Up to now, the only species in the complex Borrelia burgdorferi sensu lato known to cause Lyme borreliosis in the United States has been B. burgdorferi sensu stricto. However, some atypical strains closely related to the previously designated genomic group DN127 have been isolated in the United States, mostly in California. To explore the diversity of B. burgdorferi sensu lato group DN127, we analyzed the nucleotide sequences of the rrf-rrl intergenic spacer regions from 19 atypical strains (18 from California and one from New York) and 13 North American B. burgdorferi sensu stricto strains (6 from California). The spacer region sequences from the entire B. burgdorferi sensu lato complex available in data banks were used for comparison. Phylogenetic analysis of sequences shows that the main species of the B. burgdorferi sensu lato complex (B. afzelii, B. garinii, B. andersonii,B. japonica, B. burgdorferi sensu stricto,B. valaisiana, and B. lusitaniae) each form a coherent cluster. A heterogeneous group comprising strains belonging to the previously designated group DN127 clustered separately fromB. burgdorferi sensu stricto. Within this cluster, the deep branches expressing the distances between the rrf-rrlsequences reflect a high level of divergence. This unexpected diversity contrasts with the monomorphism exhibited by B. burgdorferisensu stricto. To clarify the taxonomic status of this highly heterogeneous group, analysis of the rrs sequences of selected strains chosen from deeply separated branches was performed. The results show that these strains significantly diverge at a level that is compatible with several distinct genomic groups. We conclude that the taxonomy and phylogeny of North American B. burgdorferi sensu lato should be reevaluated. For now, we propose that the genomic group DN127 should be referred to as a new species,B. bissettii sp. nov., and that other related but distinct strains, which require further characterization, be referred to asBorrelia spp.

The phylogenetic relationships of 20 relapsing fever (RF) Borrelia spp. were estimated on the basis of the sequences of rrs genes. Complete sequences were aligned and compared with previously published sequences, and the similarity values were found to be 97.7 to 99.9%. Phylogenetic trees were constructed by using the three neighbor-joining, maximum-parsimony, and maximum-likelihood methods. The results of the comparative phylogenetic analysis divided the RF Borrelia spp. into three major clusters. One cluster included Borrelia crocidurae, Borrelia duttonii, Borrelia recurrentis, and Borrelia hispanica. Another cluster comprised tow main branches with Borrelia coriaceae, Borrelia lonestari, and Borrelia miyamotoi on one side and Borrelia parkeri, Borrelia turicatae, and Borrelia hermsii on the other side. Borrelia anserina constituted the third cluster. The phylogenetic position of Borrelia persica was more uncertain. These results suggested that the taxonomy of these spirochetes should be revised. To overcome the problems of culturing the spirochetes, RF Borrelia primers were defined. Following PCR amplification of the rrs gene, restriction length fragment polymorphism could be used to distinguish between RF Borrelia strains.

This is the first report on the isolation of Lyme diseaseBorrelia from seabirds on the Faeroe Islands and the characteristics of its enzootic cycle. The major components of theBorrelia cycle include the puffin (Fratercula arctica) as the reservoir and Ixodes uriae as the vector. The importance of this cycle and its impact on the spread of human Lyme borreliosis have not yet been established.Borrelia spirochetes isolated from 2 of 102 sampled puffins were compared to the borreliae previously obtained from seabird ticks,I. uriae. The rrf-rrl intergenic spacer and the rrs and the ospC genes were sequenced and a series of phylogenetic trees were constructed. Sequence data and restriction fragment length polymorphism analysis grouped the strains together with Borrelia garinii. In a seroepidemiological survey performed with residents involved in puffin hunting on the Faeroe Islands, 3 of 81 serum samples were found to be positive by two commonly used clinical tests: a flagellin-based enzyme-linked immunosorbent assay (ELISA) and Western blotting. These three positive serum samples also had high optical density values in a whole-cell ELISA. The finding of seropositive Faeroe Islanders who are regularly exposed to I. uriae indicate that there may be a transfer of B. garinii by this tick species to humans.

Among the three main species of Borrelia burgdorferi sensu lato associated with Lyme borreliosis, B. burgdorferi sensu stricto (B. burgdorferi) is the sole species present both in North America and in Europe, where Borrelia garinii and Borrelia afzelii also occur. The greater genetic diversity together with the greater clinical polymorphism observed in the Old World suggests that this is the birthplace of the complex B. burgdorferi sensu lato. However, the genetic proximity of some North American and European B. burgdorferi strains in quite mystifying. A previous study of the whole genome (M. Foretz, D. Postic, and G. Baranton, Int. J. Syst. Bacteriol. 47:11-18, 1997) compared the diversity of North American and European B. burgdorferi strains. To further investigate the geographical origin and the migration of B. burgdorferi, we have focused on the study of the single variable and highly adaptive gene ospC. Both approaches demonstrated the greater diversity of North American strains and the close relatedness between European strains and between some isolates from the two areas. We discuss the significance of these features and suggest that they might be evidence of the anteriority of North American B. burgdorferi strains.

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