Prevalence of Shiga toxin-producing Escherichia coli in Free-ranging Red Deer from Italian Central Alps: a two seasons survey

Background: Shiga toxin-producing Escherichia coli (STEC) are foodborne zoonotic pathogens of priority importance. Wild ruminants are increasing their density and distribution across Europe and have been identified as potential STEC carriers. We investigated STEC prevalence in free-ranging red deer (Cervus elaphus) in Stelvio National Park (Italian Alps), where a culling plan was activated to reduce their density. Methods: Feces were collected from 201 culled animals during two winter seasons (2016-2018) from three Park areas with different anthropization levels. Bacteriological analysis was performed and E. coli colonies were tested by PCR for stx genes. PCR for additional virulence factors (eaeA, ST and LT coding genes and subAB locus) were performed on STEC isolates obtained during the first season. Red deer STEC virulence gene profiles were compared with those detected in human STEC strains causing Hemolytic Uremic Syndrome (HUS) in the same period in Italy. Results: An overall 19.9% (95% CI: 14.4%-25.4%) STEC prevalence was observed. Prevalence was significantly higher in offsprings compared to yearlings and adults. Four strains harbored both stx genes, 23 and 13 possessed stx2 and stx1 only, respectively. Nine out of the 12 strains (75%) collected from the first season possessed the subAB locus. No red deer STEC isolate possessed the eaeA gene suggesting the existence of genetic differences with national HUS-associated STEC strains. Conclusions: STEC shedding was observed in red deer population during two consecutive seasons, especially in young animals and in all areas, regardless of anthropization level, suggesting a possible role of this species as STEC carrier. Our results strengthen the hypothesis that red deer may represent a carrier for LEE-negative, subAB positive STEC strains, which have been reported in human diarrheal cases. Further characterization of virulence genes asset would help to define the zoonotic potential of wildlife-associated STEC, also considering human consumption of game meat.