Review of the Food-borne Zoonoses Research ... - ARCHIVE: Defra

Abstract of research
The VLA research work on Salmonella in commercial laying farms began officially in
2000 with Project OZ0317, although some pilot investigations had been carried out prior
to that. Voluntary investigations on laying farms where S.Enteritidis (SE) had been
identified as a result of trace back investigations from food poisoning outbreaks,
investigations of clinical disease or (rarely) identification of SE as a result of voluntary
monitoring under the British Egg Industry Council (BEIC) Lion Code scheme showed that
the principal problem was horizontal infection resulting from persistence of contamination
in poorly cleaned houses and particularly in breeding mice or rat populations in the
houses. Occasional new introductions of infection due to infection in breeding flocks or
contamination of hatcheries were also investigated but these incidents were uncommon.
Persistence of SE appeared to be independent of vaccination status, except in barn or
free-range farms where there were no rodent problems which became free of infection
when new vaccinated flocks were introduced. Contamination of eggs from infected
vaccinated flock birds reduced by around 70% compared with those from non-vaccinated
flocks. Cross-contamination during egg packing was also identified. The scope of the
work was widened with increased funding in Project OZ0321 and various investigations
involving quantification of SE demonstrated high numbers of organisms associated with
rodents and flies. Exposure studies at Bristol University demonstrated the high risk
associated with contaminated drinking equipment (a common finding in layer flocks)
regardless of vaccination. Vaccine transition studies suggested that there may be
significant differences between the efficacy of the various vaccination programmes.
Randomly recruited farms from the EU Baseline Survey showed identical problems to the
original study cohort and sampling comparisons identified significant differences in the
sensitivity of various monitoring options, especially in large barn or free-range flocks
where subdivision of floor spaces led to a dilution effect and false negative results when
limited numbers of boot swabs were used. In Project OZ0325 good progress has been
made on problem farms by including specialist pest control and decontamination services
in the project team and the project leader has been involved in redrafting various codes
of practice and SVS guidance documents as well as the BEIC Lion Code and together
with Natural England has been involved in a nationwide road show campaign for the egg
industry.
Review Summary
The work covers a very wide spectrum of issues of key relevance to the commercial egg
industry and extends the fundamental knowledge of the practical epidemiology in this
area. Different parts of the work have contributed to the evidence base, to the
development of diagnostic tests and sampling methodology and to improvement in
methods of control. It was particularly encouraging to find that salmonella-positive flocks
can turn negative, and that infection levels can be reduced.
The work was fundamental to building better relationships with the industry, which has
assisted both subsequent research and also policy development involving partnership
with industry. The current research is crucial to Defra in developing with industry a
salmonella control programme that meets EC salmonella requirements and keeps the UK
egg industry at the forefront in terms of quality. It has allowed Defra to negotiate a UK
position based on best available science and the main research worker has acted as an
independent adviser to the EC. The results of the research have been successfully
disseminated to industry by means of a road-show led by the British Egg Industry
Council.
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