Comparative pathology in bivalves: Aetiological agents and disease processes.

Comparative pathology as a scientific discipline studies animal diseases in relation to their aetiology, pathogenesis and prognosis. Among the main aspects of this discipline, regressive changes, host defense responses with pathological implications and progressive changes, represent the majority of the possible responses of cells and tissues to pathogens and exposure to chemicals. One of the most persistent issues in the field of invertebrate pathology is the variability in terminology and definition, which has led to confusion in scientific communication. The aim of this paper is to provide an overview of the pathological basis of bivalve disease (defensive, regressive and progressive phenomena) and contribute to the standardised terminology for bivalve molluscan disease in the context of comparative pathology.