title: Escherichia coli O157:H7 infection in cows and calves in a beef cattle herd in Alberta, Canada.
abstract: Escherichia coli O157:H7 infection of cows and calves in a naturally-infected beef cattle herd in Alberta, Canada, was investigated over 2 years, encompassing two calf production cycles. In both years of the study, E. coli O157:H7 was isolated from the faeces of cows shortly after but not before parturition in late winter: 6/38 (16%) in 1996 and 13/50 (26%) in 1997. At < 1 week post-partum, 13/52 (25%) calves born in 1997 were shedding the organism. Faecal shedding of E. coli O157:H7 by cows and calves continued over the 7 weeks that they were in the calving pens, with the organism being isolated from the faeces of 2-18% of cows and 23-26% of calves during this period. Five weeks after they were moved onto a native grass pasture, all the calves and all but one cow in 1997 had ceased shedding the organism. When the calves were weaned in the fall, E. coli O157:H7 was isolated from the faeces of 0-1.5% of the calves 1 week prior to weaning and from 6-14% of the calves within 2 weeks after weaning. Parturition, calving pens and weaning appear to be important factors in maintaining E. coli O157:H7 infections in this beef cattle herd. Isolates from cows and calves during the immediate post-partum period were mostly of the same pulsed-field gel electrophoresis (PFGE) type of E. coli O157:H7. Similarly, at weaning a common PFGE type of E. coli O157:H7, which differed slightly from the post-partum PFGE type, was isolated from the calves. These typing data suggest a common source of infection for the animals as well as demonstrate clonal turnover of resident populations of this pathogen.
authors.affiliation: Health Canada, Animal Diseases Research Institute, Lethbridge, Alberta.
authors.forename: V P J
authors.initials: VP
authors.lastname: Gannon
authors.forename: T A
authors.initials: TA
authors.lastname: Graham
authors.forename: R
authors.initials: R
authors.lastname: King
authors.forename: P
authors.initials: P
authors.lastname: Michel
authors.forename: S
authors.initials: S
authors.lastname: Read
authors.forename: K
authors.initials: K
authors.lastname: Ziebell
authors.forename: R P
authors.initials: RP
authors.lastname: Johnson
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology*; D016521:Electrophoresis, Gel, Pulsed-Field; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000662:veterinary*; D019453:Escherichia coli O157 / Q000145:classification / Q000302:isolation & purification; D005243:Feces / Q000382:microbiology; D005260:Female; D007743:Labor, Obstetric; D008460:Meat; D011247:Pregnancy; D014886:Weaning