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Pathogen

Escherichia coli is a bacterium that is commonly found in the lower intestine of animals. Nonpathogenic, intestinal Escherichia coli (commensal E. coli) support the physiological intestinal balance of the host, whereas pathogenic E. coli with typical virulence factor gene profiles can cause severe outbreaks of different diseases (e.g. Edema (Oedema) Disease, diarrhea).

Edema Disease is caused by Shigatoxin (Stx2e)

Edema (Oedema) Disease is caused by Shigatoxin (Stx2e). This toxin is produced by a specific virotype of Escherichia coli - which is named STEC (graphic). A virotype is determined by a particular combination of virulence genes. Important virulence factors encoded by EDEC are the fimbrial adhesin F18 and Shigatoxin (Stx2e).
While the E. coli encoding for Shigatoxin (Stx2e) occur worldwide, prevalence data particularly from healthy herds are rarely available. Nevertheless, a recently published longitudinal study in three US farms with healthy pigs observed a high prevalence (68.3%) of Shigatoxin-encoding Escherichia coli (STEC) in pigs raised for pork production. The usual detection rate of Stx2e in cases with clinical signs suspicious for ED is around 20% up to 60%.

Escherichia coli - infections in weaned pigs

The Shigatoxin has an A and B subunit

Mainly affected age group by Shigatoxin

The mainly affected production stages are recently weaned pigs, pigs during nursery and younger finishing pigs.
F18 is one of the well known adhesion factors, which enables E. coli the attachment to the intestinal mucosa. Stx2e encoding strains may possess either the fimbrial variant F18ab or F18ac.
Susceptibility to colonization and to infection with an E. coli F18 strain develops around weaning and is dependent on the presence of the porcine intestinal F18 receptor (F18R) genotype.
The expression of F18R is age-dependent and begins at around three weeks of age.
Torrison at al. (graphic) described the main stages of pigs life where E. coli encoding for Stx2e are detected with a peak in the weeks seven to nine. This corresponds with the experience of IDT in many countries worldwide.
Remarkably Stx2e can be detected also in later production stages . If so, it is generally the origin of serious clinical signs, increased mortality and impaired performance.

Yet F18 is not detectable in every case of E. coli encoding for Stx2e (up to 20%). The relevance of these particular E. coli (without the F18 but with Stx2e) is nevertheless given, as they have been isolated as only pathogen from cases with severe clinical signs.

Prevalence - when do I find STEC/VTEC?

Shiga toxin 2e (Stx2e)

Study results where to find STEC

J.Torrison, K. Rossow, S. Oliveira
University of Minnesota Veterinary Diagnostic Laboratory 2011