DEVELOPMENT OF LIVE SALMONELLA VACCINES O PTIMALLY ATTENUATED FOR CHICKENS

The objective of immunoprophylaxis for latent salmonella infections in chickens is to interrupt the chain of infection between them and man. The efficacy and financial aspects of live salmonella vaccines requir e that the attenuation is for adaptation to the chicken, which is less susceptible to S. enteritidis infection than mammals. Two metabolic d rift mutants (chromosomal antibiotic resistance) were used to provide the optimal degree of attenuation. These were deficient in the product ion of essential enzymes. The resulting disturbed metabolic pathways o f the bacteria reduced the virulence and produced a loss of susceptibi lity to certain antibiotics. These provide markers for the recognition of mutants. A further alteration of the vaccine strains was produced by a third cell membrane mutation which shortened the shedding of the vaccine strain and its survival in the environment. A four-fold increa se in the sensitivity to therapeutics also resulted. Following a singl e oral administration of day old chicks, followed by oral booster vacc inations during the seventh week of age and oral/subcutaneous noses in weeks 16 to 18, the Salmonella typhimurium vaccine produced a systemi c immunity, as determined by a significant protection in a LD-85 toxic ity test, and a rapid elimination of the wild strain following challen ge. In addition, a local, intestinal immunity prevented the colonizati on of the wild strain and reduced the shedding period. This could resu lt in the eradication of latent S. typhimurium infections within a yea r if hygienic control measures are also applied. The same principles a pply for a S. enteritidis vaccine strain, which is currently being eva luated.