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

Project code: OZ0708
Project title: A Systems Analysis Methodology to Elucidate and
Evaluate the Critical Control Points for E. coli
0157:H7 in Cattle and sheep from farm to abattoir
Start date (dd/mm/yy): 01/01/2000
End date (dd/mm/yy): 30/06/2002
£151,494.00
Total cost:
Affiliation: Silsoe Research Institute
Sub-contractor(s): Veterinary Laboratories Agency
Abstract of research
An extensive literature review on the epidemiology of E. coli O157:H7 on farms was
carried out. On the basis of this a conceptual model was proposed. This was reviewed by
an expert workshop attended by other scientists and Defra representatives, and some
revisions were made.
The original objective was to develop a network model of the system. This was found to
be inappropriate because of several cyclic features, so a simulation approach was used.
This had two aspects: a deterministic simulation of the herd or flock and a stochastic
simulation of the transmission of E. coli O157:H7 within the herd/flock.
Limited testing was possible with the available survey data. The model was found to
produce estimates of animal prevalence (the overall proportion of animals shedding) that
were consistent with the data. However, for cattle it was found to overestimate the withinherd
prevalence and underestimate the herd prevalence (the proportion of herds
containing shedding animals).
Sensitivity analyses found that the most sensitive parameters were those related to
transmission from grass and enclosures to animals, contact between animals, and
pathogen survival on grass, in slurry and in barns.
The model was used to investigate the possibility of reducing prevalence by a range of
management interventions. Among the most important risk factors were: mixing sheep
and cattle, keeping animals in large groups, high stocking density, introducing positive
animals and reducing the interval between slurry spreading and grazing.
Review Summary
This project developed simulation models for interaction between farm animals and a
large number of farm management factors, including farm waste management. The
models use data from the literature on E. coli epidemiology.
Some of the conclusions are of practical importance for a possible reduction of E. coli
O157 carriage and transmission. They are in line with what might have been expected
and do contribute to improving methods of control and the evidence base.
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