Infectious diseases, and often opportunistic pathogens, are common causes of morbidity and mortality in cetaceans. Burkholderia pseudomallei, the causative agent of melioidosis to which cetaceans at Ocean Park are highly susceptible, is one example that in humans is associated with immunodeficiency. There is limited knowledge of the immune system of cetaceans, although based on available evidence it shares similarities to those of well studied/key terrestrial species such as humans and rodents. Using techniques and reagents developed by the University of California, Davis, the immunologic health of dolphins was regularly assessed by quantifying and identifying peripheral blood leukocytes, leukocytic adhesion proteins and mediators of inflammation, and by assessing lymphocytic function. This provided baseline values for a group of captive dolphins at one institution. The objectives of the study are to improve our understanding of the cetacean immune system and determine the clinical relevance of these techniques as early indicators of disease or to detect changes that indicate greater susceptibility to disease. Potential correlations of clinical findings, general health status, differing ages, influences of potential environmental stressors and differences or aberrations in immunologic baseline values, are being examined. The potential effects and detection of the effects of an immunostimulant, beta-glucan, on the dolphins' immunological profile is also being investigated.
From April 2003 to December 2004, blood samples from 15 bottlenose dolphins (Tursiops aduncus) at Ocean Park were collected every two months during routine health checks for hematology and clinical chemistries. The six male and nine female dolphins ranged from 2-about 30 years of age. Blood was collected into acid citrate dextrose anticoagulant for immunophenotyping--determining lymphocytic sub-populations and cell surface densities of adhesive proteins. A panel of 10-12 monoclonal antibodies, specific for Tursiops-specific leukocyte differentiation antigens, was used to analyze peripheral blood leukocyte subpopulations by analytical flow cytometry. Blood also was collected into CPT (Cell preparation tube with sodium citrate, BD Vacutainer® CPTTM) and the mononuclear cells separated and cryopreserved for blastogenetic studies using an ELISA. Beta-glucan was supplemented, in a blind trial, to the diets of half the dolphins in this study. While all data analysis for this project is not yet complete, the immunologic approach described here is sure to complement future studies directed at assessing marine mammal health.
The authors are grateful to Nathalie Mauroo, Gary Wong, Harriet Chiu and the rest of the Marine Mammal Department for assistance in obtaining blood samples and the staff of the clinical laboratory at Ocean Park for processing the samples. Also to Sarah Chan who assisted with the laboratory work for the immunophenotyping at the University of Hong Kong.
This study was funded by the Ocean Park Conservation Foundation.