Studies on the use of 9R strain of Salmonella gallinarum as a vaccine in chickens.

The 9R strain of Salmonella gallinarum produced hepatitis and splenic lesions without mortality in meat-type and brown-egg-producing strains of chicks, but not in Leghorns. It was not recovered from Leghorns for as long following vaccination as from the other strains of chicks. The infectivity of the 9R strain was determined by the genetic susceptibility and age of the host. Subcutaneous vaccination of 9R produced partial immunity to S. gallinarum in Leghorns as well as in meat-type and brown-egg-producing strains of chickens. Addition of an oil adjuvant appeared to interfere with protection and gave even less protection than did a vaccine prepared from an inactivated oil-adjuvanted smooth strain. Use of the 9R vaccine did not protect against intestinal colonization by S. typhimurium or S. infantis. Potential egg transmission of 9R following vaccination and of a pathogenic strain following challenge of vaccinated birds was indicated by ovarian infection with each strain and by isolation of the pathogenic strain from one egg. All chickens vaccinated subcutaneously with the 9R strain developed antibodies detectable by the microantiglobulin test, but only a few birds developed antibody levels detected by the whole-blood, microagglutination, and tube tests. The inactivated vaccine prepared from a smooth S. gallinarum strain produced the highest and most uniform antibody response. Antibody levels were not related to protection, which is probably dependent on cellular immunity.