BORRELIA-BURGDORFERI IS CLONAL - IMPLICATIONS FOR TAXONOMY AND VACCINE DEVELOPMENT

The chromosomal genes fla and p93 and the ospA gene from a linear plas mid were sequenced from up to 15 isolates of Borrelia burgdorferi, whi ch causes Lyme borreliosis in man. Comparison of the gene trees provid es no evidence for genetic exchange between chromosomal genes, suggest ing B. burgdorferi is strictly clonal. Comparison of the chromosomal g ene trees with that of the plasmid-encoded ospA reveals that plasmid t ransfer between clones is rare. Evidence for intragenic recombination was found in only a single ospA allele. The analysis reveals three com mon clones and a number of rare clones that are so highly divergent th at vaccines developed against one are unlikely to provide immunity to organisms from others. Consequently, an understanding of the geographi c and genetic variability of B. burgdorferi will prove essential for t he development of effective vaccines and programs for control. While t he major clones might be regarded as different species, the clonal pop ulation structure, the geographic localization, and the widespread inc idence of Lyme disease suggest that B. burgdorferi should remain the n ame for the entire array of organisms.