Internal organ colonization and horizontal transmission of experimental Salmonella Enteritidis and Salmonella Kentucky infection in vaccinated 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: Journal of Applied Poultry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2020
Publication Date: 3/1/2021
Publication URL: https://handle.nal.usda.gov/10113/7198051
Citation: Gast, R.K., Jones, D.R., Guraya, R., Anderson, K.E., Karcher, D.M. 2021. Internal organ colonization and horizontal transmission of experimental Salmonella Enteritidis and Salmonella Kentucky infection in vaccinated laying hens in indoor cage-free housing. Journal of Applied Poultry Research. 30:100132.

Interpretive Summary: Laying flocks are often vaccinated to protect against Salmonella Enteritidis infections which can be transmitted to humans when infected hens lay contaminated eggs, but the ongoing transition of the commercial egg industry toward the use of non-cage housing options has raised new questions about the food safety consequences of egg production practices. ARS researchers in Athens, Georgia assessed the horizontal transmission of Salmonella infection and invasion of internal organs after experimental infection of previously vaccinated laying hens 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) and hens were euthanized during the first 12 d after infection to detect the presence of Salmonella in internal organs. After S. Enteritidis infection, pathogen colonization was detected in the intestines, livers, and spleens of 67% of orally inoculated hens and also in the intestines and livers of some uninoculated birds (exposed by horizontal contact). Significantly fewer hens were colonized by S. Kentucky. These results demonstrate that vaccines may not always provide complete exclusion of Salmonella, especially highly invasive serovars like S. Enteritidis, so a comprehensive risk reduction effort should be used to supplement vaccination of hens in cage-free housing systems to prevent extensive horizontal dissemination of Salmonella infection.

Technical Abstract: Cage-free housing of laying hens may provide opportunities for widespread environmental distribution of Salmonella contamination and horizontal transmission of infection within flocks. Salmonella Enteritidis in commercial laying flocks presents an ongoing public health concern because reproductive organ colonization in hens leads to deposition inside eggs. Many S. Enteritidis control programs include vaccination to induce protective immunity against infection. S. Kentucky is common in egg production environments but has not been associated with egg contamination. The present study compared the invasion of internal organs and horizontal spread of infection during the first 2 wk following experimental S. Enteritidis and S. Kentucky infection of vaccinated laying hens in indoor cage-free housing. All birds received a live S. Typhimurium vaccine at 17 d and 5 wk of age and an inactivated S. Enteritidis vaccine at 12 wk of age. Groups of 72 hens were housed on wood shavings in isolation rooms simulating commercial cage-free barns and 1/3 of the hens in each room were orally inoculated with 10e7 cfu of either S. Enteritidis (1 room) or S. Kentucky (1 room) at 27-31 wks of age. At 6 d and again at 12 d post-inoculation, half of the hens in each room were euthanized and samples of liver, spleen, ovary, oviduct, and intestinal tract were removed for bacteriologic culturing. Among hens inoculated with S. Enteritidis, 66.7% of intestinal, liver, and spleen samples were positive for the pathogen at 6 d post-infection, as well as 41.7% of intestines and 16.7% of livers from contact-exposed hens. Significantly (P < 0.05) fewer hens were colonized by S. Kentucky. These results demonstrate that vaccines may not always provide complete exclusion of Salmonella. In cage-free housing systems, vaccination should be supplemented with a comprehensive risk reduction effort to prevent extensive horizontal dissemination of Salmonella.