Location: Livestock Arthropod Pest Research Unit
2023 Annual Report
Objectives
Objective 1: Determine parameters such as tick range, movement and suitable habitats, to produce models of the risk of tick-borne disease outbreaks, and potential for introduction of invasive ticks in response to climate change and other perturbations.
Objective 2: Develop methods to prevent, eradicate and control introduction of exotic ticks.
Approach
Ticks are a major threat to the livestock industry and human health. Other than cattle fever ticks, Rhipicephalus (Boophilus) microplus and R. annulatus, threats to livestock by high-consequence foreign pests are always present and one example of this is the recent discovery of the Asian longhorned tick, Haemaphysalis longicornis in seventeen states with an eastern boundary from Rhode Island south to North Carolina and a western boundary from Missouri south to Arkansas. There are other potentially invasive tick vectors (e.g., Amblyomma variegatum, Hyalomma spp., Rhipicephalus appendiculatus) and species that are expanding their ranges within the United States (e.g., A. americanum, A. maculatum, A. mixtum). Likewise, there are high-consequence foreign tick-borne pathogens, like African swine fever, that could devastate U.S. animal agriculture if their emergence involved transmission by native tick species.
The research addresses the following research components in the 2019-2024 Veterinary, Medical, and Urban Entomology National Program (NP 104) Action Plan: Component 1: Veterinary Entomology, Problem Statement 1A Improved Integrated Pest Management of Ticks of Veterinary Importance and Component 2: Medical Entomology, Problem Statement 2D Improved Surveillance and Control of Ticks of Medical Importance. This research addresses ARS Performance Measure for Goal 4.3: Provide scientific information to protect animals, humans, and property from the negative effects of pests and infectious diseases. Develop and transfer tools to the agricultural community, commercial partners, and government agencies to control or eradicate domestic and exotic diseases and pests that affect animal and human health.
Progress Report
Project #3094-32000-044-000D, Management of Ticks of Veterinary Importance, was a new project beginning in fiscal year (FY) 22 as the result of a realignment Program Direction and Resource Allocation Memo (Nov. 2021). The two objectives in this project were transferred to this project from Project #3094-32000-042-000D, Integrated Pest Management of Cattle Fever Ticks, which has had critical vacancies since FY20.
In support of Objective 1, to determine variables that influence tick range, suitable tick habitats, risk of tick-borne disease outbreaks, and potential for instruction of invasive ticks, field experiments were completed in south Texas to further clarify the relationship between soil salinity and the survival rate of ixodid tick eggs. Paired field-testing sites were used to determine if the presence of invasive Guinea grass impacts predation of fallen engorged female ticks. Additionally, studies were completed to show how ixodid ticks in the field and in the laboratory interact with gulf cordgrass, a common, widespread plant along the southern Texas coastal plain. ARS researchers in Kerrville, Texas, conducted field work that demonstrated immature ixodids utilize leaf structure to improve upon their chances of survival in that hot environment, and how leaf structure changes during the year to the advantage of ixodid survival. These studies also demonstrated that the structure of gulf cordgrass can favor ixodid survival by offering distinctly cooler and more humid habitat at the plant’s base than in the more exposed canopy. This research represents one of the only studies to detail how plants can offer sanctuary to ixodids, extending their ability to quest for hosts.
