Heterogeneity in the abundance and distribution of Ixodes ricinus and Borrelia burgdorferi (sensu lato) in Scotland: implications for risk prediction

Abstract

BackgroundCases 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.MethodsNineteen 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.ResultsThe 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.ConclusionsThis 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1875-9) contains supplementary material, which is available to authorized users.

Emergence of Lyme disease on treeless islands in Scotland, UK

“…Here we detail the first investigation of LD emergence in treeless habitats in Europe and show that both environmental hazard and human tick bite exposure contribute to higher LD incidence in these settings. In contrast to previous European studies, we found that the hazard amongst treeless habitats can be comparable to forested sites which are traditionally associated with higher LD risk (31,41).…”

“…Within islands with a high incidence of LD, improved grassland, heather moorland, bog and peatland habitats and domestic gardens all had similar tick abundance and prevalence of B. burgdorferi s.l. as mainland forested sites in Scotland (31,41). Our results suggest that the microclimatic conditions in these open habitats, possibly driven by the milder oceanic climate on the Western Isles, can be as conducive to tick survival as in woodlands.…”

Prevalence and distribution of Borrelia and Babesia species in ticks feeding on dogs in the U.K.

“…Four genospecies have been recently reported in Scotland, including B. afzelii , B. garinii , B. burgdorferi s.s . and B. valaisiana (Millins et al ., ). Borrelia burgdorferi s.l .…”

Introduced Grey Squirrels subvert supplementary feeding of suburban wild birds

“…Grey Squirrels are considered to be a significant conservation threat, particularly to the native Red Squirrel (Sciurus vulgaris) (Bertolino et al, 2014). Grey Squirrels carry disease (squirrelpox, Bruemmer et al 2010; Borrelia burgdorferi, the agent of Lyme disease, Millins et al, 2015, Millins et al, 2016, and cause economic losses in forestry (Mayle and Broome, 2013). In the context of this work, evidence suggests that urban Grey Squirrel population size and density is associated with the provision of supplementary food in gardens (Bowers and Breland, 1996;Parker and Nilon, 2008) and there is some evidence that they can competitively exclude birds at supplementary feeders (Hewson et al, 2004;Bonnington et al, 2014a).…”