Forest Service Crews Double as Tick-Surveillance Teams in Collaborative Study
By Melissa Mayer
Most jobs come with occupational hazards, and for field personnel with the USDA Forest Service, those include encountering ticks—some of which carry disease-causing pathogens. For a pair of researchers at the Forest Service and the University of Tennessee, these encounters represent something more. They are an opportunity to enhance tick surveillance in the Southeastern states, a region whose ticks they describe as diverse, abundant, and poorly understood.
Ticking the Data Boxes
In their new report published last week in the Journal of Medical Entomology, Rebecca Trout Fryxell, Ph.D., associate professor at the University of Tennessee’s Department of Entomology and Plant Pathology, and Forest Service project leader J.T. Vogt, Ph.D., describe the results of a pilot tick surveillance collaboration between UT and the Forest Service’s Southern Research Station Forest Inventory and Analysis (FIA) crews.
The four-year project provided FIA crews with tick-related training and collection kits to preserve ticks they encountered on the job. The crews sent the collected ticks—1,180 of them over four years—to the university’s entomology laboratory for sorting by species, sex, and life stage. The lab also screened the most commonly collected tick, the lone star tick (Amblyomma americanum), for Ehrlichia bacteria, which causes the tickborne disease ehrlichiosis.
The authors used the collected data to calculate the frequency of encounters and descriptive statistics for the three most common species: the lone star tick, the American dog tick (Dermacentor variabilis), and the blacklegged tick (Ixodes scapularis). They determined overall prevalence and tick burdens, which they also broke down by year and state, and produced tick-encounter maps for the FIA crews.
Big Area, Big Opportunity
The Southeastern region includes 74 field-trained Forest Service crews working year-round to inventory a staggering 45,244 sites within the region’s 14 states. Each of those sites is situated within a cell of 5,937 acres. Since these site inventories take place at repeated intervals of five, seven, or 10 years, ongoing collaboration could enable researchers to monitor changes in tick populations over time and alert them if tick numbers or infection rates change.
That’s good news for scientists tracking tick populations and for the forest personnel at risk for tick encounters. Trout Fryxell and Vogt hypothesize that collaborative surveillance may benefit the crews who perform it. “We suspect that FIA crews who participate regularly in the study are developing habits that involve checking themselves for ticks regularly, thereby limiting the opportunity for ticks to bite and decreasing their risk for acquiring a tickborne pathogen,” they write.
And participation may beget more participation. The initial rates were low, with only seven FIA crews from six of the 14 states sending in specimens in 2014. By 2017, that number expanded to 30 participating FIA crews in 12 of the 14 states, a 40 percent participation rate.
The authors hope those numbers will continue to grow as they share their findings and related tick-safety recommendations at FIA meetings—and as they gather feedback from participating crews. Eventually they plan to produce a dynamic database to track the data they collect.
The model could even expand beyond the region. “Ultimately we would like to increase participation in the South, and we have been discussing the potential for broader participation of Forest Inventory and Analysis across the nation with FIA leadership,” says Vogt.
Trout Fryxell hopes to button up tick surveillance in the Southeastern region by adding active surveillance measures to the passive surveillance described in the paper. “I’d like to get someone out there dragging for ticks with [the FIA crews] to compare tick encounters in different habitats and see what happens at these sites over time,” she says. “Also, these collections can be used for downstream projects, so this surveillance is a huge asset.”
Journal of Medical Entomology
Melissa Mayer is a freelance science writer based in Portland, Oregon. Email: firstname.lastname@example.org.