Pathogens in Animal Wastes

INTRODUCTION AND BACKGROUND Concerns about potential animal waste pollution of the environment have focused mainly on water, and the potential impacts of nitrogen, phosphorous, and turbidity (suspended solids). However, contemporary issues associated with potential pollution impacts of livestock operations now include microbial pathogens, gaseous emissions (such as ammonia), and odors (odorants). Increased awareness of zoonoses (pathogenic microbes of animal origin) in animal wastes is now recognized as a public health concern, especially because of the occurrence of waterborne disease outbreaks apparently caused by fecal contamination of manure origin (for example, in Walkerton, Ontario, in 2000). Identification and characterization of zoonotic animal pathogens is one of the key steps in reducing potential human exposures via water and other routes (foods, air and soil). Various bacteria, viruses, and protozoa exist in apparently healthy animals, but upon transmission to humans these pathogens can cause illness and even death. Exposure of humans to these disease-causing pathogens of animal origin can occur via occupational exposure, water, food, air or soil. Some of the important pathways for pathogen transmission to humans are shown in Figure 1. The fecal wastes and other wastes (such as respiratory secretions, urine, and sloughed feathers, fur or skin) of various agricultural (livestock) and feral animals often contain high concentrations of human and animal pathogens (disease-causing microorganisms) (Strauch and Ballarini, 1994). Concentrations of some pathogens occur at levels of millions to billions per gram of wet weight feces or millions per ml of urine. Per capita fecal production by agricultural animals such as cattle and swine exceeds that of humans. Furthermore, the trend for production facilities to harbor thousands to tens of thousands of animals in relatively small spaces results in the generation of very large quantities of concentrated fecal and other wastes that must be effectively managed to minimize environmental and public health risks.