Investigation of the spread of Brucella canis via the U.S. interstate dog trade

Objectives: The aim of this study was to illustrate and help address a growing need for regulatory or molecular tools to track and control the spread of canine brucellosis. Our study objectives were to first characterize Brucella canis outbreaks in Wisconsin kennels in the context of the dog trade in the USA, and then to identify a molecular technique that may be useful for strain differentiation of B. canis isolates. Methods: Wisconsin Veterinary Diagnostic Laboratory (WVDL) B. canis serology data from 1995 to 2005 were reviewed, three canine brucellosis outbreaks in Wisconsin dog kennels were investigated, and eight B. canis isolates recovered from Wisconsin outbreaks and kennels in Missouri and Arkansas and four isolates received from outside sources were subjected to ribotyping, pulsed-field gel electrophoresis (PFGE), outer membrane protein analysis (OMPA), and cellular fatty acid profiling (CFAP). Results: WVDL has received increasing numbers of B. canis positive samples from Wisconsin kennels, and Wisconsin outbreaks are associated with the interstate dog trade. All of the B. canis isolates we examined were genetically homogenous and as such could not be differentiated by ribotyping, PFGE and OMPA. However, dendrogram analysis of CFAP divided the isolates into two groups, indicating that CFAP methyl ester analysis has discriminatory power. Conclusions: CFAP methyl ester analysis has promise as a tool for epidemiological tracing of B. canis outbreaks and will be useful in comparison studies as isolation of B. canis continues to expand globally.