Coral Health and Disease in the Pacific: Vision for Action

A small proportion of diseases are caused by a single agent that is both necessaryand sufficient in itself to cause a clearly defined disease. A set of rules (Koch’sPostulates) often can be used to establish a cause–effect relationship in this type ofdisease. However, the great majority of diseases, in all species, are of more complexcausation. Agents may cause disease under certain conditions but not under others,multiple agents may be required to produce disease, or several agents may independentlycause similar disease. In many diseases there is a complex web of causation that mayinvolve many inter-related factors. Disease must be considered in the context in which itoccurs. Koch’s Postulates are generally inadequate for establishing cause-effectrelationships, and other criteria that include epidemiological information are moreappropriate.Investigation of disease involves answering five basic questions: Who? Where?When? What? and Why? It is impossible to predict in advance which disciplines ordiagnostic techniques will be required to solve a problem and no one discipline isomnipotent. However, field and laboratory studies must be related back to the casedefinition (i.e., Are we looking at the same disease?) and the results should be used torefine the definition of the touchstone.243