Animal Waste, Water Quality and Human Health

74Animal Waste, Water Quality and Human Healthcapability to be transmitted to humans through water, and prevalence in a biologicalreservoir host including one or more livestock species. A biological reservoir isdefined as a host (in the context of this book: a livestock species) that allows thepathogen to amplify or reproduce and not merely pass through.Information on the prevalence, intensity and environmental load of these fivepathogens is presented along with methodological concerns on how we drawinferences from these measures of occurrence and the human health risk theyrepresent. Important aspects of the ecology and epidemiology of these fivepathogens in livestock populations are also discussed in as much as they may beuseful in the development of intervention strategies to limit their prevalence inlivestock and to reduce the risks of waterborne transmission to humans.3.1.2 Livestock status and trends in developed anddeveloping countriesAt the beginning of the 21st century, the volume and pace of expansion of theglobal livestock population is unprecedented. As a consequence, environmentalloads with livestock faeces are also unprecedented and this faecal materialpotentially contains the agents of waterborne zoonoses. The problem oflivestock-associated zoonoses starts with livestock populations, and we willbriefly review the current status of, and major trends in, these populations. In2007, the world population of domestic animals was estimated at 24 billion,out-numbering humans by nearly four to one (Table 3.1). The dramatic growthin animal husbandry is driven by the growth in the world population and therise in incomes in many emerging countries especially in Asia and SouthAmerica: the so-called “Livestock Revolution” (Delgado et al. 1999). Livestockproduction systems, both intensive and extensive, are present on a largepercentage of earth’s surface area; 26% of the earth’s terrestrial surface ispasture and 33% of global arable land is used to grow animal feed (FAO1996). Although livestock trade is growing, more than 90% of livestockproducts are consumed in the countries where they are produced so theproblem of livestock faecal load is essentially domestic. The lack of watertreatment facilities and widespread use of untreated wastewater in poorcountries suggest waterborne zoonoses may be a greater problem there thanthey are in high-income countries.The livestock sector is dichotomized into high-intensity production systems indeveloped countries and parts of Asia, and low-intensity production in the humidand sub-humid tropics (FAO 1996). An estimated 70% of poultry and 58% of pigsare raised in high-intensity systems (Robinson et al. 2011) but only a minority ofruminants. In contrast, the production of low-intensity systems is relatively small,