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

Lars Eisen


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

In This Article

Need for Local and Professionally Staffed Integrated Tick-management Programs

Basic differences in the biology of vector mosquitoes and vector ticks drive the selection of methods and implementation schemes to control these pests. In the United States, local risk associated with tickborne pathogens tend to be predictable both in space and time (across years and seasonally), whereas the local intensity of transmission of mosquitoborne viruses fluctuates dramatically among years and builds over the warm time of the year when mosquitoes are active. This advantage for tick control is counteracted by the fact that mosquito control can focus initially on known larval development sites and then, as needed based on surveillance data, move to a space spray emergency measure not requiring physical access to residential properties. For ticks, every year brings a seasonally predictable emergency situation, risk habitats are diffuse and include both private and public lands, and current options for area-wide tick suppression are limited and have weak evidence bases for impact on human tick bites and disease.[20] Even control of ticks, such as I. scapularis and A. americanum, in backyards is problematic because we have a poor understanding of how effectively host-seeking ticks are suppressed across the full extent of a residential property through broadcast of synthetic acaricides, natural acaricides, or fungal control agents by homeowners or commercial pest control companies. A large-scale study that limited application of synthetic acaricide to include only a barrier zone along the lawn–woods ecotone on residential properties did not find the observed suppression of host-seeking ticks within this treated portion of the residential properties to result in reduced human tick bites for the residents.[49] To more effectively suppress ticks in the environment and reduce human tick bites and tickborne diseases, we need to invest in studies to optimize the effect of existing technologies, as well as stimulate the development of novel approaches.

Nevertheless, elements of organized mosquito control can be used as building blocks for an integrated tick-management program. Well-functioning mosquito management programs are based on the principles of integrated pest management (striving to protect the human population from mosquito bites and mosquitoborne disease agents while at the same time minimizing the impact of pesticides on the environment) and staffed with professionals experienced in public outreach, mosquito biology, pesticide use, and operational surveillance and control concepts. Expanding the activities of existing mosquito management programs to also include ticks[50] provides an economy of scale compared with the alternative of having separate community-supported mosquito- and tick-management programs. Specific benefits from building tick responsibilities into an existing mosquito management program might include shared use of existing office/laboratory space, laboratory equipment, and vehicles; presence of professionals already skilled in morphologic vector identification and knowledgeable about basic principles for vector surveillance and control; presence of licensed and highly experienced pesticide applicator personnel; and presence of personnel with previous experience of public outreach for vector-related issues. Regarding access to experienced personnel, effective control of ticks, in backyards or elsewhere, requires control products targeting host-seeking ticks or ticks on host animals to be implemented by persons with a solid understanding of tick biology (e.g., to ensure that the product is applied to the environment in a manner that maximizes contact with host-seeking ticks), the nature of the acaricide product used (e.g., the frequency of acaricide applications needed to provide sustained control over the tick season), and the limitations of the application equipment (which, for example, can effect penetration into microhabitats in which ticks are found). Another potential benefit from strengthening the linkages between mosquito and tick control is an increased involvement by industry in tick control solutions through the already existing interface between industry and the American Mosquito Control Association. A better defined market for tick control products should stimulate industry to invest in new solutions.

The most productive way of exploring the concept of integrated tick-management programs would be (well-funded) demonstration projects focused on geographic locations with strong existing mosquito management programs and severe problems with a wide range of tick species and tickborne diseases. Such an effort is guaranteed to be challenging because it needs to include development of tick-specific knowledge and acquisition of tick-specific equipment; development, implementation, and evaluation of a locally appropriate, standardized tick/pathogen surveillance scheme to address key knowledge gaps, if they exist, for human-biting ticks of local concern and their associated pathogens; development, implementation, and evaluation of a public outreach program to raise local awareness of spatially and seasonally variable risk for exposure to locally found ticks and tickborne pathogens; and development, implementation, and evaluation of schemes for suppression of locally found human-biting ticks on high-use portions of public lands (e.g., along hiking trails, and in and around camp sites, picnic areas, and playgrounds) and on private properties in conjunction with homeowners and using different tick suppression models (e.g., by tick-management program personnel; through contracts with licensed pest control operators from the tick-management program and with oversight by tick-management program personnel; or through homeowner incentives leading to tick suppression executed either by the homeowner or a licensed pest control operator). The lessons learned from such demonstration projects to establish integrated tick-management programs staffed by public health professionals would greatly improve our ability to produce specific and realistic guidance for best management practices.

Moreover, selection of specific tick and pathogen suppression methods to include for either backyard control or area-wide tick management will be challenging because the evidence base for existing approaches is reasonably strong for acarologic outcomes (density of host-seeking ticks and pathogen-infected, host-seeking ticks) but extremely weak for human-based outcomes (human–tick encounters and human illness).[19–21,45,49] Initial evaluations of tick and pathogen suppression schemes in an integrated tick-management program would focus on acarologic outcomes; if these were deemed successful, subsequent evaluations should progress to also include human-based outcomes. One major downstream outcome would be improved guidance for best management practices for tick suppression and reduction of human tick bites based on real-world scenarios, which will need to account for local variation in tick species of public health concern needing to be addressed (e.g., only I. scapularis ticks, only A. americanum ticks, or both species). Cost assessments would be critical to clarify the resources needed to either build ticks into an existing mosquito management program or build an integrated tick-management program from the ground up in settings lacking existing mosquito management programs. Finally, the need for adequate funding for operational tick management cannot be overstated; tick management cannot be incorporated into an existing mosquito management program as an unfunded activity or mandate, and a stand-alone tick-management program equally will require substantial and sustained funding.