Submitted to: International Journal of Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 23, 2011
Publication Date: December 14, 2011
Citation: Gast, R.K., Guraya, R., Holt, P.S. 2011. Frequency and persistence of fecal shedding following exposure of laying hens to different oral doses of Salmonella enteritidi. International Journal of Poultry Science. 10:750-756. Interpretive Summary: Contaminated eggs laid by infected hens continue to pose a significant public health concern as the principal source of food-borne transmission of Salmonella enteritidis infections to humans. A recently implemented national regulatory program for egg production in the United States seeks to control egg-borne transmission of illness to consumers through a program which combines various mandatory risk reduction practices with testing to detect infected flocks. However, many important parameters of S. enteritidis infections in laying hens remain incompletely characterized, including the relationship between the oral dose of bacterial cells to which hens are exposed and the frequency and length of time that infected birds shed the pathogen in their voided feces. In the present study, groups of laying hens were experimentally infected with several different oral doses of S. enteritidis and the frequency of fecal shedding was determined at 8 subsequent weekly intervals. Significant differences between doses were observed in both the initial frequency of fecal shedding that followed oral inoculation and in the duration of this shedding over the course of the experiment. These results demonstrate that the dose of S. enteritidis that laying hens are exposed to can affect the resulting progress of infection in a manner which may significantly influence the outcome of flock testing efforts.
Technical Abstract: Infections of egg-laying poultry with Salmonella enteritidis and the associated transmission of illness to consumers of contaminated eggs has been a prominent international public health concern for many years. Testing and risk reduction programs for laying flocks have been implemented in many nations with some success. However, several critical parameters of S. enteritidis infections in chickens, including the relationship between the magnitude of oral exposure and the frequency and duration of bacterial shedding in voided feces, remain incompletely defined or explained. In the present study, groups of laying hens were experimentally infected with oral doses of 104, 106, or 108 CFU of a phage type 13a strain of S. enteritidis and the frequency at which the pathogen was shed in voided feces was determined at 8 weekly post-inoculation intervals. At 1 wk post-inoculation, the frequency of fecal shedding of S. enteritidis ranged from 23.8% for the 104 CFU dose to 87.5% for the 108 CFU dose. No fecal shedding was detected after 3 wk post-inoculation from hens inoculated with 104 CFU, but a small proportion (2.5% to 5.0%) of hens that received doses of 106 or more CFU of S. enteritidis were still shedding at 8 wk post-inoculation. The results of this study indicate that the oral exposure dose can significantly influence the frequency and duration of S. enteritidis fecal shedding into the environment by infected laying hens. A more complete understanding of how different levels of exposure are detected by particular sampling methods will support the effective application and interpretation of testing protocols for controlling poultry infections and preventing transmission to humans.