Shiga-toxin producing Escherichia coli (STEC) are important foodborne pathogens. Although most STEC infections in humans are attributed to beef products, outbreaks of STEC have been associated with pork products, and STEC have been isolated from swine and pork products. There is little information regarding the epidemiology of STEC on swine farms. The objectives of this project were to 1) describe the epidemiology of STEC in swine; 2) Characterize these STEC isolates and 3) Develop an infectious disease model of STEC transmission. A longitudinal study was conducted in one swine production company in the Midwest. Three separate groups of finisher pigs (10 -26 weeks of age) were included in the study. In each cohort, 50 pigs were randomly selected and individually identified with an ear tag (3 cohorts X 50 pigs = 150 total pigs). Fecal samples were collected every 2 weeks during the finishing period for a total of 8 samples per pig. STEC isolates recovered from fecal culture were serotyped (O type) and assayed for the presence or absence of the eae gene, as well as the shiga toxin gene subtype (stx gene). Ninety-eight of 150 pigs (65.3%) of pigs were detected as shedding STEC at least once during the finishing phase. The proportion of pigs positive at any one time point in any cohort ranged from 0 to 62%. The number of collections a pig was STEC positive ranged from 1 to 4 times. No STEC isolates were detected to harbor the intimin gene (eae). Nine different serogroups were identified, with O serogroup O59 being the most common (80.9% of isolates). Most isolates harbored the stx2e subtype of shiga-toxin. These results indicate that, at least on this farm, STEC is shed at relatively high incidence in finishing pigs, at rates similar to that reported in cattle. No isolates harbored the intimin gene, which is associated with severe disease in humans. Initial development of a susceptible-infected-susceptible model of STEC transmission in pigs suggest the potential for persistence of infection over time. More data on STEC shedding in swine is needed to fully understand transmission dynamics. These results provide the key initial data for understanding the epidemiology of STEC and determination of the foodborne hazard associated with STEC in swine.
Julie Funk, DVM, MS, PhD
Associate Professor
Department of Large Animal Clinical Sciences
College of Veterinary Medicine
Michigan State University
1129 Farm Lane
East Lansing, MI 48824
Phone: 517-884-2081""