Abstract

This study was initiated to characterize the impact of transport on dolphin health using a longitudinal assessment of the immune system. Eight dolphins (Tursiops truncatus) of varying age were included in the study. One blood sample was collected prior to transport, followed by a series of samples over a six-month post-transport period. Three dolphins from Facility A and five from Facility B were transported to Facility C on three separate occasions. All animals were sampled within 2 weeks prior to transport and seven of eight were again sampled within 1 week of arrival at Facility C. Animals were temporally sampled through six months post-transport. Leukocyte subpopulation phenotyping analysis identified B lymphocytes (CD21⁺ and CD19⁺) and naïve and memory T lymphocytes (CD2⁺ and CD45R^hi or CD45R^lo, respectively). Preliminary data analysis was with paired two-tailed Student's t-tests in comparison with the pre-transport samples.

All dolphins tested within 1 week post-transport (n = 7) presented with a relative reduction (compared to pre-transport) in circulating lymphocyte numbers including B lymphocytes (CD21⁺), total T lymphocytes and naïve and memory T lymphocytes (p = 0.033, 0.083, 0.115 and 0.082, respectively). The reduction in absolute numbers of all four lymphocyte subpopulations became significant (all with p < 0.05) at 1-to-2 months post-transport (n = 8). Memory T lymphocytes were no longer significantly reduced at the 2-to-3 month post-transport period (p = 0.080) and only B cell numbers remained significantly reduced at 4 (n = 5) and 5.5 month (n = 7) time points.

Cell-surface density of the B lymphocyte co-receptor (CD19) was closely monitored. Increased CD19 density is associated with B cell activation (abnormally high = hyper-responsive B cells) while decreased expression associates with an increase in the threshold for B cell activation (hypo-responsive B cells = suppressed phenotype). All animals expressed apparently normal densities of CD19 on the surface of B lymphocytes pre-transport. CD19 density increased immediately post-transport in six of the seven animals tested. A single outlier (one of seven animals) presented with abnormally low levels of CD19 on B lymphocytes immediately post-transport, remaining low throughout the remainder of the study period. This same animal developed a spike in neutrophils (8340 cells/µl) two months post-transport and was treated for an infection.

In summary, a relative lymphopenia was recorded in all dolphins following transport. We would hypothesize this reduction was due to alterations in traffic patterns (increased margination and migration) induced by exposure to a new set of microbes; this would be considered a normal, healthy response. The slow return towards pre-transport lymphocyte subpopulation levels (still reduced six months post-transport), due to ongoing exposure to a new microbial environment, would support the hypothesis. The unique association between transport, abnormally reduced levels of the B cell co-receptor (CD19) and subsequent development of a neutrophilia in a single dolphin warrants further investigation into the utility of CD19 cell-surface density serving as an indicator of stressor event(s) and increased susceptibility to microbial infection.

Acknowledgements

We very much appreciate the contributions provided by the Veterinary Staff at the Georgia Aquarium. This project was generously supported by a grant from Dolphin Quest, Middleburg, Virginia, USA.