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The nature of disease in the aquatic environment

What is a disease? Most diseases described in this guide are caused by infectious agents — viruses, bacteria, fungi or parasites. Another common cause of deaths in the aquatic environment is the environment itself: deaths can result from oxygen depletion, aquatic toxins, or changes in water temperature or salinity. However, diseases due to noninfectious causes are not covered in this guide.

Figure 1. Relationship between host, pathogen and the environment in disease outbreaks

A disease outbreak will not occur simply because an infectious agent is present. Rather, the cause of a disease is determined by the interaction of the host (the aquatic animal), the infectious agent and the environment.

Diseases of regional and national concern

Exotic diseases

Diseases in this field guide described as exotic to the Asia–Pacific region are those that have never been reported in any NACA member country in the region.

Endemic diseases

Endemic (enzootic) diseases are those that have established in the regional environment. They might be native to the region or have been introduced in the past.

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