title: Geographical and environmental factors driving the increase in the Lyme disease vectorIxodes scapularis.
abstract: The population densities of many organisms have changed dramatically in recent history. Increases in the population density of medically relevant organisms are of particular importance to public health as they are often correlated with the emergence of infectious diseases in human populations. Our aim is to delineate increases in density of a common disease vector in North America, the blacklegged tick, and to identify the environmental factors correlated with these population dynamics. Empirical data that capture the growth of a population are often necessary to identify environmental factors associated with these dynamics. We analyzed temporally- and spatially-structured field collected data in a geographical information systems framework to describe the population growth of blacklegged ticks (Ixodes scapularis) and to identify environmental and climatic factors correlated with these dynamics. The density of the ticks increased throughout the study's temporal and spatial ranges. Tick density increases were positively correlated with mild temperatures, low precipitation, low forest cover, and high urbanization. Importantly, models that accounted for these environmental factors accurately forecast future tick densities across the region. Tick density increased annually along the south-to-north gradient. These trends parallel the increases in human incidences of diseases commonly vectored byI. scapularis. For example,I. scapularisdensities are correlated with human Lyme disease incidence, albeit in a non-linear manner that disappears at low tick densities, potentially indicating that a threshold tick density is needed to support epidemiologically-relevant levels of the Lyme disease bacterium. Our results demonstrate a connection between the biogeography of this species and public health.
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104 USA.
authors.forename: Camilo E
authors.initials: CE
authors.lastname: Khatchikian
authors.affiliation: Bureau of Communicable Diseases Control, New York State Department of Health, Albany, New York 12201 USA.
authors.forename: Melissa
authors.initials: M
authors.lastname: Prusinski
authors.affiliation: Bureau of Communicable Diseases Control, New York State Department of Health, Albany, New York 12201 USA ; Department of Biological Sciences, University at Albany, Albany, New York 12222 USA.
authors.forename: Melissa
authors.initials: M
authors.lastname: Stone
authors.affiliation: Bureau of Communicable Diseases Control, New York State Department of Health, Albany, New York 12201 USA.
authors.forename: P Bryon
authors.initials: PB
authors.lastname: Backenson
authors.affiliation: Department of Biological Sciences, University at Albany, Albany, New York 12222 USA.
authors.forename: Ing-Nang
authors.initials: IN
authors.lastname: Wang
authors.affiliation: Center for Clinical Epidemiology and Biostatistics, Department of Biostatistics and Epidemiology, University of Pennsylvania, Philadelphia, Pennsylvania 19104 USA.
authors.forename: Michael Z
authors.initials: MZ
authors.lastname: Levy
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104 USA.
authors.forename: Dustin
authors.initials: D
authors.lastname: Brisson
keywords: GIS; Ixodes scapularis; blacklegged ticks; density increase; emerging zoonoses; geographic information systems