Animal Waste, Water Quality and Human Health

120Animal Waste, Water Quality and Human Health4.3 CONTROL POINT 1: MINIMIZING EXPOSUREOF LIVESTOCK TO PATHOGENSFor livestock to become infected, and hence a hazard source, they must first beexposed to pathogens. Waterborne zoonoses can originate from infectedlivestock, other animals (including humans) or the environment; the latter istypical of free-living pathogens which cause accidental zoonoses. These sourcesof waterborne zoonoses can be present on or off the farm, and livestock maycontract them directly (through animal to animal, or human to animal physicalcontact) or more commonly indirectly (through, e.g., vehicles (or fomites),vectors, air currents, dust particles, water, food or oral-faecal contact). In thissection we consider how exposure of livestock to waterborne zoonoses can bereduced or eliminated.4.3.1 Specific pathogen-free animalsPrevention is better than cure, and it is epidemiologically more sound to maintainanimals free from pathogens than eliminate pathogens from infected animals.Therefore, the present Danish programme relies strictly on test and slaughter andnot on vaccines and has placed emphasis on “cleaning up” the primary poultrybreeder flocks and swine herds in Salmonella and Campylobacter controlprogrammes.Caesarean section-derived germ-free or gnotobiotic animals have been usedin the swine industry to create disease-free animals. These animals are largelyfree from Salmonella, Trichinella spiralis and Toxoplasma gondii infections.Specific pathogen-free pig herds (free from Y. enterocolitica O:3/biovar 4) havealso been established and maintained in Norway. According to serologic andcultural testing results, 15 of 16 of these herds tested have been free from Y.enterocolitica O:3/biovar 4 since 1996 (Nesbakken et al. 2007).In technologically sophisticated livestock production systems such as those seenin high-income countries and many emerging economies, there is a demand foruniform, predictable food products, which in turn leads to demand for genetichomogeneity in animal populations. This is typically obtained by drawing on avery narrow range of high growth-potential genetic stock. This incidentally offersan opportunity for specific-pathogen-freedom cascading through generations tothe animals producing for consumer markets. In poultry, for example, there is aproduction pyramid, with elite and grandparent breeder flocks at the top thatprovide the seed stock necessary for the lower levels in the production system thatgive rise to the production flocks that provide our poultry meat and eggs.Considerable effort is placed on maintaining these elite flocks free of enteric