Stemming the Rising Tide of Human-Biting Ticks and Tickborne Diseases, United States

Lars Eisen

Disclosures

Emerging Infectious Diseases. 2020;26(4):641-647. 

In This Article

Abstract and Introduction

Abstract

Ticks and tickborne diseases are increasingly problematic. There have been positive developments that should result in improved strategies and better tools to suppress ticks, reduce human tick bites, and roll back tickborne diseases. However, we equally need to address the question of who is responsible for implementing the solutions. The current model of individual responsibility for tick control evolved from a scenario in the 1990s focusing strongly on exposure to blacklegged ticks and Lyme disease spirochetes in peridomestic settings of the northeastern United States. Today, the threat posed by human-biting ticks is more widespread across the eastern United States, increasingly complex (multiple tick species and >10 notable tickborne pathogens), and, across tick species, more spatially diffuse (including backyards, neighborhood green spaces, and public recreation areas). To mitigate tick-associated negative societal effects, we must consider shifting the responsibility for tick control to include both individual persons and professionally staffed tick-management programs.

Introduction

Ticks and tickborne diseases are distinctly on the increase in the United States.[1,2] Congress responded to this growing problem by establishing a Tick-Borne Disease Working Group in 2016, as part of the 21st Century Cures Act (https://www.fda.gov/regulatory-information/selected-amendments-fdc-act/21st-century-cures-act), and the first biannual Tick-Borne Disease Working Group report was published in 2018.[3] Congress also recently passed the Kay Hagan Tick Act (https://www.congress.gov/bill/116th-congress/senate-bill/1657/text/is) to combat vectorborne diseases. Federal public health agencies have generated new strategic plans aiming to strengthen both research and operational capacity to more effectively counter the threat of ticks and tickborne diseases.[4–8] The Entomological Society of America produced a position paper on tickborne diseases[9] and led the formation of a new coalition named the Vector-Borne Disease Network, which includes the Entomological Society of America and a wide range of scientific and medical societies, professional associations, and the 5 Centers for Disease Control and Prevention–funded Regional Centers for Excellence in Vector-Borne Diseases.[10] These are all positive developments expected to contribute improved strategies and better tools to suppress ticks, reduce human tick bites, and roll back tickborne diseases. However, at the root of the growing problem with ticks and tickborne diseases lies the thorny problem of who will be responsible for implementing the solutions.

In the United States, national surveillance of reportable tickborne diseases is achieved through the National Notifiable Diseases Surveillance System.[11] National surveillance of ticks and pathogens found in ticks was launched only recently as part of the Epidemiology and Laboratory Capacity for Prevention and Control of Emerging Infectious Diseases program of the Centers for Disease Control and Prevention, which provides funding to states, cities, and territories.[12] The initial focus was on the blacklegged tick (Ixodes scapularis),[13] with planned expansion to include a wider range of human-biting tick species. Collectively, these national surveillance programs provide information on when and where humans are at greatest risk for exposure to ticks and tickborne pathogens at state and county scales. When risk has been defined in space and time, the next obvious question is how to most effectively suppress ticks, reduce human tick bites, and roll back tickborne diseases. I. scapularis ticks and Lyme disease in the northeastern region is perhaps the best example of just how intractable this problem is. In parts of this region, peak risk for exposure to nymphal ticks (the primary vectors of Lyme disease spirochetes to humans) is already clearly defined in space (e.g., shady and moist habitats in backyards, neighborhood green spaces, and recreation areas) and time (spring and early summer).[14,15] There is no question that every year will be a bad year for Lyme disease in the northeastern region. However, I. scapularis ticks and their associated pathogens persist in the environment and continue to cause human illness year after year.[2,16] Potential solutions that have emerged over the past 2 decades include a wide array of approaches to prevent tick bites through personal protection measures or to suppress host-seeking ticks or disrupt enzootic pathogen transmission through environmentally based control methods, but evidence for their impact on human tick bites or illness is limited.[17–22] Moreover, uptake of these solutions by the public remains weak because of limited acceptability of some methods with perceived risk to the environment, pets, or family members, as well as low willingness to pay, combined with the consideration that the lowest-cost methods (e.g., use of tick repellents and daily tick checks) require high levels of daily vigilance over several months each year.[18,23–25]

The overall public health threat posed by ticks and tickborne diseases in the United States is steadily increasing to include new human populations because major vector ticks are expanding their geographic ranges,[14,26–29] and we are still discovering new native tickborne human pathogens.[1,2,16] For public health messaging, surveillance of ticks and their associated pathogens is especially useful at the leading edges of an expanding vector tick species range. Moreover, the negative effect of ticks on human health is expanding from long-recognized pathogen transmission and tick paralysis to also include an allergic response to red meat believed to be associated with previous bites by ticks, including the lone star tick (Amblyomma americanum).[30] Our most recent warning signal was the introduction and establishment along the Eastern Seaboard of an invasive tick species (the Asian longhorned tick, Haemaphysalis longicornis) with potential to negatively impact the cattle industry and perhaps also public health if this tick is found to commonly bite humans in the United States.[31]

The negative societal effects of ticks and tickborne diseases in the United States, including a general feeling that family members are not safe during outdoor activities in the backyard and elsewhere, has reached the point where we need to rethink the basic concepts of how to counter this threat. We still need a human Lyme disease vaccine,[32,33] and intriguing new tick and pathogen control and tick-bite prevention technologies are on the horizon.[3,19,20,34,35] However, these technologies will still not address the major issue of who should bear the responsibility for implementing proven tick control and tickborne disease prevention solutions. As noted a decade ago by Piesman and Eisen:[36] "Mosquito control is a community responsibility; tick control is an individual homeowner responsibility. This may explain why currently in the United States, several thousand people are dedicated to mosquito control, whereas only a few dozen are dedicated to public-health related tick control." Other investigators have more recently similarly noted the difference in how mosquitoborne and tickborne diseases are addressed in the United States and argued for a shift toward area-wide suppression of I. scapularis ticks and Lyme disease spirochetes.[37,38] With these considerations in mind, the relentless increase in ticks and tickborne diseases in the United States raises 2 pointed questions that are addressed in more detail in the following sections: First, is it possible to turn the tide of tickborne diseases while control of ticks and their associated disease agents remain an individual responsibility or will this ultimately require a shift to also include a strong community-based effort? Second, can we develop local, professionally staffed programs capable of working with the public to reduce the risk for tick bites on both public and private land?

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