Animal Waste, Water Quality and Human Health

98Animal Waste, Water Quality and Human Healthin susceptibility among individual animals to colonization and infection bywaterborne pathogens. It may be possible to use information concerningdifferential susceptibility to disease and/or colonization to target diseaseprevention programmes in humans and pathogen control programmes in animals.Differences in the level and frequency of shedding and persistence of pathogencolonization among individuals in herds or groups of a specific age-class have alsobeen reported. It has been stated that 20% of animals are responsible for 80% of thepathogen excretion in groups of animals. These animals have been referred to assuper-shedders (although definitions vary). Targeted treatment or exclusion ofthese super-shedders in animal groups could substantially reduce risksassociated with these waterborne zoonotic pathogens.3.5 CONCLUSIONSAnimal husbandry plays a key role in the global economy. With the growth of theworld population and the emergence of the economies of several large developingcountries, an increase in the demand for animal protein is projected to continue.Livestock production systems use large quantities of limited resources such asfresh water and can cause environmental damage and loss of productivity ofagricultural land if not properly managed. Animal husbandry generatessignificant amounts of wastes which can result in excessive nutrients andchemical pollution of waterways if improperly managed. In addition, thesewastes are a source of zoonotic pathogens responsible for significant morbidityand mortality in human populations around the world.Microbial pathogens associated with waterborne disease in humans arecommonly excreted in the faeces or passed in the urine of most domestic andwild animal species. Most animal pathogens such as viruses and certainprotozoa are host-restricted and are not associated with human disease (Carteret al. 2005, Fong et al. 2005). Among those microbial pathogens that have abroad host range that includes humans as a secondary or accidental host, only asmall number have strong scientific evidence supporting their role as importantwater-borne zoonoses.The pathogens reviewed in this chapter, Cryptosporidium parvum, Giardiaduodenalis, E. coli O157:H7, Salmonella, and Campylobacter, have beenreported in livestock populations worldwide and domestic livestock are believedto be important, and in some cases, the most important source of humaninfection. As such, understanding faecal shedding dynamics and the associatedhost, environmental, and agent factors driving these infection patterns is key toassessing risk to human health and developing control strategies.