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Listen to this siteThursday 16 February 2006
This research project will sample sheep presented for slaughter to establish the prevalence of E. coli O157and other verocytotoxin-producing E. coli (VTEC) serotypes in sheep.
Study Duration : July 2005 to September 2006
Contractor : Scottish Agricultural College (SAC)
Rates of infection of E. coli O157 in certain regions of Scotland are higher than those seen in England & Wales. In Europe, E. coli isolates of serogroups other than O157 also make a significant contribution to human diarrhoeal disease. Domestic ruminants, especially cattle and sheep, are major reservoirs of VTEC. Most epidemiological work on VTEC has focused on cattle despite sheep being identified on a number of occasions as the source of outbreaks of human VTEC infection in Scotland.
This study was undertaken to determine the prevalence of E. coli O157 and the major non-O157 VTEC in sheep at slaughter, and to see if there were seasonal or regional differences. The project sampled 1,082 sheep at slaughter at four different slaughterhouses in Scotland from July 2005 to June 2006.
Age of animal and season had a greater impact on prevalence of E. coli O157 carriage than the regional origin of the flock, with the highest risk seen during July to September in sheep that were adults or one year old. VTEC strains of serogroups O103, O111 or O145 were of low prevalence or absent from sheep at slaughter. The prevalence of E. coli O26 carriage was similar to E. coli O157 , however only 17% of E. coli O26 isolates possessed the verocytotoxin genes.
The project was successful in sampling 1,082 sheep at slaughter in Scotland at four different slaughterhouses from July 2005 to June 2006. The prevalence determined for E. coli O157 carriage by sheep at slaughter in Scotland was 3.4% with a 95% confidence interval (0.7%, 9.6%). Significant differences were identified in E. coli O157 carriage by animal age group, where strains were more commonly isolated from adult and hogg classes (one year old) of animals than from lambs. The highest risk for carriage of E. coli O157 by sheep at slaughter in Scotland was during the months of July to September and by sheep that were adults or one year old. The work found no statistical evidence of any variation in the faecal carriage of E. coli O157 by abattoir. Age and season had a greater impact on prevalence than the regional origin of the flock. Crucially, the findings do not support the hypothesis that human cases of E. coli O157 are higher in any particular Scottish region as a direct consequence of a higher rate of carriage in sheep in that region.
In Continental Europe, the most common non-O157 VTEC serogroups causing human disease are E. coli O111, O26, O103 and O145 . In this study we found that VTEC strains of serogroups O103, O111 or O145 were of low prevalence or absent from sheep at slaughter. The prevalence of E. coli O26 carriage was similar to that observed for E. coli O157 although only 17% of E. coli O26 isolates were positive for the verocytotoxin genes. Comparing these results to those from a previous FSA Scotland funded study (S01014) of cattle undertaken in Scotland suggests that sheep appear less likely than cattle to be a source of VTEC O26 strains in humans.
The results of enhanced surveillance continue to show E. coli O157 strains as the greatest threat to human health, however it is apparent that there is carriage of E. coli O26 strains in Scottish sheep that are VTEC positive and potentially virulent for humans. Therefore the findings from this study will assist in the refinement of current risk assessments for infection in humans and assist in future intervention and education strategies.
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