A field-based indicator for determining the likelihood of Ixodes scapularis establishment at sites in Ontario, Canada

PLoS One. 2018 Feb 27;13(2):e0193524. doi: 10.1371/journal.pone.0193524. eCollection 2018.

Abstract

The emergence of the vector Ixodes scapularis in Ontario, Canada poses a significant public health risk. Both passive and active surveillance approaches have been employed by public health professionals (i.e., government employees) to monitor for the range expansion of this tick. Field surveillance using drag sampling for questing ticks is a recognized and effective method to identify reproducing tick populations. The degree of effort (i.e., number of visits per site) can enhance the sensitivity and specificity of surveillance, but increased effort conflicts with the cost to public health for field surveillance. Here we developed an indicator to determine the likelihood of I. scapularis establishment based on field sampling results. Field data from two established populations of I. scapularis in Ontario were incorporated with previous analyses of surveillance data to create the indicator, which is in the form of a scoring system. The life stage(s) collected, overall abundance and past surveillance findings from a site are all considered and a level is assigned for the likelihood of I. scapularis establishment based on current field sampling results. The likelihood levels are non-zero (i.e., no I. scapularis detected, but risk still present due to adventitious ticks), low, medium or high, and recommendations for future surveillance and public health measures are provided. The indicator was validated against field sampling results from five other established sites in the province and correctly categorized all five areas as high likelihood of establishment. The indicator was also applied to field sampling results from 36 sites of unknown status that were visited twice during the period of 2014-2016. There was substantial agreement of levels between measurements, as calculated using a weighted kappa. The indicator can assist public health professionals with the interpretation of field sampling results and direct their efforts for ongoing surveillance and public health interventions for I. scapularis-borne diseases, including Lyme disease.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Ixodes / microbiology*
  • Ontario / epidemiology
  • Population Surveillance
  • RNA, Ribosomal, 23S / genetics
  • Sequence Analysis, RNA
  • Tick-Borne Diseases / diagnosis*
  • Tick-Borne Diseases / epidemiology

Substances

  • RNA, Ribosomal, 23S

Grants and funding

This work was supported by the Public Health Agency of Canada, www.phac-aspc.gc.ca; Natural Sciences and Engineering Research Council, http://www.nserc-crsng.gc.ca; Canadian Wildlife Health Cooperative, www.cwhc-rcsf.ca. KMC received stipend support from an Ontario Veterinary College Fellowship, a PostGraduate Scholarship-Doctoral from the Natural Sciences and Engineering Research Council and a Blake Graham Fellowship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. NHO, LRL and PM are all employees of the PHAC and CMJ is affiliated with CWHC, but they were not directly instructed by the funders.