Is Catalonia prepared to face the diseases to come?
Global warming accelerates and globalization connects: once distant diseases are now transmitted locally.
Dengue fever is no longer just an imported threat arriving on airplanes. It's a homegrown reality in Catalonia. By the summer of 2024, the outbreak of eight cases in Vila-seca (Tarragonès) –the largest recorded in Spain– forcefully confirmed it: the virus is circulating here, transmitted by native mosquitoes. This episode is not an anecdote, but an alarming sign that reflects a profound transformation: global warming and mass mobility have shattered old epidemiological boundaries. A patient with fever and bone pain can no longer rule out a tropical disease without traveling. Faced with this new normal, the response cannot be fragmented. Human, animal, and environmental health are intrinsically linked. The solution has a name, One Health', an integrative approach that becomes an imperative necessity.
TheAedes albopictusThe dreaded tiger mosquito, native to Southeast Asia, is no longer a stranger. This invasive species, adapted to urban environments and resilient, has extensively colonized Catalonia, especially the coastal strip, in line with its expansion throughout the Mediterranean. Its massive presence opens the door wide to the transmission of viruses such as dengue, chikungunya, and West Nile. Data from Renave—the state epidemiological surveillance network—from 2023 quantify this risk: of the 369 cases of dengue recorded in Spain that year, the vast majority (367) were imported, demonstrating the constant arrival of the virus through travelers. But, importantly, two autochthonous cases were confirmed, demonstrating that the already established presence of this mosquito allows local transmission when the pathogen arrives.
"Rising temperatures and changes in rainfall create a perfect cocktail for the spread of vectors such as mosquitoes, ticks and sandflies [[some very small flying insects]", warns Rachel Lowe, researcher and director of the Global Health Resilience group at the Barcelona Supercomputing Center. Weather conditions are no longer a barrier, but a facilitator. Alerting of bites from an unknown mosquito was key," recalls John Palmer, researcher at UPF and co-founder of Mosquito Alert. Scientific confirmation validated a reality that was already stinging citizens after the species had probably been established years before.
Since then, surveillance has become professionalized, and tools such as Mosquito Alert have become fundamental. This platform is based on the citizen science, a participatory model in which non-specialists collaborate with researchers by providing data on the presence of mosquitoes in their surroundings. This allows for near-real-time mapping of vectors like the tiger mosquito. "Citizen science not only accelerates detection but also directly connects the population with the authorities, creating an irreplaceable early warning system," Palmer notes.
Although many cases continue to be imported, local outbreaks like the one in Vila-seca are irrefutable proof that the local transmission cycle is already established. This episode required a rapid and coordinated response (inspections, treatments, monitoring) and made it clear that entomological surveillance and the capacity to react are vital. It is no longer a question of "if" it will happen, but rather "when" and "where" the next outbreak will be if preventive action is not taken.
Globalization: Highways for Viruses
The interconnected world is a breeding ground for the spread of disease. "Mosquitoes have a limited flight range, but humans cross continents," Palmer summarizes graphically. "The real driver of the epidemic is not the flight of the mosquito, but the journey of the pathogen within us."
Catalonia, and especially Barcelona as a whole, hub International travel receives a constant flow of travelers for work, tourism, or family ties. This incessant traffic is a permanent gateway for exotic viruses. When an infected traveler arrives during the active mosquito season, the risk of local transmission multiplies exponentially.
But viruses don't only travel by plane. The globalization of trade opens up other avenues: shipping containers, used tires—the most likely route forAedes albopictus arrived in Europe decades ago–, ornamental plants… These passive vectors carry resistant mosquito eggs over long distances. "Global trade was key to the initial entry and expansion ofAedes albopictus"Palmer confirms. Once an invasive species establishes itself in a territory, all it takes is one infected human to arrive for the virus to find a new ecosystem in which to thrive.
![El calendario vacunal en Cataluña fija la vacunación de la tos ferina a los dos, cuatro, seis y dieciocho meses de edad, así como a los 6 años.](data:image/svg+xml,%3Csvg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 9"%3E%3C/svg%3E)
The combination of mass tourism and climate change is particularly explosive. Peak tourist seasons often coincide with optimal conditions for mosquitoes (heat, humidity, stagnant water), turning densely populated urban centers into potential epidemic hotspots if surveillance falters.
Lowe is emphatic: "Barcelona is at high risk of pathogen emergence or re-emergence. The challenge goes beyond science; it is deeply institutional and requires coordinated and proactive action." Anticipating, preventing, and acting quickly is the only viable strategy.
