Aspects of the epidemiology and dynamics of the spread of Escherichia coli O157:H7 in different cattle production systems
To address important aspects of the epidemiology and dynamics of the spread of 'Escherichia coli' O157:H7 ('E. coli ' O157) in different cattle production systems, three studies were conducted: a cross-sectional study of 119 cow-calf operations in Ontario, Canada, a longitudinal study of 168 feedlot steers, and a repeated cross-sectional study of 150 dairy farms in Ohio, USA. Risk factors associated with the prevalence of 'E. coli' O157 among cattle in cow-calf operations included the presence of pigs on farm, use of corn silage supplementation in winter, number of times cattle were taken to a show in the previous 12 months and the proportion of cows that make up the total herd. However, for dairy cattle, risk factors associated with 'E. coli' O157 shedding included contact between adult cattle and calves, the types or number of ventilation and manure management systems on the farm as well as the number of European starlings ('Sturnus vulgaris') per milking cow. Furthermore, in order to investigate the effect of dietary interventions on 'E. coli' O157 shedding in cattle, a group of feedlot steers was followed throughout a feeding period of 14 weeks. We found that the type of corn and feed supplement in the diet had an impact on the shedding of'E. coli ' O157 in this group of animals, but the effect may vary if there is a super-shedding pen-mate present on the same sampling date depending on the type of diagnostic protocol used to identify shedding animals. However, none of these factors affected the sensitivity of the diagnostic protocols and apparent differences in the effect of dietary factors on the shedding of 'E. coli' O157 based on RAMS-IMS or fecal-IMS is likely due to their impact on other bacterial species present in the gastrointestinal tract. Understanding the epidemiology of this pathogen in different cattle environments, the role of non-bovine species in maintaining 'E. coli ' O157 and in the manner in which diagnostic tests may be affecting our perception of the epidemiology of 'E. coli' O157 in cattle are discussed in this thesis as critical points for controlling this zoonotic pathogen along the farm-to-fork continuum.