title: Heterogeneity in the abundance and distribution of Ixodes ricinus and Borrelia burgdorferi (sensu lato) in Scotland: implications for risk prediction.
abstract: Cases of Lyme borreliosis, a vector-borne zoonosis caused by bacteria in the Borrelia burgdorferi (sensu lato) species group, have increased in recent years in Europe. Knowledge of environmental factors associated with abundance of the tick vector Ixodes ricinus and the pathogen B. burgdorferi (s.l.) is of interest to understand responses to environmental changes, predict variation in risk and to inform management interventions.
  
  
  
  Nineteen woodland sites across Scotland were surveyed in 2012 for B. burgdorferi (s.l.) infection in questing I. ricinus nymphs (n = 200 per site), deer abundance and vegetation. Climatic factors were extracted for each site. Six additional sites were surveyed for questing nymphs in both 2012 and 2013 (n = 200 per site and year) to test for variation in B. burgdorferi (s.l.) prevalence between years.
  
  
  
  The mean prevalence of B. burgdorferi (s.l.) across 19 sites was 1.7% (95% CI: 1.4-2.2%; range 0-6%), all four genospecies known to be present in the UK were detected: B. garinii, B. afzelii, B. burgdorferi (sensu stricto) and B. valaisiana. A higher prevalence of B. burgdorferi (s.l.), higher densities of nymphs and higher densities of infected nymphs were found at sites with warmer climates, estimated with growing degree-days. No association between infection prevalence in nymphs and woodland type (semi-natural mixed vs coniferous) or deer density was found. At six sites sampled in 2012 and 2013, there was a significant increase in B. afzelli prevalence at two sites and a decrease in B. garinii prevalence at one site.
  
  
  
  This study highlights challenges for the prediction of risk of Lyme borreliosis, reflecting the sensitivity of both pathogen and vector ecology to habitat, host and climatic factors. Significant changes in the prevalence of individual genospecies at sites monitored across time are likely to be due to variability in the host community composition between years. Our results indicate the importance of monitoring dynamic variables such as reservoir host populations as well as climate and habitat factors over multiple years, to identify environmental factors associated with Lyme borreliosis risk.
authors.affiliation: Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, Scotland. Caroline.Millins@glasgow.ac.uk.|The Boyd Orr Centre for Population and Ecosystem Health, University of Glasgow, Glasgow, Scotland. Caroline.Millins@glasgow.ac.uk.
authors.forename: Caroline
authors.initials: C
authors.lastname: Millins
authors.affiliation: James Hutton Institute, Craigiebuckler, Aberdeen, Scotland.
authors.forename: Lucy
authors.initials: L
authors.lastname: Gilbert
authors.affiliation: Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, Scotland.|The Boyd Orr Centre for Population and Ecosystem Health, University of Glasgow, Glasgow, Scotland.
authors.forename: Paul
authors.initials: P
authors.lastname: Johnson
authors.affiliation: Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, UK.|Division of Applied Medicine, University of Aberdeen, Aberdeen, UK.|Present Address: Food Standards Scotland, Aberdeen, Scotland.
authors.forename: Marianne
authors.initials: M
authors.lastname: James
authors.affiliation: Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, Scotland.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Kilbride
authors.affiliation: School of Environment and Life Sciences, University of Salford, Salford, UK.
authors.forename: Richard
authors.initials: R
authors.lastname: Birtles
authors.affiliation: Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, Scotland.|The Boyd Orr Centre for Population and Ecosystem Health, University of Glasgow, Glasgow, Scotland.
authors.forename: Roman
authors.initials: R
authors.lastname: Biek
mesh_terms: D000818:Animals; D015748:Borrelia burgdorferi Group / Q000302:isolation & purification*; D002980:Climate; D017753:Ecosystem; D065928:Forests; D007303:Insect Vectors; D018884:Ixodes / Q000254:growth & development* / Q000382:microbiology*; D008193:Lyme Disease / Q000453:epidemiology*; D015995:Prevalence; D018570:Risk Assessment; D012606:Scotland
keywords: Borrelia burgdorferi; Host community; Ixodes ricinus; Risk prediction; Spatial heterogeneity