Chronic myelogenous leukemia in a great horned owl (Bubo virginianus).

A free-ranging adult female great horned owl (Bubo virginianus) was presented to the Wildlife Medical Clinic at the University of Illinois after being observed with anorexia and decreased activity. A severe leukocytosis (212 400 cells/microl), primarily comprised of mature heterophils, was found at presentation. Results of various diagnostic tests including radiographs, Chlamydophila serologic testing, measurement of Aspergillus antibody and antigen titers, plasma protein electrophoresis, fecal culture and acid-fast staining, coelioscopy, endoscopy, tracheoscopy, exploratory coelomotomy, nuclear scintigraphy, tissue cultures, bone marrow biopsy, and histopathology revealed no underlying cause for the persistent leukocytosis.