Animal Waste, Water Quality and Human Health

Zoonotic waterborne pathogens in livestock 141emerge as a major service provider. In low-income countries, there is a mediannumber of just 139 private veterinarians per country, woefully inadequate giventhe number of farms and animals. In these circumstances conventional diseasemanagement through command and control mechanisms are unlikely to work,and new models must be developed based on stakeholder engagement andenlightened self-interest.4.7.2 Epidemiological studies to identify putative risk factorsA starting point for developing new intervention strategies is the identification ofhost, management and environmental factors associated with an elevated risk ofanimal infection, otherwise known as risk factors. Risk factors are correlationaland not necessarily causal, because correlation does not imply causation. Forexample, as mentioned previously, farms where livestock are infected with aspecific pathogen may have the same pathogen present in livestockdrinking-water. However, this does not imply that treating the drinking-waterwill reduce the prevalence in livestock: it could be that the water iscontaminated by livestock but that this is not important in maintaining the agent.Nonetheless, risk factor studies can be powerful tools for generating hypothesesthat can be tested more rigorously using follow-up study designs such asrandomized clinical trials. Examples of this epidemiological approach wouldinclude cross-sectional or longitudinal studies on management risk factors forinfection of Cryptosporidium spp. in beef calves in the USA (Atwill et al.1999), US and Mexican dairy calves (Maldonado et al. 1998, Garber et al.1994), and Swedish dairy cattle (Silverlås et al. 2009), G. duodenalis infectionin U.S. feedlot steers (Hoar et al. 2009), E. coli O157:H7 infection in Canadiancattle (Callaway et al. 2003, Dargatz et al. 1997, LeJeune & Wetzel 2007),Salmonella infection in European swine (Fosse et al. 2009), and Campylobactercolonization in broilers in the United Kingdom (Ellis-Iversen et al. 2009).Common recommendations from many of these studies are improvedbiosecurity of housing facilities, clean water supplies, improved manuremanagement practices, physical separation of non-infected and infected groups,and calving pen hygiene, along with segregation of different age classes ofanimals (e.g. pre-weaned from post-weaned).4.7.3 Emerging trends in the control of zoonotic pathogens atthe farm levelAll diseases are dynamic and waterborne zoonoses are no exception. The lastcentury has seen unprecedented change in livestock farming systems: never