Science in Society Archive

E. coli Outbreak not Exclusive to Humans

Erroneous claim of EFSA exposes the underlying inadequacies of current surveillance systems especially in the face of rampant horizontal gene transfer and recombination. Prof. J. Cummins

The Escherichia coli O104:H4 outbreak that began in Germany in May 2011 is declared “almost over”. According to the World Health Organization update on 22 July based on new, more stringent clinical criteria, 4075 cases were confirmed including 908 cases of HUS (haemolytic uremic syndrome) and 50 deaths in 14 European countries plus Canada and USA [1]. The vast majority of cases were in Germany.

E. coli O104:H4 is a new strain more threatening than the E. coli O157:H7 that has killed many in North America and Europe during the past thirty years, and is a recombinant of two pathogenic types: Shiga toxin (Stx) E. coli and  enteroaggregative E. coli (EAEC) [2, 3] (Escherichia coli O104:H4 A Newly Emergent Pathogen, and How Genetic Engineering May Have Created E. Coli Outbreak, SiS 51).

EAEC is a recognized cause of diarrhoea in children in developing countries, and has been particularly associated with persistent diarrhoea, a major cause of illness and death. Recent outbreaks implicate EAEC in foodborne illnesses in industrialized countries. EAEC bacterial cells form biofilms that adhere to the intestinal mucosa and elaborate enterotoxins and cytotoxins causing diarrhoea and mucosal damage. EAE’s ability to stimulate the release of inflammatory mediators may also play a role in intestinal illness. The O104:H4 strain was mostly likely created through mating between male and female E. coli that produced new and deadly recombinants, or by repeated horizontal gene transfer [2, 3].

Inaccurate advice from EFSA on EAEC being exclusive to humans

The European Food Safety Authority (EFSA) published a report [4] giving “Urgent advice on the public health risk of Shiga-toxin producing Escherichia coli in fresh vegetables” soon after the outbreak. The report included and extensive review of the genetics of the newly emergent strain O104:H4 and its parent EAEC, and  claimed that “EAEC have rarely been identified in animals, suggesting that they are not zoonotic, but exclusive to humans as a pathogen….The German outbreak strain seems to share virulence characteristics of STEC and EAEC strains. STEC strains usually have an animal reservoir, while EAEC have a human reservoir.”  The EFSA report cited a single reference to a 2004 study - “Absence of enteroaggregative Escherichia coli in farmed animals in Great Britain” [5] – to back up its claim, implying that farm animals and their manure are free of EAEC and only direct human contact is likely to spread EAEC and O104:H4.

However, many peer reviewed publications report that EAEC strains are important animal pathogens, which can be readily modified to infect humans. For example, a recent study  found both neonatal and weaned mice provide models for a vicious cycle of EAEC infection that causes stuntinig and under nutrition, thus worsening infection [6].  EAEC bearing the  EAST 1 toxin gene was found in farm animals including swine, cattle and sheep [7].  EAEC were isolated from the faeces of individuals with diarrhoea including humans, calves, piglets, and horses. The E. coli from humans differed significantly in traits and virulence factors from those in the animals, and on that basis, the animal strains were deemed unlikely to cause human infections [8]. However, the microbial ecology of the faeces of calves, horses and piglets differ from each other and that of human faeces. Most significantly, human EAEC causes diarrhoea and death in animals and animal EAEC may form biofilms on human cells.

Two strains of EAEC of human origin fed to gnotobiotic (germ free) piglets caused diarrhoea or death of the majority [9].  The presence of the astA gene responsible for production of EAEC heat-stable enterotoxin 1 (EAST1) was examined in E. coli strains isolated from pigs with postweaning diarrhoea; 46 percent of the pigs carried the markers for  EAEC [10]. EAST1 was detected in cattle with septicaemia or diarrhoea [11]. A total of 720 E. coli strains isolated from diarrhoeic piglets on 756 swine farms were screened for the presence of the EAST 1 enterotoxin; and 22.7 percent of the 720 E. coli isolates carried genes for EAEC (including  EAST 1) [12]. EAST was found in 17.3 percent of the field strains isolated from internal organs of poultry that died from E. coli infections [13].  An EAEC  of sera type O92:H33 was found in a 2008 outbreak of foodborne gastroenteritis  in an Italian holiday resort; a cheese made from sheep’s milk was implicated in the outbreak [14]. These examples are representative of a large body of scientific studies showing the presence of EAEC  in animals or their faeces.

Contaminated fenugreek seeds to blame?

