2023-07-19 12:38:12
DECRYPTION – This mite carries with it various pathogens capable of infecting humans, in addition to Lyme disease. In recent years, it has taken advantage of favorable conditions for its sustainability.
Forests, cities and gardens, ticks are now everywhere. For several decades, certain ticks, mainly forest ticks, have been expanding in France, spreading with them a procession of more or less serious diseases. These mites thus become a real public health problem.
Emerging diseases at our borders
Lyme disease has long been the only health risk mentioned in relation to the bites of these animals. But the health authorities are reporting the emergence of other pathologies, the symptoms and number of cases of which are increasingly worrying in France and in other European countries. At the beginning of July, the French public health agency published an initial assessment of one of these new pathologies: tick-borne encephalitis. This disease caused by a virus mainly transmitted by ticks Ixodes ricinus can affect the cerebral system with sometimes lifelong sequelae.
Cases are still rare, but the increase in their incidence in homes far from areas already known to circulate the virus, mainly the Grand Est, has drawn the attention of the authorities. Another great first, it is an infection transmitted both by ticks but also by food from infected animals. ” Encephalitis transmitted by ticks to animals can then pass to humans through the consumption of products made from contaminated raw milk, such as certain goat cheeses “, indicates the Pr Hansmann, head of the infectious and tropical diseases and internal medicine department at the Strasbourg University Hospital.
” READ ALSO – Tick bite: what is the risk of developing Lyme disease?
Anaplasmosis, which causes fevers and muscle pain, babesiosis, whose symptoms resemble those of malaria, or Crimean-Congo hemorrhagic fever are other diseases transmissible to humans whose incidence is little known because of their rarity, but which could gradually settle in the territory. Crimean-Congo fever is not yet present in France, but its vector, the tick Hyalommacirculates around the Mediterranean. « Migratory birds are suspected of bringing specimens back to France, which are currently safe because the seasons are not conducive to their development, but this could change in the years to come with global warming. »explains Nathalie Boulanger, entomologist specializing in infectious diseases and emerging diseases and professor of parasitology at the University of Strasbourg.
Ticks, good pathogen vectors
Of the 900 species of ticks existing in the world, two of them predominate in France. The most common is the “sheep tick” (Ixodes ricinus)closely followed by the tick of the genus Dermacentor. Difficult to distinguish with the naked eye, or even to feel on the skin, these mites feed on the blood of various mammals, birds and reptiles. It is this particular mode of feeding which makes them very effective vectors of diseases. Adult female ticks can ingest up to 100 times their weight in blood over a period of about 10 days.
« The injection of anesthetic substances contained in the saliva of the ticks is a determining factor, because, by this means, any bite is painless, which allows them to go unnoticed »explains the Pr Yves Hansmann. Fortunately, not all ticks carry pathogens and their bites are mostly harmless. « Only 10 % to 15 % of ticks responsible for Lyme disease are actually infected. Moreover, we know that the transmission of the pathogenic bacteria by the tick generally takes place 24 hours after the start of the meal, so if we manage to remove the’animal early enough, he’there is no risk of disease transmission »specifies the Pr Hansman.
Why are there more and more ticks ?
Urbanization and landscape modification have contributed to creating favorable conditions for ticks, and have enlarged their habitat areas. Changes in logging practices in particular have had a significant impact. Until the 1970s, every part of the cut tree found a use. Today, a considerable amount of wood is abandoned on the ground, constituting new moist refuges for ticks, but also for their hosts.
” READ ALSO – 30% of ticks carry pathogens
The prohibition of certain insecticides, such as DTT, or herbicides used for land clearing in the 1970s and 1980s also favored ticks. « Even if their ban is justified, it has indirectly contributed to the reappearance of ticks in places where these products were once used. », emphasizes Nathalie Boulanger. Another favorable factor: artificial feeding of game or « agrainage »which consists of placing food away from the fields in order to keep wild boars away. « The problem with these practices, in principle highly regulated, is that they bring together hosts of interest, including rodents, birds, deer, wild boars, in forest areas where ticks are also found. », explains the entomologist. Added to this is a change in hunting practices, resulting in a significant increase in deer and other large wild ungulates, which are very favorable to tick populations.
On a much more global scale, the repercussions of climate change are also held responsible for an increase in the presence of ticks, due to warmer temperatures and longer seasons. Generally, they are present from March to June, with a significant peak of activity in May. However, they could come to persist during milder winters or even colonize environments located at higher altitudes which are experiencing significant changes in vegetation.
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