title: Quantitative genetic analysis of the bTB diagnostic single intradermal comparative cervical test (SICCT).
abstract: Bovine tuberculosis (bTB) is a disease of significant economic importance and is a persistent animal health problem with implications for public health worldwide. Control of bTB in the UK has relied on diagnosis through the single intradermal comparative cervical test (SICCT). However, limitations in the sensitivity of this test hinder successful eradication and the control of bTB remains a major challenge. Genetic selection for cattle that are more resistant to bTB infection can assist in bTB control. The aim of this study was to conduct a quantitative genetic analysis of SICCT measurements collected during bTB herd testing. Genetic selection for bTB resistance will be partially informed by SICCT-based diagnosis; therefore it is important to know whether, in addition to increasing bTB resistance, this might also alter genetically the epidemiological characteristics of SICCT.
  
  
  
  Our main findings are that: (1) the SICCT test is robust at the genetic level, since its hierarchy and comparative nature provide substantial protection against random genetic changes that arise from genetic drift and from correlated responses among its components due to either natural or artificial selection; (2) the comparative nature of SICCT provides effective control for initial skin thickness and age-dependent differences; and (3) continuous variation in SICCT is only lowly heritable and has a weak correlation with SICCT positivity among healthy animals which was not significantly different from zero (P > 0.05). These emerging results demonstrate that genetic selection for bTB resistance is unlikely to change the probability of correctly identifying non-infected animals, i.e. the test's specificity, while reducing the overall number of cases.
  
  
  
  This study cannot exclude all theoretical risks from selection on resistance to bTB infection but the role of SICCT in disease control is unlikely to be rapidly undermined, with any adverse correlated responses expected to be weak and slow, which allow them to be monitored and managed.
authors.affiliation: The Roslin Institute and R(D)SVS, University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG, Edinburgh, UK. Smaragda.Tsairidou@roslin.ed.ac.uk.
authors.forename: Smaragda
authors.initials: S
authors.lastname: Tsairidou
authors.affiliation: Institute of Evolutionary Biology, University of Edinburgh, King's Buildings, West Mains Road, EH9 3JT, Edinburgh, UK.
authors.forename: Susan
authors.initials: S
authors.lastname: Brotherstone
authors.affiliation: Animal and Veterinary Sciences, SRUC, Roslin Institute Building, Easter Bush Campus, Midlothian, EH25 9RG, Edinburgh, UK.
authors.forename: Mike
authors.initials: M
authors.lastname: Coffey
authors.affiliation: The Roslin Institute and R(D)SVS, University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG, Edinburgh, UK.
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Bishop
authors.affiliation: The Roslin Institute and R(D)SVS, University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG, Edinburgh, UK.
authors.forename: John A
authors.initials: JA
authors.lastname: Woolliams
mesh_terms: D000367:Age Factors; D000818:Animals; D001947:Breeding / Q000706:statistics & numerical data*; D002417:Cattle; D060467:Disease Resistance / Q000235:genetics*; D005260:Female; D005820:Genetic Testing; D040582:Inheritance Patterns; D008297:Male; D009163:Mycobacterium bovis / Q000254:growth & development / Q000302:isolation & purification; D012885:Skinfold Thickness; D014374:Tuberculin Test / Q000706:statistics & numerical data*; D014380:Tuberculosis, Bovine / Q000175:diagnosis* / Q000235:genetics* / Q000382:microbiology