Abstract
Human cases of bacterial gastro-enteritis are often caused by the consumption of eggs contaminated with Salmonella species, mainly Salmonella enterica serovar Enteriditis (Salmonella Enteritidis). To reduce human exposure, in several countries worldwide surveillance programmes are implemented to detect colonized layer flocks. The sampling schemes are based on the within-flock prevalence, and, as this changes over time, knowledge of the within-flock dynamics of Salmonella Enteritidis is required. Transmission of Salmonella Enteritidis has been quantified in pairs of layers, but the question is whether the dynamics in pairs is comparable to transmission in large groups, which are more representative for commercial layer flocks. The aim of this study was to compare results of transmission experiments between pairs and groups of laying hens. Experimental groups of either 2 or 200 hens were housed at similar densities, and 1 or 4 hens were inoculated with Salmonella Enteritidis, respectively. Excretion was monitored by regularly testing of fecal samples for the presence of Salmonella Enteritidis. Using mathematical modeling, the group experiments were simulated with transmission parameter estimates from the pairwise experiments. Transmission of the bacteria did not differ significantly between pairs or groups. This finding suggests that the transmission parameter estimates from small-scale experiments might be extrapolated to the field situation.
Highlights
Worldwide, many human cases of bacterial gastroenteritis are caused by the consumption of eggs contaminated with Salmonella spp., mainly Salmonella enterica serovar Enteriditis (Salmonella Enteritidis) [1,2]
The European Union (EU) has implemented a surveillance programme [3] to detect laying hen flocks colonized with Salmonella Enteritidis with the aim to reduce the number of contaminated eggs placed on the market
The aim of this study was to compare infection dynamics of Salmonella Enteritidis in pairs of laying hens with the dynamics in groups of 200 hens housed at similar densities, and to test whether the mathematical model used to analyze transmission in pairs was valid to be used for larger groups
Summary
Many human cases of bacterial gastroenteritis are caused by the consumption of eggs contaminated with Salmonella spp., mainly Salmonella enterica serovar Enteriditis (Salmonella Enteritidis) [1,2]. Reduction of human exposure is an important task for public health organizations and producers of poultry products. The European Union (EU) has implemented a surveillance programme [3] to detect laying hen flocks colonized with Salmonella Enteritidis with the aim to reduce the number of contaminated eggs placed on the market. The efficacy of a surveillance programme depends, amongst others, on sample size and frequency, which in turn depend on the within-flock prevalence. Sample size is often based on a fixed, static prevalence.
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