Shiga Toxin Genes Detected in Fecal Samples of Illinois Finisher Pigs

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(1) Background: Pigs can be another host of Shiga toxin-producing E. coli (STEC), suggesting that pork products could be a potential risk to public health. A USDA National Animal Health Monitoring System (NAHMS) study revealed that Shiga toxin genes were detected in more than half of samples nationwide but only about a quarter of samples from the state of Illinois. To characterize the presence of STEC in Illinois pigs better and to explore the discrepancy between Illinois and other swine-producing states, we increased the sampling size and collected samples in different regions of the state and in different months to detect Shiga toxin genes in Illinois finisher pigs and subtyped the Shiga toxin genes further to assess any potential risk of STEC originating from Illinois pigs to human health. (2) Methods: Fecal samples were collected from 471 Illinois finisher pigs at different locations from October 2021 to September 2022. DNA samples were extracted from individual fecal samples and PCR-tested for Shiga toxin genes (stx1, stx2) and then toxin subtypes (stx2a, stx2c, stx2d, and stx2e). (3) Results: The data showed that the stx2 gene was detected in 61% of the fecal samples (285/471), whereas stx1 was detected only in 0.4% of the samples (2/471). The data also indicated a lower prevalence of stx genes in the samples collected in certain cold months (36% in October and 19% in March) compared to that in those from warm months (56% to 100% from April to September). Stx2d, a subtype associated with severe human illness, was detected in 2% of the samples (10/471); in contrast, stx2e, which is expressed by E. coli strains causing diarrhea and edema disease in pigs, was the most detected (49%; 229/471). (4) Conclusions: The high prevalence of Shiga toxin genes in the fecal samples from Illinois finisher pigs suggests that Stx-positive E. coli strains circulate in Illinois pig farms. However, the highly detected stx2e-positive STEC (or enterotoxigenic E. coli, ETEC) strains are associated with diarrhea and edema disease in pigs, indicating the need for disease prevention or control for pigs but unlikely a safety concern for Illinois pork products or a major risk of human illnesses.

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