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Meat from wild-living animals underestimated as source of EHEC infections

16/2007, 21.08.2007

Research project is to clarify the source of contamination and of foodborne infections with enterohaemorrhagic E. coli (E-HEC)

Enterohaemorrhagic Escherichia coli (EHEC) cause acute, in some cases, bloody diarrhoea in humans. In children, in particular, an EHEC infection can lead to damage to the kidneys that may progress to renal failure - haemolytic-uraemic syndrome (HUS). Up to now there have mainly been reports of livestock as the source of EHEC infections: cattle, sheep and goats excrete EHEC in their faeces without manifesting any signs of disease themselves. Humans can contract the disease through contact with the infected animals or other humans. Foods contaminated with EHEC are frequently the vehicle (meat and raw milk). Studies have now shown that wild-living animals also excrete EHEC and that meat from them is contaminated, too. "Meat from wild-living animals is now a more important source of EHEC infection than beef", says Professor Dr. Dr. Andreas Hensel, President of the Federal Institute of Risk Assessment (BfR). This is the conclusion drawn from the results of a survey by the National Reference Laboratory for the Epidemiology of Zoonoses within BfR which monitored the development of foodborne infections. A research project by the National Reference Laboratory for Escherichia coli within BfR now aims to clarify on the one hand whether wild-living animals are an original reservoir of EHEC, infect livestock and then indirectly humans who come into contact with the infected livestock. On the other hand, the EHEC pathogens in meat from wild-living animals may also directly trigger infections in humans. Further studies are to examine whether the frequent detection of EHEC in meat samples from wild-living animals can be traced back to a lack of hygiene during meat processing or whether the zoonotic agent has a particularly high incidence in wild-living animals.

Enterohaemorrhagic Escherichia coli (EHEC) bacteria can cause severe infections in humans, in some cases bloody diarrhoea down to renal failure. The severe disease symptoms are triggered by strong cell toxins which produce EHEC bacteria, Shiga toxins. People normally contract the infection from the meat or raw milk from infected animals or through direct contact with the infected animals. Since 2001 approximately 1,100 cases of human EHEC infections have been recorded annually in conjunction with mandatory reporting in Germany. This corresponds to 1.4 cases per 100,000 inhabitants. Up to now, beef was deemed to be the main source of infection.

Surveys by the National Reference Laboratory for the Epidemiology of Zoonoses within BfR have now painted a different picture: in 2002 three percent of the meat samples from wild-living animals were contaminated with EHEC. By 2005 this number had climbed to 14.8 percent. The proportion of contaminated samples of meat from wild-living animals was thus considerably higher than that of beef during this period. According to the available data and information from other scientific institutions, wild-living animals have been underestimated up to now as a reservoir for EHEC. The same applies to meat from wild-living animals as a possible source of human EHEC infections.

In recent years the National Reference Laboratory for Escherichia coli (NRL-E. coli) within BfR has been sent more and more EHEC isolates from meat samples of wild-living animals for typing and virulence identification. Up to now, the bacteria have not been examined in a comprehensive manner to determine the periods within which they can trigger disease symptoms in humans and the severity of the course of the disease. For this, it is necessary to type the Shiga toxin produced by the bacteria and to take bacterial colonisation factors into account. A study of this nature is one of the main components of a new research project of the National Reference Laboratory E. coli within BfR. The results of the first phase of this project already point to the major potential of wild-living animals and meat from them as a possible source of human EHEC infections. This is because certain EHEC types have been detected which are known to be zoonotic agents of severe diseases in humans (O103:H2, O128:H2, O26:H11).

This research project will compare the EHEC strains isolated from meat from wild-living animals, pets and humans in order to assess the importance of wild-living animals and meat products from them as the source of human EHEC infections on the one hand and, on the other, to assess them as possible transmitters of EHEC to livestock and indirectly to humans. Final studies are to clarify whether the high incidence of bacterial contamination with EHEC in meat samples from wild-living animals is linked to a lack of hygiene during meat production or whether the zoonotic agents are present to a disproportionately frequent degree in wild-living animals.

Based on the results obtained, BfR would like to formulate specific hygiene recommendations for manufacturers and food control agencies that would help to prevent dangerous EHEC infections in humans.