ABSTRACT
Soil is probably the most complex microbial ecosystem, and may have the highest abundance and diversity of microorganisms of any ecosystem as a result of its macrobiological, chemical, and physical heterogeneity. The numbers, diversity, and roles of soil microorganisms are not completely understood. Although some soil microorganisms are absolutely essential for biogeochemical cycles, others may have an impact in other areas, such as public health. The latter role has not been studied in detail, although it has been shown that soil may serve as a vector and/or reservoir of some human enteric pathogens.Soil is a solid phase and thus is not very amenable to mixing [1]. Consequently, microorganisms associated with soil are relatively immobile. This, in turn, has resulted in assigning soil a small role in the dissemination of human enteric diseases. Microorganisms in soil are, as indicated by Knudsen [2], unseen and underappreciated (or underestimated) by most public health workers. Many studies on soil microorganisms have focused on their importance as plant pathogens and in biogeochemical cycles, and there is an ample body of literature on these subjects. However, little is known about the role of soil as a vector of enteric disease and not simply a reservoir of opportunistic pathogens.Soil is important in the dissemination of some intestinal worm infections, according to the World Health Report [3]. The same report indicates that Clostridium tetani is the deadliest pathogen in soil, killing 450,000 newborns and about 50,000 mothers each year [3]. Although it is known that soil is important in 461
the transmission of some diseases, the total number of human pathogens and opportunistic pathogens associated with soil is enormous and beyond the scope of this chapter. For this reason the focus will be on some possible soil-borne human enteric pathogens.In epidemiology it is assumed that disease is the outcome of interactions between the pathogen, the host, and the environment [4], and public health may be placed at risk not only as a direct result of the presence of pathogenic microorganisms in soil, but also as the indirect result of anthropogenic disturbances, including the still controversial global warming phenomenon. Although the true impact of global warming is not known, it may have serious deleterious effects on public health as a result of changes in temperature and weather patterns.The purpose of this chapter is to provide an overview of the impact that indigenous and transient soil microbial communities may have on human enteric disease.
