Why are ticks carrying diseases spread in Europe?

For more than fifty years, there has been an increase in tick numbers in Europe, accompanied by an even greater spread Diseases they carry.

Climate change, human activities, changes in EcosystemsSeveral factors have been put forward to explain the reasons for this situation. More specifically, what are its causes and what is the human role in this phenomenon?

Mainly forest ticks

In Europe, ticks most affected by this overpopulation are Ixodes ricinus And to a lesser extent, ticks Dermacentor reticulatus.

Ixodes ricinus It is the most abundant tick inNorthern Hemisphere. It feeds exclusively on the blood of a variety of hosts: small and large Mammalsand birds and even reptiles… more than 300 Ocean Animals are prone to being bitten! On the other hand, the human Occasional guest. After hatching, the development of this tick follows several stages (called “stagnation”): the larva, mermaidThen the adults. Young nymphs are particularly involved in transporting Bacteria (such as those responsible for Lyme disease), viruses and even parasites in humans.

Ixodes ricinus need strong Humidity and a minimum temperature of 5°C to be active. It grows in vegetation, mainly in Forests (Even if he’s in town It is increasingly being reportedoften in spaces Lots of vegetation). Live inhumus and the excrement From the leaves, it spends its time climbing on the grass to look for sentry and then descending on the ground to rehydrate. in winterYou go into hibernation and stop all activity.

Since this tick lives mainly in the forest, all practices that increase forest cover favor its spread. However, these have changed somewhat in recent years.

Evolution of logging practices

Previously, after cutting wood, all parts the trees Exploited: tree trunks were used to make furniture, and firewood was provided for the crown or issue To produce chips or pulp. On the other hand, nowadays, a large amount of wood is left on the ground. Rodents and birds can take shelter and nest there, while ticks find the right protection (and food…). Environmentally questionable, echobog (cleaning by burning) and chipping have largely been abandoned, making the environment unsuitable for ticks.

The presence of bark beetles on certain types of trees has led to the use ofInsecticides By flicking damaged trees in the 1950s (and more recently by spraying with pyrethrins), which may also have indirectly affected ticks in the forest environment.

Moreover, in our country, the spread of ticks has been favored by landscape modification: the forest is now occupied 31% of the land (67% of the terraces are hardwood). However, the development of road infrastructure,Agriculture Intensive (new dimensions of agricultural holdings) and urbanization led to a fragmentation of the landscape. In some areas, forest masses are now isolated plots where a wild animals Favorable population (and Pathogens partners), Like rodents and deer.

The role of wildlife

Ticks are very blood-sucking: they feed only on blood. a lot of blood: tick Females need blood 100 times their body weight! To get it, they must have a variety of animals available. Their favorite hosts are deer in particular SpinnerAnd suids like Pig.

However, over the past forty years, the population of these two species has been Generally increased by a factor of 10, although there are regional variations. The result: deer and wild boars are increasingly found in urban and suburban areas, feeding in gardens.

If deer hunting and sweden can contribute to the organization of their societies, then some practices such as agrainage (artificial game feeding) on ​​the contrary favor their spread. Indeed, if deterrent feeding is intended to keep suicides in the heart of the forests, then feeding sites attract not only wild boars, but also whole animals that carry ticks: rodents, birds and their predators, badgers, and even roe deer and deer.

By concentrating more animals on a restricted surface, constant feeders create spaces that not only favor tick development, but also other wildlife-borne diseases.

The role of social and economic changes

A number of social and economic transformations He may have an increase in tick numbers in France. In many areas, desertification Rural areas and the abandonment of plots of land for cultivation helped the planting of trees (or afforestation), often spruce. Barren lands have also evolved, favored habitats for small and large mammals, and the preferred hosts for ticks. Ixodes.

Added to this is the fact that some of the human practices that altered the tick’s ecology and potentially lowered its population have also disappeared. Today we consume less game, we no longer collect the remains of crown wood after felling, and the dead leaves are no longer used in garden manure …

Climate change

The impact of climate change is often mentioned, especially in the potential decline in tick numbers Ixodes ricinus. This tick needs high ambient humidity (at least 80% humidity). If the frequency and severity heat waves Increase, ticks can disappear from certain areas. However, this effect on residentsIxodes spp. Currently limited.

On the contrary, the weather changes It can also create favorable conditions for the colonization of other places by ticks, especially at altitude if changes in vegetation cover. They can also become active all year round if season Less noticeable winter.

Many of these phenomena Well documented in the US. If the European context is not completely identical, we can expect the same observations on our continent.

Take coordinated action

Due to its wide distribution in the environment, it is an illusion to hope for its eradication tick. The causes of an increase in its population require multiple factors, reducing its size and controlling its spread require coordinated actions involving many actors: foresters, hunters, farmers, competent authorities, etc.

At the same time, we must also think about the definition of biodiversity suitable for the coexistence of humans and ticks. In a few years, we have moved from one extreme to the other in terms of “environment”. We must now ask ourselves how to properly protect our environment without making it conducive to the reproduction of these ectoparasites.

Picture of a white wooden fence outlining a garden.

Installing barriers around your garden helps keep wildlife away, and so you may carry ticks. © Randy Fateh, Unsplash

A few simple steps It can already be applied by everyone to achieve this: install barriers to prevent deer and deer from approaching dwellings, mow the lawn around them (ticks do not like drought), eliminating wet areas, deworming pets…

Tick ​​control is increasingly covered in the media, but it still struggles to become part of a real public health problem in France. Until the situation improves, it will therefore be necessary to continue to carry out a thorough physical examination after each march in the “retail areas” …

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