Department of Pathology, The University of Texas Medical Branch, Department of Marine Biology, Texas A&M University at Galveston, and the Texas Marine Mammal Stranding Network
Galveston, TX, USA
Two dolphins among 96 stranding along the Texas coast of the Gulf of Mexico examined by necropsy during the years 1991-2002 were found to have lymphoproliferative disorders. One was diagnosable as granulocytic leukemia, the other as a lymphoproliferative disorder, probably a lymphocytic lymphoma.
A 206-cm female bottlenose dolphin stranded alive on Galveston Island, Texas, on April 16, 1991. She was active but clumsy, and struggled intermittently until her spontaneous death two hours and 45minutes after recovery. Necropsy revealed marked diffuse lymphadenopathy, especially of the nodes in the pelvic recess and in the neck. The spleen was enlarged for the animal's size. Microscopy revealed infiltration of lymph nodes, bone marrow and liver by abnormal cells with granulocytic features and many mitoses. Diagnosis was lymphoproliferative disorder, favoring granulocytic leukemia.
A 250-cm-long, 268-kg female bottlenose dolphin stranded one mile north of Brazos Santiago Pass, Cameron County, Texas, on August 1, 1996. Because of bone-deep shark bites, she was euthanized. Necropsy revealed infection with Aspergillus of the trachea and bronchi, enlarged lymph nodes, and infiltration of the lymph nodes, liver and meninges with atypical leukocytes. Diagnosis was lymphoproliferative disorder, favoring leukemia/lymphoma. Bone marrow was not available for study. Morbillivirus was ruled out.
Leukemia and lymphoma are both malignant proliferations of white blood cells. Leukemias arise in the bone marrow, and may involve any of the blood cell lines, while lymphomas arise in the lymph nodes, and derive from lymphocytes. Either may infiltrate other tissues. Differential diagnosis should include reactive adenopathy and leukemoid reaction. So few cases of leukemia/lymphoma are reported in dolphins that revealing, consistent patterns of disease have not been established. Two cases out of 96 animals (two percent) seems to be a high incidence, warranting further investigation.
This work would not have been possible without the enthusiastic participation of the volunteers of the Texas Marine Mammal Stranding Network. This work was supported by grants from the National Oceanic and Atmospheric Administration through the National Sea Grant College Program, (NA16RGO457-01) and the Environmental Protection Agency Gulf of Mexico Program (MX822147-01-0). The views expressed herein are those of the author and do not necessarily reflect the views of NOAA, the EPA, or any of their sub-agencies.