Food and Environmental Safety
The Food and Environmental Safety Programme, often in collaboration 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.
Programme Manager
Epidemiology and Risk Research
Epidemiological, risk modelling and molecular approaches improve our understanding of the acquisition, maintenance and spread of food borne zoonoses (e.g. Salmonella, Campylobacter, E.coli and Cryptosporidium) in animals and their environment. Projects often consist of a comprehensive package of multidisciplinary research aimed at supplying data on which to base practical policy decisions and include research to control Campylobacter in broiler production, Salmonella in pigs and Salmonella in chicken egg laying flocks.
Investigation into the epidemiology of VTEC O157 and VTEC O26 in farmyard manure, slurry and dirty water on cattle farms was also carried out to produce a set of recommendations that can be adopted by farmers to reduce the risk of human VTEC infection attributable to farm waste. The project reviewed existing farm waste management methods; organised engineering visits and carried out epidemiological studies, risk assessment and mathematical modelling and it was concluded that farmers adhering to existing guidelines were managing their waste that minimises the risk of environmental contamination with VTEC.
Back to top
Food borne Pathogens Surveillance
The aim of surveillance is to identify trends in carriage of food borne pathogens by livestock, to improve our knowledge of these infections and to promote their control through effective measures on farms, feedmills and hatcheries.
We achieve this by three means:
- the investigation of clinical diseases, reported outbreaks on farms or positive samples from monitoring schemes
- trace-back investigations where animal premises are linked to human outbreaks
- by conducting carefully structured surveys in farms or abattoirs.
In 2005, we were involved in nine investigations of human outbreaks of VTEC O157 and two of cryptosporidiosis linked to farm premises. We are continuing to develop our methods for farm investigations so that we can be confident of the interpretation of our results, especially in those cases where sampling does not disclose a suspected infection. Work has also commenced on the implementation of an Early Detection Model for routine alerting to increases in numbers of reports of Salmonella serovars of public health concern.
for testing at a VLA Regional Laboratory
A statutory programme for the control of Salmonella Enteritidis and Typhimurium in chicken breeding flocks has been in operation since 1989 and these infections are now rare. Recent EU legislation has extended compulsory Salmonella control to other livestock sectors and the VLA is involved in implementation in the UK. In 2005, an EU-wide survey of Salmonella in chicken laying flocks was carried out to establish the baseline prevalence. The VLA was involved in survey design, sample testing and data analysis of the UK survey. The opportunity was also taken to investigate risk factors for infection and results will be used to develop control plans. A survey is currently underway of Salmonella in broiler flocks.
The British Pig Executive introduced an industry wide Salmonella monitoring scheme in 2003 for the collection of Meat Juice (MJ) samples from pigs slaughtered in quality-assured abattoirs. ELISA testing for antibodies to Group B and C1 Salmonella is carried out and high prevalence farms must develop an action plan and reduce their prevalence or face eventual loss of their Quality Assured status. VLA is funded by Defra to offer free farm visits to high prevalence farms and there was an encouraging increase in demand for visits this year. Salmonella Typhimurium was the most commonly recovered isolate and Salmonella Derby being second most common, reflecting current trends in pig samples submitted from other sources.
Back to topAntimicrobial Resistance
E.coli organisms carrying the CTX-M enzyme (a group of enzymes called extended-spectrum beta-lactamases (ESBLs), that are important because they can inactivate a very wide range of advanced penicillin and cephalosporin compounds) were detected on a Welsh dairy farm in 2004. A longitudinal investigation took place on the premises and it was found that the particular ESBL detected was quite different from the predominant ESBLs currently affecting humans in the UK. Complete containment of the ESBL was considered unfeasible and the ESBL continued to persist on the farm in cows and calves and was also detected on two other subsidiary rearing farms linked by direct calf movements. Several other European countries are also now reporting the emergence of strains of E.coli carrying ESBLs in animals. Salmonella isolates are also now screened for the presence of ESBLs but none have so far been detected.
The persistence of organisms resistant to antimicrobials was investigated in a large research project by assessing the impact of farm management and medication strategies on antimicrobial resistant commensal organisms on organic and conventional pig and poultry farms. The use of antimicrobial drugs on the organic farms was very low, whilst the conventional farms showed a wide range of levels of drug use. Resistant bacteria were detected on all of the study farms, including those where antimicrobials had not been used for many years. Some resistant E.coli not only persisted but also proliferated in the absence of antimicrobial use, suggesting that carriage of resistance resulted in no loss of competitive fitness. Multiple resistance was more common in E.coli on conventional farms and resistant bacteria were capable of surviving cleaning and disinfection; contamination rates being associated with clean out regime and resistance levels in bacteria shed by the previous flock, whilst the E.coli brought on to the farms by incoming chicks were largely sensitive.
Back to topPathogenesis and Control of Food borne Infections
Understanding fundamental information on host pathogen interactions underpins VLA’s approach to development of effective control strategies. Recent advances in genome sequencing and post genomic strategies have been exploited to further characterise and understand the biology of organisms and develop novel non-antimicrobial control methods.
A number of probiotic approaches are being investigated, including the potential use of Bacillus subtilis spores in controlling Salmonella, avian E.coli, Campylobacter and Clostridium perfringens in poultry. Preliminary data suggest a laboratory strain suppresses colonisation of Cl.perfringens and that the mechanism(s) of this action depend upon germination of the spores. A novel Salmonella vaccine has been designed, which is of interest to the commercial sector of the animal health industry. VLA is also working on developing a consortium approach to ‘The Healthy Gut in Animal Health and Welfare’. A Defra-funded project has been awarded in conjunction with Reading University on the suppression of antibiotic resistant S.Typhimurium in pigs by synbiotics.
E.coli O157:H7 is primarily associated with cattle but the organism has been reported in other ruminants, such as sheep and goats and at low levels in pigs. Little is known about colonisation of these less frequent hosts and this was the subject of recent research. Both pigs and goats were shown to be a potential reservoir of human infection. The early events of colonisation are dependent on bacterial intimin but longer-term persistence depends on other factors also. Flagella, Long Polar Fimbriae, Non-Lee Encoded factors (NleC and D) appear to play minor roles. The extent of colonisation and faecal shedding is greater in younger animals, as seen in cattle, but there is evidence that receiving milk from dams is protective. In lambs, colostrum deprivation and co-infection with Cryptosporidium increased shedding through the enhancement of attaching effacing lesions.
Back to topChemical Food Safety
VLA has provided advice to the Advisory Committee on the Microbiological Safety of Food on the risk of increased incidence of suspected cattle botulism. Many incidents are circumstantially associated with the spreading of poultry litter on grazing land or inadvertent exposure to poultry carcasses. Lead poisoning was also regularly diagnosed; many cases associated with exposure to known risk factors such as lead paint, batteries and old lead mine workings. Advice has been published on both issues warning of the risks associated with these hazards.
Radiochemical analysis of food and environmental samples were carried out for the Food Standards Agency (FSA) to assess human exposure to radionuclides and to provide information for risk management. In addition, VLA responded to several incidents involving potential radioactivity in foods.
Back to top
