Factors Involved in the Dissemination of Disease in Fish Populations

Abstract

Infectious diseases have been observed in both human and animal populations for millenia. Unlike diseases of “higher” animals, the dispersal of disease in fish populations rarely has been studied quantitatively. However, the principles that govern the spread of diseases of humans and other mammals should, with modification, be applicable to the study of infectious diseases in fishes. Disease in populations is a dynamic phenomenon; fluctuations in prevalence and impact are dependent on the interactions among host, pathogen, and environment. Models of the dynamics of infectious diseases in salmon and other fishes can be constructed and refined to reflect the characteristics of diseases by integrating the most important factors in the process. Among the factors that have been shown to be important in other systems are the “contagiousness” of the pathogen (transmission coefficient, β), duration of infection, host population density, development of immunity, and efficacy of therapeutants.