Submitted to: World Wide Web
Publication Type: Proceedings
Publication Acceptance Date: 3/13/2012
Publication Date: 3/22/2012
Citation: Gast, R.K., Guard, J.Y. 2012. Controlling Egg Contamination by Understanding Salmonella Enteritidis Infections in Laying Hens. World Wide Web. http://egg-cite.com/presentations/NCADC/Slideshow.aspx.
Technical Abstract: For more than twenty years, public health authorities have reported the transmission of Salmonella Enteritidis to consumers of internally contaminated eggs produced by infected hens. Egg contamination is both a cause of food-borne human illness and a principal diagnostic criterion for identifying infected laying flocks. Improved characterization of bacterial attributes (phenotypic and genetic) responsible for flock infection and egg contamination would support S. Enteritidis control efforts. Salmonella deposition inside developing eggs results from colonization of reproductive tissues in systemically infected hens, especially the ovary and the upper oviduct. Both the yolk and albumen of developing eggs laid by infected hens can be contaminated by S. Enteritidis, with the initial site of deposition determined by which regions of the reproductive tract are colonized. The observed incidence of internal egg contamination with S. Enteritidis is typically low and involves small initial numbers of bacterial cells. Identifying the underlying genetic differences between egg-associated and non-egg-associated Salmonella strains has been a complex and difficult task. The complementary action of phenotypic properties relevant to different environmental contexts in the infected avian host, expressed by distinct bacterial subpopulations, may link the complicated series of events which leads to egg contamination. Flock testing and vaccination are among the most frequently discussed and widely applied strategies for controlling S. Enteritidis infection and egg contamination in breeding and laying flocks. Testing identifies infected flocks or contaminated eggs which require intervention responses and verifies the efficacy and cost-effectiveness of risk reduction practices. Vaccination reduces the susceptibility of poultry to Salmonella infection if risk reduction practices fail to prevent pathogen introduction into flocks. The potential effectiveness of both of these approaches depends on the extent to which they are guided by a thorough and realistic understanding of the course and consequences of S. Enteritidis infections in chickens.