Efficacy of a live avirulent Salmonella typhimurium vaccine in preventing colonization and invasion of laying hens by Salmonella typhimurium and Salmonella enteritidis

An avirulent live Δcya Δcrp Salmonella typhimurium strain (χ)3985 that precludes colonization and invasion of chickens by homologous and heterologous Salmonella serotypes was evaluated for its long-term protection efficacy. Chickens vaccinated orally at 2 and 4 wk of age were assessed for protection against oral challenge with wild-type S. typhimurium and Salmonella enteritidis strains at 3, 6, 9, and 12 mo of age. A comparison of Salmonella isolation from vaccinated and nonvaccinated layers after challenge with S. typhimurium or S. enteritidis showed that Δcya Δcrp S. typhimurium (χ)3985 induced excellent protection against intestinal visceral, reproductive tract, and egg colonization, invasion, and/or contamination by Salmonella. The duration of protection lasted for 11 mo after vaccination at which time the experiment was terminated. S. enteritidis and S. typhimurium were isolated from the yolk, albumen, and shells of eggs laid by nonvaccinated chickens challenged with Salmonella. S. typhimurium caused pathological lesions in nonvaccinated chickens, whereas vaccinated and nonvaccinated chickens challenged with S. enteritidis showed no pathological lesion in the visceral and reproductive organs. Vaccination with (χ)3985 prevented transmission of S. typhimurium or S. enteritidis into eggs laid by vaccinated layers with no effort on egg production. To our knowledge, this is the first publication confirming that vaccination with live avirulent Salmonella can induce long-term protection against Salmonella infection in layers.