Identical strains of Borrelia hermsii in mammal and bird.
To investigate the distribution and prevalence of B. hermsii , during the summer of 2008, we began a study at Flathead Lake, Lake County, Montana, USA, where 9 persons have contracted relapsing fever since 2002 (3-5). A blood smear from 1 pine squirrel (Tamiasciurus hudsonicus) captured July 9 at Yellow Bay on the east shore of the lake (elevation 887 m; geographic coordinates 47[degrees]52'35"N, 114[degrees]01'54"W) contained spirochetes detected when stained with Giemsa and examined by microscopy (600x brightfield with oil immersion). Whole blood from the squirrel contained live spirochetes visible by dark-field microscopy, and ~50 [micro]L of this blood was injected intraperitoneally into a laboratory mouse. The next day, a few spirochetes were observed in the peripheral blood of the mouse, and during the next 3 days, the density of spirochetes increased. We used intracardiac puncture to collect blood from the mouse for spirochete isolation in BSK-H medium (Sigma-Aldrich, St Louis, MO, USA) and for analysis by PCR and DNA sequencing of multiple bacterial loci as described elsewhere (4,6).
The spirochetes observed in the squirrel's blood failed to grow in BSK-H medium after passage in the laboratory mouse; however, we acquired DNA sequences from infected squirrel and mouse blood from PCR amplicons for 6 spirochete loci including 16S rDNA, flaB, gyrB, glpQ, IGS, and vtp. Sequences for the loci were each aligned with homologous sequences from other borrelia in our collection, and each locus grouped the spirochete within the 2 genomic groups of B. hermsii described previously (4,6). The unique squirrel spirochete differed from all other B. hermsii identified in our previous studies; deep branches in each phylogram grouped the spirochete more closely with B. hermsii genomic group I than with genomic group II (data not shown).
Next, we compared the sequences from the squirrel spirochete with those available in the National Center for Biotechnology Information database (www.ncbi.nlm.nih.gov), including those sequences reported for the spirochete found in the spotted owl (AY515269.1, AF116903.1, AF116904.1) (1,2). The 3 trimmed and aligned sequences for the 16S rDNA (1,290 bases), flaB (467 bases), and IGS (665 bases) from the squirrel spirochete were identical to those of the owl spirochete; no base differences were found among the 2,422 bases compared. We also examined DNA extracted from the spotted owl's liver during the first investigation (1) (provided by Alan G. Barbour). We successfully PCR amplified most of the 16S rDNA and the complete flaB, gyrB, glpQ, and vtp genes from the owl spirochete DNA and determined their sequences. The complete sequences of the first 4 loci from the owl and squirrel spirochetes were identical and differed from all other B. hermsii sequences. A phylogram of the concatenated sequences totaling 5,188 bases demonstrated that the owl and pine squirrel spirochetes were identical and were divergent members of B. hermsii genomic group I (Figure).
Finding the same strain of B. hermsii, separated by [approximately equal to] 525 km, in a pine squirrel and a spotted owl demonstrates a broader geographic distribution and host range for this spirochete than what could have been envisaged previously. The possible role of birds as hosts for the vector Ornithodoros hermsi ticks has been demonstrated elsewhere (4). Given the ecologic overlap of pine squirrels and coniferous forest-dwelling birds, we believe that the previous finding of the infected spotted owl is likely not an isolated event. Instead, it may represent a tick-spirochete cycle for B. hermsii that includes a broader host range for this group of relapsing fever spirochetes than previously appreciated.
We thank Jake Beldsoe and Michaela Ponce for their help in the field, Colleen Miller for arranging all travel, Kerry Foresman for advice and equipment, and staff of the University of Montana Flathead Lake Biological Station.
This work was supported by the Division of Intramural Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health.
Robert J. Fischer, Tammi L. Johnson, Sandra J. Raffel, and Tom G. Schwan
Author affiliations: National Institutes of Health, Hamilton, Montana, USA (R.J. Fischer, T.L. Johnson, S.J. Raffel, T.G. Schwan); and The University of Montana, Missoula, Montana, USA (T.L. Johnson)
(1.) Thomas NJ, Bunikis J, Barbour AG, Wolcott MJ. Fatal spirochetosis due to a relapsing fever-like Borrelia sp. in a northern spotted owl. J Wildl Dis. 2002;38:187-93.
(2.) Bunikis J, Tsao J, Garpmo U, Berglund J, Fish D, Barbour AG. Typing of Borrelia relapsing fever group strains. Emerg Infect Dis. 2004;10:1661-4.
(3.) Schwan TG, Policastro PF, Miller Z, Thompson RL, Damrow T, Keirans JE. Tick-borne relapsing fever caused by Borrelia hermsii, Montana. Emerg Infect Dis. 2003;9:1151-4.
(4.) Schwan TG, Raffel SJ, Schrumpf ME, Porcella SF. Diversity and distribution of Borrelia hermsii. Emerg Infect Dis. 2007;13:436-42. DOI: 10.3201/ eid1303.060958
(5.) Uhlmann EJ, Seed PC, Schwan TG, Storch GA. Polymerase chain reaction of tick-borne relapsing fever caused by Borrelia hermsii. Pediatr Infect Dis J. 2007;26:267-9. DOI: 10.1097/01. inf.0000254392.99545.69
(6.) Porcella SF, Raffel SJ, Anderson DE Jr, Gilk SD, Bono JL, Schrumpf ME, et al. Variable tick protein in two genomic groups of the relapsing fever spirochete Borrelia hermsii in western North America. Infect Immun. 2005;73:6647-58. DOI: 10.1128/IAI.73.10.6647-6658.2005
Address for correspondence: Tom G. Schwan, Laboratory of Zoonotic Pathogens, Rocky Mountain Laboratories, NIAID, NIH, 903 South 4th St, Hamilton, MT 59840, USA; e-mail: firstname.lastname@example.org
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|Author:||Fischer, Robert J.; Johnson, Tammi L.; Raffel, Sandra J.; Schwan, Tom G.|
|Publication:||Emerging Infectious Diseases|
|Date:||Dec 1, 2009|
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