Project : USDA ARS

ARS Home » Plains Area » Kerrville, Texas » Knipling-Bushland U.S. Livestock Insects Research Laboratory » Cattle Fever Tick Research Unit » Research » Research Project #436694

Research Project: Integrated Pest Management of Cattle Fever Ticks

Location: Cattle Fever Tick Research Unit

2021 Annual Report

Objectives
Objective 1: Determine variables that influence tick range, suitable tick habitats, risk of tick-borne disease outbreaks, and potential for introduction of invasive ticks. Objective 2: Develop population genetic, ecological, and computational methods to improve cattle fever tick surveillance. • Subobjective 2A: Integrate cattle fever tick (CFT) genetic data with geographic information system (GIS) tools to enhance understanding of the geographic source and population structure of ticks causing outbreaks. • Subobjective 2B: Enhance GIS-based tools for CFT surveillance. • Subobjective 2C: Develop novel, and refine existing, CFT sampling methods. • Subobjective 2D: Model tick habitat suitability using machine/deep learning to predict favorable cattle fever tick locations in South Texas and Puerto Rico. Objective 3: Develop methods to control cattle fever ticks on livestock including new vaccines, genetic approaches, and other approaches to mitigate acaricide resistance. • Subobjective 3A: Evaluate the efficacy of novel acaricides and delivery systems against ticks on livestock, and through the targeted treatment of infested pastures and protected and sensitive habitats. • Subobjective 3B: Identify candidate antigens for anti-tick vaccines and formulate as vaccines for animal trials. • Subobjective 3C: Compare the genomes of R. microplus, R. annulatus, and Haemaphysalis longicornis to identify sex determination genes for the development of genetic control methods. • Subobjective 3D: Evaluate novel long-acting (LA) acaricide formulations to reduce the number of systematic treatments needed to manage cattle fever tick infestations. • Subobjective 3E: Define the role of genetics in the immunobiology of cattle-tick interactions to develop effective immunogenetics-based strategies to protect cattle from ticks and tick-borne diseases. Objective 4: Develop methods to mitigate the impact of invasive and exotic ticks. • Subobjective 4A: Determine genetic differences between H. longicornis populations from the U.S., and its native and invaded range through comparative molecular studies. • Subobjective 4B: Characterize genes known to be associated with resistance to commonly used acaricides in invasive and exotic tick species. Objective 5: Develop methods to control cattle fever ticks on wildlife, including anti-tick vaccine delivery, ecologically-friendly compounds, chemical delivery mechanisms and biological control organisms. Component 1: Problem Statement 1A • Subobjective 5A: Refine the remotely-activated sprayer to treat CFT infestation in nilgai and white-tailed deer. • Subobjective 5B: Evaluate delivery of anti-tick vaccines for use in white-tailed deer and nilgai. • Subobjective 5C: Evaluate natural botanicals, abrasives, and desiccants against cattle fever tick for use in sensitive wildlife habitats. • Subobjective 5D: Discover and evaluate classical biological control agents for cattle fever tick.

Approach
Cattle fever ticks, Rhipicephalus microplus and R. annulatus, are invasive pests that remain a threat to the livestock industry. They were eradicated from the United States in 1943; however, they remain established in Mexico and these populations tend to recolonize suitable habitats north of the Rio Grande. Cattle fever ticks transmit the microbes that cause bovine babesiosis and anaplasmosis. Significant cattle damage and economic loss would result if bovine babesiosis re-emerged in the United States. Research on new technologies to improve Integrated Pest Management (IPM) of cattle fever ticks is needed for implementation in the Cattle Fever Tick Eradication Program (CFTEP). This Program is operated in the Permanent Quarantine Zone established in south Texas along the Rio Grande to eliminate incursions from Mexico. The overall goal of this project is to conduct research on risk assessment and biology, surveillance, control, and monitoring and sustainability to improve integrated cattle fever tick management. The outcomes of this research will be effective, long-term adaptable technological solutions for the challenges that the CFTEP is facing. These include climate variability, acaricide resistance, involvement of native and exotic wildlife as alternative tick hosts, and the economic impact of tick outbreaks. The project will also benefit transdisciplinary efforts to achieve optimal health for animals, humans, and the environment, a concept known as “One Health”, by adapting this research to tick disease vectors expanding their range and exotic ticks that threaten animal and human health in the United States.

