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Lymphoid Neoplasia in the Koala (Phascolarctos Cinereus) - A Review and Classification of 31 Cases

 

Alison J. Spencer, B.Sc, B.VetMed., Ph.D., and Paul J. Canfield, B.V.Sc, Ph.D.

 

From the Department of Veterinary Pathology, University of Sydney, Sydney, New South Wales 2006, Australia.

Present address (Spencer): 29 Barker Parade, Narooma, New South Wales 2546, Australia

 

ABSTRACT

Lymphoid neoplasia is the most common form of neoplasia in the koala (Phascolarctos cinereus), but limited clinical, hematologic, and biochemical data have been recorded for this condition. A clinicopathologic survey was performed on 31 koalas with lymphoid neoplasia. Tumors were classified on the basis of anatomic distribution at necropsy, with the majority (18) being multicentric. Organs commonly affected by the multicentric type included superficial lymph nodes (always involved), liver, spleen, and bone marrow. Alimentary lymphosarcoma (six), primary lymphoid leukemia (three), and miscellaneous forms (four) were also found. Lymphoid neoplasia was most common in middle-aged animals, with no sex predilection. At presentation, body condition ranged from very poor to good, suggesting variability in either intensity of disease or duration of illness. Animals were often listless and appeared to have muscular weakness. Lymphadenomegaly was not always determined clinically in cases of multicentric lymphosarcoma. Abdominal pain was present in three of the six animals with alimentary lymphosarcoma. Concurrent disease was detected in six of the 31 animals. Based on blood smears or bone marrow aspirates of 15 leukemic animals (and supported by histologic examination), seven koalas in three anatomic categories had neoplastic cells with small to medium noncleaved nuclei. Four koalas had neoplastic cells with large cleaved nuclei. Fourteen of 14 koalas analyzed with multicentric forms were leukemic, as were three of three with primary lymphoid leukemia, although none of the four with alimentary lymphosarcoma that were analyzed were leukemic. Anemia was present in 14 of 22 koalas analyzed and across all anatomic categories. In 18 animals analyzed biochemically, hypoalbuminemia was detected in 12, increased lactate dehydrogenase in eight, and azotemia in eight. There was no correlation with a particular anatomic group. Cytologic or histologic examination of bone marrow confirmed all cases of primary lymphoid leukemia and detected secondary leukemia associated with the other anatomic forms. The anatomic classification used for lymphoid neoplasia in domestic animals appears to have applicability to the koala. However, further delineation will require examination of additional animals and correlation with immunophenotyping.

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