In support of Objective 2, develop methods to prevent, eradicate and control introduction of exotic ticks, research by ARS scientists in Kerrville and Edinburg, Texas, previously discovered that ticks and several other vectors of disease secrete acetylcholinesterases in their saliva. Injection of salivary acetylcholinesterase at the tick bite site is hypothesized to modulate innate and acquired immune responses in the host. Dendritic and other immune cells have been reported in the literature to produce acetylcholine upon activation which could act as an autocrine or paracrine modulator of innate and acquired immunity. As a model of tick-borne disease transmission and development, murine dendritic cells were developed in cell culture from mouse bone marrow and utilized to investigate whether recombinant tick acetylcholinesterase (BmAChE1) altered gene expression when the dendritic cells were activated by exposure to bacterial lipopolysaccharide and lipoteichoic acid in the presence of enzymatically-active or inactive BmAChE1. Surprisingly, activity of recombinant BmAChE1 did not significantly alter dendritic cell gene expression following exposure to bacterial marker stimulation. Follow-up research demonstrated that the dendritic cells did not produce acetylcholine in response to bacterial marker stimulation. Immune regulation is known to be highly complex involving interactions and signaling between different immune cell types. Further studies are planned with a murine macrophage cell line known to produce acetylcholine in response to stimulation with bacterial lipopolysaccharide and lipoteichoic acid. New research identified, sequenced, and expressed a novel recombinant salivary cholinesterase in the lone star tick, Amblyomma americanum. In addition to potential transmission of pathogens, tick bites from A. americanum have been reported to be responsible for development of alpha-gal syndrome, or red meat allergy, in humans. The recombinant salivary cholinesterase of A. americanum exhibits novel biochemical properties suggesting a potential novel role that could be involved in development of red meat allergy or in transmission and establishment of pathogens in vertebrate hosts. The physiological and biochemical roles of this and other salivary cholinesterases remains under continuing investigation.
Accomplishments
1. Standardized method to artificially infest captive white-tailed deer with ticks. White-tailed deer (WTD) are a main host for the adult life stages of tick species of veterinary importance. Since WTD play a vital role in tick ecology, research is often conducted to understand tick–host relationships. Previously reported methodology for WTD-tick studies was not always descriptive and was often inconsistent regarding how and what region of the WTD was infested with ticks. ARS researchers in Kerrville, Texas, in collaboration with Texas A&M University, developed and described a proven standardized methodology to artificially infest captive WTD with ticks for research purposes.
2. Desiccant dusts lethal to larval cattle fever ticks. Cattle fever ticks (CFT) are one of the most economically damaging parasites of cattle worldwide. Because the main control tactic for CFT involves the use of conventional acaricides, resistance poses a constant problem. ARS researchers in Kerrville, Texas, demonstrated that desiccant dust products, Deadzone (renamed Celite 610, a diatomaceous earth product), Drione (silica gel + pyrethrins + piperonyl butoxide synergist), and EcoVia (silica gel + thyme oil), with and without bioactive botanical additives, when applied dry were strongly lethal to larval CFT in the laboratory and after being released on dust-treated cattle.
Review Publications
Baker, A.S., Persinger, K.A., Olafson, P.U., Johnson, T.L. 2023. Artificial infestation of white-tailed deer with ticks (Acari: Ixodidae) to study tick-host interactions. Journal of Insect Science. https://doi.org/10.1093/jisesa/iead029.
Wulff, J.P., Temeyer, K.B., Tidwell, J.P., Schlechte, K.G., Lohmeyer, K.H., Peitroantonio, P.V. 2022. Periviscerokinin (Cap2b; CAPA) receptor silencing in females of Rhipicephalus microplus reduces survival, weight, and reproductive output. Parasites & Vectors. https://doi.org/10.1186/s13071-022-05457-7.
Temeyer, K.B., Schlechte, K.G., Gross, A.D., Lohmeyer, K.H. 2023. Identification, baculoviral expression and biochemical characterization of a novel cholinesterase of Amblyomma americanum (Acari: Ixodidae). International Journal of Molecular Sciences. https://doi.org/10.3390/ijms24097681.
Dos Santos, E.G., Dos Santos Bezerra, W.A., Temeyer, K.B., Perez De Leon, A.A., Costa-Juior, L.M., Dos Santos Soares, A.M. 2021. Effect of essential oils on native and recombinant acetylcholinesterase of Rhipicephalus microplus. Brazilian Journal of Veterinary Parasitology. 30. Article e002221. https://doi.org/10.1590/S1984-29612021024.
Showler, A., Harlien, J.L. 2023. Desiccant dusts, with and without bioactive botanicals, lethal to Rhipicephalus (Boophilus) microplus Canestrini (Ixodida: Ixodidae) in the laboratory and on cattle. Journal of Medical Entomology. https://doi.org/10.1093/jme/tjad010.
