The growing threat of vector-borne diseases, many of which are climate-sensitive, demands more robust monitoring systems and coordinated response efforts in both endemic and emerging regions. Climate change, expanding mosquito habitats and seasons, and shifting bird migration patterns drive the spread of diseases like West Nile virus (WNV) into new areas.

In response to these challenges, a team of international researchers affiliated with leading European initiatives, including the research projects  IDAlert and E4Warning and the Dutch Pandemic and Disaster Preparedness Center (PDPC), gathered at the Centre for Advanced Studies of Blanes (CEAB-CSIC) to discuss and enhance our understanding of the ecological pathways of WNV circulation and transmission within European wetlands. Their objective was to share and develop more integrated and effective surveillance strategies that bring together data on vectors, avian host dynamics, and their interactions, strengthening early warning capabilities and preparedness in the face of a changing climate and land use transformations.

Wetlands as crucial sentinels: integrated approaches

Wetlands and their peri-urban surroundings are recognized as critical hotspots for the surveillance of vector-borne diseases like WNV. These landscapes represent complex socio-ecological interfaces where natural and human-modified environments converge.

This ecologically rich region, characterized by wetlands and rice fields, provides ideal breeding grounds for mosquitoes and critical habitat for both resident and migratory birds, key components in the WNV transmission cycle. During the summer months, the human population in the area more than doubles due to seasonal tourism, significantly increasing the risk of human exposure to emerging pathogens.

As a result, Aiguamolls serves as a strategic study site for the E4Warning and IDAlert projects, offering an ideal setting to investigate the ecological drivers of arboviral circulation and to test innovative field tools. A central goal of this work is to improve the collection of blood-fed female mosquitoes, which can be analyzed to determine their host feeding preferences, providing insight into potential transmission routes of WNV.

To share and develop more integrated and effective surveillance strategies, a three-day meeting was organized. During this visit, one of the key goals was to further explore collaboration and comparison with wetlands near Rotterdam, another study site shared by the PDPC and IDAlert projects. By contrasting ecological dynamics and surveillance methods between these northern and southern European wetlands, researchers aim to better understand regional variability in West Nile virus circulation and improve transnational early warning systems.

Throughout the meeting, researchers carried out intensive fieldwork within the park, deploying BG-Sentinel and resting traps, and conducting mosquito aspirator sampling across a range of habitats, including rice fields, wetlands, and peri-urban areas. Furthermore, participants explored the use of passive acoustic monitoring systems to assess bird community composition and detect shifts that may impact viral dynamics. These acoustic tools offer new opportunities to track the presence and behavior of avian reservoir species over time.

Complementing these efforts, researchers received hands-on training in the use of FTA cards, which are small sampling devices placed in the field to collect mosquito saliva. These cards, developed at Erasmus MC, enable the non-invasive detection of arboviruses using molecular techniques and represent a promising method for monitoring viral circulation.

A meeting shaped by diverse expertise and career stages

One of the key strengths of the gathering was the rich diversity of disciplines and career stages represented, fostering dynamic exchange and cross-pollination of ideas. The meeting brought together experts in epidemiological modeling, virology, vector ecology, and environmental science, creating a vibrant forum for advancing integrated approaches to climate-sensitive disease surveillance.

Among the participants was Joacim Rocklöv, from Heidelberg University (Germany), coordinator of the IDAlertEuropean project, which focuses on understanding how climate change influences the emergence and transmission of infectious diseases to strengthen Europe’s public health resilience. He was joined by PhD candidate Julian Heidecke, who contributed to the modeling and risk assessment discussions.

Reina Sikkema, a virologist from Erasmus MC (The Netherlands), participates in IDAlert and represents the Pandemic and Disaster Preparedness Center (PDPC), which brings together experts to improve readiness for emerging health threats. She co-leads a frontrunner project at PDPC together with Maarten Schrama, ecologist, from Leiden University, who also participated. Within a large transdisciplinary team, they investigate how salinization and landscape change influence the ecology of mosquitoes and birds and how these changes modulate the risk of virus transmission. They were accompanied by team members Jordy Van der Beek, Tijmen Hartung, and Erley Lizarazo, each contributing to the interdisciplinary dialogue.

