Citizen Science Provides an Efficient Method for Broad-Scale Tick-Borne Pathogen Surveillance of Ixodes pacificus and Ixodes scapularis across the United States

Abstract

Tick-borne diseases have expanded over the last 2 decades as a result of shifts in tick and pathogen distributions. These shifts have significantly increased the need for accurate portrayal of real-time pathogen distributions and prevalence in hopes of stemming increases in human morbidity. Traditionally, pathogen distribution and prevalence have been monitored through case reports or scientific collections of ticks or reservoir hosts, both of which have challenges that impact the extent, availability, and accuracy of these data. Citizen science tick collections and testing campaigns supplement these data and provide timely estimates of pathogen prevalence and distributions to help characterize and understand tick-borne disease threats to communities. We utilized our national citizen science tick collection and testing program to describe the distribution and prevalence of four Ixodes-borne pathogens, Borrelia burgdorferi sensu lato, Borrelia miyamotoi, Anaplasma phagocytophilum, and Babesia microti, across the continental United States. IMPORTANCE In the 21st century, zoonotic pathogens continue to emerge, while previously discovered pathogens continue to have changes within their distribution and prevalence. Monitoring these pathogens is resource intensive, requiring both field and laboratory support; thus, data sets are often limited within their spatial and temporal extents. Citizen science collections provide a method to harness the general public to collect samples, enabling real-time monitoring of pathogen distribution and prevalence.

Keywords: Anaplasma phagocytophilum; Babesia microti; Borrelia; Borrelia burgdorferi; Borrelia miyamotoi; Lyme disease; anaplasmosis; babesiosis; relapsing fever; tick-borne.

FIG 1

Distribution and number of I. scapularis (A) and I. pacificus (B) collected through the citizen science program from 2016 to 2019 by county. Gray counties indicate counties without tick submissions, and in both panels, color scales are individually calibrated.

FIG 2

Number of I. scapularis (A) and I. pacificus (B) ticks collected by CDC week (Sunday to Saturday) and across years.

FIG 3

Distribution of Lyme group Borrelia (B. burgdorferi sensu lato) and Lyme disease cases across the continental United States. (A) Presence (red) and absence (blue) via real-time PCR for B. burgdorferi sensu lato by county. Gray counties indicate counties without tick submissions. (B) Prevalence of positive Ixodes ticks via real-time PCR for B. burgdorferi sensu lato by county. Gray counties indicate no tick submissions, blue counties indicate no positive ticks, green indicates a tick prevalence between 0 and 10%, yellow indicates a prevalence between 10 and 20%, and red indicates a prevalence greater than 20%. The color’s opacity indicates the estimate’s confidence, with darker opacity indicating a smaller confidence interval, while lighter opacities indicate wider confidence intervals. (C) Average number of human Lyme disease cases per year and county reported to CDC’s National Notifiable Disease Surveillance System between 2009 and 2018.

FIG 4

Distribution of B. miyamotoi (TBRF Borrelia) across the continental United States. (A) Presence (red) and absence (blue) via real-time PCR for B. miyamotoi. Gray counties indicate counties without tick submissions. (B) Prevalence of positive Ixodes ticks via real-time PCR for B. miyamotoi by county. Gray counties indicate no tick submissions, blue counties indicate no positive ticks, green indicates a tick prevalence between 0 and 10%, yellow indicates a prevalence between 10 and 20%, and red indicates a prevalence greater than 20%. The color’s opacity indicates the estimate's confidence, with darker opacity indicating a smaller confidence interval, while lighter opacities indicate wider confidence intervals.

FIG 5

Distribution of A. phagocytophilum across the continental United States. (A) Presence (red) and absence (blue) via real-time PCR for A. phagocytophilum by county. Gray counties indicate counties without tick submissions. (B) Prevalence of positive Ixodes ticks via real-time PCR for A. phagocytophilum by county. Gray counties indicate no tick submissions, blue counties indicate no positive ticks, green indicates a tick prevalence between 0 and 10%, yellow indicates a prevalence between 10 and 20%, and red indicates a prevalence greater than 20%. The color’s opacity indicates the estimate's confidence, with darker opacity indicating a smaller confidence interval, while lighter opacities indicate wider confidence intervals.

FIG 6

Distribution of Babesia microti across the continental United States. (A) Presence (red) and absence (blue) via real-time PCR for Bab. microti by county. Gray counties indicate counties without tick submissions. (B) Prevalence of positive Ixodes ticks via real-time PCR for Bab. microti by county. Gray counties indicate no tick submissions, blue counties indicate no positive ticks, green indicates a tick prevalence between 0 and 10%, yellow indicates a prevalence between 10 and 20%, and red indicates a prevalence greater than 20%. The color’s opacity indicates the estimate’s confidence, with darker opacity indicating a smaller confidence interval, while lighter opacities indicate wider confidence intervals.

FIG 7

County-level comparison of I. scapularis (A) and I. pacificus (B) distributions from a recent CDC report (23) and citizen science tick collections. Counties that had reported (established or reported) I. scapularis or I. pacificus populations were recorded as present (blue or green).

FIG 8

County-level comparison of B. burgdorferi distributions from Fleshman et al. (5) (B. burgdorferi sensu stricto) and citizen science pathogen testing results (B. burgdorferi sensu lato).