Animal Waste, Water Quality and Human Health

Zoonotic waterborne pathogens in livestock 127food- and waterborne pathogenic bacteria do not cause illness nor illicit a strongimmunological response in the host animal, development of vaccines againstthese pathogens has been difficult. In the context of the five agents identified asfrequently associated with waterborne zoonotic disease, good success has beenachieved in vaccines against Salmonella responsible for disease in swine anddairy cattle (House et al. 2001) and to reduce Salmonella colonization in poultry(Zhang-Barber et al. 1999). In the United Kingdom, many breeder and layerflocks are now vaccinated against Salmonella serovar Enteritidis, which has ledto a reduced prevalence of this serovar in poultry (Barrow 2007). LiveSalmonella vaccines generally confer better protection than killed vaccines,because the former stimulate both cell-mediated and humoral immunity(Imersaal et al. 2005). Vaccines have also been developed for use in cattle toreduce faecal shedding of E. coli O157:H7 (Judge et al. 2004, Moxley et al.2009, Sargeant et al. 2007).While vaccination has long been used to prevent animal diseases of economicimportance, many of the zoonotic waterborne pathogens seem to have limited or noeffect on the health of animals; swine and poultry frequently excrete Salmonellaand Campylobacter, and young calves excrete E. coli O157 in their faeces,without apparent ill effect. The gold standard for vaccines has traditionally beenprevention of disease and economic loss associated with animal disease.However, in the case of zoonotic pathogens, vaccines should not only preventfaecal shedding but also ideally eliminate the carrier state. Until recently,veterinary vaccines have been very crude and have consisted only of killed ormodified-live pathogenic organisms. This lack of sophistication is related to therequired low cost of production of these vaccines and difficulties with regulatoryapproval of recombinant vaccines. There is also concern about loss in quality ofmeat and poultry products as a result of vaccination via intramuscular routes,and more and more emphasis is being placed on adjuvants and routes ofvaccination that stimulate mucosal immunity and prevent colonization and thecarrier state.It has been reported that infection of calves with zoonotic pathogens such asE. coli O157:H7 and Crypto. parvum occurs within hours and days of birth (Harpet al. 1996, Gannon et al. 2002). Therefore, it may be more logical to mount aspecific immune response in the dams through vaccination prior to birth sothat protection against colonization and infection can be provided passivelythrough colostrum and milk. This approach was initially developed for protectionof lambs and calves against K99-bearing enterotoxigenic E. coli (Sojka et al.1978, Nagy 1980). Perryman et al. (1999) reported that the severity ofCryptosporidium parvum infection and oocyst shedding can be reduced byfeeding calves immune colostrum obtained from dams vaccinated with a