Spatial Distribution of Counties in the Continental United States With Records of Occurrence ofAmblyomma americanum(Ixodida: Ixodidae)

Abstract

In addition to being a major nuisance biter, the lone star tick, Amblyomma americanum (L.), is increasingly recognized as an important vector of pathogens affecting humans, domestic animals, and wildlife. Despite its notoriety, efforts have been lacking to define the spatial occurrence of A. americanum in the continental United States with precision beyond that conveyed in continental-scale distribution maps. Here we present a county-level distribution map for A. americanum generated by compiling collection records obtained from a search of the published literature and databases managed by the USDA, U.S. National Tick Collection, and Walter Reed Biosystematics Unit. Our decadal and cumulative maps, which visually summarize 18,121 collections made between 1898 and 2012, show that A. americanum is either established (≥six ticks or ≥two life stages) or reported (<six ticks of a single life stage or number of ticks not specified) in 1,300 counties distributed among 39 states and the District of Columbia. Our cumulative map depicts a species with a core distributional area in the southern part of the eastern United States, but that also occurs further north, especially along the Atlantic Coast and into the Midwest. Although our decadal maps suggest a northward shift in the tick’s distribution in recent decades, the lack of systematic tick surveillance makes this difficult to confirm. The data presented herein should aid in identifying areas posing risk for A. americanum-associated illnesses and environmental correlates that define the tick’s distributional limits.

Modeling the Present and Future Geographic Distribution of the Lone Star Tick, Amblyomma americanum (Ixodida: Ixodidae), in the Continental United States

“…We used published data on the geographic distribution of A. americanum collection records in the United States as the basis of our modeling. 56 These data were generated by compiling Lone star tick collection records obtained from a search of the published literature and databases managed by the U.S. Department of Agriculture, U.S. National Tick Collection, and Walter Reed Biosystematics Unit. A total of 18,121 A. americanum collection records, involving sampling events conducted at locations across the continental United States (48 states and the District of Columbia, hereafter DC) and reported from 1898 to 2012, were summarized at the county level.…”

“…On the basis of these data, Springer and others 56 categorized A. americanum as established in 653 counties distributed across 32 states and the DC (Supplemental Table 1 Figure 1A). 56 In our analyses, we excluded two of these counties from our list of those classified as present (Ravalli county, Montana and Sacramento county, California) because they fall far outside of the geographic core of the species' distribution and associated collections were likely the result of importation rather than sampling of locally established populations.…”

“…56 In our analyses, we excluded two of these counties from our list of those classified as present (Ravalli county, Montana and Sacramento county, California) because they fall far outside of the geographic core of the species' distribution and associated collections were likely the result of importation rather than sampling of locally established populations. In addition, while Springer and others 56 categorized A. americanum as reported in an additional 647 counties, we classified the species as absent from these locations in our analyses. Because these collection records reflect where efforts were made to sample or study ticks, the geographic distribution of A. americanum inferred from these data, and that forms the basis of our analyses, likely underestimates the species' true current distribution.…”

“…[51][52][53][54][55] In spite of its significant impacts on wildlife, livestock, and human health, relatively little is known about the current and potential future distribution of A. americanum. Building on a published summary of tick collection records reported from 1898 to 2012, 56 we use an ensemble approach involving five different algorithms to model the current distribution of localities climatically suitable for establishment of the Lone star tick (hereafter suitable habitat) in the continental United States. By integrating multiple algorithms, ensemble modeling reduces the potential for predictive bias that may arise when only a single algorithm is considered.…”

Retrospective Case Reports of Two Central North Carolina Residents

“…This occurred even though the subjects attempted to limit their exposure to ticks by following CDC-recommended prevention measures as practical. Numerous studies have documented the ascendancy of A. americanum ticks across the Southeast, their extension as far north as Massachusetts as early as 1947 [20,22], and more recently into Maine and west to Nebraska [3,23,24]. Lone star tick pathogens include the long-implicated Rickettsia rickettsii, the agent of RMSF [25,26]; Francisella tularensis, the agent of tularemia; Ehrlichia chaffeensis, Ehrlichia ewingii, Panola Mountain Ehrlichia; [3] and other rickettsial organisms including R. parkeri and R. amblyommii [3].…”