Local hosts from the Centre for Advanced Studies of Blanes (CEAB-CSIC) included Frederic Bartumeus, co-director of Mosquito Alert, coordinator of the E4Warning project, and partner in IDAlert. He was joined by his research team members Alex Richter-Boix, Catuxa Cerecedo-Iglesias, PhD candidates Nina Bogdanovic and Júlia Rodriguez-Grabalosa, and Olatz San Sebastián; Elisa Mora and Santi Escartín from the Mosquito Alert operational team.

Throughout the workshop, participants engaged in rich, collaborative discussions focused on the development of scalable, ecological, and epidemiological risk indicators, combining traditional and novel technologies in the field, e.g., smart mosquito traps (with automated count and identification of mosquito species), field-grounded molecular techniques, and automated acoustic recording of birds. Together, they explored strategies to model and forecast the risk of WNV and other climate-sensitive vector-borne diseases across Europe, leveraging the strengths of diverse data streams and scientific perspectives.

A recent study, published in The Lancet Regional Health – Europe, sheds light on the short-term effects of temperature and precipitation on the incidence of West Nile Neuroinvasive Disease (WNND) in Europe. Conducted by researchers from the E4Warning partners from the Barcelona Supercomputing Center (BSC) and international collaborators, the study utilized a nine-year dataset (2014–2022) to analyze 3,437 WNND cases across 20 European countries.

To estimate the association between lagged meteorological variables and WNND cases, the study employed a space-time-stratified case-crossover design. This design treats each case as its control, comparing exposures during the “hazard period” (the weeks before symptom onset) to exposures in comparable “reference periods.” Cases and controls were matched within the same region, calendar month, and year, as well as by the day of the week, enabling precise control of confounding factors such as geography, long-term trends, and seasonality.

For each case, weekly mean temperature and cumulative precipitation were attributed to the 8 weeks preceding the symptom onset day and matched control days. For instance, if a case occurred on May 17, 2019, in a given region, control days were selected from other Fridays in the same month and year. This method allowed researchers to infer associations between meteorological conditions and WNND incidence.

Meteorological data were obtained from the ERA5-Land climate reanalysis database, produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). Researchers retrieved gridded daily mean temperature and daily cumulative precipitation data for the European continent over the entire study period (2014–2022). ERA5-Land provides atmospheric and land-surface variables with a spatial resolution of approximately 9 km × 9 km. To align with epidemiological data, daily meteorological data were spatially averaged at the NUTS3 level.

Key Findings:

• Temperature and Precipitation as Drivers: Weekly mean temperatures exceeding 25°C (the 90th percentile) were associated with 36.4% of WNND cases, with the strongest effect observed two weeks before symptom onset. Similarly, weekly cumulative precipitation above 40 mm contributed to 13.1% of cases, with a delayed peak effect three weeks before symptom onset.
• Regional Variation: The study highlighted consistent effects of temperature across regions but noted moderate variability in precipitation’s impact, reflecting differences in local ecosystems and mosquito ecology.
• Implications for Early Warning Systems: The findings underline the potential of integrating meteorological data into early warning systems. These systems could enhance preparedness for WNV outbreaks, particularly in areas lacking robust vector and host surveillance infrastructure.

Broader Implications:

This study reinforces the link between climate variability and the transmission of mosquito-borne diseases, emphasizing the need for a One Health approach to address the complex interactions between climate, ecosystems, and human health. The results provide actionable insights for tailoring early warning systems and vector control strategies to mitigate the growing burden of WNV outbreaks in Europe.

For more details, check out the paper: Moirano, G., Fletcher, C., Semenza, J. C., & Lowe, R. (2025). Short-term effect of temperature and precipitation on the incidence of West Nile Neuroinvasive Disease in Europe: a multi-country case-crossover analysis. The Lancet Regional Health – Europe, 48, 101149. https://doi.org/10.1016/j.lanepe.2024.101149

And in the E4Warning Zenodo repository: https://zenodo.org/records/14383572