ZÜRICH, SWITZERLAND — After collecting samples of various complete-and-balanced raw meat-based pet food diets produced in Switzerland and Germany, a group of Swiss researchers found genes of Shiga toxin-producing E. coli (STEC) in more than half of the products tested, which can cause several adverse health symptoms in humans.

The study was conducted by Andrea Treier, Roger Stephan, Marc J. A. Stevens, Nicole Cernela and Magdalena Nüesch-Inderbinen (Treier et al.). An article summarizing the study was published in a 2021 issue of Microorganisms to bring awareness to health and safety risks associated with feeding raw pet foods.

STEC is a zootonic pathogenic bacteria which can cause gastrointestinal illnesses such as diarrhea, hemorrhagic colitis and hemolytic uremic syndrome (HUS) in humans, the last of which can be life-threatening, according to the report.

While STEC-related illnesses appear to be rare in companion animals, the article stated, dogs and cats can act as carriers for these pathogens and pet owners can be exposed either during feeding, handling or interaction with the pet or pet waste.

In the study, researchers collected 59 raw meat-based diets from 10 manufacturers throughout Switzerland and Germany between September 2018 and May 2020. The diets contained either pure muscle or pure organ meat, mixed muscle and organ meat, or meat supplemented with plant ingredients. Proteins included beef (represented in 17 samples), poultry (15), horse (8), lamb (6), rabbit (4), venison (4) and fish (5).

Of the 59 samples collected, 59% (35 products) tested positive for the presence of Shiga toxin genes stx1 and/or stx2, according to the report. This was found through real-time PCR testing. STECs representing 28 different strains were found in 41% of those 59 samples. Roughly 29% of those strains carried the stx2a or stx2d gene, “which are linked to STEC with high pathogenic potential,” researchers wrote.

Additionally, stx genes were found in raw meat-based diets collected from nine of the 10 manufacturers included in the sample.

“Twenty different serotypes were identified, including STEC O26:H11, O91:H10, O91:H14, O145:H28, O146:H21, and O146:H28, which are within the most common non-O157 serogroups associated with human STEC-related illnesses worldwide,” Treier et al. stated in the article. “Considering the low infectious dose and potential severity of disease manifestations, the high occurrence of STEC in RMBDs [raw meat-based diets] poses an important health risk for persons handling raw pet food and persons with close contact to pets fed on RMBDs, and is of concern in the field of public health.”

The study found there is an “overall prevalence” of 41% regarding STEC contamination, which is considerably higher than that found in raw pet diets manufactured in the United States, which is 4% according to another study published in Foodborne Pathogens and Disease in September 2014. The prevalence of STECs in Swiss and German raw pet foods in this study also exceeded the reported prevalence among raw meat dog foods produced in the United Kingdom, which is 14% according to an August 2017 report in Public Health England Publications.

“However, comparative data are still scarce, and discrepancies between results of different studies may be due to differences in the testing methodologies,” Treier et al. stated in the article. “Nevertheless, the present study provides evidence that the occurrence of STEC in RMBDs may currently be underestimated.”

Read the full article: “High Occurrence of Shiga Toxin-Producing Escherichia coli in Raw Meat-Based Diets for Companion Animals.”

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