Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 7, 1999
Publication Date: N/A
Technical Abstract: Environmental manipulations, such as cleaning of livestock pens and water sources, have been proposed as preharvest interventions against bovine EHEC O157 infections. From a cohort of 200 feedlot beef cattle, 60 steers were identified on d -7 as natural fecal shedders of EHEC O157. The 60 steers were randomly assigned to 4 treatment groups (TGs) (with 5 replicates/group) defined by 2 variables: penning (penned as individual or in groups of 5); & cleaning (pen cleaned & disinfected twice/wk or pen not cleaned). On d 0, steers were moved to 20 pens in an isolated cement- floored open-front building with an empty pen kept between each treatment pen. Cattle were tested for EHEC O157 fecal shedding once/wk for 6 wks. On d 0, 53 of 60 steers (88.3%) in all 4 TGs were fecal shedding EHEC O157. Between d 7 & 35, large fluctuations in fecal shedding occurred in all groups and replicates. However, overall trend was towards lower fecal shedding, so that by d 42, only 8 cattle (13.3%) were fecal EHEC O157 shedders. There was no detectable effect of pen cleaning or individual vs group housing on this outcome. Furthermore, the shedding status of individual cattle changed rapidly from wk to wk. These results suggest that 1) pen cleaning does not effect EHEC O157 fecal shedding in cattle; 2) fecal EHEC O157 shedding is an unstable bovine phenotype over time at the individual level, & 3) EHEC O157 shedding may decrease greatly over time even from very high initial prevalence levels if cattle are kept in small groups & not mixed.