On 28 June 2011, 15 cases of HUS were identified in the Gironde, south-west France. Investigations suggest the vehicle of transmission was sprouts, served at an event in Bègles on 8 June 2011. A strain of Shiga toxin-producing E. coli O104:H4 was isolated from five cases, and found to be genetically related to the E. coli O104:H4 outbreak in Germany, and shares the same virulence and antimicrobial resistance characteristics [15]. According to EFSA, the comparison of the back tracing information from the French and German outbreaks led to the conclusion that lot # 48088 of fenugreek seeds imported by the Importer from Egypt is the most likely common link. Fenugreek is used both as a herb (the leaves) and as a spice (the seed). The plant is cultivated worldwide as a semi-arid crop and is a common ingredient in many curries. The findings of the EFSA study are consistent with other investigations conducted thus far. Specifically, it supports the hypothesis that the outbreaks in Germany and France are linked through the import of fenugreek seeds, which became contaminated with E coli O104:H4 at some point prior to leaving the Importer, probably with faecal material of human origin.  Typically such contamination could occur during production at the farm level. The thus far negative test results from the microbiological tests carried out on seeds (and sprouts) cannot be interpreted as proof that a batch is not contaminated with the E coli O104:H4 according to EFSA [16].

Asymptomatic carriers of O104:H4

After four students in Germany at the Kreis Paderborn school were sickened by E. coli O104:H4 infections, tests indicated that 22 out of 30 children at the same school were also infected with the outbreak strain but had no symptoms. Asymptomatic E. coli O104:H4 infection was also found in three kitchen workers at the school in Kreis Paderborn, four child care employees at four different day-care centres in the district and three workers at the catering company that supplied school food. According to the European Centre for Disease Prevention and Control, this [17, 18] “resulted most likely from foodborne” transmission rather than from person-to-person transmission,  a “significant proportion of asymptomatic carriers” of the pathogen “represent a risk for new foodborne outbreaks,” in particular if those carriers are food handlers. While new cases may arise as the result of other contaminated foods or contaminated seeds still in circulation, the “main reason for concern at this stage” in the outbreak, is evidence from clusters like the one at the Kreis Paderborn school of “a substantial proportion of subclinical infections.”

Asymptomatic infection is not unique to E. coli O104:H4. There are publications documenting asymptomatic infections with Shiga toxin-bearing E. coli O157 and EAEC.

E. coli O157 infected farmers of North Italy had neither intestinal symptoms at the moment of sampling nor a history of bloody diarrhoea or renal failure [19]. Asymptomatic carriers of Shiga toxin-producing E. coli in Denmark were treated with antimicrobials to allow them back to normal society and to work [20]. Faecal specimens were obtained at 3-4 monthly intervals from 349 subjects constituting a 20 percent age-stratified sample of a rural community for a period of two years. HEp-2 cell adherent E. coli were found in 210 subjects, and repeat isolations of EAEC belonging to the same serogroup were found in 12.6 percnet of children less than 12 years of age, indicating that this organism can asymptomatically colonize the intestinal tract. These children may act as a reservoir of infection for the community [21]. In an industrialized country  Switzerland, EAEC isolates were found in the specimens of 19 (10.2 percent) of 187 children with diarrhoea and in those of 3 (2.2 percent) of 137 children without diarrhoea [22].  Asymptomatic infections are well documented in the diarrhoea causing E. coli  and it is therefore no surprise to find  asymptomatic E. coli O104:H4 infection.

The existence of asymptomatic E. coli O104:H4 infections and its presence in livestock, contrary to what EFSA has reported expose the underlying inadequacies of our surveillance system for infectious diseases, especially in the light of rampant horizontal gene transfer and recombination greatly enhanced by the our regulators’ inability to control the release of transgenic DNA into the environment [3].

Article first published 01/08/11


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Todd Millions Comment left 3rd August 2011 16:04:16
Alarming-That this potential resovior of contamination was covered up.Feeeguk was a vital foarage crop in ancient times(before wintre storage of hay was developed),as as well as seed and leaves for direct human consumption,contamination of dry season forage by domestic livestock may be or become a concern. This would be a repeat of the last bse outbreak in Namerica.I personally tried very hard too get dierect info from the world's expert on these pirons about latency and testing limits.Which was like talking to a vacum,leaving me-vexed. Two years later,I learned that under the new secertly imposed security regulations,that permission to speak too me with me on the matter whould have too have come from the war criminal (unindited-yet)tony blair.Or one of his evil minions.Would it be too much too ask, more than the house of lords-too pull their heads out of there back passages and put a stop too such deadly deliberaetly engineered ignorance?