New findings indicate that warming winters are driving more Lyme disease. The work in question was presented to the American Geophysical Union Fall Meeting during a session held in San Francisco from December 9 to 13.
Climate change is not only manifested by an average rise in temperatures, melting ice or even a rise in sea level. It is also expressed by multiple indirect effects, less scientifically controlled. One example concerns vector-borne diseases, the evolution of which in a warmer world is still poorly understood.
Expansion of Lyme disease: the case of the United States
In recent decades, cases of Lyme disease have increased in the United States. Also, the question arises of the role played by climate change in this trend. If suspicion suggested an effective influence, this had never been clearly demonstrated until now. However, this step has recently been taken. Indeed, new results have established a clear link between the progression of the disease and the evolution of the climate.
“There is a lot of evidence that the climate, especially the temperature and humidity conditions, affects different parts of the life cycle of the tick that transmits Lyme disease,” said Lisa Couper, ecologist and lead author of the ‘study. “But what is less clear is how it translates concretely into impacts on Lyme disease cases.”
It will be recalled in this regard that the disease is transmitted by tick bite, when the latter is carrying a Borrelia bacteria. Symptoms associated with infection are usually similar to those of the flu.
The major role of winter temperatures
In their work, the researchers analyzed the changes that have occurred in Lyme disease over the past two decades. And this, across 7 sectors in 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 spring rains or the drying up of summers did not participate in the increase in Lyme cases.
Out of the 7 regions studied, only the Midwest and northeastern United States experienced a multiplication of infections. Areas where thermal conditions are such that winter warming provides substantial room for the insect to progress. In addition, the influence extends considerably to the north. “It extends to southern Canada. They’re starting to see Lyme disease where they’ve never had it before, ”reports Lisa Couper.
As global warming continues, Lyme disease will migrate to increasingly northern latitudes. In addition, cases from regions that have experienced recent increases are expected to continue to increase. In contrast, the arid areas of the south may experience a decrease. But nothing is less certain because the insect knows how to adapt. Results that could serve as a basis for other regions of the world. We are thinking in particular of Europe, where the disease is also showing signs of progression.