Project : USDA ARS

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Research Project: Ticks and Human Health

Location: Invasive Insect Biocontrol & Behavior Laboratory

2022 Annual Report

Objectives
Objective 1: Develop novel approaches and improve upon existing technologies for surveillance of ticks of medical importance. Objective 2: Develop novel approaches and improve upon existing technologies for control of ticks of medical importance. Objective 3: Conduct fundamental research on established and invasive ticks to understand the roles of tick species in disease transmission.

Approach
Molecular techniques will be either modified or developed to identify field specimens of four species of medically-important ticks, the pathogens they transmit, and remnant blood meals (from previous hosts) in questing (“flat”) ticks, collected by conventional means (dragging). Though not a pathogen, per se, mammalian meat allergy as it relates to ticks will also be investigated by existing and developed immunological means in an effort to understand this malady and to limit its impact on people. New tick repellents and formulations will be developed and the mechanism of repellent detection by ticks characterized. This will involve the optimization of an in vitro feeding system for ticks, using a silicone-based feeding system. The use of electrophysiological techniques to characterize tick responses to repellents and antifeedants will also be investigated using state-of-the-art equipment. A project to limit the negative impact of Lyme disease in human will be studied using tracking devices attached to deer (a host of ticks) and rodents (carriers of the Lyme Disease pathogen and other pathogens)The nature of the pathogen will be identified using molecular techniques initially with collaborators, and subsequently, in-house. Additionally, we will conduct molecular identification and artificial feeding studies with a newly-invasive parthenognetic tick and determine any pathogens this tick may acquire and transmit to humans.

Progress Report
ARS scientists in Beltsville, Maryland, established a new Cooperative agreement with The Rutgers University Center for Vector Biology to work collaboratively on development of technologies for surveillance of the invasive Asian longhorned tick. A postdoctoral scientist has been selected for hire through the Rutgers agreement; this post-doc will be working on development of tools for molecular population genetics to track invasive tick populations as this species expands its range into new areas. In addition, we continue to develop our capability for laboratory testing of ticks collected in our research activities including identification of tick species using molecular tools, identification of previous tick blood-meal sources, and identification of tick-borne pathogens they may be carrying. A full year of fieldwork was completed for the artificial mouse nest box project. Nest boxes are a tool for surveillance and control tick-borne zoonotic pathogens that have their natural reservoirs in mice, which are key to zoonotic maintenance of a guild of Ixodes tick-borne pathogens causing Lyme disease and other illnesses in humans. The artificial nesting boxes are well accepted by mice (Peromyscus leucopus) and using the boxes for surveillance allows repeated sampling of mice in their nests. The removable sticky trap underneath the nest collects ticks that drop off and the nest materials themselves can be sampled with a Berlese funnel. Repeated sampling makes it possible to collect different tick life stages at different seasons of the year and minimizes negative impacts on mice due to conventional trapping methods. Ticks from sticky traps inside the nest box can be tested by PCR to identify pathogen(s) they carry. In this preliminary study we placed boxes on a 15-meter grid within a one-hectare wood lot and checked them weekly; sticky traps were changed, and mice were sampled, tagged, and their location recorded each week. Recapture data as well as Sherman trapping among the boxes confirms that within 8 months all the mice inhabiting the wood lot had been tagged and sampled. Data was collected on mouse numbers and incidence of infection (with repeated sampling), ticks from sticky traps and their infection prevalence, as well as other nest associated ectoparasites. Based on observations from this study we propose that artificial mouse nest boxes may be an ideal method for surveillance and for application of host targeted tick control strategies to reduce the risk of tick-borne transmission of zoonotic pathogens associated with mice. These nest boxes are a technology that was developed by ARS scientists in Beltsville, Maryland, to facilitate host (mouse) targeted surveillance and control methodologies. An invention disclosure was submitted, and funding was received from the ARS Innovation Fund. This project also received funding for an administrator funded postdoctoral position, who will take over the project and see it to completion. Four commercial tick control products were successfully evaluated against ticks in the laboratory. Testing results were shared with a local school, where ticks are a major problem, to assist the school’s decision-making on tick control measures. A natural compound was identified through laboratory experiments as a promising inhibitor of a major tick-borne pathogen. However, work to determine its efficacy against ticks and pathogens in an animal model have not yet been completed due to COVID-19 related work restrictions. Depending on successful completion of the animal study through a cooperator and favorable results from the animal trials, a patent application could be filed on this new compound at some point in the future. Field work for the area-wide tick control project was completed in 2021, but analysis of data and preparation of publications continues. All field work designed for post-treatment assessment of questing tick population density, tick loads on mice, and prevalence of tick-borne pathogens in both ticks and white-footed mice has been completed. Tick and mouse samples were sent to cooperators for pathogen testing, and we are awaiting results. All field study data were systemically organized and archived for easy retrieval to facilitate data analysis. The baseline tick and tick-borne pathogen prevalence data collected in the first year of the area wide tick control project from Maryland and Connecticut field study sites was published. ARS scientists in Beltsville, Maryland, established research collaborations with colleagues at Rutgers University (New Brunswick, New Jersey) and Kansas State University (Manhattan, Kansas) to conduct fundamental research on established and invasive populations of the Asian longhorned tick to understand the relationship between the parthenogenetic invasive strain that has invaded the U.S. and the non-invasive native sexually reproducing strain found in Asia. We will use population genetic, genomic, and gene expression studies to understand the role of these reproductive adaptations in competence as a vector of disease-causing pathogens. An in vitro artificial tick feeding system continues to be developed by ARS scientists in Beltsville, Maryland, for use in collaborative studies. Once this tick feeding system is up and running, it will also be valuable for use as a bioassay system for repellent, attractant, and toxicant research on native and invasive human-biting ticks.

