Development and evaluation of an experimental vaccination program using a live avirulent Salmonella typhimurium strain to protect immunized chickens against challenge with homologous and heterologous Salmonella serotypes

A stable live avirulent, genetically modified Δcya Δcrp Salmonella typhimurium vaccine strain, χ3985, was used in several vaccination strategies to evaluate its use in the control of Salmonella infection in chickens. Oral vaccination of chickens at 1 and at 14 days of age with 10⁸ CFU of χ3985 protected against invasion of spleen, ovary, and bursa of Fabricius and colonization of the ileum and cecum in chickens challenged with 10⁶ CFU of virulent homologous Salmonella strains from group B. Chickens challenged with heterologous Salmonella strains from groups C, D, and E were protected against visceral invasion of spleen and ovary, while invasion of the bursa of Fabricius and colonization of ileum and cecum was reduced in vaccinated chickens. Oral vaccination at 2 and at 4 weeks of age induced an excellent protection against challenge with virulent group B Salmonella serotypes and very good protection against challenge with group D or E Salmonella serotypes, while protection against challenge with group C Salmonella serotypes was marginal but significant. Vaccination at 2 and at 4 weeks of age also protected vaccinated chickens against challenge with 10⁸ CFU of highly invasive S. typhimurium or S. enteritidis strains. The protection of chickens vaccinated with χ3985 against challenge with homologous and heterologous Salmonella serotypes is outstanding, and the complete protection against ovarian invasion in chickens challenged with 10⁸ CFU of highly invasive S. typhimurium or S. enteritidis strains suggests that vaccination of chickens with χ3985 can complement the present hygiene- and sanitation-based Salmonella control measures. This paper reports a breakthrough in the use of live avirulent vaccine to control Salmonella carriers in chickens.