The research team, led by Danyang Wang of Wageningen University together with collaborators in Spain, Portugal, Italy, France, and the Netherlands, set out to fill a persistent gap. Although leishmaniasis is endemic in southern Europe and public health authorities worry about outbreaks and geographic spread, the risk factors driving human disease in this region have been understudied. Most previous work focused narrowly on the parasite, its sand fly vectors, or climatic suitability models. The new analysis instead took a deliberately broad view, testing associations between leishmaniasis incidence and an array of variables spanning socioeconomics, immunocompetence, climate, land use, biodiversity, and the ecology of the pathogen, its vectors, and its animal reservoirs.

The findings carry a pointed message for policymakers. Socioeconomic factors were strongly associated with leishmaniasis incidence in endemic regions, although the specific factors and the magnitude of their effects varied among the five countries studied. In practice, this means that the profile of vulnerability looks different in, say, rural Portugal than in suburban Italy: occupational exposure, crowded or poorly constructed housing, and demographic composition each weighed differently depending on local context. The authors argue that this heterogeneity is precisely why one-size-fits-all control programs have struggled, and why national surveillance systems need to incorporate social and economic data alongside entomological monitoring.

Perhaps the most striking single result concerned human immunosuppression. The prevalence of immunosuppressive conditions in the human population was highly correlated with leishmaniasis risk in Spain and Italy, the two countries where relevant data were available. This aligns with the clinical understanding that Leishmania parasites, which persist inside host macrophages, are normally held in check by cell-mediated immunity. People receiving immunosuppressive therapy, living with HIV, or otherwise experiencing compromised immune function can experience reactivation of dormant infections or severe primary disease. In epidemiological terms, a growing population of immunocompromised individuals acts as an amplifier of apparent disease incidence, even where transmission intensity has not changed.

Climate, by contrast, played a more limited and geographically specific role. In the analysis, climatic variables likely delineated leishmaniasis-free regions from endemic regions in France, marking the northern edge of suitable conditions for the parasite and its vectors. But within endemic areas, climate did not emerge as a dominant driver of incidence. The authors draw a consequential inference from this pattern: climate change alone may not drive the spread of leishmaniasis within this century. That conclusion challenges a common narrative in which warming temperatures are expected to march the disease steadily northward across the continent, and it suggests that factors governing human exposure and susceptibility deserve at least equal attention in forecasting models.

The study also weighed the relative importance of the pathogen’s ecological partners. Where data permitted, the hazard posed by the parasite itself and the abundance of animal reservoirs—typically dogs and other canids that maintain the infection cycle—affected leishmaniasis risk more strongly than the hazard posed by sand fly vectors. This is a subtle but important distinction for control strategy. Interventions that target sand flies, such as insecticide-treated nets and residual spraying, address only part of the transmission equation. Reducing reservoir abundance, improving veterinary screening and treatment of infected dogs, and monitoring the circulation of Leishmania in animal populations may yield greater epidemiological returns, particularly in foci where reservoirs are numerous and closely associated with human dwellings.

Biodiversity emerged as a quieter influence. The researchers found that biodiversity was weakly but negatively related to leishmaniasis incidence, a pattern consistent with the dilution effect hypothesis, in which more diverse ecological communities reduce the probability that a vector encounters an competent reservoir host. The relationship was modest, and the authors are careful not to overstate it, but it adds leishmaniasis to the growing list of infectious diseases whose dynamics may be partly regulated by the integrity of surrounding ecosystems. Land use change, urbanization, and habitat simplification could therefore carry hidden costs for public health, even when their direct effects on sand fly habitat appear neutral or favorable.

Methodologically, the work illustrates the value of integrative risk modeling. Rather than testing one category of variables at a time, the team assembled a multi-country dataset and evaluated competing explanations—social, immunological, climatic, and ecological—within a common statistical framework. This design allowed them to rank the relative importance of drivers, something single-factor studies cannot do. It also exposed the data gaps that hamper such analyses: reservoir abundance estimates, standardized surveillance of vectors, and accessible human incidence records were unavailable or uneven across the region, constraining the precision of the models and complicating cross-country comparison.

