Edward Atwill
Western Institute for Food Safety and Security, School of Veterinary Medicine,
University of California Davis

Zoonotic pathogens present in the faeces and urine of wild and domestic animals have a long history of causing human enteric disease through consumption of contaminated foods of animal origin, occupational exposure, and inadequately treated drinking water. More recently, there is a growing realization that many fruits, vegetables, and nuts that are consumed raw or after minimal processing are equally vulnerable to pathogen contamination. Global food trends such as the consumption of raw or minimally processed vegetables and the increasing reliance on mass processing of produce commodities such as spinach, spring salad mix, and chopped lettuce suggest that raw produce will continue to grow as a significant contributor to the annual incidence of foodborne illness.
Despite regulatory pressure and increased governmental funding that has focused on produce food safety, we have a poor understanding of the primary routes of entry of microbial pathogens into various produce commodities. There are several scenarios of heightened concern that could allow animal waste to contaminate produce in the preharvest production environment:
(1) improperly processed animal composts used as soil amendment, (2) irrigation water that is contaminated with animal waste, and (3) direct defecation of domestic animals and wildlife into the produce field, especially for commodities that contact soil surface during grow-out or processing.
Regarding composts, there is a continuing need to diversify cost-effective technologies for liquid and solid manure management systems common to intensified animal agriculture. In much of the world these manure commodities are only minimally treated, such as passive stacking of livestock manure solids for weeks to months which can allow a range of zoonotic pathogens to persist in relevant concentrations. As the mean annual income among many countries continues to grow, animal intensive industries continue to expand in order to satisfy the growing demand for foods of animal origin. As a consequence, produce fields are a common and often needed recipient of these minimally-treated manure commodities and thereby create the conditions for a recycling of zoonotic pathogens back into the human food chain. Cost-effective methods to protect and insure the microbiological quality of irrigation water remain poorly developed for many regions of the world, relying on technology such as fecal coliform monitoring despite overwhelming evidence that bacterial indicators poorly predict the occurrence of zoonotic pathogens. Numerous management techniques have been developed to safeguard surface irrigation supplies from fecal contamination of extensive livestock populations.
Lastly, recent food-borne outbreaks such as the U.S. outbreak of E. coli O157:H7 traced to strawberries exposed to wildlife feces highlight the need for new biosecurity protocols that prevent animal defecation into fields of produce, especially when the environmental or biodiversity community demand no-kill interventions for free-ranging wildlife. These are a but a few of the many compelling challenges still facing the public health community in the area of food safety and water quality.