Use of DNA analysis of Pasteurella haemolytica biotype T isolates to monitor transmission in bighorn sheep (Ovis canadensis canadensis)

Pneumonia has been identified as a major cause of poor lamb survival in indigenous herds of Rocky Mountain bighorn sheep (Ovis canadensis canadensis) in central Idaho. Pasteurella haemolytica was isolated from five adult Rocky Mountain bighorn ewes captured from a free-ranging herd in central Idaho. The lambs from two of these ewes delivered by cesarean section were free of P. haemolytica until 40 days of age and after repeated contact with their dams. The lambs subsequently developed signs of pneumonia, and P. haemolytica was isolated from nasal, pharyngeal, and transtracheal wash samples from each lamb. All P. haemolytica biotype T isolates from the ewes and lambs, as well as those from a 9-month-old lamb of the same herd from which samples for culture were obtained 2 years earlier, were subjected to HaeIII restriction enzyme analysis (REA) and ribotyping. Two ribotypes and seven REA patterns were visually distinguishable by these procedures. Similarity coefficients (SAB) of 0.09 to 0.95 were calculated for the seven REA patterns. The REA patterns of the isolates from the lambs were identical (SAB = 1.0). The isolates from the lambs also had SAB values of 1.0, which was indicative of identity with one of the seven isolates cultured from the ewes at the time of capture and with the organism isolated from the 9-month-old lamb. These procedures have the discriminatory capabilities necessary to monitor the transmission of specific strains of bacteria within and between animal populations.