Animal Waste, Water Quality and Human Health

Zoonotic waterborne pathogens in livestock 131implementation of HACCP systems, carcass pasteurization procedures, trimming andchemical treatments of carcasses, cold chain maintenance, irradiation of ground beef,implementation of the five log reduction rule for cooking, and other bactericidal foodprocesses and consumer education.In addition, studies on “pre harvest” or on-farm control of E. coli O157:H7 werealso initiated. Studies on the epidemiology and ecology of this organism in cattlerevealed it to be very widespread in the cattle population (Karmali et al. 2009).E. coli O157:H7 could be isolated on most farms from calves shortly after birth andagain at weaning and throughout the growing and finishing period. In North America,peak faecal shedding of this pathogen occurs during the summer months. Withingroups of cattle the distribution of colonization, and of the duration and number oforganisms shed by cattle is not normal; instead, specific individuals in a group knownas “super-shedders” are responsible for most of the faecal output of this pathogen(Chase-Topping et al. 2008) and represent the largest source for contamination of theenvironment and of carcasses at slaughter.E. coli O157:H7 possesses a genomic island termed the locus of enterocyteeffacement (LEE) which encodes a type three secretion system (TIIISS) (Dean &Kenny 2009). The system consists of a syringe-like structure which injects a series ofproteins directly into the host cell and allows the bacteria to attach to the intestinal cellsurface. The LEE-encoded protein intimin and other TIIISS proteins have been usedas vaccine components in attempts to disrupt or prevent intestinal colonization by thispathogen. However, studies carried in the United Kingdom reported that vaccinationof young calves with recombinant intimin and EspA do not prevent colonization andsubsequent faecal shedding of E. coli O157:H7 (Dziva et al. 2007, van Diemen et al.2007). In contrast, a vaccine prepared from the culture supernatant of E. coli O157:H7strains (and shown to contain several key LEE proteins) was shown to reducefaecal shedding of the organism in groups of challenged and naturally infected feedlotcattle in Canada (Potter et al. 2004). However, when the latter vaccine was tested in alarge study involving cattle from nine commercial feedlots no significant difference inshedding of the organism was found between vaccinates and non-vaccinates (VanDonkersgoed et al. 2005). Subsequent studies with this vaccine in USA feedlot cattlehave shown that its efficacy increases with the number of doses given (Peterson et al.2007, Moxely et al. 2009). Other bovine E. coli O157 vaccines have also been testedor are undergoing development, including a plant-expressed intimin vaccine andothers based on the O157 lipopolysaccharide, H7 flagellar antigen and a siderophorereceptor/porin (SRP) preparation from the organism (Conlon et al. 2000, MacNeillyet al. 2008, Fox et al. 2009, Thompson et al. 2009). The SRP vaccine like the TIIISSvaccine also appears to significantly reduce faecal shedding of E. coli O157:H7 infeedlot cattle. In addition to different vaccine formulations, alternative routes ofdelivery such as intranasal vaccination are also being explored (Babiuk et al. 2008). Ithas been estimated that there are over 74,000 cases of E. coli O157:H7 infection per