Zoonotic infections infections in livestock and the risk to public health - Abstract

Prevalence of Verocytoxigenic E.coli O157 (VTEC O157) in Cattle, Sheep and Pigs at Slaughter in Great Britain and in Cattle on Farms in England and Wales

G A Paiba

Introduction

Worldwide, VTEC O157 has been found in cattle, sheep and pigs. A UK-wide survey of beef carcass contamination in 1994/5 recovered VTEC O157 from 0.47% of carcasses and suggested that cross-contamination was probable. Then a 1-year study conducted in a Sheffield abattoir in 1995/6 isolated VTEC O157 from 15.6% of cattle and 2.2% of sheep, but not in 1000 pig rectal faeces samples. However, no national abattoir or farm surveys have been conducted in food animals in the UK to determine the prevalence of VTEC O157 carriage. Initial results of three such studies are presented here.

Abattoir studies

Two 12-month abattoir studies to investigate the faecal carriage of VTEC O157 in animals sent for slaughter for human consumption in Great Britain have recently been concluded. In the cattle and sheep survey, the annual prevalence of VTEC O157 faecal carriage measured over 12 months from Jan 1999 was 4.7% [CI_95% 4.1 - 5.4] in slaughter cattle and 1.8% [CI_95% 1.3 - 2.2] in sheep. Faecal carriage was detected throughout the year, but was greatest in the summer in both species and least in the autumn in cattle and in the winter in sheep (see Figure 1). VTEC O157 was detected in animals slaughtered throughout GB, but there was a significantly greater incidence of VTEC O157 in cattle in abattoirs in the east of GB.

Figure 1: Prevalence of faecal carriage of VTEC O157 by season

In the pig survey, 4 isolates of VTEC O157 were recovered giving a prevalence of 0.16% [CI_95% 0.15 - 0.17].

On-farm studies

A study was conducted to determine the prevalence of faecal excretion of VTEC O157 by cattle on randomly selected farms in England and Wales. VTEC O157 was isolated from 4.7% [CI_95% 4.1 - 5.3] of individual animals and 44.0% [CI_95% 32.5 - 55.9] of herds between June and Dec 1999. In infected herds, 10.2% [CI_95% 8.2 - 11.5] of individual cattle were excreting VTEC O157. Excretion was significantly associated with age and was greatest in cattle under 24 months. Cattle in fattening herds were twice as likely to excrete VTEC O157 than those in dairy or suckler herds even allowing for the age of the cattle (see Figure 2).

Figure 2: Prevalence of cattle excreting VTEC O157 by age by herd type

Conclusions

VTEC O157 was present in the faeces of 4.7% of cattle slaughtered in GB for human consumption in 1999/2000.
The prevalence of faecal carriage of VTEC O157 by sheep slaughtered for human consumption in GB in 1999/2000 was 1.8%. This was significantly less than the rate of faecal carriage by cattle.
In pigs slaughtered for human consumption in GB, the prevalence of faecal carriage of VTEC O157 was 0.16%.
VTEC O157 was isolated from cattle on 44% of randomly selected herds in England and Wales and is therefore likely to be present on 1/3 to ½ of the herds in the general population. The individual animal prevalence was similar to the faecal carriage by animals at slaughter. VTEC O157 was more commonly detected in calves than in adults and independent of age, was more common in fattening herds than dairy or suckler herds.
The faecal carriage and excretion of VTEC O157 in cattle, sheep and pigs in Great Britain is similar to that reported by other workers in the UK and world-wide.

The three studies outlined used the current Gold Standard test for the isolation of VTEC O157. However, additional work on cattle samples using a more sensitive but not fully validated method demonstrated that up to half of the positive samples may fail to be detected. Therefore, the prevalence of faecal carriage and excretion in cattle may be up to twice that reported here.

Acknowledgements

Thanks are due to all the farmers, abattoir owners/staff, the MHS staff and VLA staff involved in these projects. These studies were funded by MAFF and Meat and Livestock Commission.

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