The emergence and spread of new or previously unknown infectious diseases is an increasing global phenomenon that has had very significant impacts on public health, food security and international trade. The number of emerging infectious diseases (EIDs) affecting humans has risen more than 3-fold since the 1940s and many are expanding in global distribution. Well known human diseases that have emerged or re-emerged in recent times include SARS, MERS, Ebola, Hendra/Nipah and H5N1 avian influenza. However, disease emergence is also a growing problem for livestock and agricultural farming systems and, of course, for aquaculture.

Disease emergence is the consequence of environmental and/or sociological changes that disrupt the ecological relationship between pathogens and their natural hosts. Emerging pathogens fall primarily into three categories: i) those that do not naturally cause disease but become highly pathogenic when their host is immune-compromised or stressed; ii) those that have jumped to a new host in which they are pathogenic; and iii) those that are naturally pathogenic in their host and increasing in geographic distribution.

Aquaculture is an important seafood industry that has provided employment and been a major driver of socio-economic development in poor rural and coastal communities and has relieved pressure on the sustainability of the natural harvest from our rivers, lakes and oceans. However, the rapid growth of aquaculture has been the source of anthropogenic change on a massive scale. Aquatic animals have been displaced from their natural environment, cultured in high density, exposed to environmental stress, provided artificial or unnatural feeds, and a prolific global trade has developed both live aquatic animals and their products. Not surprisingly, the consequence has been the emergence and spread of an increasing array of new diseases.

Understanding the underlying drivers of disease emergence will help us develop policies and practices that will reduce opportunities for disease emergence and improve prospects of containment when new diseases do emerge.