Lymphoproliferative disorder in a great horned owl (Bubo virginianus)

An adult free-ranging great horned owl (Bubo virginianus) was presented depressed and in poor body condition. Results of hematologic testing revealed severe leukocytosis and lymphocytosis, and large lymphocytes containing large eccentric nuclei and prominent nucleoli were present on a peripheral blood smear. Hepatomegaly and renomegaly were evident radiographically. The owl was treated supportively but died 9 days after presentation. At necropsy, the liver and kidneys were severely enlarged, focal yellow plaques were present on air sac membranes, and small yellow granulomas were present in the lung parenchyma. On histopathologic examination, the liver, spleen, and kidneys were infiltrated with a homogeneous population of large lymphocytes with mitotic figures, and clusters of septate fungal hyphae resembling Aspergillus species were evident in lung parenchyma. Virus isolation was negative. The diagnosis was a lymphoproliferative disorder of unknown etiology and concurrent pulmonary aspergillosis.