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

During the summer of 2024, project partners in Spain and Germany have been actively tagging birds with bio-loggers at key study sites to monitor their local and regional movements. Understanding bird movements and space usage during mosquito season is essential, as birds are the primary reservoirs for West Nile Virus (WNV). This project focuses on quantifying the mobility of key reservoir species, filling a crucial gap in current research by examining the local movement and dispersal patterns of resident bird species. Unlike the more extensively studied migratory birds, resident birds’ space usage near human settlements has been less explored. By gathering empirical data on these local movements, we aim to enhance our understanding of how resident bird populations contribute to virus transmission in areas close to human activity.

Fieldwork involves capturing and tagging various bird species with bio-loggers provided by the Max Planck Institute (MPI). For smaller bird species, such as blackbirds (Turdus merula) and starlings (Sturnus vulgaris), we are using bio-logging devices developed by MPI that operate with SigFox technology. Although the SigFox IoT network offers lower spatial accuracy compared to satellite navigation, it supports the creation of particularly small devices thanks to the network’s low power demands requiring fewer electronic components. This allows tracking of smaller species with minimal impact on their natural behaviour.  This innovative technology also allows for near real-time tracking and data transmission to the MovBank platform, making it ideal for monitoring the movements of these smaller species across different environments.

The data collected from these birds will be compared with similar data from other study sites within the project during the next years, allowing us to gain a deeper understanding of the potential WNV transmission dynamics across various landscapes. In addition to blackbirds and starlings, other species being tagged include mallards (Anas platyrhynchos), pigeons (Columba livia), and either western marsh harriers (Circus aeruginosus) or northern goshawks (Accipiter gentilis). The capture and tagging process began in June 2024 and will continue until September 2024, providing valuable insights into how these birds move through different landscapes and potentially contribute to the spread of WNV.

• Read more about the SigFox technology for animal tracking here: A multi-species evaluation of digital wildlife monitoring using the Sigfox IoT network.

In November, Kamran Safi from the Max Planck Institute of Animal Behavior visited the CEAB-CSIC team leaded by Frederic Bartumeus and the Girona study area: the Aiguamolls de l’Empordà Natural Park. This visit was instrumental in familiarizing with the study area and engaging with local stakeholders: the park staff, regional mosquito control officials, and local ornithologists.

The meeting facilitated the selection of five common and abundant bird species present across various study zones for tracking their mobility patterns using GPS or Sigfox biologging. While bird migration and mobility have been studied on large scales, there’s limited data on the daily mobility of resident species and the impact of the landscape on their movements. Understanding these aspects is vital to determine the role different species play in transmitting pathogens like the West Nile virus across areas, such as from marshes or rice fields to peri-urban or urban zones.

Wild birds, being primary hosts of the virus, play a crucial role in its spread, thereby shaping the epidemiology of the disease. Assessing how they connect habitats and transfer pathogens is particularly crucial in human-altered landscapes where pathogen spillover between birds and humans can be facilitated. The lack of detailed information in the dissemination process of zoonotic pathogens undermines risk assessments and management plans. A key goal of WP5 is to quantify the mobility of various host species to develop a spatially-explicit approach to wildlife epidemiology.