Abstract
Immunopathology is broadly defined as the study of immune responses associated with disease, including the study of the pathology of an organism, organ system or disease with respect to the immune system. As other chapters in this book discuss topics such as the immune responses of fish to infectious agents and the effects of stressors on the immune response, this chapter addresses a subcategory of immunopathology. Immunopathology is defined here as the study of pathological changes in organs of the immune system resulting from a variety of aetiologies, including infectious agents (viruses, bacteria, fungi and parasites) and non-infectious conditions (nutrition-related, toxicant-related and neoplasia). Whereas numerous studies on fish have focused on the host response to various stressors, relatively few have investigated immunopathology. This review utilises examples of infectious and non-infectious diseases in teleost fishes to summarise our knowledge of teleost immunopathology. For some diseases, the presence of an infectious agent or toxin may directly or indirectly cause destruction of immune organs. In other diseases, an intense inflammatory response, or conversely, suppression of the immune response, may contribute to disease progression in these organs. Other factors such as the virulence of a pathogen biotype, degree of toxicity or carcinogenicity of an exogenous element or compound, the species and age of exposed fish and environmental conditions such as water temperature and water quality can also contribute to determining the outcome of a disease. Additional research is needed to investigate the mechanisms responsible for immunopathology observed in many diseases.