Salmonella enteritidis infection for consumer protection
Karen E. BurnsA, Sandra M. Kelly-AehleB, Julie A. LawrenceC
A D.V.M., M.A.M, diplomate A.C.P.V, Technical Services Veterinarian, Lohmann Animal Health International, Inc., 1146 Airport Parkway, Gainesville, GA 30501
B Biologicals Development Director, AVANT Immunotherapeutics, Inc. dba Megan Health, Inc., 8620 Pennell Drive, St. Louis, MO 63114
CResearch Scientist, AVANT Immunotherapeutics, Inc. dba Megan Health, Inc., 8620 Pennell Drive, St. Louis, MO 63114
In response to a rise in food safety concerns over Salmonella enteritidis, vaccination with inactivated bacterins started in the late 1980’s in the United States. These bacterins offered reduction in Salmonella excretion in feces, reduced invasion by the challenge organisms and provided passive protection through antibodies being present in the egg (3,4,5,6,9). Science progressed to the development of live attenuated vaccines derived from Salmonella typhimurium (ST) that would offer cross protection to other Salmonella species, most notably Salmonella enteritidis (SE)(2,7). The first live vaccine of this type licensed in the United States was MeganVac 1– a double gene modified ST organism that was designed for protection of broilers through slaughter to reduce Salmonella contamination of carcasses (2). Another vaccine against SE infection has recently received USDA license. The researchers at Megan Health have developed MeganEgg, a new vaccine for pullets. This product contains the same MeganVac 1 organism, however, MeganEgg is formulated for immunization of older birds. Vaccine Characteristics: The vaccine is derived from a naturally occurring Salmonella typhimurium that has been genetically modified to impair two genes that are important for normal growth and metabolism. The modifications to the genes, cya and crp, result in an organism that is completely distinct from Salmonella species (2, 7). When cultures are examined using a rapid identification system, the results correlate with the species, Hafnei alvei (10). For this reason, along with the low shed rate of the vaccine strain, MeganEgg will not interfere with environmental monitoring of a Salmonella reduction program.
Label Indications: MeganEgg is the first USDA licensed live Salmonella typhimurium vaccine to carry a label claim for protection of the ovaries and oviducts. This protection of the reproductive organs is significant against strains of Salmonella enteritidis proven to infect the ovary with consequent contamination of the egg. Additionally, MeganEgg carries a label claim to reduce colonization of the intestinal tract and ceca by SE. As a result of the broad-based protection provided by the vaccine in the internal organs, ovaries, oviduct, intestinal tract and ceca, the risk of egg shell contamination is greatly reduced.
The label recommendation for age of application is 2, 4 and 16 weeks of age by coarse spray application. The vaccine has been used in field safety tests in commercial layer houses, with no adverse vaccine reaction observed. Vaccine efficacy in laying hens:
Vaccination protocol: Birds were administered MeganEgg by coarse spray application at 2, 4, and 16 weeks of age. Nonvaccinated controls were administered distilled water by coarse spray. Challenge: Birds were challenged with a very large dose of wild-type nalidixic acid-resistant Salmonella enteritidis organism, Phage Type 13a 8, 19 and 40 weeks after receiving the last booster vaccination. Sample Collection: Eggs were collected daily for 5 days post challenge, then birds were euthanized and spleen, liver, kidney, ovaries, oviduct, duodenum, ileum, large intestine and cecal tissues with contents were collected for culture.
Results – Vaccine efficacy in laying hens:
Figure 1 shows the results of egg cultures post challenge from vaccinated and nonvaccinated birds at various ages. Protection provided by...