Animal Waste, Water Quality and Human Health

Zoonotic waterborne pathogens in livestock 125humidity (Doyle & Erikson 2006). Studies on E. coli O157:H7 have shown that itpersists longer in sawdust used for cattle bedding than in sand (LeJeune &Kauffman 2005).4.3.6 Reducing exposure from feedGiven that most enteric pathogens are transmitted by the faecal-oral route, cleanfeed is essential in their control. It has been shown that many of the Salmonellaserovars shed by poultry probably originated from meat and fish products inpoultry feeds, introduced to increase protein content (Crump et al. 2002). From5 to 20% of livestock feeds have also been reported to have Salmonellacontamination (McMullan 2000), although the upper estimates may beexceptional, heating during processing of poultry and swine “complete” feeds isefficacious in the killing of most microbial pathogens (Cox et al. 1986, Danielset al. 2003). Gamma-irradiation also appears to be effective in reducingpathogen loads in animal feeds (Leeson & Marcotte, 1993). A maximum dose of15 to 35 kGy is sufficient to produce Salmonella-free feed under commercialconditions. As well as processing to reduce pathogens, feeds must be stored in amanner that will prevent recontamination. Contamination of commercial feed isprobably a greater problem in developing countries where quality assurance offeed is often lacking, and animals are usually fed directly from the ground.Moreover, cultural practices, such as the feeding of household waste to animalswill increase the likelihood of zoonotic pathogen presence in feed. In somepig-keeping communities, farmers defecate directly into pig-pens as a way ofproviding additional feed: this practice facilitates the transmission of “reversezoonoses”, that is, diseases readily transmissible from man to animals. For somediseases, such as cysticercosis, the animals in turn can be an important source ofinfection for humans.4.3.7 Reducing exposure from waterLeJeune & Wetzel (2007) noted that there is a strong association between thepresence of pathogens such as E. coli O157:H7 in drinking-water and thepresence of pathogens in cattle faeces. Water for poultry also frequently containsSalmonella. However, it is not always clear if the water contamination is thecause or simply the consequence of gastrointestinal colonization of the animalsby these enteric pathogens. Bacteria in drinking-water systems are thought toescape antibacterial agents present in the water by adhering to the surfaces oftanks and tubes and forming resistant structures termed “biofilms”(Tuschewitzki et al. 1983, Zimmer & Slawson 2002, Kalmokoff et al. 2006);therefore, thorough cleaning and sanitation of animal water troughs is