Climate change: the relentless accelerator
The Mediterranean is experiencing accelerated warming, and Catalonia is a direct reflection of this. In fact, according to the World Meteorological Organization (WMO), Europe is the fastest-warming continent, at a rate double the global average since the 1980s. This alarming trend, also documented by reports such as the Lancet Countdown Europe 2024, is no longer a future projection: it is the present that is transforming ours. Where once the climate was a barrier to vectors, it is now an increasingly powerful ally.
"Higher temperatures lengthen the active season for mosquitoes and accelerate their life cycle," explains Lowe. Warming also alters rainfall, often concentrating it and favoring the accumulation of stagnant water in urban environments (drains, flowerpots, drains) and multiplying breeding sites. Every summer is getting warmer and longer: data from the Catalan Meteorological Service confirm, for example, that in Barcelona, the number of tropical nights above 20°C has quadrupled in the last 50 years, rising from around 15 per year to more than 60 on average recently. These warm nights prolong mosquito activity and increase the likelihood of contact with humans.
But the climate impact goes beyond the vector. It affects viral replication within the mosquito, making it potentially more infectious more quickly. Furthermore, heat stress in humans, energy poverty, and social vulnerability aggravate the risk of medical complications, weaving a dangerous web of social inequality and the health impact of climate change.
Institutions like the Barcelona Supercomputing Center are already modeling these complex interactions, integrating climate, environmental, and health data to try to anticipate outbreaks and optimize responses. "Climate prediction can give us crucial weeks or months of advantage, but only if we know how to interpret it and act accordingly," says Lowe. But reality is stubborn: what were once seasonal annoyances are becoming permanent health risks. The Mediterranean is a new active epidemiological frontier.
In an interconnected world where zoonoses—diseases transmitted between animals and humans, such as avian flu or rabies—and climate-sensitive diseases dominate the scene, separating human, animal, and environmental health is a dangerous anachronism. The One Health approach is not an option, but the only coherent strategy. Catalonia is beginning to adopt it, but it needs to accelerate.
"One Health is an urgent operational necessity," Lowe emphasizes. "These diseases arise from the complex interactions between ecosystems, animals, and people. We can only manage them by overcoming the barriers between doctors, veterinarians, ecologists, urban planners, climate scientists, and politicians."
This translates into projects like IDAlert, which integrate different indicators, or local health plans that incorporate climate as a determining factor. But it goes further: it also involves, for example, rethinking urban design. "A simple, poorly designed drain can become a mosquito factory," warns Palmer. True coordination between urban planning, the environment, and public health is necessary in every decision that affects the environment.
Effectively implementing One Health faces real obstacles: insufficient or fragmented funding, bureaucratic rigidity between departments, institutional inertia, and often a lack of political will to address cross-cutting problems that require long-term investments. Overcoming these barriers is critical.
This is no longer a future hypothesis; it's our present reality. The growing presence of climate- and globalization-related diseases in Catalonia is a warning we cannot ignore. It forces us to understand health as an interconnected system: our well-being directly depends on the health of the ecosystems we alter, the cities we build, and the species we live with.
Catalan science responds
Catalonia not only suffers from the problem, but is also a key node in the search for solutions at the European level. Leading institutions combine epidemiology, big data, environmental monitoring, and citizen science.
Mosquito Alert is a paradigmatic example: this platform has achieved global impact, receiving and validating more than 286,000 citizen reports to date, and its data is used by managers and researchers in more than 100 countries. It has radically transformed vector detection thanks to citizen collaboration validated by experts. "We reach where traditional surveillance cannot, empowering citizens and fine-tuning the institutional response," Palmer emphasizes.
The Barcelona Supercomputing Center, led by Lowe, participates in European projects such as IDAlert and EpiOutlook, developing early warning systems that integrate multiple variables to predict outbreaks. "The key is to break down silos and integrate data from diverse disciplines for truly robust surveillance," Lowe insists.
Collaboration with the Barcelona Public Health Agency, the Global Health Institute, CREAF (Center for Ecological Research and Forestry Applications), and other entities is a strength of the Catalan system, connecting research and territorial action.
However, challenges remain: real-time data integration must be drastically improved, stable and ongoing funding for these monitoring systems must be secured, and—crucially—guarantee that scientific knowledge is translated into bold and effective public policies. Lowe makes this clear: "Research is only useful if it reaches decision-makers and they have the political will to act."
