Rodents serve as amplifiers of Salmonella infections in poultry flocks and can serve as source of Salmonella contamination in the environment even after thorough cleaning and disinfection. This study aims to determine the dynamics of Salmonella occurrence in rodents and its relation to Salmonella contamination in layer farm environment including air dusts and eggs. From 2008 to 2017, roof-rats, environmental swabs, air dusts and eggs were collected from an intensive commercial layer farm in East Japan and were tested for Salmonella using standard procedures. In roof-rat samples, the Salmonella isolation rate was reached at 10% (95% CI 8.1-21.9) in which S. Corvallis, S. Infantis, S. Potsdam and S. Mbandaka were the frequent isolates from cecal part of intestines. On the other hand, prevalence rate of Salmonella in environmental swabs was at 5.1% (95% CI 2.2-7.4) while air dusts were at 0.9% (95% CI 0.2-1.8). It was observed that the prevalence of predominant Salmonella serotypes shifted over time; in roof-rats, it was noted that S. Potsdam gradually replaced S. Infantis. In environmental swabs and eggs, S. Corvallis and S. Potsdam increased significantly while S. Infantis became less frequent. In air dusts, S. Corvallis was observed to decrease and S. Potsdam became more common. Based on our findings, the role of roof-rats in the epidemiology of Salmonella in layer farms was expanded from being a reservoir, and amplifier host into shifting vessel of the most predominant serotypes.

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