Maintaining homeostasis in a stressed or diseased condition includes cellular and humoral immune responses. These responses and their diagnostic and prognostic capabilities are not as well defined in the bottlenose dolphin as in other animals.

Stress in terrestrial mammals is monitored by measuring elevations in serum concentration of adrenal corticosteroids. Significant changes in prostaglandin levels have been recorded during simulated transports designed to examine the dolphins stress response, (Schroeder et al. 1985). It has been suggested that eosinophil counting is useful and practical tool to assess the extent and duration of stress tress in dolphins, (Thompson and Geraci, 1986).

Common diseases of small cetaceans have been described by Sweeney and Ridgway (1,975), and Dailey (1985). At least five serotypes of marine mammal Calicivirus have been described, (Smith et al. 1981). There has been interspecies transmission of Calicivirus induced vesicular disease in the dolphin, (Smith et al. 1983). Opportunistic pathogens can produce serious debilitating disease in the immuno­compromised host, (Thurman and Windsory, 1984). Therapy with gamma globulin may be possible but it requires that an appropriate level of antibody to selected pathogen(s) be determined, (Vedros et al. 1984).

The effect of stress on the immune response may be positive and enhance an animal's ability to avoid infection, or, if the stress is prolonged, the animal's immune system or other homeostatic mechanisms may become depleted. Marine mammals' ability to develop and maintain immunity should be defined. Application of new technology in stress assessment, epidemiology and immunology should be adapted to marine mammal medicine.

Therefore, discussion of the interrelationship of stress, infectious disease and immunology is important to those interested in aquatic animal medicine and science. The two main goals to keep in mind during this discussion: 1) emphasizing the importance of relating new knowledge about stress to its effect on the immune system, relating that to medical management decision making processes as we deal with dolphins in the wild, during capture and transport and while they are in captivity; 2) proving that captivity is synonymous with well-being; well-being defined as, "free from stress," for marine mammals particularly, and small cetaceans specifically.

How can stress be defined? That can be done only by defining stressors and an organism's response to them. To objectively define well being requires physiological facts. Responding to a stressor is a continuum from the beneficial to distress, to pathology. Any stimulus that challenges homeostasis can be viewed as a stressor and changes in biological function to maintain homeostasis constitutes the animal's stress response. Perception of an external threat, whether a change in temperature, a social change, social interaction with a peer, or the experience of pain is dependent upon the central nervous system's perception of that external stimuli, (Moberg, 1985).

There are many types of external stimuli that our animals are subject to. The central nervous system assesses whether the stressor or stimulus or a group of stimuli represents a significant challenge to the animal. If the stimulus is perceived as threatening, then the stimulus is a stressor. Three general types of biological responses are available to the animal; behavioral, autonomic and neuroendocrine. Behavior can remove the animal from the threat, if possible. In the wild that is sometimes possible, but in captivity it's usually not. If the animal cannot remove itself, the autonomic and neuroendocrine systems controlled by the hypothalamus redirect the body's biological machinery to enable the animal to cope with the stressor and to maintain homeostasis.

The neuroendocrine system modulates the function of almost all physiological systems and can influence directly or indirectly immune responses and shifts in metabolism. There are volumes of human literature relating stress and immune functions. Bereavement, Depression, Stress and Immunity by Stein (1985) provides a review of the subject. Stress responses of laboratory animals and some domestic animals are discussed in Stress and Immune Function, a bibliographic review by Kelly (1980) in the Annals of Veterinary Research. New findings have been reported in Diseases of Aquatic Organisms; by Olson (1986), Quantification and Serum Immunoglobins in Rainbow Trout Under Various Environmental Conditions and by Sayeed (1987) Immune Response of Channel Catfish to Lipopolysaccharides and whole cell; Edwardisella ictaluri Vaccines. The interrelationship of stress and immune function is basic to the response of aquatic animals to infectious diseases.

In summary, we must be able to understand the interrelationship of stress, immunology and infectious diseases to use medications based on objective measures of stress, status of the immune system and presence or absence of microorganisms. Some steroids should be used only when indicated rather than prophylactically risking increased serum iron concentration thereby increasing the susceptibility of an animal to bacterial infection, (Smith, et al., 1986). Antibiotics should be used when antibiotic sensitivity has been determined to avoid risking development of microbial resistance. A stimulator of the immune system to improve lymphopenic or hypoproteinemic animals should be developed. Standardization and application of available immunodiagnostic tools to marine mammal medicine will allow diagnosis of autoimmune diseases, immunodeficiency syndromes and the presence of medical risk due to stress.

Using the above capabilities, it will be possible to objectively determine the presence of stress related medical and/or behavioral problems in marine mammals. Being able to define absence of stress, i.e., the presence of well-being, will further validate holding of dolphins and other small cetacean in captivity.

References

1.  Dailey, M. D., 1985, Diseases of Mammalia: Cetacea, in: "Diseases of Marine Animals,"0. Kinne, ed., Vol. IV, Part 2: 805-547.

2.  Kelley, K. W., 1980, Stress and Immune Function: A Bibliographic Review, Ann. Rech. Vet. 11 (4): 445-478.

3.  Moberg, G. P., 1985, Biological Response to Stress: Key to assessment of animal well-being, In: "Animal Stress," G. P. Moberg, ed., 20-49.

4.  Saeed, M. 0. and J, A, Plumb, 1986, Immune response of channel catfish to lipopolysaccharide and whole cell Edwardsiella ictaluri vaccines, Dis. aquat. Org., 2:21-25.

5.  Schroeder, J. P., H. R. Parker, S. Giri and M. B. Cates, 1985, Effects of simulated transports or. prostaglandin levels in Tursiops truncatus, in: Proceedings International Association for Aquatic Animal Medicine, 1(2): 64--72.

6.  Smith, A. W., D. E. Skilling, and A. B. Latham, 1981, Isolation and identification of five new serotypes of calicivirus from marine mammals, JAVMA, 693-694.

7.  Smith, A. W., D. E. Skilling and S. Ridgway, 1983, Calicivirus-induced vesicular disease in cetaceans and probable interspecies transmission, JAVMA, 183(11): 1223-1225.

8.  Smith, J. E., R. M. DeBowes and J. E. Cipriano, 1986, Exogenous corticosteroids increase serum iron concentrations in mature horses and ponies, JAVMA, 188(11): 1296-1298.

9.  Stein, Marvin, 1925, Bereavement, Depression, Stress, and Immunity, in: "Neural Modulation of Immunity," R. Guillemin et al., ed., Raven Press, New York, 29-44.

10. Sweeney, J. C. and S. H. Ridgway, 1975, Common Diseases of Small Cetaceans, JAVMA, 167(7): 533-540.

11. Thomson, C. A. and J. R. Geraci, 1986, Cortisol, aldosterone, and leucocytes in the stresss response of bottlenose dolphins, Tursiops truncatus, Can. J. Fish. Aquat. Sci. 43: 1010-1016.

12. Thurman, G. D, and 1. M. Windsor, 1984, Serological testing for viral and mycoplasma antibodies in a captive dolphin as an aid in diagnosis and epidemiological control, 15th Annual Conference and Workshop, IAAAM Proceedings, Vol. 1, No. 1, 75-79.

13. Vedros, N. A., K. MacDonald and D. Vandenbrock, 1984, The potential use of gammaglobulin therapy in marine mammals: A preliminary report, 15th Annual Conference and Workshop, IAAAM Proceedings, Vol.1, No.1, 63-65.