Field and climate-based model for predicting the density of host-seeking nymphal Ixodes scapularis, an important vector of tick-borne disease agents in the eastern United States

Authors

  • Maria A. Diuk-Wasser,

    Corresponding author
    1. Yale School of Public Health, 60 College Street, New Haven, CT 06520, USA,
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  • Gwenaël Vourc'h,

    1. National Institute for Agricultural Research, UR346 Animal Epidemiology, F-63122 Saint Genès Champanelle, France,
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  • Paul Cislo,

    1. Yale School of Public Health, 60 College Street, New Haven, CT 06520, USA,
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  • Anne Gatewood Hoen,

    1. Yale School of Public Health, 60 College Street, New Haven, CT 06520, USA,
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    • Present address: Children's Hospital Informatics Program, Harvard-MIT Division of Health Sciences and Technology, 1 Autumn Street, Boston, MA 02215, USA.

  • Forrest Melton,

    1. Division of Science and Environmental Policy, California State University Monterey Bay, 100 Campus Center, Seaside, CA 93955, USA,
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  • Sarah A. Hamer,

    1. Department of Fisheries and Wildlife, College of Agricultural and Natural Resources, Michigan State University, 13 Natural Resources Building, East Lansing, MI 48824, USA,
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  • Michelle Rowland,

    1. College of Veterinary Medicine, University of Illinois, 2001 S. Lincoln Ave., Urbana, IL 61802, USA,
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  • Roberto Cortinas,

    1. Department of Entomology, University of Nebraska, Lincoln, 12BA Entomology Hall, East Campus, Lincoln, NE 68583, USA,
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  • Graham J. Hickling,

    1. Department of Forestry, Wildlife and Fisheries, College of Agricultural Sciences and Natural Resources, University of Tennessee, Knoxville, TN 37996, USA,
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  • Jean I. Tsao,

    1. Department of Fisheries and Wildlife, College of Agricultural and Natural Resources, Michigan State University, 13 Natural Resources Building, East Lansing, MI 48824, USA,
    2. Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, D202 Veterinary Medical Center, East Lansing, MI 48824, USA,
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  • Alan G. Barbour,

    1. Department of Microbiology and Molecular Genetics, University of California Irvine, Irvine, CA 92697, USA,
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  • Uriel Kitron,

    1. Department of Environmental Studies, Emory University, 400 Dowman Drive, Atlanta, GA 30322, USA,
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  • Joseph Piesman,

    1. Centers for Disease Control and Prevention, Division of Vector-Borne Infectious Diseases, Bacterial Zoonoses Branch, 3150 Rampart Rd., Fort Collins, CO 80521 USA
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  • Durland Fish

    1. Yale School of Public Health, 60 College Street, New Haven, CT 06520, USA,
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Maria A. Diuk-Wasser, 60 College Street, PO Box 208034, New Haven, CT 06520-8034, USA.
E-mail: maria.diuk@yale.edu

ABSTRACT

Aim Ixodes scapularis is the most important vector of human tick-borne pathogens in the United States, which include the agents of Lyme disease, human babesiosis and human anaplasmosis, among others. The density of host-seeking I. scapularis nymphs is an important component of human risk for acquiring Borrelia burgdorferi, the aetiological agent of Lyme disease. In this study we used climate and field sampling data to generate a predictive map of the density of host-seeking I. scapularis nymphs that can be used by the public, physicians and public health agencies to assist with the diagnosis and reporting of disease, and to better target disease prevention and control efforts.

Location  Eastern United States of America.

Methods  We sampled host-seeking I. scapularis nymphs in 304 locations uniformly distributed east of the 100th meridian between 2004 and 2006. Between May and September, 1000 m2 were drag sampled three to six times per site. We developed a zero-inflated negative binomial model to predict the density of host-seeking I. scapularis nymphs based on altitude, interpolated weather station and remotely sensed data.

Results  Variables that had the strongest relationship with nymphal density were altitude, monthly mean vapour pressure deficit and spatial autocorrelation. Forest fragmentation and soil texture were not predictive. The best-fit model identified two main foci – the north-east and upper Midwest – and predicted the presence and absence of I. scapularis nymphs with 82% accuracy, with 89% sensitivity and 82% specificity. Areas of concordance and discordance with previous studies were discussed. Areas with high predicted but low observed densities of host-seeking nymphs were identified as potential expansion fronts.

Main conclusions  This model is unique in its extensive and unbiased field sampling effort, allowing for an accurate delineation of the density of host-seeking I. scapularis nymphs, an important component of human risk of infection for B. burgdorferi and other I. scapularis-borne pathogens.

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