Animal Waste, Water Quality and Human Health

284Animal Waste, Water Quality and Human Healthpoultry, cattle, hogs and birds, but the nature and magnitude of these risks islargely unknown (Steven Esrey, UNICEF, pers. comm.). Therefore, the utility oftraditional faecal indicators may be rightly questioned when assessing waterquality throughout much of the world (Scott et al. 2002). The diversity ofpotential inputs necessitates a multi-tiered approach to identify the pollutantsources and to establish a framework for the assessment of the risks that thesesource may pose in exposed populations (Molina 2007).Multi-tiered approaches such as those combining sanitary surveys with expandedmonitoring programmes, including assessments of traditional faecal indicatororganisms and tracking of microbial sources (source attribution), may provide thisconceptual framework for risk assessment (Ruecker et al. 2007). Identification ofpollution sources and quantifying the plausibility of illness from each source arenecessary steps in the development of effective exposure or managementinterventions. Trends in animal husbandry and agricultural practices haveincreased the potential for large scale contamination events and the socio-politicalcontext in which these serious incidents occur is often outside the realm of formalpublic health and epidemiological investigations (Ali 2004, Hubbard et al. 2004).Large scale contamination events may also be exacerbated by climate changeeffects such as projected increases in average precipitation (WHO 2009). Theimpacts of climate change on the epidemiology of waterborne diseases arethrough increased flooding, heavy rainfall and increased temperatures which canexpand the range and geographic distribution of known pathogens (WHO 2003).Scientific studies have linked substantial increases in microbial loads inwatercourses and drinking-water reservoirs as a result of extreme rainfall and theresulting runoff (Kistemann et al. 2002). This was the case in 2000 whenCanada had one of the largest outbreaks of waterborne disease in NorthAmerica. Over 2300 people became ill and seven died in Walkerton, Ontario asa result of consuming contaminated drinking-water following heavy rains (Auldet al. 2004). In a 2005 study Schuster and colleagues analyzed information onCanadian waterborne outbreaks occurring between 1974 and 2001 (Schusteret al. 2005). They found that severe weather events and close proximity toanimal populations were correlated with disease outbreaks that could be trackeddown to drinking-water supplies. The geographic distribution of climate changewill show significant variation and human exposure will be “location-specificand path-dependent” (Yohe & Tol 2002, Hess et al. 2008). Therefore, inaddressing potential environmental or behavioural human exposureinterventions, the historic relationships with land use and (agri-)culturaltraditions must be considered (Hess et al. 2008).The advent of climate change is not the only development that may increase thelikelihood of direct and indirect waterborne disease transmission originating from