Defining the genetic and semiochemical basis of tick resistance in cattle

• Grant number: 13/00626-7
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: March 01, 2013
• End date: March 31, 2013
• Field of knowledge: Agronomical Sciences - Veterinary Medicine - Preventive Veterinary Medicine
• Principal Investigator: Isabel Kinney Ferreira de Miranda Santos
• Grantee: Aline Girotto
• Host Institution: Faculdade de Medicina de Ribeirão Preto (FMRP). Universidade de São Paulo (USP). Ribeirão Preto , SP, Brazil

Abstract

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. 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. (AU)