Epidemiological studies have demonstrated that enterohaemorrhagic strains of Escherichia coli which cause the haemolytic uremic syndrome in humans and the oedema disease in pigs more frequently produce Shiga-like toxin type II (SLT-II) than any other member of the Shiga-like toxin family.
The A and B subunit genes of the vtx2ha operon exhibited 98.6% and 95.5% DNA homology, respectively, with those of the slt-II operon encoding Shiga-like toxin II (or VT2) cloned from a strain from a patient with hemorrhagic colitis, while the A and B subunit genes of the vtx2ha operon showed 94.5% and 82.8% DNA homology, respectively, with those of the slt-IIv operon encoding a SLT-II variant cloned from a strain isolated from a pig with edema disease.