Bilateral BBSRC-FAPESP: Defining the Genetic and Semiochemical Basis of Tick Resistance in Cattle

Lead Research Organisation: Rothamsted Research
Department Name: Biointeractions and Crop Protection

Abstract

Ticks and tick-borne diseases have major impacts on livestock, humans and companion animals. In particular, the cattle tick is found worldwide in areas with high temperature and humidity. Tick infestations lead to weight loss, anaemia and secondary infections, as well as transmitting diseases such Babesiosis, Theileriosis and Anaplasmosis. Traditionally, chemicals (acaricides) are the main tick control strategy, but this approach is increasingly problematic, mainly due to the evolution acaricide-resistant ticks and generation of chemical residues. Because vaccines have only had mixed success, there is an urgent requirement for new control measures. Cattle vary greatly in the tick loads, and much of this variation is known to be controlled by the genetic composition of the host, therefore breeding for increased tick resistance is possible. We hypothesize that the primary means by which host cattle differ in the tick resistance is through their production of attractant/repellent volatile chemicals on the skin surface, i.e. semiochemicals, which ultimately determine how many ticks remain attached to the skin surface. Identification of these chemicals and the genetic factors that lead to different chemicals being produced by different animals would give us powerful new control opportunities. We could either breed animals that will be more resistant to ticks or we could devise repellents to reduce tick load. This project is designed to achieve this: the goal is to understand the factors underlying genetic variation in the resistance of Brazilian cattle to tick infestations, at both the genetic and biochemical levels.

Firstly, on more than 1000 commercial Girolando cattle in Brazil we will collect detailed data on tick load, biological samples and factors which conceivably influence tick load. These data will provide an overview of factors influencing tick burden. After extracting DNA from the blood, we will genotype each animal using a tool known as a high density SNP chip. This allows us to genotype animals simultaneously for genetic markers at more than 750,000 locations throughout the genome. Analyses of these data will tell us where in the genome are the genes which have a large influence on tick burden, and hence tick resistance. But it doesn't tell us which genes.

To work out which genes are important, we will then examine the extreme animals in much more detail. Using skin rubbings obtained from the animals with the consistently highest and lowest tick burdens we will characterise the behaviour-modifying chemicals (semiochemicals) produced by these two groups of animals using chromatography and spectroscopic analysis. We will test the hypothesis that ticks respond to the same semiochemicals as for biting flies (e.g. 6-methyl-5-hepten-2-one). We will also purchase animals with genotypes that we predict to represent the extremes of susceptibility and resistance, and challenge these animals with ticks. We will then look at the RNA profile of these animals before and after challenge, using skin biopsies. The RNA profiles will tell us which genes are being expressed, and we can compare these profiles between resistant and susceptible animals. This will tell us which genes and biochemical pathways are predictive of resistance.

Using bioinformatics we will then bring all our results together. We will combine the gene expression and the semiochemistry studies to determine which genes are most likely to underpin variation in resistance. We will then relate these results to the SNP chip results: if likely genes fall in regions of the genome that have been shown to influence tick resistance then we have very strong evidence for genes (and genetic markers) that influence resistance. We will then validate our results by genotyping a further 200 phenotyped cows, and devise breeding strategies to improve resistance. We will also investigate semiochemical based or husbandry interventions from our data.