Progress Report
In support of Objective 1, to determine variables that influence tick range, suitable tick habitats, risk of tick-borne disease outbreaks, and potential for introduction of invasive ticks, a database was developed describing live ticks collected on white-tailed deer and nilgai hosts. These hosts were harvested during public hunts on a national wildlife refuge site. Tick species on each host was recorded and individual specimens were used in molecular assays to identify pathogens harbored by the various ticks. The tropical horse tick predominated the collections, and Gulf Coast tick, blacklegged tick, and inornate tick specimens were also identified. Tick-borne piroplasms and bacteria were detected in specimens, including Theileria cervi, Rickettsia parkeri, Anaplasma sp, and Ehrlichia sp. This provides valuable information about the tick species that overlap in habitat with cattle fever ticks and about pathogens that are circulating in this southern Texas environment. In support of Objective 2, deploy data visualization tools, including geographic information system (GIS)-based tools for cattle fever tick (CFT) surveillance, the GIS database incorporating location, collection, and infestation records for fever ticks infesting cattle, white-tailed deer, and nilgai continued to be updated regularly. This GIS database is used by the Cattle Fever Tick Eradication Program to inform operational decisions inside and outside of the Permanent Quarantine Zone in South Texas. Additionally, in collaboration with ARS partners a prototype was developed of a web mapping application combined with data collection via Collector and Survey123 Apps. This application will streamline spatial data collection, editing, and dissemination tasks in the field when a tick outbreak is discovered removing the potential for data errors and lag times in data collection and distribution. Access to the web map application in the field will allow tick inspectors to verify their location with landowners immediately with a selected premise and visualize data that pertains to program management and planning. In support of Objective 3, continued development of new tick control technology, the efficacy of novel acaricides and delivery systems were evaluated against ticks on livestock. Diatomaceous earth and silica gel augmented with botanical pyrethrins or thyme oil were determined to be highly effective against immature ixodid ticks. Additionally, silica gel and silica gel + pyrethrins, were evaluated for controlling immature ticks feeding on cattle. The nonaugmented silica gel prophylactically protected cattle from tick feeding, but it did not kill ticks that were already attached to the host and imbibing blood. The pyrethrin-augmented silica gel provided prophylactic protection as well as controlling ticks engaged in feeding. Potential genetic targets for tick control can be validated through gene silencing using RNAi. RNA interference (RNAi) was utilized to silence gene expression in tick cell culture and in live ticks. RNAi identified as acaricidal when microinjected into southern cattle fever ticks was commercially prepared and utilized to develop a qRT-PCR assay to quantitate RNAi presence in bovine blood, including use of a control dsRNA utilized to spike bovine blood samples to control and quantitate RNA recovery. RNAi silencing of the R. microplus pyrokinin receptor and another GPCR (G-protein coupled receptor) protein was completed. Refine the remotely activated sprayer to treat CFT infestation in nilgai and white-tailed deer. A large-scale field test of remotely operated sprayers to eradicate CFT on free-ranging nilgai antelope was repeated. More than 100 sprayers were deployed to apply locally native nematodes that kill CFT as the nilgai passed through fence crossings at private ranches in South Texas. Numbers of CFT on treated nilgai were significantly lower again for the second year. Compare the genomes of R. microplus, R. annulatus, and Haemaphysalis longicornis to identify sex determination genes for the development of genetic control methods. Utilizing the genomes of the southern cattle tick, R. microplus, and the Asian longhorned tick, H. longicornis, candidate genes associated with sex determination found in R. annulatus were compared to those found in H. longicornis. Highly conserved genes were gathered that may play a role in the sex determination of H. longicornis that shows orthology to R. annulatus. Novel long-acting (LA) acaricide formulations will reduce the number of systematic treatments needed to manage CFT infestations. Collaboration with the animal health industry on the research and development of safe LA acaricide formulations that could be used to treat cattle for the eradication of fever ticks continued. In support of Objective 4A, determine genetic differences between H. longicornis populations from the U.S. and its native and invaded range using comparative molecular studies, next generation sequencing was utilized to identify unique sequence differences between individual Asian longhorned ticks originating from the northeastern U.S. These sequence differences can now be used to compare populations of the Asian longhorned tick from other regions of the U.S. This provides an opportunity to understand population relatedness of this invasive species. In support of Objective 4B, characterize genes known to be associated with resistance to commonly used acaricides in invasive and exotic tick species, research continued in support of efforts by the Cattle Fever Tick Eradication Program to understand the development of acaricide resistance in outbreak strands of CFT in south Texas. A single mutation was discovered that provides acetylcholinesterase resistance to the acaricide coumaphos. Additional polymorphisms were expressed as recombinant proteins that indicate that combinations of acetylcholinesterase mutations may play a role in organophosphate resistance.

