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Host associations and genomic diversity of Borrelia hermsii in an endemic focus of tick-borne relapsing fever in western North America

BACKGROUND: An unrecognized focus of tick-borne relapsing fever caused by Borrelia hermsii was identified in 2002 when five people became infected on Wild Horse Island in Flathead Lake, Montana. The terrestrial small mammal community on the island is composed primarily of pine squirrels (Tamiasciuru...

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Autores principales: Johnson, Tammi L., Fischer, Robert J., Raffel, Sandra J., Schwan, Tom G.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: BioMed Central 2016
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5105259/
https://www.ncbi.nlm.nih.gov/pubmed/27832805
http://dx.doi.org/10.1186/s13071-016-1863-0
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author Johnson, Tammi L.
Fischer, Robert J.
Raffel, Sandra J.
Schwan, Tom G.
author_facet Johnson, Tammi L.
Fischer, Robert J.
Raffel, Sandra J.
Schwan, Tom G.
author_sort Johnson, Tammi L.
collection PubMed
description BACKGROUND: An unrecognized focus of tick-borne relapsing fever caused by Borrelia hermsii was identified in 2002 when five people became infected on Wild Horse Island in Flathead Lake, Montana. The terrestrial small mammal community on the island is composed primarily of pine squirrels (Tamiasciurus hudsonicus) and deer mice (Peromyscus maniculatus), neither of which was known as a natural host for the spirochete. Thus a 3-year study was performed to identify small mammals as hosts for B. hermsii. METHODS: Small mammals were captured alive on two island and three mainland sites, blood samples were collected and examined for spirochetes, and serological tests performed to detect anti-B. hermsii antibodies. Ornithodoros hermsi ticks were collected and fed on laboratory mice to assess infection. Genomic DNA samples from spirochetes isolated from infected mammals and ticks were analyzed by multilocus sequence typing. RESULTS: Eighteen pine squirrels and one deer mouse had detectable spirochetemias when captured, from which 12 isolates of B. hermsii were established. Most pine squirrels were seropositive, and the five species of sciurids combined had a significantly higher prevalence of seropositive animals than did the other six small mammal species captured. The greater diversity of small mammals on the mainland in contrast to the islands demonstrated that other species in addition to pine squirrels were also involved in the maintenance of B. hermsii at Flathead Lake. Ornithodoros hermsi ticks produced an additional 12 isolates of B. hermsii and multilocus sequence typing identified both genomic groups of B. hermsii described previously, and identified a new genomic subdivision. Experimental infections of deer mice with two strains of B. hermsii demonstrated that these animals were susceptible to infection with spirochetes belonging to Genomic Group II but not Genomic Group I. CONCLUSIONS: Pine squirrels are the primary hosts for the maintenance of B. hermsii on the islands in Flathead Lake, however serological evidence showed that numerous additional species are also involved on the mainland. Future studies testing the susceptibility of several small mammal species to infection with different genetic types of B. hermsii will help define their role as hosts in this and other endemic foci.
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spelling pubmed-51052592016-11-14 Host associations and genomic diversity of Borrelia hermsii in an endemic focus of tick-borne relapsing fever in western North America Johnson, Tammi L. Fischer, Robert J. Raffel, Sandra J. Schwan, Tom G. Parasit Vectors Research BACKGROUND: An unrecognized focus of tick-borne relapsing fever caused by Borrelia hermsii was identified in 2002 when five people became infected on Wild Horse Island in Flathead Lake, Montana. The terrestrial small mammal community on the island is composed primarily of pine squirrels (Tamiasciurus hudsonicus) and deer mice (Peromyscus maniculatus), neither of which was known as a natural host for the spirochete. Thus a 3-year study was performed to identify small mammals as hosts for B. hermsii. METHODS: Small mammals were captured alive on two island and three mainland sites, blood samples were collected and examined for spirochetes, and serological tests performed to detect anti-B. hermsii antibodies. Ornithodoros hermsi ticks were collected and fed on laboratory mice to assess infection. Genomic DNA samples from spirochetes isolated from infected mammals and ticks were analyzed by multilocus sequence typing. RESULTS: Eighteen pine squirrels and one deer mouse had detectable spirochetemias when captured, from which 12 isolates of B. hermsii were established. Most pine squirrels were seropositive, and the five species of sciurids combined had a significantly higher prevalence of seropositive animals than did the other six small mammal species captured. The greater diversity of small mammals on the mainland in contrast to the islands demonstrated that other species in addition to pine squirrels were also involved in the maintenance of B. hermsii at Flathead Lake. Ornithodoros hermsi ticks produced an additional 12 isolates of B. hermsii and multilocus sequence typing identified both genomic groups of B. hermsii described previously, and identified a new genomic subdivision. Experimental infections of deer mice with two strains of B. hermsii demonstrated that these animals were susceptible to infection with spirochetes belonging to Genomic Group II but not Genomic Group I. CONCLUSIONS: Pine squirrels are the primary hosts for the maintenance of B. hermsii on the islands in Flathead Lake, however serological evidence showed that numerous additional species are also involved on the mainland. Future studies testing the susceptibility of several small mammal species to infection with different genetic types of B. hermsii will help define their role as hosts in this and other endemic foci. BioMed Central 2016-11-10 /pmc/articles/PMC5105259/ /pubmed/27832805 http://dx.doi.org/10.1186/s13071-016-1863-0 Text en © The Author(s). 2016 Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
spellingShingle Research
Johnson, Tammi L.
Fischer, Robert J.
Raffel, Sandra J.
Schwan, Tom G.
Host associations and genomic diversity of Borrelia hermsii in an endemic focus of tick-borne relapsing fever in western North America
title Host associations and genomic diversity of Borrelia hermsii in an endemic focus of tick-borne relapsing fever in western North America
title_full Host associations and genomic diversity of Borrelia hermsii in an endemic focus of tick-borne relapsing fever in western North America
title_fullStr Host associations and genomic diversity of Borrelia hermsii in an endemic focus of tick-borne relapsing fever in western North America
title_full_unstemmed Host associations and genomic diversity of Borrelia hermsii in an endemic focus of tick-borne relapsing fever in western North America
title_short Host associations and genomic diversity of Borrelia hermsii in an endemic focus of tick-borne relapsing fever in western North America
title_sort host associations and genomic diversity of borrelia hermsii in an endemic focus of tick-borne relapsing fever in western north america
topic Research
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5105259/
https://www.ncbi.nlm.nih.gov/pubmed/27832805
http://dx.doi.org/10.1186/s13071-016-1863-0
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