Diffuse cutaneous leishmaniasis in a cat.

An adult long-haired domestic cat native to South Texas developed signs consistent with diffuse cutaneous leishmaniasis. Cutaneous leishmaniasis, caused by Leishmania mexicana, was initially diagnosed from lesions confined to the left ear. A radical pinnectomy was done and the cat was returned to its owner. Two years later, lesions developed at the stump, and lesions later developed on the cat's muzzle and nasal mucosa. All of the lesions contained numerous L mexicana amastigotes. Several treatment regimens were attempted, but without evidence of resolution. The cat was tested multiple times for evidence of impaired immunologic competence and was found to be normal. The cat failed to respond to Leishmania antigen given interdermally (Montenegro test) on several occasions. On one occasion, however, there was partial regression of the lesions following the Montenegro test. Cats in areas endemic for cutaneous leishmaniasis (South Texas) may serve as sentinels for the agent. The epidemiology of the infection in this area is largely unknown, as is the importance of cats in the spread of disease.