Spatial distribution of counties in the continental United States with records of occurrence of Amblyomma 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 ofA. 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 (> or = 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.

Fig. 1

Spatial distribution of counties in which A. americanum is known to be established or reported, cumulative from the 1890s to present time.

Fig. 2

Number of counties (cumulative by decade) where A. americanum is known to be established or reported, by decade of collection and region (based exclusively on records from the published literature). Map depicts Standard Federal Regions within the continental United States.

Fig. 3

Number of publications and unique county records of collection for A. americanum plotted against decade of publication (based exclusively on records from the published literature). The number of publications (×100) for the subject word “entomology,” determined using a Web of Science literature search, is plotted as a reference trend.