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Changing geographic ranges of ticks and tick-borne pathogens: drivers, mechanisms and consequences for pathogen diversity.

Ogden NH, Mechai S, Margos G - Front Cell Infect Microbiol (2013)

Bottom Line: The geographic ranges of ticks and tick-borne pathogens are changing due to global and local environmental (including climatic) changes.In this review we explore current knowledge of the drivers for changes in the ranges of ticks and tick-borne pathogen species and strains via effects on their basic reproduction number (R 0), and the mechanisms of dispersal that allow ticks and tick-borne pathogens to invade suitable environments.Lastly we explore how historic population and range expansions and contractions could be reflected in the phylogeography of ticks and tick-borne pathogens seen in recent years, and conclude that combined study of currently changing tick and tick-borne pathogen ranges and diversity, with phylogeographic analysis, may help us better predict future patterns of invasion and diversity.

View Article: PubMed Central - PubMed

Affiliation: Zoonoses Division, Centre for Food-borne, Environmental and Zoonotic Infectious Diseases, Public Health Agency of Canada, Saint-Hyacinthe, QC, Canada. nicholas.ogden@ phac-aspc.gc.ca

ABSTRACT
The geographic ranges of ticks and tick-borne pathogens are changing due to global and local environmental (including climatic) changes. In this review we explore current knowledge of the drivers for changes in the ranges of ticks and tick-borne pathogen species and strains via effects on their basic reproduction number (R 0), and the mechanisms of dispersal that allow ticks and tick-borne pathogens to invade suitable environments. Using the expanding geographic distribution of the vectors and agent of Lyme disease as an example we then investigate what could be expected of the diversity of tick-borne pathogens during the process of range expansion, and compare this with what is currently being observed. Lastly we explore how historic population and range expansions and contractions could be reflected in the phylogeography of ticks and tick-borne pathogens seen in recent years, and conclude that combined study of currently changing tick and tick-borne pathogen ranges and diversity, with phylogeographic analysis, may help us better predict future patterns of invasion and diversity.

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Geographic distribution of B. burgdorferi-infected Ixodes scapularis ticks collected in passive surveillance in Canada in which the ospC major groups were identified in Ogden et al. (2011). A significant spatial cluster of ticks infected with B. burgdorferi carrying ospC major group I is indicated by the red circle. Reproduced with permission from Ogden et al. (2011).
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Figure 3: Geographic distribution of B. burgdorferi-infected Ixodes scapularis ticks collected in passive surveillance in Canada in which the ospC major groups were identified in Ogden et al. (2011). A significant spatial cluster of ticks infected with B. burgdorferi carrying ospC major group I is indicated by the red circle. Reproduced with permission from Ogden et al. (2011).

Mentions: The I. scapularis and B. burgdorferi s.s. expansion process now extends to invasion of southern Canada. Analysis of field and surveillance data suggest that invasion of these species is taking place along trajectories determined by all three environmental factors: climate, habitat and host range and abundance (Ogden et al., 2010; Bouchard et al., 2011, 2013; Leighton et al., 2012). In this region the occurrence of small-scale (<30 km radius) spatial clusters of ticks carrying the same mitochondrial gene haplotypes support the hypothesis that I. scapularis populations in south eastern Canada have (or have until recently) arisen from isolated founder events (Figure 2). Empirical observations (Ogden et al., 2010; Leighton et al., 2012) are consistent with a hypothesis of climate change-driven range expansion of I. scapularis in this region (Ogden et al., 2006b). The occurrence of small-scale clusters of ticks collected in surveillance that carried specific MLST sequence types of B. burgdorferi s.s., also support the occurrence of founder populations of B. burgdorferi s.s. within founder populations of I. scapularis (Figure 2). Evidence for founder events of B. burgdorferi s.s. at the geographic scale of a single woodland have been identified by MLST analysis in south eastern Canada (Ogden et al., 2010). Evidence of founder events in the form of clusters of ticks Infected with B. burgdorferi s.s. that carried the same allele of the outer surface protein C (ospC) gene of B. burgdorferi s.s. have also been found in Canada (Figure 3). Although ospC is maintained under balancing selection, a high degree of linkage disequilibrium in the northeastern part of the US amongst B. burgdorferi s.s. genes suggests that phylogeographic patterns may be partially congruent between ospC and MLST, although this may not be the case for all Borrelia species and geographic ranges (Barbour and Travinsky, 2010; Hellgren et al., 2011). Together these observations suggest that expansion into Canada is being ‘pulled’ by establishment of founder populations. This supports the hypothesis that recent invasion in this region has occurred via introduction by migratory birds (Ogden et al., 2008) rather than by terrestrial hosts. The Great Lakes and Appalachians have likely posed significant geographic barriers to introduction by terrestrial hosts from the USA to regions of Canada from the Maritimes to Western Ontario. However, the occurrence of one large-scale cluster of ticks carrying the same mitochondrial gene haplotype (radius > 300 km; Figure 2) could provide evidence of a novel genotype ‘surfing’ the rapid growth of I. scapularis populations in southern Canada (Leighton et al., 2012), and in the near future range expansion of I. scapularis and B. burgdorferi s.s. may follow the “pushed” pattern seen in the US with greater importance of terrestrial hosts in tick and pathogen dispersion.


