Tiger mosquito: climate change extends the risk of dengue fever to almost all of France

THE ESSENTIAL

• The tiger mosquito could conquer up to 96% of mainland France by 2085.
• Dengue, as well as Zika and chikungunya, could thus emerge across almost all of mainland France, a new study shows
• Rural and peri-urban areas will be the most at risk.

The tiger mosquito (Aedes albopictus) arrived accidentally in France in 2004. But by 2085, it could be found throughout mainland France except for high mountain areas, and perhaps some inland northern regions. As a result, our new study shows, dengue and the Zika and chikungunya viruses transmitted by this insect could also spread throughout all these colonized areas, except perhaps the Channel coast.

The expansion of these diseases is the direct consequence of climate change, which is altering the geographical distribution of different species, mainly through rising temperatures, and will continue to do so for several more decades.

When temperatures in mainland France approach those of tropical regions, where the tiger mosquito evolved over thousands of years, this insect reproduces and develops faster, lives longer, and bites more often. Understanding this change is essential to prevent the major risk it poses to public health. This is what we wanted to do through our new study.

How were these forecasts made?

To do this, we used mathematical models that estimate the mosquito population at a given place at a specific time. These models allow us to simulate the evolution of these mosquito populations using sets of weather projections that allow us to group together parameters such as temperature, precipitation, the abundance of breeding sites...

For this study, we used IPCC projections for the next sixty years, which vary depending on future climate policies: we distinguished between a "high pressure" scenario (+3°C and over the period 2066-2085 compared with the period 1986-2005) and a "medium pressure" scenario (+1.8°C).

These two trajectories have a direct effect on the expansion of the tiger mosquito: in the first case, between 89 and 96% of the territory would become favorable to its establishment; in the second, this expansion falls to 72%.

What this work allows us to understand

If this study is not the first to examine the impact of climate change on tiger mosquitoes, it nevertheless offers forecasts of unprecedented precision for mainland France.

It thus allows us to characterize the epidemiological risk by observing the differences in risk at different latitudes as well as between urban and peri-urban areas.

Although cities host more mosquitoes, our simulations show that rural and peri-urban areas will be more vulnerable to transmission than large cities, because each mosquito there bites a smaller number of people repeatedly, thereby increasing the potential for spread.

We are also among the first to have studied the possibility of mosquitoes being active all year round because of mild winters, which would allow them no longer to need to hibernate.

How can this research be continued?

Mainland France will therefore have to deal with the tiger mosquito. To minimize the risks of disease transmission, studies at an even finer scale could be of great help, in order to document the interaction between the tiger mosquito and humans depending on local conditions such as urban greening, water management, and vector control practices. By comparing all these data, we could thus identify the practices that minimize the risks.

At the same time, the operational implementation of the models must be studied, in order to develop a tool that every citizen could consult. In Montpellier (Hérault), the modeling community is working closely with local authorities, public health officials, and vector control agencies to produce a suitable tool. Soon, beyond weather forecasts, we will thus be able to offer the public a "mosquito forecast."

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