Biosecurity - Pandemics and the aquatic environment

Biosecurity, the protection of particular animals from particular areas from specific pathogens by exclusion and containment, is of great importance in relation to national and international transfer of stocks. The history of transfaunation of aquatic animals and their associated microorganisms is littered with disastrous outcomes. Occasionally, the effects are limited and localized, but from Aeromonas salmonicida in Europe in the 19th century to Aphanomyces invadans in Asia and North America in the 21st, the aquatic medium populated by wild susceptible hosts has proved itself to be a ready environment for the propagation of introduced pathogens. In order for any rational control or containment regime for infectious disease in any environment to prove effective, a number of specific conditions need to be met. In the aquatic environment, and particularly in open aquaculture operations, these are generally impossible to achieve. National control programmes may aim at preventing the introduction of specific pathogens or reducing the incidence of clinical disease. It is essential, however, if these are to have any success, that objectives are realistic, and that once a control system is seen to have been breached, they do not confuse the control of clinical outbreaks, which may be possible, with eradication of the agent once it is established. The latter may be claimed as an objective, but will be impossible if the agent and a susceptible wild host are both present in or have been released into the aquatic ecosystem within which the control measures are to be implemented.