Cutaneous Habronemiasis in a Dog

Abstract

Cutaneous habronemiasis (summer sores), a common condition in horses, is characterized by ulcerative, non-healing skin lesions and the formation of exuberant granulation tis~ue.~.6.~.9 It is caused by aberrant intradermal migration by third-stage larvae (juveniles) of equine spiruroid stomach worms, Habronema musca, Habronema microstoma, and Draschia megastoma. 1,4,6~10 The normal life cycle of these nematodes involves development into the infective thirdstage larvae in a muscid intermediate host.4 Infective larvae are deposited by the adult fly on the mouth and lips of horses and are then swallowed and mature to adults in the stomach. Cutaneous infections occur when infective larvae are deposited by flies feeding in moist areas or open wounds instead of the mouth and lips. Experimentally, it has been demonstrated that infective larvae can penetrate normal, intact skin.4 Areas frequently involved include the lower limbs, medial canthus of the eye, the urethral process, and prepuce.’ There are no previous reports of this condition in other species. This report describes a case of cutaneous habronemiasis in a dog. In early July, a 9-year-old, spayed female, mixed-breed dog was examined because of a large, ulcerated lesion on the face. This lesion started as a small swelling lateral to the right naris. During the following 2 weeks, the lesion ulcerated and spread to involve most of the right side of the nose and face rostra1 to the medial canthus of the right eye. A biopsy from the edge of the lesion was fixed in 10% neutral buffered formalin and submitted for histopathologic evaluation. Histologically, the epidermis was ulcerated and overlaid with a thin layer of necrotic cellular debris admixed with neutrophils. The dermis and subcutis were markedly edematous and contained extensive infiltrates of inflammatory cells, predominantly eosinophils, with fewer plasma cells, macrophages, and lymphocytes. Variably-sized tracts of necrotic cellular debris admixed with fragmented collagen and large numbers of degenerate eosinophils were also present in