forces begin to act on these introduced or exotic microorganisms, whether eukaryotes or prokaryotes.
This chapter describes basic principles of ecology and evolution for waterborne viruses, bacteria, and protozoa (and yeasts and molds to a lesser extent) of public health concern as an aid to better understand how selective forces may alter one’s ability to assess the microbial quality of water. Indeed, indicators of microbial water quality can be the pathogenic organisms themselves, other microorganisms, or other physical or chemical aspects of the aquatic environment (see Chapter 4 for further information), and any biological indicator is subject to evolutionary and ecological changes. The final section is a summary of the chapter and its conclusions and recommendations.
Answers to several sets of related and fundamental questions (summarized in Box 3-1) are imperative to facilitate the understanding of indicators of waterborne pathogens and emerging infectious diseases. These questions include but are not limited to the following:
What is the natural distribution and abundance of waterborne pathogens? Are there environmental reservoirs of these microorganisms and, if so, what environmental conditions promote their maintenance or growth? Are these environmental reservoirs biotic or abiotic (i.e., from the living or nonliving)? Can waterborne pathogens colonize and proliferate in sediments or within aquatic systems? The concepts of growth and regrowth are most often applied to water distribution systems and wastewater discharges (and their receiving waters), respectively.