Technical Summary

Ticks have major impacts on animals and humans, worldwide. As well as transmitting disease, ticks lead to weight loss, anaemia and secondary infections. Acaricides are used for tick control, but this is problematic due to acaricide-resistance and chemical residue issues. But animals differ substantially in tick load, and this is genetically controlled. We hypothesize that the primary means by which host cattle differ in tick resistance is via their semiochemicals profiles, i.e. attractant/repellent volatile chemicals on the skin surface, with 6-methyl-5-hepten-2-one (a generic stress compound) being our primary candidate. We will perform a genome-wide association study (GWAS) for tick resistance, characterize semiochemicals which differ between cattle with high and low tick infestations (resistant and susceptible animals), identify genes differentially expressed between resistant and susceptible animals, integrate the results to obtain insights into the genetic and biochemical basis of tick resistance, and devise control options. The GWAS will be performed on >1000 Girolando cattle in Brazil, which will have been intensively phenotyped for tick burden with detailed epidemiological data (to identify risk factors). GWAS will be performed using data from the high density bovine SNP chip, giving >750,000 genotypes per animal, and analysed with current state-of-the-art techniques. From skin rubbings from animals with extreme tick counts, semiochemical profiles will be characterised using high resolution chromatography (GC, HPLC) and spectroscopic analysis. Gene expression will be performed using RNAseq on skin biopsies from extreme animals, before and after infestation, and pathways co-expressed with resistance determined. Together these data will inform on true extent of genetic control, underlying mechanisms and indicate actual loci contributing to variation. Validated SNPs for resistance will be identified, as will potential semiochemicals to be used as repellents.

Planned Impact

The impact of this project will be upon 1) Brazilian and UK academia and R&D, specifically research institutes and university departments undertaking animal health and agricultural/food production research, 2) business, particularly dairy industries worldwide, 3) Government and inter-Governmental policy makers, particularly those involved in tick control and livelihoods of animal keepers, 4) animal welfare, 5) the environment and 6) the general public. Currently, world food production is characterized by rising commodity prices and concerns over environmental impacts of livestock production. These are difficult challenges at a time when there is increased world-wide demand for animal protein yet continual pressure on animal producers.

Tick infestations are an intractable problem in many parts of the world, worsening with reduced efficacy of acaricides and pressures to limit acaricide usage. Ticks affect animal health, directly and through tick-borne diseases, animal welfare, productivity and the environmental. Sustainable solutions are urgently sought: those provided by this project potentially include the use of host genetics, refined repellents and improved management strategies - and hence will be appropriate for livestock production systems varying greatly in sophistication and technological capabilities. For example, this project will identify SNPs that can be used to breed animals for enhanced resistance. This is a simple, sustainable, cumulative and long term solution, exploiting the fact that dairy industries world-wide now select animals using SNP chip assays. However, it requires a sophisticated breeding infrastructure to work, making it an appropriate technology for most but not all cattle breeders. However, if semiochemicals are identified that can be used as tick repellents we will have a control technique that can be implemented in most situations, particularly where breeding solutions are challenging or immediate control is required. Lastly, if improved management practices can be identified from the epidemiological analyses, these can be applied in any situation, alongside (and enhancing) other control strategies.

The project will impact considerably at the environmental level. The cattle industry has a large carbon footprint and is responsible for a significant proportion of the gaseous emissions that impact on global warming. Switching away from cattle production is not an option in the short term, as the major products (milk and beef) are highly valued by society. Thus, the most straightforward way of reducing these environmental impacts is through increasing the efficiency of the production system, whilst respecting animal welfare; it can be demonstrated that this will lead to significant reductions in environmental impact. Outputs of this project will lead towards this goal. Secondly, tick control has traditionally been through acaricide usage. In addition to acaricide resistance, such chemicals carry a high environmental and human health impact, with chemical residue concerns, and their usage should be minimized. This project will move towards providing the solutions to substitute these chemicals by more sustainable, environmentally friendly solutions.

The project will impact on the general public through more efficient and productive ruminant livestock industries, as this will lead to a more sustainable supply of high quality dairy and beef products. The public will also take comfort knowledge that animals are being farmed in a more welfare-friendly way. The public will also benefit in the medium term from decreased chemical usage, and in the long term from the contributions to decreased environmental impact from cattle production.

In summary, this project will make major contributions to animal health, welfare and productivity, hence to food security, with impacting on Government, through industry, to the general public. The return on investment for the research is potentially enormous.

Publications

10 25 50
 
Description The overarching goal of this collaborative project between Rothamsted Research, University of Edinburgh (Roslin) and University of Sao Paulo, Brazil, was to provide fundamental understanding of the factors underlying genetic variation in the resistance of Brazilian cattle to tick infestations, at both the genetic and biochemical levels. The study design and knowledge gained was aimed at serving as a paradigm for dissecting genetic variation in host-ectoparasite interactions whilst, simultaneously, providing practical information necessary to provide sustainable improvements in tick control.