Accomplishments
1. Improved tick control in suburban environments. Mice and deer are critical hosts for the ticks that transmit Lyme disease. Host-targeted tick control technologies like rodent bait boxes and ARS-developed ‘4-Poster’ deer treatment stations are two control products which have not seen widespread use in tick management. Research led by ARS scientists in Beltsville, Maryland, resulted in better understanding of factors that improve the efficacy of these devices. Knowledge of factors contributing to improved performance of rodent bait boxes and 4-Poster technologies will help stakeholders implement integrated tick management strategies in ways most likely to result in significant tick population suppression, which may correspond to lowered disease transmission.

2. Behavioral differences identified between medically important tick species to improve the ability of individuals to avoid tick bites. Most human tick bites come from the blacklegged tick and the lone star tick, which co-exist in many areas and transmit pathogens including the agents causing Lyme disease, ehrlichiosis and others. Repellents are recommended by the Centers for Disease Control and Prevention (CDC) to reduce or prevent tick bites, but cases of Lyme disease, Ehrlichiosis, and other diseases continue to rise. ARS scientists in Beltsville, Maryland, led studies of host detection behaviors in these tick species including movement towards human body heat and host seeking behaviors that differ between southern vs. northern regions. This information may help explain reduced incidence of Lyme disease in the south, will help to improve of currently available personal protective measures, and guide development of new products and approaches for protection against tick bites.

3. Development of tick artificial feeding systems to facilitate studies of tick feeding behavior and vector competence. Research on tick control and methods for blocking transmission of tick-borne pathogens, such as Lyme disease, require blood feeding live ticks in the lab. As part of ongoing efforts to reduce the number of animals used in research, USDA scientists in Beltsville, Maryland, and Pullman, Washington, developed and patented an artificial tick feeding system which uses a silicone infused membrane, a temperature controller, and a pump that circulates blood to simulate blood flow. Studies of tick feeding behaviors and their ability to acquire and transmit pathogens while feeding are critically important for development of new methods to control ticks and to block pathogen transmission. Development of this artificial tick feeding system benefits stakeholders and researchers by facilitating more rapid development of new acaricides, repellents, and anti-tick and transmission blocking vaccines, while decreasing the use of laboratory animals for research.

U.S. DEPARTMENT OF AGRICULTURE

Invasive Insect Biocontrol & Behavior Laboratory: Beltsville, MD