Tick-borne relapsing fever in British Columbia, Canada: first isolation of Borrelia hermsii.

The spirochete that causes tick-borne relapsing fever, Borrelia hermsii, was isolated in pure culture during 1995 and 1996 from three acutely ill human patients infected in southern British Columbia, Canada. The geographic area of exposure is a known focus of this disease dating back to 1930 when the first case was recognized in a human. Analyses of plasmid DNA, protein profiles, and reactivity with a species-specific monoclonal antibody identified the new isolates of spirochetes as B. hermsii, all of which were most similar to an isolate of this spirochete from northern California described previously. These are the first reported isolates of B. hermsii from Canada.