The practical implications are broad. The authors highlight the need for surveillance of Leishmania species in humans, vectors, and reservoirs; systematic assessment of reservoir abundance; and improved data accessibility as crucial elements of disease prevention and preparedness. Because socioeconomic vulnerability and immunosuppression emerged as major drivers, they argue, control and prevention policies should extend well beyond entomology—into housing improvement, occupational protection, and clinical vigilance for at-risk patients. Public health systems in Spain, Italy, France, Portugal, and neighboring countries could integrate these findings into screening protocols, targeting immunocompromised individuals in endemic foci for earlier detection and treatment.

Finally, the study’s authors advocate a One Health approach to understanding and controlling leishmaniasis, one that brings together epidemiologists, social scientists, ecologists, veterinarians, and clinicians. The disease, they note, sits at the intersection of human poverty, animal reservoirs, vector ecology, and environmental change, and no single discipline can map that intersection alone. As southern Europe’s climate warms and its rural landscapes transform, the new evidence suggests that the leishmaniasis map of the coming decades will be drawn less by thermometers than by the living conditions, immune status, and surrounding ecosystems of the people at risk—a reframing that could reshape surveillance priorities across the Mediterranean basin.

Subject of Research: Socioeconomic and immunological risk factors for human leishmaniasis in southern Europe

Article Title: Socioeconomic risk factors and human immunosuppressive conditions are major drivers of human leishmaniasis in southern Europe

Article References: Wang, D., Matson, K. D., Hof, A. R., Berriatua, E., Maia, C., Bruno, F., Castelli, G., Pérez Cutillas, P., Risueño Iranzo, J., Verdú Serrano, E., Vitale, F., Xufre, Â., & van Langevelde, F. (2026). Socioeconomic risk factors and human immunosuppressive conditions are major drivers of human leishmaniasis in southern Europe. PLOS Neglected Tropical Diseases, 20(10), e0014787. https://doi.org/10.1371/journal.pntd.0014787

Image Credits: AI Generated

DOI: 10.1371/journal.pntd.0014787

Keywords: leishmaniasis, Leishmania, sand flies, socioeconomic risk factors, immunosuppression, southern Europe, climate change, One Health, disease reservoirs, biodiversity, PLOS Neglected Tropical Diseases, epidemiology

The methodological innovation at the heart of the study lies in what the authors call health impact event attribution. Traditional extreme event attribution, which has matured rapidly over the past decade, typically asks how climate change altered the probability of a meteorological anomaly such as a heatwave, using metrics like regional temperature maxima. But a hotter day does not translate directly into a death, and the relationship between temperature and mortality varies enormously with geography, climate, age structure and adaptation. The new approach closes that gap by coupling attribution statistics to epidemiological exposure-response functions calibrated for each of 34 European countries. Rather than asking how much more likely the 2022 heatwave was, the team asked how much more likely the mortality event itself was, the actual human toll, in a climate warmed by roughly 1.2 degrees Celsius compared with a pre-industrial baseline.

Technically, the researchers constructed generalized extreme value distributions for both temperature and heat-related mortality, allowing them to estimate return periods, how often an event of a given magnitude would be expected to occur, under current and counterfactual pre-industrial conditions. The ratio of these probabilities, known as the probability ratio, then expresses how much climate change has multiplied the odds of an extreme. Crucially, the mortality side of the analysis was built on weekly death counts from Eurostat, publicly available data that are updated in near real time. Temperature inputs came from the ERA5-Land reanalysis produced by the European Centre for Medium-Range Weather Forecasts, while global mean surface temperature changes were drawn from NASA’s GISTEMP record. The reliance on weekly rather than daily mortality data was validated using recent methodological work showing that temporally aggregated health data can yield unbiased temperature-mortality estimates, a finding that dramatically expands where such analyses can be performed.

The results reveal a continent divided. Across Europe as a whole, 2022-like heat-mortality events became substantially more probable, but the amplification in Southern Europe dwarfed the continental average. The Mediterranean region, already identified in the scientific literature as a climate change hotspot, experienced nonlinear increases in the likelihood of deadly heat, meaning that each additional fraction of a degree of warming multiplies the risk faster than the last. The study also projected forward, estimating probability ratios at 1.5 and 2.0 degrees Celsius of global warming, the benchmark thresholds of the Paris Agreement. Those projections show the risk continuing to climb steeply, with Southern Europe again bearing the steepest increases. The nonlinear character of these changes is particularly troubling because it implies that modest additional warming will produce disproportionately large jumps in mortality risk, compressing the time available for societies to adapt.

