Climate change is reshaping the landscape of infectious disease worldwide, but the epidemiologic data needed to respond effectively remain insufficient. A May 2026 report by the American Academy of Microbiology and the American Geophysical Union concluded that climate-driven changes in temperature, precipitation, sea level, and extreme weather are already altering where and when pathogens and vectors thrive. The problem is global, and Italy is emerging as a particularly exposed hotspot.

Climate is a central driver of infectious disease dynamics. Higher temperatures, altered precipitation patterns, floods, and rising sea levels are changing the ecology, evolution, distribution, and prevalence of vectors and pathogens. The Intergovernmental Panel on Climate Change highlighted this in its Sixth Assessment Report, describing how the spatial and temporal spread of various pathogens is increasing with climate change. A 2022 study estimated that 58% of infectious diseases have been exacerbated by climate change at some point, while only 16% have been mitigated.

The 2025 Countdown report, published by The Lancet, showed a surge in dengue transmission — 7.6 million cases globally by early 2024, triple the previous year’s total. The risk increased by 29.6% between 2015 and 2024 compared with the period from 1951 to 1960, and for tick-borne diseases, the area with suitable climatic conditions increased by 3%-7%, depending on the disease, putting an additional 364 million people at risk between 2015 and 2024 compared with the 1950s.

What’s Happening in Europe and Italy

Italy is one of Europe’s hotspots for climate-sensitive infectious diseases. The European Centre for Disease Prevention and Control (ECDC) has identified Italy as one of the countries most exposed to mosquito-borne tropical diseases in a context where “longer, more widespread, and more intense transmissions of mosquito-borne diseases are becoming the new normal.”

“The role of climate change in Italy is clear for arboviruses, as can be seen from the trends of their vectors, mosquitoes. It is climate change that has allowed Aedes albopictus, the Asian tiger mosquito, to adapt to our country. We see it in the emergence of viruses like West Nile, dengue, and chikungunya, diseases that we were unaware of 15 or 20 years ago,” Massimo Ciccozzi, PhD, associate professor in epidemiology and health statistics at the Campus Bio-Medico University of Rome in Rome, Italy, told Univadis Italy, part of the Medscape Professional Network.

Rising temperatures create more favorable conditions for vectors: Another classic case is ticks, which in Italy are now found at altitudes of 1200-1400 m, previously inaccessible to these species. However, rising temperatures could also become a limit for these vectors, Ciccozzi said: “Mosquitoes are at their peak breeding activity between 25 °C and 30 °C; above these temperatures, mosquitoes are less active. When it’s hot, like 38 °C-39 °C, there are very few mosquitoes.”

Climate also reshapes animal migration and habitats, altering disease pathways. West Nile virus, whose main reservoir is migratory birds, has shifted its impact as bird routes change; recent outbreaks in central Italy correlate with these altered flyways. West Nile virus cases in Italy have tripled over 3 years, and early 2026 already recorded a case in the Province of Caserta. Ciccozzi said that until 20 years ago, the main migration routes of these birds ran from Morocco, Portugal, and Spain to the Pyrenees, then north through Italy, with a brief stop in the northeast before reaching the Balkans. There, the birds are bitten by mosquitoes, which can then transmit the virus to horses — a major incidental host — or, in their absence, to humans. Now, climate change has altered the routes of these birds, which now pass through southern Lazio and northern Campania. This shift has led to outbreaks of arboviral disease in central Italy, as seen last year. Even malaria’s former vector, Anopheles sacharovi, which had been absent since the 1960s, was detected again in September 2022.

Risk Multipliers Beyond Vectors

Climate change multiplies other risks too. Changing weather can worsen air pollution, which in turn increases susceptibility to respiratory infections (including viral diseases) such as SARS-CoV-2 infection or other respiratory viruses such as respiratory syncytial virus and influenza. A 2025 study by ARPA Lombardia — the environmental protection agency in Italy’s Lombardy region — established that climate change can worsen air quality, creating weather conditions in which pollutants such as particulate matter ≤ 10 micrometers, fine particulate matter with a diameter of ≤ 2.5 micrometers, nitrogen oxides, and ozone tend to stagnate, especially in areas such as the Po Valley. 

Extreme events such as floods and droughts strain water and health systems: Floods can cause wastewater overflows that raise the risk for norovirus, hepatitis A, rotavirus, and bacterial and parasitic enteric infections. Some studies also suggest links between warming and antibiotic resistance, though causality is still unclear.

The Missing Data

Despite clear signals, countries lack the integrated, high-quality data needed to predict, attribute, and respond to climate-related disease threats. Addressing the relationship between the climate crisis and infectious diseases requires collecting and correlating climate, health, and epidemiologic data, both to understand the relationship between climate and pathogens and, above all, to actively respond to new threats.

According to the May 2026 American Academy of Microbiology report, surveillance and diagnostic capacity for emerging infectious diseases needs to be strengthened. In particular, the report highlights a shortage of rapid, climate-resilient, and low-cost diagnostic platforms that can be used systematically, including in low-resource settings.

