Prevalence of Shiga Toxin-Producing IEscherichia coli/I O157 in Wild Scottish Deer with High Human Pathogenic Potential

Shiga toxin-producing E. coli (STEC) serogroup O157 can cause serious infections in humans, with symptoms ranging from bloody diarrhoea to kidney failure, and, in some instances, can be life-threatening. The natural reservoir for these bacteria is livestock, particularly cattle; however, there is an increasing number of human cases associated with wildlife species such as deer. In Scotland, a human STEC O157 outbreak in 2015 that was associated with the consumption of venison prompted us to investigate the prevalence of STEC O157 in Scottish wild deer species. Although the estimated prevalence was low (0.28%), we found that STEC O157 isolates were shed at high levels from positive deer and that these isolates had the potential to cause severe disease in humans. Furthermore, retrospective analysis identified an isolate from this study as the likely source of another Scottish human outbreak in 2017. Shiga toxin-producing E. coli (STEC) infections associated with wildlife are increasing globally, highlighting many ‘spillover’ species as important reservoirs for these zoonotic pathogens. A human outbreak of STEC serogroup O157 in 2015 in Scotland, associated with the consumption of venison meat products, highlighted several knowledge gaps, including the prevalence of STEC O157 in Scottish wild deer and the potential risk to humans from wild deer isolates. In this study, we undertook a nationwide survey of wild deer in Scotland and determined that the prevalence of STEC O157 in wild deer is low 0.28% (95% confidence interval = 0.06–0.80). Despite the low prevalence of STEC O157 in Scottish wild deer, identified isolates were present in deer faeces at high levels (>10[sup.4] colony forming units/g faeces) and had high human pathogenic potential based on whole genome sequencing and virulence gene profiling. A retrospective epidemiological investigation also identified one wild deer isolate from this study as a possible source of a Scottish human outbreak in 2017. These results emphasise the importance of food hygiene practices during the processing of wild deer carcasses for human consumption.