Needed: a national tick strategy

Collage of four images of ticks.
Clockwise from left: Ambylomma americanum, female (lone star stick); Ambylomma americanum, nymph; Dermacentor variabilis, female (American dog tick); and Ioxedes scapularis, female (deer tick). Tick images courtesy of Claudia Ganser.

Planning to hike, camp or hunt this summer? Putter in the garden?

Please use tick repellant.

Around a dozen different kinds of ticks live in the United States, and many carry bacteria, viruses or parasites that can sicken people and animals. As climate and land-use patterns change, ticks are spreading to new areas. Their expanding ranges potentially place more people at risk for tick-borne diseases.

But the lack of a national strategy for surveying ticks of medical importance means that the big-picture effect on public health is poorly understood.

A new national survey integrates maps that show where ticks and their pathogens occur with the identification of core problems thwarting a cohesive approach to managing this vector. A University of Florida postdoctoral researcher assisted with the survey’s analysis, which published today in the Journal of Medical Entomology.

Harnessing the tick network

In 2017, the Centers for Disease Control and Prevention created five regional Centers of Excellence in Vector Borne Diseases to understand and prevent illnesses transmitted to people from mosquitoes and ticks. The northeastern center, which is located where Lyme disease is prevalent, spearheaded a first-of-its-kind survey to gather baseline data on regional efforts of tick surveillance and control. This center then asked the other four centers to partner.

“We of course obliged since the whole notion of risk for tick-borne diseases in the Southeast, especially as far south as Florida, was controversial and highly topical,” says Rhoel Dinglasan, who directs the Southeastern Center of Excellence in Vector Borne Diseases. This center is housed at UF where Dinglasan is a professor in the College of Veterinary Medicine Department of Infectious Diseases & Immunology, and the Emerging Pathogens Institute.

Map showing the relative abundance of medically important tick species within climate regions defined by the National Oceanic and Atmospheric Administration.

When tapped to coordinate the survey for the southeast, Dinglasan consulted with Gregory Glass, a professor at UF’s College of Liberal Arts and Sciences Department of Geography and the Emerging Pathogens Institute, who leads the tick program in the southeastern center. Dinglasan suggested that Glass’ postdoctoral researcher Claudia Ganser was well qualified to represent the center for the national survey.

Ganser was already working with Glass within the tick program, where she had recently conducted six statewide tick surveys in Florida. For two years, she swept a white fleece-covered pole through systematically-selected vegetation to collect, identify and count ticks. Ganser and Glass’ work contributed to greatly refined tick species distributions maps. It also augmented current understanding of where ticks can be found in mainland Florida, which habitats they like best, how densely distributed they are, and where the public is at increased risk from ticks and tick-borne diseases.

“Historically in the U.S., public health has focused more on mosquitoes versus ticks,” Ganser says.

Globally, mosquitoes kill more people compared with any other vector. But ticks are responsible for about three-quarters of the illnesses transmitted to people by vectors in the U.S., the authors report. Even though 47,743 people fell ill from tickborne diseases in 2018, the most recent year for which the CDC has annual data, researchers lacked a clear picture as to how states, counties and municipalities conducted surveillance or control of ticks across the nation — which underscores the need for a national strategy to manage ticks.

“A lot of the public health infrastructure of surveillance programs that is already in place focuses on mosquitoes rather than ticks,” Ganser says. “The idea behind this project was to take inventory of what we know, to gather what information exists in the regions that have ticks, and to identify the gaps in making things more uniform.”

State of the nation’s ticks

Emily Mader of Cornell University and the Northeastern Center of Excellence in Vector Borne Diseases led the survey’s development and is the paper’s lead author. Ganser made significant contributions to analyzing the results and is the paper’s co-second author. The research team divided the contiguous lower forty-eight states into climate regions to evaluate the relative importance of ticks by species:

Next, they extended these findings to show the pathogens reported by responders, and the level of funding each state enjoys:

The researchers found that fewer than half of the respondents reported active tick surveillance (going into the field to look for them methodically), but almost two-thirds reported passive surveillance in their region (for example, samples sent from citizen scientists or concerned people).

While most respondents were interested in surveillance to verify the presence of ticks, few programs supported testing ticks for pathogens. And only 12% of respondents reported having funds for tick control programs.

The survey results revealed the most significant roadblocks to expanding tick surveillance and control programs: funding gaps, training for personnel, limits in infrastructure, a lack of guidance in best practices, and a lack of institutional capacity to carry out surveillance and control goals.

“Our center’s tick program has addressed the basic gaps in knowledge and training infrastructure in tick-borne disease research in the Southeast,” says Dinglasan.

Map showing the prevalence of 11 bacterial agents carried by ticks and capable of making people ill, broken out by climate regions defined by the NOAA.

Over the past three years, his center has focused on refining public health knowledge of the distribution, prevalence and risk of tick-borne pathogen transmission through molecular screening techniques. Medical geographers then map tickborne disease risks based on environmental and ecological factors to yield a fine-grained picture of the problem.

“We are proud of the training we’ve accomplished over the past three years,” says Dinglasan. “And we will continue to train the next generation of public health entomologists in these interdisciplinary approaches to ensure that we remain in front of the problem of tick-borne diseases.”

Detecting new ticks and diseases

The researchers also found that while regional tick programs tended to emphasize species already known in their area, some jurisdictions and climate regions did not prioritize detecting new kinds of ticks. A new species, the Asian long-horned tick, recently expanded into the northeast prior to the survey being distributed. It’s unclear if it can pass pathogens to people, but its emergence put the northeastern and mid-Atlantic regions on alert. Other regions might take a cue from this and put protocols in place for surveillance programs that might provide an early warning of new ticks in their area, which could translate to new public health risks.

But such forethought needs funding.

The study’s senior author, Rebecca Eisen of the CDC’s Division of Vector-Borne Diseases, was instrumental in writing the Kay Hagan Tick Act, which became law last December. Although it’s yet to be funded, the legislation seeks to develop a national strategy for vector-borne diseases. It would also give states financial support for surveillance efforts and other activities related to managing and understanding vector-borne diseases.

Until then, enjoy the great out-of-doors — and use tick repellant.

EPI Explainer: Lyme disease and Rocky Mountain spotted fever are two tick-borne illnesses that tend to have the highest awareness in the general public. But ticks are vectors for many diseases, including Powassan virus disease, tularemia, ehrlichiosis and anaplasmosis. In Florida, the most common species to watch out for include American dog ticks, deer ticks (also called black-legged ticks) and lone star ticks. Visit the CDC’s tick pages to learn more.

Written by: DeLene Beeland