Prevalence of Escherichia coli O157:H7 in range beef calves at weaning

Abstract

This study was designed to determine the prevalence of Escherichia coli O157:H7 infection of beef calves at weaning, prior to arrival at the feedlot or mixing with cattle from other sources. Fifteen range cow-calf herds, which weaned calves in October and November, were sampled in Kansas, Missouri, Montana, Nebraska and South Dakota. Faecal culture for E. coli O157:H7 was performed and anti-O157 serum antibody titres were determined by blocking ELISA. Thirteen of the 15 herds (87%) were found to have at least one positive isolation of E. coli O157:H7 in faecal samples. Within positive herds, prevalence ranged from 1.7-20.0%, with an average of 7.4+/-6.2% S.D. of individual animals shedding E. coli O157:H7 in faeces. All herds had high prevalence of anti-O157 antibodies, ranging 63-100% of individuals within herds seropositive. This study indicates that E. coli O157:H7 infection before weaning, prior to entry into feedlots, is widespread. Furthermore, serologic evidence suggests that most calves (83%) and all herds (100%) have been exposed to E. coli O157.

From the Cover: Correlation of enterohemorrhagic Escherichia coli O157 prevalence in feces, hides, and carcasses of beef cattle during processing

“…Isolation methods and time of year are the likely reasons for the difference between the results of this study and those previously reported. In other EHEC O157 studies, immunomagnetic separation and enrichment broth selection played a key role in the isolation of the target organism (8,12,21). In the absence of a reliable ''gold standard'' for the presence of EHEC O157 in samples, it is difficult to directly compare the methods used in this study with other culture techniques (8,12,21,22).…”

“…In other EHEC O157 studies, immunomagnetic separation and enrichment broth selection played a key role in the isolation of the target organism (8,12,21). In the absence of a reliable ''gold standard'' for the presence of EHEC O157 in samples, it is difficult to directly compare the methods used in this study with other culture techniques (8,12,21,22). In addition, because operator experience can have a significant effect on the outcome obtained by different culture techniques, comparisons should be made on split samples in laboratories experienced in performing a given culture method.…”

“…Fecal samples were cultured as previously described with minor modifications (8). For each fecal sample, the distal colon was ligated and transected approximately 750 cm proximal to the rectum, before complete evisceration, and the colorectal tissues were placed in individual clean plastic bags.…”

“…However, it was noted in this study that 63 of 100 feedlots had at least one positive fecal sample, indicating widespread distribution of EHEC O157. Recent studies using improved enrichment and isolation procedures have indicated that the overall prevalence of EHEC O157 infection in cattle may be significantly higher than originally estimated (8,11,12). These studies found that peak EHEC O157 fecal shedding rates occur during summer and early fall, and they vary from a low of 0% to as high as 61% on some farms.…”

“…Cattle have been implicated as the primary reservoir of EHEC O157 (7,8). Prevalence surveys conducted on fed cattle estimated the overall fecal prevalence of EHEC O157 to be very low (7,9).…”