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Ahead of Print -Tickborne Relapsing Fever, Bitterroot Valley, Montana, USA - Volume 21, Number 2—February 2015 - Emerging Infectious Disease journal - CDC

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Ahead of Print -Tickborne Relapsing Fever, Bitterroot Valley, Montana, USA - Volume 21, Number 2—February 2015 - Emerging Infectious Disease journal - CDC

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Volume 21, Number 2—February 2015


Tickborne Relapsing Fever, Bitterroot Valley, Montana, USA

Joshua Christensen, Robert J. Fischer, Brandi N. McCoy, Sandra J. Raffel, and Tom G. SchwanComments to Author 
Author affiliations: St. Patrick Hospital, Missoula, Montana, USA (J. Christensen)University of Montana College of Health Professionals and Biomedical Sciences, Missoula (J. Christensen)National Institute of Allergy and Infectious Diseases, Hamilton, Montana, USA (R.J. Fischer, B.N. McCoy, S.J. Raffel, T.G. Schwan)


In July 2013, a resident of the Bitterroot Valley in western Montana, USA, contracted tickborne relapsing fever caused by an infection with the spirochete Borrelia hermsii. The patient’s travel history and activities before onset of illness indicated a possible exposure on his residential property on the eastern side of the valley. An onsite investigation of the potential exposure site found the vector, Ornithodoros hermsi ticks, and 1 chipmunk infected with spirochetes, which on the basis of multilocus sequence typing were identical to the spirochete isolated from the patient. Field studies in other locations found additional serologic evidence and an infected tick that demonstrated a wider distribution of spirochetes circulating among the small mammal populations. Our study demonstrates that this area of Montana represents a previously unrecognized focus of relapsing fever and poses a risk for persons of acquiring this tickborne disease.
Seminal research on tickborne diseases of humans in North America began more than a century ago with the discovery in 1906 that an illness locally called black measles, which affected persons in the Bitterroot Valley of western Montana, USA, resulted from the bite of a bacteria-infected Rocky Mountain wood tick (1,2). What soon followed was the establishment of a multidisciplinary public health program to control this newly identified disease, now called Rocky Mountain spotted fever, which was caused by Rickettsia rickettsii, and a search was conducted for other diseases in nature that resulted from the bite of pathogen-infected ticks. These programs were based at a newly funded state laboratory in Hamilton in the Bitterroot Valley, a facility that was soon incorporated into the US Public Health Service and is now the Rocky Mountain Laboratories (RML) of the National Institute of Allergy and Infectious Diseases.
One of the many diseases studied at the RML since the early 1930s has been tickborne relapsing fever (RML, unpub. data) (3,4). In North America, this zoonosis is associated with 3 species of spirochetes, but most human cases are caused by Borrelia hermsii, which is found in scattered foci in the western United States and southern British Columbia, Canada (5,6). The specific vector of this spirochete is the Ornithodoros hermsi tick (7), which is found in higher-elevation coniferous forests where its preferred rodent hosts, primarily squirrels and chipmunks, are also found (6). In spite of the many decades of intensive research on ticks and tickborne diseases in the Bitterroot Valley, the tick O. hermsi, the spirochete B. hermsii, or an autochthonous human case of relapsing fever has not been observed in this region of Montana, until now. We report a case of tickborne relapsing fever in a person in this region.

Thumbnail of A) Spirochetes in blood smear of a 55-year-old man with tickborne relapsing fever, Bitterroot Valley, Montana, USA (Giemsa stain). Erythrocyte diameters are ≈6–8 µm. B) Spirochetes in blood smear of the patient visualized by indirect immunofluorescent antibody staining with mouse monoclonal antibody H9724 and goat anti-mouse antibody conjugated with fluorescein isothiocyanate (original magnification ×1,000).
Figure 1. A) Spirochetes in blood smear of a 55-year-old man with tickborne relapsing fever, Bitterroot Valley, Montana, USA (Giemsa stain). Erythrocyte diameters are ≈6–8 µm. B) Spirochetes in blood smear of the...
Dr. Christensen is an infectious disease specialist at St. Patrick’s Hospital and the University of Montana, Missoula, Montana. His research interests include zoonotic and mycobacterial infections.


We thank Charles Nead for detecting the spirochetes in the blood smear; Karra Markley for providing the image of the Giemsa-stained blood smear; George Risi, David Safronetz, and Joe Hinnebusch for reviewing the manuscript; and Gary Hettrick for assistance with the figures.
This study was supported in part by the Intramural Research Program, National Institute of Allergy and Infectious Diseases, National Institutes of Health.


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Suggested citation for this article: Christensen J, Fischer RJ, McCoy BN, Raffel SJ, Schwan TG. Tickborne relapsing fever, Bitterroot Valley, Montana, USA. Emerg Infect Dis. 2015 Feb [date cited]. http://dx.doi.org/10.3201/eid2102.141276
DOI: 10.3201/eid2102.141276

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