Controlling Ticks by Treating Deer with Acaricides
Published on 21 February 2014 in Sustainability and Communities , Food, health and wellbeing
Introduction
Ixodes ricinus ticks are the most important vector of disease-causing pathogens in Europe. Ticks and tick-borne diseases such as Lyme borreliosis and louping ill virus are increasing. Lyme borreliosis damages human health, as well as taking up resources within the NHS, while louping ill virus kills sheep and red grouse, animals crucial to the economic sustainability of many rural areas in Scotland.
Several approaches are being taken in some areas to control ticks and tick-borne diseases. Notably these include large-scale intensive culls of mountain hares, which carry both ticks and louping ill virus, or using sheep treated with acaricides to act as “tick mops”. However, mathematical models predict that neither technique will adequately control ticks if deer are present, because deer are the most important host for ticks (see photograph).
Most upland areas of Scotland have deer populations and many studies show that reducing deer numbers can reduce tick numbers. However, deer have economic value from hunting and venison and they have a cultural value. Therefore, we asked the question: in theory, could treating deer with acaricide, rather than killing them, control ticks?
Key Points
- We used a mathematical modelling approach to explore whether treating deer with acaricide could, in theory, be an effective way of controlling ticks as an alternative to culling deer.
- Our models predicted that, theoretically, treating deer with acaricide could help control ticks and louping ill virus where deer densities are low and if high acaricide efficacies can be achieved.
- However, there are many caveats and practical considerations. It would be essential to run field trails before consideration as a practical management tool.
- Crucial considerations include the legality of using acaricides on wildlife, and welfare and environmental impacts of acaricides in the environment, uncontrolled doses, and withdrawal periods for using the meat as venison.
Research Undertaken
A mathematical model was constructed to predict how quickly ticks and louping ill virus could be reduced, depending on deer density and acaricide efficacy.
We ran the model using a theoretical population of deer treated with acaricide of 70% efficacy (because this was achieved in studies of white-tailed deer in the USA). The model predicted that tick reduction would be slower and less effective with higher densities of deer (10-20 years if 20 deer km-2), and faster with lower densities of deer (5 years if <10 deer km-2).
With higher deer densities, the model also predicted that better acaricide efficacy is needed but for lower deer densities, lower (and therefore more easily achieved) acaricide efficacies should be sufficient (e.g. for <7 deer km-2 only 20% efficacy may be sufficient).
When the model compared culling deer versus treating deer with acaricide, it predicted that both approaches perform equally at reducing ticks when there are low deer densities (<10 deer km-2). However, for higher deer densities the model predicted that both approaches were slow to reduce ticks, with acaricide treatment slightly more effective than culling.
In conclusion, the model always predicted that the fewer deer there are, the easier it is to control ticks.
Caveats and Practical Considerations
We emphasise this is a theoretical study. In practice, grouse populations are also regulated by habitat quality, weather, intestinal nematodes and predators. Land managers would need to ascertain that ticks and louping ill virus are the most important factor before considering a tick control strategy.
Achieving acaricide treatment may be problematic. In the USA, white-tailed deer used feeders with rollers impregnated with acaracide. However, red deer in Scotland generally use feeders in the winter when there are few ticks; during the tick season they move up the hills where maintaining feeders with acaricide may be impractical. However, this approach could potentially be used for roe deer, which behave more similarly to American white-tailed deer.
Finally, acaricides are not currently licenced for use on wildlife in the UK – licencing policy would need to change.
This research was co-funded by the Scottish Government, the Natural Environment Research Council and the Macaulay Development Trust. These results are published in the journal Parasitology:
Porter, R. Norman, R.A. and Gilbert, L. 2013. An alternative to killing? Treating wildlife hosts to protect a valuable species from a shared parasite. Parasitology 140, 247-25. (doi:10.1017/S0031182012001400)
Policy Implications
- This study was conducted in response to land managers wanting to explore the possibilities of alternative and novel ideas for tick control.
- Policy on licencing acaricides for use on wildlife would need to be amended if this approach is to be realistically considered.
- Evidence suggests that Policy and strategies that reduce deer densities should help control ticks.
Authors
Dr Lucy Gilbert, James Hutton Institute lucy.gilbert@hutton.ac.uk
Professor Rachel Norman, Stirling University
Dr Ros Porter, Sheffield Hallam University
Topics
Sustainability and Communities , Food, health and wellbeing
