VTEC 0157 is a bacterium found worldwide in cattle, sheep and pigs. Abattoir surveys in Great Britain have found it present in the faeces of almost 5% of cattle slaughtered, with a much lower incidence in pigs and sheep. On a herd basis it is possibly present in 30-50% of cattle herds in the general population. Studies in Scottish beef cattle have shown a shedding incidence of 7-10% in individual animals. However, VTEC 0157 rarely causes disease in animals, appearing as an inapparent infection.

What is the history?
The bacterium was first diagnosed as a human pathogen about 20 years ago. Since then, it has caused large outbreaks of disease in Scotland, Japan, Canada and the USA. In 1992 a working group was set up here to look at its significance as a foodborne pathogen, then in 1996 a major disease outbreak occurred in Central Scotland with 496 confirmed cases of whom 21 died, mainly elderly patients.The outbreak was traced to contaminated meat products. The Pennington inquiry which was subsequently set up established that animals, particularly ruminants, are a source of VTEC 0157 infection for the human population.

Animal and Public Health Issues
The bacterium rarely causes clinical signs in infected animals. However it can cause clinical disease in people, ranging from mild diarrhoea to life threatening haemorrhagic colitis and kidney failure. Treatment is limited, mainly fluid therapy, with antibiotics possibly doing more harm than good. The infectious dose is very small and can be picked up via contaminated food or water, animal contact or the environment. Spread may also occur from person to person. Meat and dairy products have certainly been implicated in outbreaks. However studies suggest that meat and milk contamination is not high and although it can be catastrophic (for example in the Scottish outbreak), it is relatively uncommon.

Risk Factors
Highest risk is associated with contact with farm/zoo animals and the disease has also occurred in children playing in gardens near to livestock farms. Interestingly, red meat consumption does not appear to be associated with an increased risk of infection. Simple hygiene measures such as appropriate hand washing, not eating near animals, cleaning clothes and removing possibly contaminated footwear indoors are all effective in reducing risk. Cooking food at adequate temperature is another precaution. However the bacterium does have a very low infectious dose and has been identified in some processed foods such as salami and apple juice. The presentation of clean animals at slaughter should reduce the percentage of carcases contaminated with faeces.

The Future
Much research continues to be done in this area - including epidemiology, control measures, pathogenesis and investigation of virulence factors.

User comments - post a comment