Environmental aspects and diseases related to immunosuppression in cetaceans: a concise review

Abstract

The analysis of the health status of sentinel animals is a key element for the evaluation of ecosystem health conditions, since these animals respond to small and large scale changes in ecological factors and the quality of the environment. In the marine environment, the changes are systemic and accumulate impacts of coastal zones and oceanic activities, with aquatic mammals being species that reflect changes in biological and health parameters. For these animals several studies have reported an increase in the frequency and diversity of diseases, including infections by pathogens from the terrestrial environment. This increase may be related to impairment of the immune system activity of these organisms in response to potential synergistic factors. In cetaceans, immunosuppression may be caused by infection with viral agents, such as Morbillivirus, which induce severe lymphoid depletion and is responsible for several cases of mass mortality; chemical contamination, highlighting the organochlorines and trace elements (mainly mercury and cadmium); and even by chronic stress. Anthropic impacts are important stressors, and the consequences are more evident in animals of coastal habits, which leads to a constant release of glucocorticoid hormones and consequent lymphoid depletion, a mechanism similar to that occurring in terrestrial mammals. Immunosuppressed animals are susceptible to opportunistic diseases, some more severe and rare, with the risk of decline of populations. The objective of this review was to provide information on the aspects related to immunosuppression in cetaceans, associating etiological factors and pathological findings, and to highlight the relevance of the evaluation of the endocrine and immune system of marine animals as a reflection of the health status of marine ecosystems.