Cutaneous leishmaniasis in two horses.

This report contains the clinical, histologic, immunohistochemical, and electron microscopic findings in two cases of equine cutaneous leishmaniasis. Nodular, sometimes crusty or ulcerated lesions were confined to the pinna and adjacent neck in both animals. The dermal inflammatory infiltrate was lymphohistiocytic in horse No. 1 and pyogranulomatous with formation of tuberculoid granulomas in horse No. 2. Numerous Leishmania organisms were found within macrophages in both animals. There was moderate to intense and specific reaction by immunoperoxidase using a polyclonal antiserum against Leishmania in both horses. Leishmania amastigotes were also revealed by electron microscopy. This is the first report of equine cutaneous leishmaniasis recognized in North America and Puerto Rico. Leishmaniasis should be considered in the differential diagnosis of cutaneous nodular diseases in the horse.