Overall, we have defined the Girolando breed in Brazil as the target cattle population (ca. 1150 individuals) and shared the phenotype data between Rothamsted, USP and Roslin. We have intensively phenotyped cattle for tick load (every 2 weeks for 5 months), through assessment of ticks counts following body and leg brushes, tick reproductive capability and hair follicle characteristics. We have collected blood from phenotyped cattle, and have genotyped animals with a high density bovine single nucleotide polymorphism array (BovHD chip/750K SNP chip) at Roslin. Preliminary analyses indicate that the genetics of resistance to ticks is influenced by multiple loci.

For the Rothamsted component of this project, we have collected skin rubbings and volatile samples from phenotypically extreme animals wrt tick resistance. Semiochemical profiles (attractant/repellent volatile chemicals) were sent to Rothamsted for GC, HPLC, MS analysis, compound identification and quantification, structure confirmation using authentic standards obtained from commercial suppliers/ chemical synthesis and multivariate analysis. Multivariate analysis has been used to measure differences between samples from extreme phenotypes. Collection of skin rubbings and volatiles for analysis was facilitated by a six month visit to University of Sao Paulo by junior researcher Andre Sarria, a recently recruited Brazilian PDRA at Rothamsted, with skills being transferred to the USP team for further development of the project in Brazil; a visit to the Federal University of Goias by Dr Sarria to study assays for investigating tick chemical ecology.
Exploitation Route Globally, sustainable intensification of livestock production systems requires the delivery of new livestock protection tools via breeding of resistance traits against ectoparasites (flies, ticks, mites). The findings here underpin the practical development of new livestock protection interventions based on chemical ecology, specifically animal stress signalling, and which can be delivered via the breeding-in of associated genetics for stress signal production. Delivery of impact from the findings in 3 ODA countries (Brazil, South Africa and Kenya) is being supported by 2 BBSRC GCRF-IAA projects and a newly awarded BBSRC Newton-Kenya grant (see further funding for details) and by a patent filing on a new tick repellent from non-hosts.
Sectors Agriculture, Food and Drink

 
Description Developing a New Tool for Phenotyping Tick Resistance in Cattle
Amount £100,809 (GBP)
Funding ID BB/S004882/1 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 11/2018 
End 10/2019
 
Description GCRF-IAA
Amount £6,000 (GBP)
Funding ID BB/GCRF-IAA/18 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 03/2017 
End 03/2017
 
Description GCRF-IAA
Amount £10,500 (GBP)
Funding ID BB/GCRF-IAA/17/18 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 01/2018 
End 02/2018
 
Description Collaboration with ARC Animal Production Institute, South Africa, on Genetic and Semiochemical Basis of Tick Resistance in Cattle 
Organisation Agricultural Research Council (ARC)
Country South Africa 
Sector Public 
PI Contribution Expertise in cattle-tick semiochemistry
Collaborator Contribution Livestock production systems
Impact Publications expected
Start Year 2017
 
Description Collaboration with Centre for Tropical Livestock Genetics and Health, University of Edinburgh 
Organisation University of Edinburgh
Country United Kingdom 
Sector Academic/University 
PI Contribution Expertise in livestock - tick semiochemistry
Collaborator Contribution Expertise in livestock genetics
Impact No outcomes have yet been achieved.
Start Year 2018
 
Description Collaboration with Egerton University 
Organisation Egerton University
Country Kenya 
Sector Academic/University 
PI Contribution Expertise in cattle - tick semiochemistry
Collaborator Contribution Expertise in livestock health and nutrition
Impact No outcomes have yet been achieved.
Start Year 2018
 
