Can stress in farms animal increase food safety risk ?

(review Marcos H. Rostagno, 2009, U.S. Departement of Agriculture, USDA)

The dissemination of bacterial pathogens into the human food chain is a major public health and economic concern for the food industries. 

The gastrointestinal tract of infected animals leaving the farm is considered as the main source of abattoir contamination. The review made by the USDA shows that there is increasing evidence to demonstrate that stress can have a significant deleterious effect on food safety. Field observations show that stress increases the risk of contamination of farms animals enteric pathogens such as E. Coli O157:H7, Salmonella and Camphylobacter. It has been observed that heat stress increases the resistance of E. Coli to tetracycline and ampicilline in pigs.

During hot period, there is also a higher level of d’E. Coli O157:H7 in cattle. Besides, Broiler chickens exposed to stress (heat and lack of food) are more subjected to Salmonella
and Camphylobacter. 

To explain these observations, a new area of the scientific knowledge has recently emerged.

Scientific studies investigate the direct effects of the enteric nervous system (ENS) on the gastrointestinal tract microbial population including foodborne pathogens. During stress periods, the ENS releases norepinephrine. In vitro, it has been observed that this neurotransmitter stimulates the virulence of E. coli and Salmonella Typhimurium.

This endocrinologic effect requires some researches and in vivo knowledge is limited.
However, understanding when pathogen loads on the farm are the highest or when animals are most susceptible to infection will help identifying times when intervention strategies for athogen control may be most effective, and consequently, increase the safety of food of animal origin. These strategies could come through the use of natural additives in the ration or in drinking water.