Horizontal transmission and internal organ colonization by Salmonella Enteritidis and Salmonella Kentucky in experimentally infected laying hens in indoor cage-free housing.

Authors: Gast, Richard; Jones, Deana; Guraya, Rupinder - Rupa; ANDERSON, KENNETH - North Carolina State University; KARCHER, DARRIN - Purdue University

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2020
Publication Date: 10/30/2020
Citation: Gast, R.K., Jones, D.R., Guraya, R., Anderson, K.E., Karcher, D.M. 2020. Horizontal transmission and internal organ colonization by Salmonella Enteritidis and Salmonella Kentucky in experimentally infected laying hens in indoor cage-free housing. Poultry Science. 99:6071-6074.
DOI: https://doi.org/10.1016/j.psj.2020.08.006

Interpretive Summary: Salmonella infections can be transmitted to humans by contaminated eggs produced by infected laying hens. Salmonella Enteritidis is deposited inside eggs after it invades to the internal organs of infected hens. A diversity of housing systems are used for laying hens, but the full food safety consequences of these various options remain unresolved. The present study assessed the horizontal transmission of Salmonella infection and invasion of internal organs after experimental infection of laying hens in indoor cage-free housing. Groups of hens were housed on wood shavings in isolation rooms simulating commercial cage-free barns with nest boxes and perches. One-third of the hens in each room were orally infected with either S. Enteritidis or S. Kentucky (a common environmental strain but not associated with egg-borne disease transmission). During the course of the first 12 d after infection, hens were euthanized and their internal organs were tested to detect the presence of Salmonella. After S. Enteritidis infection, intestinal colonization by the pathogen was detected in all orally infected birds as well as a high percentage of uninfected (contact-exposed) birds. S. Enteritidis was also found at a high frequency in livers and ovaries from inoculated hens plus a substantial proportion of contact-exposed hens. After S. Kentucky infection, intestinal colonization was observed at high frequencies in both orally infected and contact-exposed hens, but invasion to internal organs was seldom detected. These results demonstrated that Salmonella infection can spread rapidly and extensively among hens in cage-free indoor housing, including a high frequency of internal organ invasion for S. Enteritidis.

Technical Abstract: The transmission of Salmonella infections to humans via contaminated eggs is an international public health concern. S. Enteritidis is deposited inside eggs after colonizing reproductive tissues of infected hens. Diverse housing facility characteristics and flock management practices can influence Salmonella persistence and transmission in poultry flocks, but the full food safety consequences of different housing system options for egg-laying hens remain unresolved. The present study assessed the horizontal transmission of infection and invasion of internal organs after experimental S. Enteritidis and S. Kentucky infection of laying hens in indoor cage-free housing. Groups of 72 hens were housed on wood shavings in isolation rooms simulating commercial cage-free barns with community kick-out nest boxes and perches. 24 hens in each room were orally inoculated with 6.5 × 10e7 cfu of 2-strain mixtures of either S. Enteritidis or S. Kentucky (2 groups each). At 6 d and 12 d post-inoculation, 12 inoculated and 24 contact-exposed hens in each room were euthanized and samples of liver, spleen, ovary, oviduct, and intestinal tract were removed for bacteriologic culturing. All orally inoculated hens were positive for intestinal colonization by S. Enteritidis at 6 d post-infection and 70.8% of contact-exposed hens had become colonized by 12 d post-infection. S. Enteritidis was isolated from 100% of livers and 50.0% of ovaries from inoculated birds at 6 d post-inoculation and from 41.7% of livers and 10.4% of ovaries from contact-exposed birds at 12 d. The majority of both orally inoculated and contact-exposed hens were positive for intestinal colonization by S. Kentucky at 6 d post-infection, but S. Kentucky was found in other internal organs of both inoculated and contact-exposed hens significantly (P < 0.05) less often than S. Enteritidis at both sampling intervals. These results indicate that Salmonella infection can spread rapidly and extensively among hens in cage-free indoor housing, including a high frequency of internal organ involvement for invasive serovars such as S. Enteritidis.