Food and Environmental Safety
Sarah Evans Food and Environmental Safety Programme Manager
The Food and Environmental Safety Programme, often in conjunction with the Health Protection Agency (HPA) provides consultancy, research and surveillance on food and environmental safety issues on farms and their environment, in support of both public and animal health.
Epidemiology and Risk Research
Research projects often consist of a comprehensive multi-disciplinary package and this year have included new projects aimed at developing practical methods for controlling Campylobacter in broiler production and Salmonella in poultry meat and egg production.
Defra commissioned a one year study to review recent research related to diagnostic and epidemiological techniques used in animal and human Salmonella investigations. It sought to provide a rational basis for the harmonisation and enhancement of these techniques between VLA and HPA.
Recommendations included development of shared protocols, standardised data collection methods, harmonised subtyping, molecular characterisation and inter-laboratory quality assurance.
A simulation model of E.coli O157 transmission within beef farms has been produced and will be used to predict the effect of various intervention methods. A randomised controlled trial of biosecurity interventions to control E.coli O157 on cattle farms revealed that keeping the bedding consistently dry was particularly important and significantly reduced the prevalence of E.coli O157 in young stock along with, using boot dips, keeping the animals clean and not introducing new animals into existing groups. A low adoption rate to this scientific evidence and a higher adoption rate to habits created during the study did not concur with another survey where farmers were asked to value and rate factors that would motivate them to implement control measures. The farmers valued improved animal welfare, quality of produce, increased safety for staff and family, increased production and proof of effect.
A National Survey to establish the prevalence of Campylobacter in broiler flocks, involving over 85% of UK plants started in January 2007. The effect of season and management practices will be examined.
3-D cell culture incubator
Surveillance of Food Borne and Environmental Zoonoses
A UK survey of Salmonella infection on commercial layer flock holdings concluded that the holding-level Salmonella prevalence was estimated at 11.7%. The most common serovar identified was S.Enteritidis followed by S.Typhimurium. The three other serovars given top priority by the EU, due to their public health significance were S.Virchow and S.Infantis, each isolated from one holding and S.Hadar, which was not isolated from any holdings. VLA is leading a new research study aimed at developing a monitoring, control and education package to assist the egg industry to reduce the level of Salmonella and achieve EU targets.
An early detection system for Salmonella incidents from clinically ill livestock and the statutory monitoring of chicken breeding flocks was implemented during the year. Monthly counts were compared with historical data using a detection algorithm and expected and threshold values derived. The system is used to flag up potential outbreaks for further investigation.
The British Pig Executive introduced an industry wide Salmonella monitoring scheme in 2003, Zoonoses Action Plan (ZAP). VLA offers an advisory visit service to farms identified with a high seroprevalence of Salmonella to assist in the development of biosecurity action plans to control Salmonella. There has been a marked increase in demand for these visits and 110 visits were carried out in 2006.
At the request of the Health Protection Agency, VLA visited premises that were tentatively linked to the serious sorbitol fermenting (SF) VTEC O157 outbreak in Yorkshire. Sorbitol non-fermenting (SNF) VTEC O157 was isolated from an open farm, but no SF VTEC was found. VTnegative SF O157 was detected on a commercial cattle farm. A further cluster of cases of SNF VTEC O157 (PT 8) in children was subsequently linked to visits to the open farm and an identical Pulsed Field Gel Electrophoresis (PFGE) match was found between human and animal isolates retained from the initial investigation.
Antimicrobial Resistance
VLA has enhanced surveillance for Extended Spectrum Beta-Lactamase (ESBL) enzymes in E.coli since the first report in UK livestock in 2004 (see feature article on page 12). Methicillin-resistant Staphylococcus aureus (MRSA) has been isolated from cattle, pigs and chickens outside the UK, but the organism has not been detected in farmed livestock within the UK. A Defra funded study is underway to test Staphylococcus aureus isolates obtained from bovine clinical submissions and of the 400 samples examined, all have tested negative. A veterinary sample, submitted from another laboratory did test positive for MRSA but contamination from a human source at the point of sampling or thereafter was considered responsible. VLA also assisted the British Veterinary Association in finalising a standard protocol for the presumptive identification of MRSA in veterinary practice laboratories.
Pathogenesis and Control of Food Borne Infections
Novel approaches have been used to identify genetic differences between epidemic and non-epidemic strains of Salmonella whereby unique DNA fragments are identified using an improved searching process. Findings have been reported on the differences between S.Newport (USA and GB strains) and S.Enteritidis strains. A number of unique sequences from current S.Gallinarum strains have been tentatively identified but none appear to be significant in terms of pathogenesis.
Micro-array validation studies on sequenced Salmonella strains have been carried out and results compared to sequence information available for these strains. The resulting sensitivity ranged between 97 to 99% for our panel of 7 strains and the specificity ranged between 84 to 94%. As the genome annotation is completed it is anticipated that the accuracy of results will increase. Preliminary work has showed that galacto-oligo-saccharide (GOS), given orally to mice prior to oral challenge with Salmonella gave a significant protective effect and may be a potential candidate for Salmonella control.
Chemical Food Safety
VLA was successful in a competitive tender for a new 5-year contract to continue providing radiochemical analyses of food and environmental samples to support the national monitoring programmes on behalf of the Food Standards Agency. Extensive support was also provided to HPA in the analysis of urine samples for Polonium 210 (see feature article on page 15). This assistance gave HPA extra surge capacity and demonstrated the practical benefits of the InterLab Forum. The development of policy and control methods on botulism and lead poisoning are two recent examples where VLA has been able to provide advice where there has been a need to revise policy and control risks to public health.