The Shifting Map Series: No. 1
For a long time, the geographical distribution of many infectious diseases remained relatively stable across different regions of the world. When changes occurred, they were largely attributable to human efforts to make endemic areas healthier. In Italy, for example, we recall the large-scale reclamation of the Pontine Marshes and the subsequent widespread use of DDT after World War II, as writer Antonio Pennacchi ironically reminded us in his novel Canale Mussolini.
Therefore, if malaria were considered, certain regions of Africa would have been identified; for dengue, parts of Latin America and various tropical areas of Asia. Climate change, however, by altering temperatures across vast regions, is reshaping this geography, with risks whose full extent is still difficult to identify.
Malaria
Regarding malaria, for example, we are witnessing not only a reversal of the trend in the fight against the disease, which had seen considerable progress between 2000 and 2015, but also a shift in the African regions where malaria is most widespread.
Until recently, travellers could generally identify at-risk areas in advance and, where appropriate, undergo prophylaxis or adopt simple precautionary measures. Today, however, the boundaries separating at-risk areas from those considered safe are increasingly shifting and becoming less defined.
As temperatures rise, a progressive shift is being observed in areas exposed to malaria transmission across several African regions.
The consequences could be severe, given the limited capacity of local health systems to deal with the disease in areas where it was not previously endemic. Medical and paramedical personnel in these regions may lack direct experience with the disease, as well as adequate diagnostic tools or appropriate prevention protocols.
The geographical boundaries of malaria risk are changing and, as a result, health systems must adapt to address this.
Moreover, this scenario is not confined to Africa. Several areas of southern Europe are also affected, although the availability of established epidemiological databases and the greater resilience of European health systems significantly reduce the risk of transmission.
Change begins with a biological fact. The Anopheles mosquito, the vector responsible for malaria transmission, lives and thrives within a temperature range of approximately 16 to 34 degrees Celsius. The pathogen it carries finds its most favourable conditions at temperatures between 25 and 27 degrees.
By causing a rise in average temperatures, climate change is effectively reducing the risk of malaria in some lowland areas that have become too hot for the survival of the vector. At the same time, however, it is shifting the risk to higher altitudes – affecting mountainous areas and highlands where temperatures were previously too low for mosquitoes – as well as to regions located at more temperate latitudes.
The intensification of extreme precipitation events also favours the accumulation of stagnant water, creating ideal conditions for egg-laying and vector reproduction. Added to this is the species’ own adaptability: mosquitoes are increasingly colonising urban areas by exploiting small, artificial pools of stagnant water – sites for which adequate preventive measures are often not implemented. The phenomenon has been recorded in several countries, including Kenya and Papua New Guinea, as well as Ethiopia and Uganda, and is spreading toward regions of southern Africa that were once cooler, including South Africa.
Two studies published in Nature provide a particularly clear indication of this trend. The first, published earlier this year, highlights how extreme climate events such as floods and cyclones could cause an additional 500,000 deaths by 2050 by disrupting disease control systems. The second, published more recently, points to a new malaria map showing a risk increase of up to 20% in the coastal areas of southern Africa and the eastern highlands, alongside a reduction in lowlands that have become too hot.
In any case, the current figures are already extraordinarily high. The World Health Organization’s global monitoring data speak for themselves: the latest epidemiological estimates indicate 282 million malaria cases and approximately 610,000 deaths worldwide in 2024.
The WHO also reports a reversal of trends or stagnation in progress against malaria, with Africa continuing to account for 94% of global cases and 95% of deaths worldwide.
Not Only Malaria, but Also Dengue
Another worrying change in the realm of infectious diseases involves dengue fever, which was once largely confined to tropical and subtropical regions. It, too, is transmitted by mosquitoes, although in this case the mosquitoes are of the Aedes genus, which includes the tiger mosquito.
Temperatures favouring their proliferation range from approximately 24 to 28 degrees Celsius. According to data published by the Italy’s National Institute of Health, clusters of local transmission have been identified in Italy as well. Similar situations have been recorded in France and Spain; in these countries, however, the disease generally has a favourable clinical outcome.
In Latin America, by contrast, the geographical boundaries of the disease are shifting increasingly towards the south.
However, the number of deaths due to dengue has decreased significantly after reaching a peak of more than 11,000 in 2024, falling to approximately 3,000 in 2025 and 700 in the first half of this year, according to WHO data.
West Nile Virus and Lyme Disease: The Shift Is Already Visible in Europe
The changing geography of infectious diseases is perhaps even more evident when looking at the West Nile virus. Unlike malaria and dengue, West Nile is not a new disease for Europe, but its geographical distribution and transmission intensity are changing.
The virus is primarily transmitted by mosquitoes of the genus Culex, and temperature is one of the environmental factors influencing both mosquito reproduction and viral replication within the vector. Higher temperatures, combined with suitable water conditions and the presence of wetlands, can therefore favour the emergence of the virus in new areas.
The data recorded in Europe are increasingly significant. In 2025, 14 European countries reported 1,112 locally acquired human cases and 97 deaths. Italy alone recorded 779 cases – the highest annual number ever – while France reported cases in several regions where human infections had not previously been recorded.
Consequently, the European Centre for Disease Prevention and Control has warned that Europe could be entering a new phase characterised by increasingly frequent, longer and more intense transmission seasons for mosquito-borne diseases. Rising temperatures, prolonged summers, milder winters, and changing precipitation patterns are creating increasingly favourable conditions for vectors.
A similar, although different, process is observed in the case of Lyme disease. Here, the vector is not a mosquito but the Ixodes tick. In recent years, ticks have been detected at higher altitudes and more northerly latitudes, while their seasonal activity periods have also shifted. Climate change is one of the factors contributing to these changes, alongside land use and alterations in wildlife populations.
The significance of these developments goes beyond individual diseases. They demonstrate that the boundaries of infectious disease risk are not fixed geographical lines, but rather evolving ecological boundaries influenced by temperature, precipitation, human activity, animal populations, and the adaptive capacity of pathogens and vectors.
The Emerging Geography of Infectious Disease Risk
The changing distribution of infectious diseases therefore necessitates a series of measures, starting with the need for continuous monitoring of newly emerging risk areas, in order to implement appropriate preventive measures.
The changing geography of at-risk areas affects not only tourism but also investment and, more broadly, global economic activity.
Global warming is thus emerging as a significant geopolitical factor. It compels us to confront not only melting ice and the opening of new Arctic routes but also the resurgence of health threats that seemed to have been left behind. Changes in infectious disease risk must therefore become a key element to monitor and anticipate.