Description Collaboration with ILRI 
Organisation International Livestock Research Institute (ILRI)
Country Kenya 
Sector Charity/Non Profit 
PI Contribution Expertise in cattle - tick semiochemistry
Collaborator Contribution Expertise in livestock - tick interactions and tick biology
Impact No outcomes have yet been achieved.
Start Year 2018
 
Description Genetic and semiochemical basis of tick resistance in Brazilian cattle 
Organisation Federal University of Goiás
Country Brazil 
Sector Academic/University 
PI Contribution Co-Investigator; post doctoral scientist
Collaborator Contribution Principal Investigator (Roslin); co-investigator (Sao Paulo; Goias)
Impact Peer-review papers on tick resistance in vertebrates;
Start Year 2014
 
Description Genetic and semiochemical basis of tick resistance in Brazilian cattle 
Organisation Federal University of São Paulo
Country Brazil 
Sector Academic/University 
PI Contribution Co-Investigator; post doctoral scientist
Collaborator Contribution Principal Investigator (Roslin); co-investigator (Sao Paulo; Goias)
Impact Peer-review papers on tick resistance in vertebrates;
Start Year 2014
 
Description Genetic and semiochemical basis of tick resistance in Brazilian cattle 
Organisation University of Edinburgh
Department The Roslin Institute
Country United Kingdom 
Sector Academic/University 
PI Contribution Co-Investigator; post doctoral scientist
Collaborator Contribution Principal Investigator (Roslin); co-investigator (Sao Paulo; Goias)
Impact Peer-review papers on tick resistance in vertebrates;
Start Year 2014
 
Description GCRF-IAA workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Attended GCRF-IAA funded workshop at ARC-ODI, South Africa, 5-8 December 2017. Gave presentation "Volatile-Based Resistance against Ectoparasites"
Year(s) Of Engagement Activity 2017
 
Description Institute for Crop Science, Chinese Academy of Agricultural Sciences 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact Oral presentation given at Institute for Crop Science, Chinese Academy of Agricultural Sciences, Beijing, 12th November 2014. "New Chemical Ecology Based Opportunities for Agriculture in the Face of Global Climate and Population Challenges".
Year(s) Of Engagement Activity 2014
 
Description International Symposium on Biotechnology and the Environment, 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact 2nd International Symposium on Biotechnology and the Environment, Pucon, Chile, 28 November - 2 December 2016 (invited plenary). "Vector/host interactions: new opportunities for protection of plants and vertebrate animals against arthropod vectored pathogens by exploiting stress related signalling"
Year(s) Of Engagement Activity 2016
 
Description Oral presentation at Federal University of Goias Veterinary School. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Professional Practitioners
Results and Impact Invited oral presentation at Federal University of Goias Veterinary School, 8th September 2016
Year(s) Of Engagement Activity 2016
 
Description Oral presentation at IUPAC Pesticide Chemistry Congress, San Francisco, USA 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Oral presentation given at 248th ACS National Meeting, IUPAC Pesticide Chemistry Congress, San Francisco, 12th August 2014. "New Chemical Ecology Based Opportunities for Agriculture in the Face of Global Climate and Population Challenges".
Year(s) Of Engagement Activity 2014
 
Description Oral presentation given at University of Edinburgh, Roslin Institute 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact Seminar given on 'Volatile Phenotypes in Hosts: Can They Be Exploited for Improved Animal Health?'
Year(s) Of Engagement Activity 2018
 
Description Poster presentation at 3rd Agriscience Chemical Biology Forum 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact Poster presentation given at 3rd Agriscience Chemical Biology Postgraduate Forum, 31st March 2017. "Defining the semiochemical basis of tick resistance in farmed livestock and companion animals"
Year(s) Of Engagement Activity 2017
 
Description Presentation at KNUST, Ghana 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Undergraduate students
Results and Impact 2 Seminars given - 1 by Mike Birkett, 1 by Jozsef Vuts
Year(s) Of Engagement Activity 2018
 
Description Talk at Federal University of Goias - Brazil 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact Oral presentation given in Chemistry Department in Federal University of Goias - Brazil, 11th September 2016
Year(s) Of Engagement Activity 2016