The genetic polymorphism of Borrelia burgdorferi and Borrelia afzelii, two species that cause Lyme borreliosis, was estimated by sequence typing of four loci: the rrs-rrlA intergenic spacer (IGS) and the outer-membrane-protein gene p66 on the chromosome, and the outer-membrane-protein genes ospA and ospC on plasmids. The major sources of DNA for PCR amplification and sequencing were samples of the B. burgdorferi tick vector Ixodes scapularis, collected at a field site in an endemic region of the north-eastern United States, and the B. afzelii vector Ixodes ricinus, collected at a similar site in southern Sweden. The sequences were compared with those of reference strains and skin biopsy isolates, as well as database sequences. For B. burgdorferi, 10-13 alleles for each of the 4 loci, and a total of 9 distinct clonal lineages with linkage of all 4 loci, were found. For B. afzelii, 2 loci, ospC and IGS, were examined, and 11 IGS genotypes, 12 ospC alleles, and a total of 9 linkage groups were identified. The genetic variants of B. burgdorferi and B. afzelii among samples from the field sites accounted for the greater part of the genetic diversity previously reported from larger areas of the north-eastern United States and central and northern Europe. Although ospC alleles of both species had higher nucleotide diversity than other loci, the ospC locus showed evidence of intragenic recombination and was unsuitable for phylogenetic inference. In contrast, there was no detectable recombination at the IGS locus of B. burgdorferi. Moreover, beyond the signature nucleotides that specified 10 IGS genotypes, there were additional nucleotide polymorphisms that defined a total of 24 subtypes. Maximum-likelihood and parsimony cladograms of B. burgdorferi aligned IGS sequences revealed the subtype sequences to be terminal branches of clades, and the existence of at least three monophyletic lineages within B. burgdorferi. It is concluded that B. burgdorferi and B. afzelii have greater genetic diversity than had previously been estimated, and that the IGS locus alone is sufficient for strain typing and phylogenetic studies.3These two authors contributed equally to the study.Abbreviations: IGS, intergenic spacer; LB, Lyme borreliosis; MLST, multilocus sequence typing.The GenBank accession numbers for the sequences reported in this paper are: AY275189-AY275212 for B. burgdorferi rrs-rrlA IGS types 1-9 and nt10, as well as subtypes of each IGS genotype; AY363692-AY363702 for B. afzelii rrs-rrlA IGS types 1-9, and nt10 and nt11; AY275213-AY275225 for B. burgdorferi ospC types 1-9 and nt10-nt13; and AY363710-AY363721 for B. afzelii ospC types 1-6, 7A, 7B, 8, 9, nt10 and nt11.Tables showing pairwise nucleotide and amino acid distances between ospC alleles and OspC proteins of both B. burgdorferi and B. afzelii are available as supplementary data with the online version of this paper at http://mic.sgmjournals.org.

Birds host vector ticks and Borrelia species and vary in effectiveness as reservoirs.

During spring and autumn 2001, we screened 13,260 migrating birds at Ottenby Bird Observatory, Sweden, and found 3.4% were infested with ticks. Four birds, each a different passerine species, carried tickborne encephalitis virus (TBEV)–infected ticks (Ixodes ricinus). Migrating birds may play a role in the geographic dispersal of TBEV-infected ticks.

Partial sequencing of the 16S-23S rDNA intergenic spacer showed two to four genotypes each for Borrelia hermsii and B. turicatae , both relapsing fever agents transmitted by argasid ticks, and for B. miyamotoi and B. lonestari , transmitted by ixodid ticks. Field surveys of Ixodes ticks in Connecticut and Sweden showed limited local diversity for B. miyamotoi .