As a likely consequence of global warming, ticks areas are expanding in Europe. In Switzerland, a study using artificial intelligence has made it possible to predict the location of these areas and to evaluate their expansion. The researchers even managed to locate ticks carrying a specific bacterium. This is a valuable prevention tool, as ticks transmit several pathologies.
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Ticks are gaining ground. In Switzerland, these mites are proliferating due to global warming. Particularly active from March to November, the ticks transmit more and more diseases. 2020 was a special year: Favorable weather conditions and the need for social distancing led many people to take up outdoor leisure activities. At the same time, the health crisis slowed down access to vaccination against tick-borne encephalitis (TBE).
Every year1, the Swiss Federal Office of Public Health (Office Fédéral de la Santé Publique or OFSP) records tick bites and transmitted diseases:
For 2020, the figures are fixed at the end of September (graph 1-2) and the end of July (graph 3). Source: OFSP
Number of TBE cases, cumulative since the beginning of the year, comparison 2000-2020
Number of tularemia cases, cumulative since the beginning of the year, comparison 2004-2020
Estimated number of medical consultations in case of Lyme borreliosis and following a tick bite, per month during the season, comparison 2018-2020
To curb this alarming development, the OFSP will now have a valuable tool: the precise mapping of tick distribution in the country. Estelle Rochat, a researcher at the EPFL*, and her colleagues have succeeded, in the course of a vast study2, in accurately predicting the tick preferred zones, and in comparing these zones with those meeting the same criteria in 2009. She first identified the environmental factors favouring the presence of the sheep tick (Ixodes ricinus), based on:
The researcher used artificial intelligence to predict the probability of tick presence based on environmental variables around the collection points. Indeed, scientists know that the presence and activity of ticks are influenced by many environmental factors such as rainfall, temperature, humidity, etc.
By comparing the surface area of areas favorable to tick development with that of 2009, Estelle Rochat showed that it had increased by 10% in ten years4, reaching 25% of the Swiss territory in 2018. The North-East of the country as well as the Jura and Rhone valley are particularly concerned. For Gilbert Greub, Director of the Institute of Microbiology at the Centre Hospitalier Universitaire Vaudois (Lausanne, Switzerland) and a world specialist in ticks, this increase in areas at risk of tick exposure is explained by global warming. He observes that in the ten-year period "ticks have risen from 300 to 400 metres up the Alpine foothills".
The scientist's work did not stop there. She also succeeded in specifically locating the ticks that carry certain bacteria, the chlamydiales. Recent research has shown that ticks often carry large quantities of these still little-known bacteria, with a risk of transmission and secondary disease in humans. The algorithms developed by Estelle Rochat's team are in Open Access and may be used for future research on other tick-borne pathogens, including tick-borne encephalitis and Lyme disease.
* École Polytechnique Fédérale de Lausanne (Lausanne Federal Polytechnic School)
1. OFSP (Swiss Federal Health Office) - Maladies transmises par les tiques - Situation en Suisse
(in French only)
2. American Society for Microbiology (ASM) - Nested species distribution models of Chlamydiales in tick host Ixodes ricinus in Switzerland
3. "Tique" phone app
4. EPFL - Mapping to predict the distribution of ticks in Switzerland