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Investigation of the Role of Environmental Contamination in the Epidemiology of Salmonella Infection in Egg-Laying Flocks


Salmonella has been shown to be capable of prolonged survival in the enivornment and has been associated with persistent and recurrent infections on poultry (especially on multistage sites for egg production) and pig farms as well as in hatcheries and feedmills. Although Salmonella contamination may be present this is not always associated with acquisition of infection by animals places in contaminated housing and other vectors such as rodents and arthropods may also be involved. There may also be as yet unknown management and stress factors, which could contribute to the risk.

Although reproted cases of Salmonella have been falling humans and in poultry it is not certain if this willbe sustainable, especially if a new epidemic strain similar to S. Enteritidis or S. Typhimurium DT104 emeges in the egg inducstry. Achievement of Government targets for a 20% reduction in foodbourne disease could be comprised by a new major egg-borne epidemic.
The objective of this work is to gather as much information as possible about the risks of carry-over of Salmonella infection in the various sectors of the layer industyry by a combination of approaches:
<OL> <LI> Investigations of carry-over of Salmonella into flocks where infection has been found in previous flocks. THis work will include the various production categories in the commercial sectors of egg production. These investigations will be supported by the use of molecular genetic typing of strains. Persistently infected sites will be visited and sampled both qualitarively in an intensive manor and quantitatively for key sample types.

<LI> Laboratory investigation of the phenotypic and genetic characteristics of persistent strains of Salmonella in terms of characterisitics such as survivability, disinfectant resistance, acid and heat tolerance and virulence.

<LI> Exposure experiments in which chickens would be exposed to known levels of Salmonella on environmental survival, under different conditions, on infectivity.
The results of this work will be used to formulate improved advice for DEFRA on the need for changes in policy or Codes of Practice on egg production, and practical advice for poultry company veterinarians and quality managers. Results will be communicated via internal reports, scientific papers, presentations at specialist poultry disease meetings and targeted articles in the poultry farming press so that new knowledge can be distributed as widely and effectively as possible.

University of Bristol
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