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