Diversity and distribution of Borrelia hermsii

Borrelia hermsii is the most common cause of tickborne relapsing fever in North America. DNA sequences of the 16S-23S rDNA noncoding intergenic spacer (IGS) region were determined for 37 isolates of this spirochete. These sequences distinguished the 2 genomic groups of B. hermsii identified previously with other loci. Multiple IGS genotypes were identified among isolates from an island, which suggested that birds might play a role in dispersing these spirochetes in nature. In support of this theory, all stages of the tick vector Ornithodoros hermsi fed successfully on birds in the laboratory and advanced in their life cycle. B. hermsii produced a detectable spirochetemia in 1 chicken inoculated subcutaneously. Additional work is warranted to explore the role of birds as enzootic hosts for this relapsing fever spirochete.