Clinical ehrlichiosis in a cat.

Clinical ehrlichiosis was diagnosed in a cat from Colorado on the basis of cytologic, serologic, and clinical findings. Clusters of gram-negative organisms that were morphologically similar to morulae of Ehrlichia spp were found only in mononuclear cells. The cat had clinical signs that were referable to infection by a rickettsial organism, and antibodies against E canis (titer, 1:80) and E risticii (titer, 1:40) were detected in serum. Exclusion of other obvious causes inducing similar clinical signs, and positive clinical response to doxycycline, an antibiotic with known antirickettsial actions, aided in diagnosis. The cat was clinically normal within days following initiation of treatment, and was clinically normal, as well as seronegative for antibodies against E canis and E risticii, 1,365 days after discharge.