae were seen in the digest or on histology. The location within the ligaments of the leg and the geographic origin of the horse (Europe) both suggest O. reticulata 10 . In addition, it was previously observed that O. cervicalis always had uteri full of eggs whereas most specimens of O. reticulata females did not have any or as many eggs as were seen in the cross‐sections and in the digest of the nodule in our case 11…”

“…The location within the ligaments of the leg and the geographic origin of the horse (Europe) both suggest O. reticulata. 10 In addition, it was previously observed that O. cervicalis always had uteri full of eggs whereas most specimens of O. reticulata females did not have any or as many eggs as were seen in the cross-sections and in the digest of the nodule in our case. 11 Necropsy examination of the central nervous system was performed, resulting in a diagnosis of multifocal asymmetrical spinal cord funicular axonal degeneration suggestive of prior inflammatory or vascular injury such as the previous episode of EHM, considered to be the most likely source of the gelding's progressive ataxia.…”

“… 10 Necropsy examination disclosed marked enlargement of the distal suspensory ligaments in the affected limbs, and numerous adult nematodes were embedded within the suspensory ligament branches. 10 Ours is the first report of onchocerciasis causing parasitic suspensory ligament desmitis in a European Warmblood horse imported into the United States.…”

“…Onchocerciasis resulting in parasitic suspensory desmitis in the equid rarely has been reported in the veterinary literature, including a single report of 3 donkeys in the United Kingdom euthanized because of chronic multi‐limb lameness and fetlock hyperextension 10 . Necropsy examination disclosed marked enlargement of the distal suspensory ligaments in the affected limbs, and numerous adult nematodes were embedded within the suspensory ligament branches 10 . Ours is the first report of onchocerciasis causing parasitic suspensory ligament desmitis in a European Warmblood horse imported into the United States.…”

“…Onchocerca raillete has been identified in the nuchal ligament of donkeys in Africa 9 . Onchocerca reticulata is of particular concern because adult worms reside in the connective tissues of the flexor tendons and suspensory ligaments, potentially causing damage and discomfort 10 . Onchocerca reticulata in the horse causing suspensory ligament desmitis has not been reported in the United States, and parasitic suspensory ligament desmitis typically is not included as a differential diagnosis for horses with suspensory ligament pathology.…”