Identical Strains of Borrelia hermsii in Mammal and Bird | CDC EID

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Volume 15, Number 12–December 2009
Letter
Identical Strains of Borrelia hermsii in Mammal and Bird
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)

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To the Editor: On August 5, 1994, a northern spotted owl, Strix occidentalis caurina, was found dead in Kittitas County, Washington, USA (1). A thorough investigation and necropsy identified the probable cause of death to be a spirochete infection. The organisms were seen in sections of the bird's liver with use of modified Steiner silver stain and microscopy. DNA was extracted from the infected liver, and PCR–DNA sequencing of the 16S ribosomal RNA (rRNA) locus identified the bacterium as a relapsing fever spirochete related most closely to Borrelia hermsii (1). The lack of additional data surrounding this case precluded Thomas et al. from concluding that this spirochete infecting the owl was B. hermsii. Yet, in a subsequent analysis using the intergenic spacer region, the owl spirochete was included with isolates of B. hermsii (2).

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°52´35´´N, 114°01´54´´W) contained spirochetes detected when stained with Giemsa and examined by microscopy (600× brightfield with oil immersion). Whole blood from the squirrel contained live spirochetes visible by dark-field microscopy, and ≈50 μL 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).

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