Project : USDA ARS

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Research Project: Ticks and Human Health

Location: Invasive Insect Biocontrol & Behavior Laboratory

2024 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
In support of Objective 1, Researchers at Beltsville, Maryland, and scientists at The Rutgers University Center for Vector Biology in New Brunswick, New Jersey, continued to develop molecular population genetic tools based on microsatellite markers to track populations of the invasive Asian longhorned tick (ALT) as this species expands its range into new areas. In support of Objective 2, fieldwork was conducted using artificial mouse nesting boxes, a new surveillance technology developed by Researchers at Beltsville, Maryland. The nest boxes may also be useful as a tool for deployment of host targeted control technologies. Field work for the area-wide tick control project was completed in FY21, but we continued to analyze data on behaviors of white-footed mice collected as part of that project, to determine factors related to habitat selection and territoriality. We have also analyzed data on aggressive interactions of whiter-tailed deer at 4-poster tick control devices, and this analysis resulted in two peer-reviewed publications in FY24. Developing an understanding of mouse and deer behaviors will have significant implications for host-targeted control approaches. Analysis of overall tick control efficacy from the area-wide project is ongoing. We have discussed various approaches for analysis of these very complex data sets with USDA statisticians to determine tick control efficacy of different combinations of interventions for tick control and we expect a manuscript reporting tick control efficacy to be submitted soon. In support of Objective 3, Researchers at Beltsville, Maryland, are continuing research collaborations with ARS scientists in Pullman, Washington, to understand the vector relationships of the invasive Asian longhorned tick (ALT). An exotic tick-borne Theilera of cattle (Theileria orientalis) has been spread by ALT in areas of the US where this tick has become established. Although it is not known how T. orientalis was first introduced into the United States, its transmission by ALT and association with the expanding distribution of ALT has resulted in its spread to areas where it may be maintained and transmitted by native north American tick species if they are competent vectors. This work is part of ongoing studies to establish what vector relationships will develop with native tick species as a result of the introduction and spread of the invasive ALT and this associated exotic pathogen. As part of our continued efforts to search for better tick repellents and acaricides, vertical filter paper bioassays are in progress to determine repellency of approximately 40 natural products, and we have planned electrophysiological research to investigate the mode of action of several of these and other new repellent compounds against ticks. Research tools are being discussed for implementation with university collaborators. We have submitted a proposal to the ARS Innovation Fund Program for development of a novel research approach to study tick feeding physiology and modes of action of systemic acaricides.

Accomplishments
1. Nootkatone acts as both an effective repellent and contact toxicant against adult deer ticks. Previous tick repellent studies focused on nymphal stages of the deer tick (the vector that transmits Lyme disease) and other blood-feeding ticks. Nootkatone, known to repel immature ticks, is a naturally occurring chemical found in plants such as Alaskan cedar, grapefruit, and other natural sources. ARS researchers at Beltsville, Maryland, in collaboration with scientists from several other institutions, tested nootkatone for repellency against adults of the three most important human-biting tick species of North America. Results from laboratory bioassays indicate nootkatone is more effective against adults of the deer tick than it is against adults of the American dog tick and the lone star tick. More importantly, a brief contact with nootkatone-treated substrate can lead to significant mortality in adult deer ticks. The study highlighted the potential of nootkatone, a natural compound, to be developed as an active ingredient in potential new products to protect humans from tick bites and tick-borne diseases.

2. A promising natural compound with superior tick repellency is identified. There are continued efforts to search for new tick repellents that can perform better than DEET- or pyrethroid-based synthetic repellent products on the market. ARS researchers in Beltsville, Maryland, and Gainesville, Florida, in collaboration with University of Florida researchers evaluated a number of essential oils and organic compounds for repellency against nymphs of the lone star tick. 1R-trans-chrysanthemic acid (TCA), a compound derived from natural pyrethrin, was found to repel the lone star tick nymphs equally to or better than DEET and nootkatone in three different laboratory assays. Given its superior repellency against ticks and positive mammalian safety profile, this natural compound can be further explored as a candidate tick repellent for commercial development to protect humans from tick bites.

3. American dog ticks are not competent vectors for “exotic” Theileria orientalis. ARS researchers in Beltsville, Maryland, and Pullman, Washington, previously showed that the introduced invasive Asian longhorned tick (ALT) is competent to transmit the exotic pathogen T. orientalis. In ongoing work on the potential of native north American tick species to act as vectors T. orientalis ARS scientists have now shown that, the American dog tick (Dermacentor variabilis)is not a competent transstadial vector of T. orientalis. Although it is not known how T. orientalis was first introduced into the United States, its transmission by and association with the expanding distribution of ALT has resulted in the spread of T. orientalis into areas where it may be maintained and transmitted by other native north American tick species. This work is part of ongoing studies to establish the vector relationships that will develop as a result of the introduction and spread of the invasive ALT and its associated exotic pathogen T. orientalis. This work will contribute towards mitigation of the potentially devastating economic impacts of T. orientalis on the U.S. cattle industry.

U.S. DEPARTMENT OF AGRICULTURE

Invasive Insect Biocontrol & Behavior Laboratory: Beltsville, MD