Equally significant are the demographic disparities the analysis uncovered. When the researchers stratified their models by age, they found that the elderly, particularly those aged 80 and older, faced sharply elevated probability ratios compared with younger populations. This pattern reflects well-documented physiological vulnerabilities, including diminished thermoregulatory capacity, higher prevalence of chronic disease, and greater use of medications that impair the body’s ability to cope with heat stress. Prior research has also documented sex-specific differences in heat vulnerability and adaptation, and the new framework’s ability to dissect such heterogeneity is one of its principal strengths. The authors emphasize that these findings make the case for population-specific analyses: a national average can conceal the fact that a small, highly vulnerable subgroup absorbs a wildly disproportionate share of the climate-driven mortality increase.

The 2022 summer serves as the study’s anchor case because it was, by most measures, the hottest summer ever recorded in Europe. Spain registered its warmest summer in its historical series, the United Kingdom breached 40 degrees Celsius for the first time, and the Copernicus Climate Change Service documented the season as a continental anomaly. Previous work by several of the same authors estimated that the summer of 2022 caused more than 60,000 heat-related deaths across Europe, while companion studies attributed a substantial fraction of that toll directly to anthropogenic warming. The new attribution analysis reframes those mortality counts in probabilistic terms: without human influence on the climate, an event of that lethality would have been extraordinarily rare, whereas in today’s climate it has become a recurring hazard with a return period measured in years rather than centuries.

What distinguishes this work from earlier impact attribution efforts is not only its scope, spanning 34 countries, but its speed and reproducibility. Because the mortality data are public and updated weekly, and because the analytical code has been released openly on GitHub, the framework can in principle be deployed rapidly after any extreme heat episode, transforming attribution from a retrospective academic exercise into a near-real-time public health tool. The authors argue that this capability could feed directly into health emergency forecasting systems, several of which are already being developed and tested in Europe, allowing authorities to anticipate and respond to deadly heat before the peak toll is counted. Rapid attribution of health impacts also carries weight beyond epidemiology, providing quantified evidence relevant to climate litigation, loss-and-damage negotiations and the legal and moral accounting of emissions.

The study arrives amid a broader scientific consensus that heat has become Europe’s leading weather-related killer. The Lancet Countdown and the World Meteorological Organization have both documented rising heat mortality, and modeling studies covering hundreds of European cities project that the burden will grow substantially without aggressive adaptation. Yet adaptation itself remains uneven. Research from Spain and the Netherlands shows that populations can shift their minimum mortality temperature over time, a signature of acclimatization, but the pace of such physiological and behavioral adaptation lags far behind the pace of warming. Heat-health warning systems exist across much of Europe but vary widely in coverage, trigger thresholds and effectiveness. The new findings sharpen the argument that adaptation investments, from cooling centers and urban greening to occupational heat protections and targeted outreach to the elderly, should be prioritized precisely where and for whom the probability ratios are highest.

Ultimately, the study delivers a double message. First, the fingerprint of climate change is now legible not just in thermometers but in mortality statistics: the deaths of thousands of Europeans in recent summers are statistically attributable to emissions, with Southern Europeans facing risks an order of magnitude beyond the continental average. Second, the tools needed to see that fingerprint are now fast, transparent and grounded in freely available data, meaning that the era of waiting years to understand the human cost of an extreme summer is over. As global temperatures continue to rise toward and potentially past the 1.5-degree threshold, the nonlinear escalation of heat-mortality risk documented in this analysis offers both a warning and a roadmap. The regions and populations identified as most vulnerable are known, the data streams needed to monitor the threat in real time exist, and the remaining variable is the speed with which societies choose to act on the evidence.

Subject of Research: Attribution of extreme heat-related mortality events in Europe to anthropogenic climate change

Article Title: Extreme event attribution for heat-related mortality due to anthropogenic climate change across Europe

Article References: Beck, T. M., Gudmundsson, L., Schumacher, D. L., Seneviratne, S. I., Achebak, H., & Ballester, J. (2026). Extreme event attribution for heat-related mortality due to anthropogenic climate change across Europe. Nature Health. https://doi.org/10.1038/s44360-026-00193-z

Image Credits: AI Generated

DOI: 10.1038/s44360-026-00193-z

Keywords: extreme event attribution, heat-related mortality, climate change, Europe, heatwaves, Nature Health, epidemiological models, Southern Europe, public health, adaptation, probability ratio, 2022 heatwave