Changing geographic ranges of ticks and tick-borne pathogens: drivers, mechanisms and consequences for pathogen diversity.

Ogden NH, Mechai S, Margos G - Front Cell Infect Microbiol (2013)

Geographic distribution of B. burgdorferi-infected Ixodes scapularis ticks collected in passive surveillance in Canada in which the ospC major groups were identified in Ogden et al. (2011). A significant spatial cluster of ticks infected with B. burgdorferi carrying ospC major group I is indicated by the red circle. Reproduced with permission from Ogden et al. (2011).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3756306&req=5

Figure 3: Geographic distribution of B. burgdorferi-infected Ixodes scapularis ticks collected in passive surveillance in Canada in which the ospC major groups were identified in Ogden et al. (2011). A significant spatial cluster of ticks infected with B. burgdorferi carrying ospC major group I is indicated by the red circle. Reproduced with permission from Ogden et al. (2011).
Mentions: The I. scapularis and B. burgdorferi s.s. expansion process now extends to invasion of southern Canada. Analysis of field and surveillance data suggest that invasion of these species is taking place along trajectories determined by all three environmental factors: climate, habitat and host range and abundance (Ogden et al., 2010; Bouchard et al., 2011, 2013; Leighton et al., 2012). In this region the occurrence of small-scale (<30 km radius) spatial clusters of ticks carrying the same mitochondrial gene haplotypes support the hypothesis that I. scapularis populations in south eastern Canada have (or have until recently) arisen from isolated founder events (Figure 2). Empirical observations (Ogden et al., 2010; Leighton et al., 2012) are consistent with a hypothesis of climate change-driven range expansion of I. scapularis in this region (Ogden et al., 2006b). The occurrence of small-scale clusters of ticks collected in surveillance that carried specific MLST sequence types of B. burgdorferi s.s., also support the occurrence of founder populations of B. burgdorferi s.s. within founder populations of I. scapularis (Figure 2). Evidence for founder events of B. burgdorferi s.s. at the geographic scale of a single woodland have been identified by MLST analysis in south eastern Canada (Ogden et al., 2010). Evidence of founder events in the form of clusters of ticks Infected with B. burgdorferi s.s. that carried the same allele of the outer surface protein C (ospC) gene of B. burgdorferi s.s. have also been found in Canada (Figure 3). Although ospC is maintained under balancing selection, a high degree of linkage disequilibrium in the northeastern part of the US amongst B. burgdorferi s.s. genes suggests that phylogeographic patterns may be partially congruent between ospC and MLST, although this may not be the case for all Borrelia species and geographic ranges (Barbour and Travinsky, 2010; Hellgren et al., 2011). Together these observations suggest that expansion into Canada is being ‘pulled’ by establishment of founder populations. This supports the hypothesis that recent invasion in this region has occurred via introduction by migratory birds (Ogden et al., 2008) rather than by terrestrial hosts. The Great Lakes and Appalachians have likely posed significant geographic barriers to introduction by terrestrial hosts from the USA to regions of Canada from the Maritimes to Western Ontario. However, the occurrence of one large-scale cluster of ticks carrying the same mitochondrial gene haplotype (radius > 300 km; Figure 2) could provide evidence of a novel genotype ‘surfing’ the rapid growth of I. scapularis populations in southern Canada (Leighton et al., 2012), and in the near future range expansion of I. scapularis and B. burgdorferi s.s. may follow the “pushed” pattern seen in the US with greater importance of terrestrial hosts in tick and pathogen dispersion.

Bottom Line: The geographic ranges of ticks and tick-borne pathogens are changing due to global and local environmental (including climatic) changes.In this review we explore current knowledge of the drivers for changes in the ranges of ticks and tick-borne pathogen species and strains via effects on their basic reproduction number (R 0), and the mechanisms of dispersal that allow ticks and tick-borne pathogens to invade suitable environments.Lastly we explore how historic population and range expansions and contractions could be reflected in the phylogeography of ticks and tick-borne pathogens seen in recent years, and conclude that combined study of currently changing tick and tick-borne pathogen ranges and diversity, with phylogeographic analysis, may help us better predict future patterns of invasion and diversity.

View Article: PubMed Central - PubMed

Affiliation: Zoonoses Division, Centre for Food-borne, Environmental and Zoonotic Infectious Diseases, Public Health Agency of Canada, Saint-Hyacinthe, QC, Canada. nicholas.ogden@ phac-aspc.gc.ca

ABSTRACT
The geographic ranges of ticks and tick-borne pathogens are changing due to global and local environmental (including climatic) changes. In this review we explore current knowledge of the drivers for changes in the ranges of ticks and tick-borne pathogen species and strains via effects on their basic reproduction number (R 0), and the mechanisms of dispersal that allow ticks and tick-borne pathogens to invade suitable environments. Using the expanding geographic distribution of the vectors and agent of Lyme disease as an example we then investigate what could be expected of the diversity of tick-borne pathogens during the process of range expansion, and compare this with what is currently being observed. Lastly we explore how historic population and range expansions and contractions could be reflected in the phylogeography of ticks and tick-borne pathogens seen in recent years, and conclude that combined study of currently changing tick and tick-borne pathogen ranges and diversity, with phylogeographic analysis, may help us better predict future patterns of invasion and diversity.

Show MeSH
Related in: MedlinePlus