B-cell leukemia in an adult sheep

Authors: FURTADO, ADRIANNA - Washington State University; Fry, Lindsay; Piel, Lindsay; Bastos, Reginaldo; Schneider, David; VARVIL, MARA - Washington State University

Submitted to: Veterinary Clinical Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2023
Publication Date: 11/27/2023
Citation: Furtado, A.P., Fry, L.M., Piel, L.M., Bastos, R.G., Schneider, D.A., Varvil, M.S. 2023. B-cell leukemia in an adult sheep. Veterinary Clinical Pathology. 52(4):716-721. https://doi.org/10.1111/vcp.13303.
DOI: https://doi.org/10.1111/vcp.13303

Interpretive Summary: This case describes the clinical presentation and diagnosis of B-cell leukemia in a sheep that was part of a long-term research project. This report will assist veterinarians and owners in identifying and diagnosing leukemia of small ruminants, which is rarely encountered. Leukemia often leads to a non-specific presentation, including fever of unknown origin, weight loss, and lethargy. Clinicians should suspect leukemia when there is marked expansion of the buffy coat, and when differential leukocyte counts are severely elevated, as in this case. This report discusses differential diagnoses clinicians should consider, including infectious disease, and cancers of other white blood cell lineages. It also provides detailed description of the diagnostic findings to expect in these cases, including cytology, histopathology, flow cytometry, and basic complete blood count findings.

Technical Abstract: B-cell leukemia is a rare form of hematologic neoplasia in sheep, and its occurrence in adult individuals is even more uncommon. We present a case report of a 5-year-old White Face Sheep wether with suspected acute lymphoblastic leukemia. The patient, a second-generation relative of ewes experimentally inoculated with atypical scrapie, exhibited acute lethargy and loss of appetite. Laboratory investigations revealed marked leukocytosis, lymphocytosis, and abnormal serum chemistry panel results. Microscopic examination of blood and bone marrow smears exhibited a high percentage of large neoplastic cells with lymphoid characteristics. Histopathological analysis of the spleen, liver, and other organs confirmed the presence of neoplastic cells infiltrating the tissues. Immunohistochemical labeling demonstrated strong intracytoplasmic labeling for CD20, consistent with B-cell neoplasia. Flow cytometric analysis confirmed the B-cell lineage of the neoplastic cells. Despite screening for common infectious diseases, no definitive infectious etiology was identified. The diagnosis of B-cell leukemia was further supported by comprehensive diagnostic evaluations, including cytology, histopathology, immunohistochemistry, and immunophenotyping. This case report highlights the significance of accurate diagnosis and classification of hematologic neoplasms in sheep, emphasizing the need for immunophenotyping to aid in the diagnosis of B-cell leukemia. It also emphasizes the importance of considering spontaneous leukemia as a differential diagnosis in sheep with lymphoid neoplasia, even in the absence of common infectious diseases.