Fungal diseases have risen alongside extreme weather, yet testing is limited and costly. There is a shortage of rapid, affordable, climate-resilient diagnostic platforms for fungal infections. Health, climate, environmental, mobility, and demographic data are often siloed, aggregated at coarse spatial resolutions, or locked in non-computable formats (such as portable document format [PDF]s), hindering timely analysis and modeling. A positive example cited is the European Environment and Epidemiology Network of the ECDC, a network aimed at collecting and disseminating climate, environmental, demographic, and infectious disease data produced by a wide range of research projects, institutes, and government bodies, mainly in Europe.

The Complex Cause-Effect Relationship

Demonstrating a causal link between climate variables and disease spread — rather than a simple correlation — requires laboratory studies, long-term observational data, and models that account for social and health-system factors. As of May 2026, formal attribution studies remained rare and were largely limited to some mosquito-borne diseases. That does not mean there is no evidence that other infectious diseases are expanding because of climate change; rather, it means the evidence base remains incomplete, and few studies have established direct attribution with high confidence. The May 2026 American Academy of Microbiology report concludes that realizing the potential of more advanced predictive models will require sustained investment in research infrastructure and funding mechanisms to support long-term, collaborative, and integrated work.

Lessons From Italy’s Response

Italy has surveillance plans for arboviruses that are updated to reflect seasonal and geographic changes, and institutions such as the Istituto Superiore di Sanità (Italy’s National Institute of Health) are active in detection and response. Regional bodies such as ARPA Lombardia are documenting how climate can worsen air quality and related health risks. Yet Italian researchers note persistent problems with data accessibility and culture. Building usable databases requires manually extracting data from bulletins and PDFs. Where researchers have created integrated platforms, for example, ArboItaly, built from historical West Nile reports, these tools have helped produce predictive models showing factors such as minimum temperature having a major impact on case numbers. But such efforts remain labor-intensive and fragmented. The researchers also added: “We emphasize the importance of promptly seeking medical attention if you return from travel to endemic areas or if you develop symptoms consistent with vector-borne diseases, such as fever, rash, and joint pain, especially during mosquito season. Early diagnosis allows us to quickly identify any local transmission episodes and implement the necessary control and prevention measures. Finally, healthcare workers are encouraged to remain vigilant during mosquito season, even if you have not travelled to endemic areas, for the possible emergence of arboviruses in Italy.”

According to Francesco Branda, PhD, a researcher in epidemiology and medical statistics at the Faculty of Medicine, Surgery, and Dentistry at the Campus Bio-Medico University of Rome, "At the European level, we have the ECDC, which is sort of the hub where all the data on the diseases listed so far converge. And it’s a surveillance network that works. We’ve used ECDC data several times to create ad hoc databases; for example, we built our own platform, ArboItaly, for arboviruses. Since 2023, we’ve built a database based on all the historical West Nile data, starting with the PDF bulletins. However, it was a huge amount of work because we had to try to transform all the text into data that the algorithm could interpret and understand. Thanks to this data, last year we were able to build a predictive model. We discovered that, for example, the minimum temperature was the parameter that had the greatest impact on case prevalence. But Italy still lacks a data culture.”

From Data to Action

In 2023, Branda wrote in Scienza in Rete that a more integrated and open approach to data could be crucial in combating pandemics and, more generally, the spread of infectious diseases.

Experts call for a shift from passive surveillance to proactive, predictive systems. The so-called 3M model — Monitoring, Modeling, and Managing — used during COVID-19 can be adapted for climate-linked infectious diseases: continuous data collection, forecast modeling, and timely management decisions. But this approach needs open, granular, linked data; sustained research infrastructure; accessible diagnostics; and better communication to rebuild public trust. “The recent pandemic can be an opportunity to renew our focus on improving the quality, timeliness, and completeness of health data produced by governments, strengthening existing information management practices,” wrote Branda in 2023.

The May 2026 American Academy of Microbiology report stresses that global collaboration is complicated by differing national priorities and resources but is nevertheless necessary. “Public health systems will only be able to respond effectively to climate-related infectious disease threats if they enjoy strong public support and adequate public funding. This will require rebuilding social capital and trust in public institutions, vaccines, and public health, as well as ensuring effective communication and countering misinformation,” the report stated.

What Would Be Needed?

Data also need to be freely accessible in directly computable formats, without the need for laborious extraction from PDFs or other non-machine-readable sources. They should be as granular as possible in both space and time. Much epidemiologic data, for example, is still aggregated at a regional level, a scale that is often too coarse to capture local patterns of transmission. Just as importantly, datasets need to be integrated. Climate, mobility, demographic, and epidemiologic data are often held in separate systems that do not communicate with one another, limiting their value for prediction and response.

Branda argued that this fragmentation leaves health systems reacting too late, once emergencies are already underway. He said better data integration, combined with AI, could help shift the approach from passive response to proactive prediction by identifying at-risk areas earlier and clarifying which variables are driving transmission. But, he cautioned, the quality of any model will depend on the quality of the underlying data.

No country can manage climate-driven infectious disease risks alone. Yet building global collaboration remains difficult, given differences in national priorities, resources, and public health challenges.

Recent hantavirus events have shown that infectious threats do not respect borders. The report concluded that tackling climate-linked infectious diseases will require stronger health systems, closer international cooperation, and more robust cross-border institutions and agreements. It also calls for new partnership models, including city and regional networks, better data integration, wider use of modern technologies, and stronger integration of climate, microbiology, and environmental sciences into public health training and practice.

This story was translated from Univadis Italy.