The risk of Lyme borreliosis is greatest in spring and early to mid-summer, with Ixodes ticks being found in abundance on vegetation and animals. However, significant tick activity can occur in mild winters, and disease transmission may occur unusually early or late in the year (Dautel et al. 2008. Int J Med Microbiol. 298 Suppl 44: 50-4). Ixodes ricinus s.l. ticks prefer to live in dense woodland where there is little air movement and high humidity. However, they will conduct their ambush strategy from anywhere that has a good cover of foliage and a mat of decaying vegetation that maintains adequate humidity for ticks to rehydrate themselves. This can include gardens or campsites, particularly if the area is also populated by large mammals such as deer, sheep, cows and horses, which are essential for feeding adult female ticks.
Livestock
Ixodes ricinus has been the subject of control measures in Europe for many years because of its importance as a livestock parasite. These control measures consist mainly of the application of persistent acaricides to animals, usually as dips, but more recently in the form of pour-on synthetic pyrethroids and insect growth regulators. Destruction of the tick microhabitat, principally as a by-product of the improvement of agricultural land, has also been widely carried out.
Woodland
These measures are not appropriate for a sylvatic zoonosis such as Lyme borreliosis, which is generally associated with woodlands. European vectors of Lyme borreliosis, ticks of the I. ricinus complex, have attracted attention in the past as the vector of another zoonosis, tick-borne encephalitis, and woodland is the main habitat for this disease as well. Extensive studies on tick-borne encephalitis have shown that such habitats cannot be readily modified (by vegetation clearance, burning, etc.) to affect tick populations without significantly changing their nature.
Area control with acaricides on such a scale is expensive, impractical, and environmentally damaging. No similar studies seem to have been carried out in Europe regarding Lyme borreliosis control. However, gardens, parks, and campsites, which may harbour Borrelia-infected ticks, are more amenable to these approaches.
Wild animals
The tick maintenance hosts and spirochaete reservoir hosts in Lyme borreliosis foci are usually wild animals and targeting ticks on these animals clearly presents very different problems compared with controlling ticks on livestock. Success depends largely on the development of self-medication systems. Studies have been conducted on the provision of treated cotton waste for use as nesting material
by small mammals, the use of self-applicators impregnated with acaricides such as amitraz at deer feeding stations, the feeding to deer of systemic acaricides such as avermectins (e.g., ivermectin) and anti-chitin growth regulators (e.g., benzoylphenylurea derivatives), and the application of biological agents such as pathogenic fungi (e.g., Metarhizium anisopliae).
Measures focused more on reducing the number of deer in the habitat, the maintenance host for ticks, include exclusion by fencing and depopulation by culling and removal (and perhaps contraception in the future). Several studies have been conducted , and although the effects have been demonstrated, there is a widespread view that such measures are not sufficiently practical for large-scale use. Most of the methods considered so far would probably be even more difficult to implement in Europe, where the roe deer, Capreolus capreolus, the commonest species, is solitary and secretive. However, effective methods of controlling ticks on wildlife could have an important impact in peri-domestic situations and in parks, and continued efforts should be made to develop appropriate technologies.
Domestic areas
The following should be used as a guide for managing gardens, campsites and picnic areas in endemic areas:
- Discourage animals such as birds, rodents, deer, sheep and horses from coming to feed.
- Remove foliage and decaying vegetation from the area.
- Keep grass short and trim any overhanging bushes.
- Consider the use of pesticides in extreme cases *.
- Pesticides can be used to control ticks on domestic hosts (see Stafford & Kitron 2002. In ‘Lyme borreliosis: Biology, epidemiology and control. Eds JS. Gray, O. Kahl, Lane RS, G Stanek, CABI pp. 301-334; Piesman & Eisen 2008. Annu. Rev. Entomol. 53: 323-43)*
*Pesticides may have harmful effects on humans, animals and the environment. A decision to use chemical control methods should only be taken after careful consideration of the benefits of usage, together with the threat posed by tick-borne diseases in the area
Humans
The most effective prophylactic measures against ticks consist of preventing them from feeding on humans by wearing appropriate clothing, applying various repellents such as N,N-diethyl-toluamide (DEET), synthetic pyrethroids (e.g., permethrin), and most importantly, disseminating information and advice, including the need for inspection and prompt removal of any ticks.