Animal Waste, Water Quality and Human Health

372Animal Waste, Water Quality and Human Healthrelation to the establishment of disability estimates, and their relevance toundeveloped nations, was reviewed King & Bertino (2008).10.2.4 The sourcesThe sources considered here will be confined to four major groups of domesticanimals in the world: cattle, swine, sheep and poultry. The world-wide animalcensus developed by the Food and Agriculture Organization of the UnitedNations (http://faostat.fao.org) in 2009 lists cattle as the largest animalpopulation at 1.34 billion. Sheep are the next most numerous at 1.09 billion(note that sheep tend to shed similar amounts of annual faecal material per unitarea, compared with cattle—Wilcock 2006) and hogs follow at 0.92 billionpopulation. Poultry outnumber all of the above three large animal populationsby 5.3 to 1 with a world population of 17.86 billion. These high populationnumbers are mainly due to the great commercial value associated with thesedomestic birds and animals. They are the major groups related to foodproduction around the world. This particular group of domestic livestock is alsoof special significance because in many countries they are held in ConcentratedAnimal Feeding Operations (CAFO) where many thousands of animals areconfined in very small areas. Faecal wastes from CAFO’s are usually treated inseptic lagoon systems before discharge to receiving waters. The risks of illnessassociated with exposure to the discharged animal wastes is, however, largelyunknown (see: Chapter 11).The world population of other birds and animals, such as geese, ducks, horsesand goats, are very small relative to the above four species. Although urbanizedgeese and gulls are well recognized as major polluters of bathing beaches, theywill not be considered because of their relatively small populations. Wildanimals and wild birds are likewise not considered, even though their populationdensities in the world might be quite high and their faecal contribution torecreational waters is well recognized. Furthermore, good estimates of feral birdand animal populations in the world are not available and the linkage of humanenteric illness attributable to zoonotic pathogens from feral animals and birds isnot very strong.10.3 THE EXPOSURES AND RISK FACTORSWe consider risk of human infection from recreational water contact by ingestiononly, excluding any risk from inhalation. We do not consider the “knock-on”effects whereby food gets contaminated via water (e.g., irrigation, or processing