Accomplishments
1. Sequence and assembly of Rhipicephalus microplus and Rhipicephalus annulatus genome data. Ticks from the genus Rhipicephalus have global economic impact as ectoparasites of cattle. These ticks are known to harbor pathogens that cause diseases in cattle like cattle fever and anaplasmosis. ARS scientists in Kerrville and Edinburg, Texas, collaborated with researchers from Texas A&M University, Prairie View A&M University, and Carnegie Mellon University to sequence and assemble the genomes of R. microplus and R. annulatus. Having reference quality genomes of these two species of cattle fever ticks will advance research to identify genetic targets for developing new vaccines or novel anti-tick compounds.

2. Tropical horse ticks from white-tailed deer harbor theileriosis parasite, a protozoan that can cause anemia and animal death. The border region of south Texas shares a tropical tick fauna with Mexico that is unlike that found in the rest of the U.S. Cattle fever ticks, vectors of cattle tick fever, occupy this landscape, but other tick species that inhabit this region are understudied, as are the parasites that may be harbored by these tick populations. ARS researchers in Kerrville and Edinburg, Texas, described tick species collected from white-tailed deer and nilgai antelope that were harvested during public hunts on a national wildlife refuge site. The tropical horse tick predominated the collections, and Gulf Coast tick, blacklegged tick, and inornate tick specimens were also identified. Larval, nymphal, and adult tropical horse ticks harbored a theileriosis parasite reported from white-tailed deer; this parasite is typically transmitted by the lone star tick, which was not encountered in the study region. This provides valuable information about the tick species that overlap in habitat with cattle fever ticks and about pathogens that are circulating in this southern Texas environment.

3. Remotely operated nematode sprayers provide non-chemical control of cattle fever ticks. Cattle fever ticks (CFT) threaten U.S. animal agriculture because they transmit the microbes that cause bovine babesiosis, a disease that causes rapid death in cattle. In south Texas, wildlife such as white-tailed deer and nilgai antelope serve as alternative hosts for CFT, complicating eradication efforts. A novel technology to treat wildlife infested with cattle fever ticks was successfully tested and shown to be effective. ARS scientists in Edinburg, Texas, worked closely with the Animal and Plant Health Inspection Service-Veterinary Services and ranchers in South Texas to conduct large-scale field tests of a nematode sprayer to eradicate CFT on free-ranging nilgai antelope. More than 100 sprayers were deployed over 5000 acres to apply entomopathogenic nematodes (Nemasys-R, BASF Co.) as the nilgai transited through fence crossings. Numbers of cattle fever ticks on nilgai were significantly lower on nilgai at treated vs. untreated control ranches.

4. Population models explore the impacts of host, host habitat use, and eradication practices on cattle fever tick population dynamics. Cattle fever ticks (CFT) are vectors of bovine babesiosis and pose a threat to the U.S. livestock industry. Efforts by the Cattle Fever Tick Eradication Program (CFTEP) along the U.S.-Mexico border in south Texas are complicated by the involvement of wildlife hosts, including white-tailed deer and nilgai antelope. ARS scientists in Kerrville, Texas, in collaboration with partners at Texas A&M University, developed two CFT population models to explore the infestation scenarios. The first model assessed potential effects of host species composition and host habitat use patterns on CFT infestations and assessed the risk for CFT infestations across the landscape in the Permanent Quarantine Zone. The second model investigated the potential role of nilgai in sustaining CFT populations by simulating infestation and eradication scenarios. The developed models suggest: 1) integration of such data into these models will facilitate the development of new eradication strategies and will allow near-real-time infestation forecasts that can be used to predict and prevent wildlife impacts on CFT eradication efforts, and 2) infestations of CFT on nilgai add to populations of CFT larvae in the landscape and promote the persistence of CFT. The models develop the utility of enhanced biosurveillance using simulation tools to lessen risk and enhance area-wide tick management programs like the CFTEP.

U.S. DEPARTMENT OF AGRICULTURE

Cattle Fever Tick Research Unit: Kerrville, TX