New findings indicate that warming winters are contributing to increased cases of Lyme disease. The work in question was presented at the American Geophysical Union Fall Meeting during a session held in San Francisco from December 9 to 13.
Climate change is not only reflected by an average rise in temperatures, melting ice or a rise in sea levels. It is also expressed by multiple indirect effects , less scientifically controlled. An example concerns vector-borne diseases, whose evolution in a warmer world remains poorly understood.
Over the past few decades, cases of Lyme disease have been on the rise in the United States. Also, the question arises of the role played by climate change in this trend. If suspicions suggested an effective influence, this had never been clearly demonstrated so far. However, this step has recently been taken. Indeed, new findings have established a clear link between disease progression and climate change.
“There is a lot of evidence that climate, particularly temperature and humidity conditions, affects different parts of the life cycle of the tick that transmits Lyme disease,” recalls Lisa Couper, ecologist and lead author of the study. “But what is less clear is how this translates concretely into impacts on cases of Lyme disease » .
It should be remembered that the condition is transmitted by tick bite, when the latter carries a bacterium Borrelia . The symptoms associated with the infection are usually similar to those of the flu.
In their work, the researchers analyzed the changes that have occurred in Lyme disease over the past two decades. And this, in 7 sectors of the United States. By isolating the climate-related effects, they were able to show that the average rise in winter temperatures was a key factor . On the contrary, the increase in rains in the spring or the drying of the summers have not contributed to the increase in Lyme cases.
Of the 7 regions studied, only the Midwest and Northeast United States saw an increase in infections. Areas where thermal conditions are such that winter warmingoffers substantial room for improvement to the insect. In addition, the influence spills over significantly to the north. “It extends into southern Canada. They are starting to see cases of Lyme disease where they never had before,” reports Lisa Couper.
As global warming continues, Lyme disease will migrate to increasingly northern latitudes . In addition, cases in regions that have seen a recent increase are expected to continue to increase. In contrast, the arid southern sectors could experience a decrease. But nothing is less certain because the insect knows how to adapt. Results that can serve as a basis for other regions of the world. One thinks in particular of Europe where the disease also shows signs of progression.
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