title: Rapid spread of a unique strain of Pasteurella haemolytica serotype 1 among transported calves.
abstract: OBJECTIVE
  To determine the rate and mode of infectious spread of Pasteurella haemolytica among calves maintained under typical conditions during collection, transport, and the first month of feeding.
  
  
  METHODS
  101 two- to five-month-old Angus-crossbred calves.
  
  
  METHODS
  Samples obtained from cattle prior to and after they were transported to a feedlot were used for isolation and characterization of P haemolytica. Samples were also obtained from additional calves, some of which were sick, and these calves were then commingled with the transported calves for 3 days. A strain of P haemolytica that contains a rare deletion of the 4.2-kilobase streptomycin- and sulfonamide-resistance plasmid was inoculated into both palatine tonsils of 12 calves. Nasal secretions were aspirated from the ventral nasal meatus. Tonsillar wash specimens were procured. Pasteurella haemolytica organisms were quantitatively cultured and identified on the basis of colony morphology and response to specific antisera. Plasmids were isolated by an alkaline lysis procedure and identified by agarose gel electrophoresis.
  
  
  RESULTS
  A single plasmid profile was observed from P haemolytica isolated from samples obtained prior to shipment. Commingled calves were shedding P haemolytica containing each known plasmid profile. After shipment, samples contained P haemolytica isolates with each known plasmid profile. The plasmid profile of the unique P haemolytica isolate was recovered from all 12 inoculated calves and 10 other calves. Some calves simultaneously shed P haemolytica isolates with differing plasmid profiles.
  
  
  CONCLUSIONS
  Pasteurella haemolytica serotype 1 was horizontally transmitted among calves within days of commingling, which continued after calves were transported to a feedlot.
authors.affiliation: National Animal Disease Center, USDA, ARS, Ames, IA 50010, USA.
authors.forename: R E
authors.initials: RE
authors.lastname: Briggs
authors.forename: G H
authors.initials: GH
authors.lastname: Frank
authors.forename: C W
authors.initials: CW
authors.lastname: Purdy
authors.forename: E S
authors.initials: ES
authors.lastname: Zehr
authors.forename: R W
authors.initials: RW
authors.lastname: Loan
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases; D004352:Drug Resistance, Microbial / Q000235:genetics; D017353:Gene Deletion; D016978:Mannheimia haemolytica / Q000145:classification / Q000235:genetics; D009297:Nasal Mucosa / Q000382:microbiology; D014066:Palatine Tonsil / Q000382:microbiology; D010326:Pasteurella Infections / Q000635:transmission / Q000662:veterinary*; D011815:R Factors; D013307:Streptomycin; D013449:Sulfonamides; D014186:Transportation
chemical_list: D013449:Sulfonamides; D013307:Streptomycin