Modified from Wilson, 2001; p. 286

The classic disease triad of agent, host and environment is usually portrayed simplistically as a static triangle. However, this can be more appropriately conceived as a process of dynamic interactions (Wilson, 2001). The interactions may produce indirect and non-linear effects with time lags and various feedbacks. Figure 2 below shows the interactions of each component with their many variables and effect.

The word environment refers to whatever surrounds an object or some other entity. Humans experience the environment in which they live as an assemblage of physical, chemical, biological, social, cultural and economic conditions which differ according to local geography, infrastructure, season, time of day and activity undertaken (WHO, 1997).

The complex relation between health and the environment must be looked at from different perspectives to better understand how best to intervene and improve human health. Thus, information on health impacts attributable to environmental conditions at local and national level is needed so that the implications of environmental health decisions can be assessed. However, information is only a tool, which needs to be applied constructively for appropriate action.