Abstract
Global environmental changes are causing Lyme disease to emerge in Europe. The life cycle of Ixodes ricinus, the tick vector of Lyme disease, involves an ontogenetic niche shift, from the larval and nymphal stages utilizing a wide range of hosts, picking up the pathogens causing Lyme disease from small vertebrates, to the adult stage depending on larger (non-transmission) hosts, typically deer. Because of this complexity the role of different host species for emergence of Lyme disease remains controversial. Here, by analysing long-term data on incidence in humans over a broad geographical scale in Norway, we show that both high spatial and temporal deer population density increase Lyme disease incidence. However, the trajectories of deer population sizes play an overall limited role for the recent emergence of the disease. Our study suggests that managing deer populations will have some effect on disease incidence, but that Lyme disease may nevertheless increase as multiple drivers are involved.
Highlights
Global environmental changes are causing Lyme disease to emerge in Europe
In North America, access to white-tailed deer Odocoileus virginianus or other large hosts are required for tick reproduction, but annual fluctuations in deer numbers play a minor role in limiting Lyme disease (LD) under conditions of moderate to high deer density[12,13]
Most human cases in Europe are caused by Borrelia afzelii having a small mammal reservoir and Borrelia garinii having a bird reservoir, while B. burgdorferi sensu stricto causing LD in North America is present, but less common
Summary
The life cycle of Ixodes ricinus, the tick vector of Lyme disease, involves an ontogenetic niche shift, from the larval and nymphal stages utilizing a wide range of hosts, picking up the pathogens causing Lyme disease from small vertebrates, to the adult stage depending on larger (non-transmission) hosts, typically deer Because of this complexity the role of different host species for emergence of Lyme disease remains controversial. With only three main transmission hosts, any additional host species in the community may lead to a higher proportion of larvae feeding on non-transmission hosts, lowering pathogen prevalence in the tick population This is termed a dilution effect or buffering of disease with increasing biodiversity. Long-term and spatially extensive empirical data have been lacking from Northern Europe where LD is emerging
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