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

A recent study, published in Insects with E4Warning participation, explores the residual longevity of sterile male mosquitoes and its significance for understanding their field performance in Sterile Insect Technique (SIT) programs: an eco-friendly vector control method where sterile male mosquitoes are released to mate with wild females, reducing mosquito populations over time.

The study aimed to assess the longevity and quality of sterile and non-sterile male Aedes albopictus mosquitoes by using the “mark-release-recapture” (MRR) method. The findings revealed several important insights:

1. Sterile Males’ Longevity: Contrary to expectations, the study found that sterile male mosquitoes had a longer lifespan than their non-sterile counterparts when released into the wild. This extended longevity is a significant advantage for SIT programs, as it increases the likelihood of sterile males mating with wild females, thereby enhancing the effectiveness of population suppression efforts.

2. Effect of Wild Exposure: Sterile males that had been released into the wild lived longer when recaptured and monitored in a laboratory setting. This suggests that exposure to the wild, including factors like fluctuating environmental conditions and access to richer food sources, may improve the performance of sterile males.

3. No Negative Effect of Marking or Sterilization: The process of marking the mosquitoes with fluorescent dyes (following IAEA protocols) and sterilization via gamma radiation did not negatively affect their longevity. This supports the continued use of these practices in SIT programs.

4. Transport and Mass Rearing: Males reared and transported from large-scale production facilities exhibited slightly shorter lifespans compared to those reared locally under small-scale conditions. This suggests that optimizing transportation and rearing conditions can further improve the performance of sterile mosquitoes in the field.

Understanding the longevity and quality of sterile mosquitoes is crucial for optimizing SIT programs, particularly in areas where mosquito populations pose a significant public health threat. The study underscores the importance of refining rearing, sterilization, and transportation techniques to maximize the success of SIT in controlling vector populations and reducing the risk of mosquito-borne diseases.

This research advances our understanding of how sterile males perform in the field, providing valuable insights that can be applied to ongoing and future SIT initiatives and vector dispersal capacity estimation within the E4Warning project.

The study was a collaborative effort involving several institutions and experts across Europe. Key contributors included researchers from the following institutions: Benaki Phytopathological Institute (BPI) in Greece, Centre d’Estudis Avançats de Blanes (CEAB-CSIC), CREAF, and ICREA in Spain, Centro Agricoltura Ambiente “G. Nicoli” in Crevalcore, Italy, Centre for Vectors and Infectious Diseases Research Doutor Francisco Cambournac (CEVDI) at the National Institute of Health Doutor Ricardo Jorge (INSA) in Palmela, Portugal, and the Faculty of Medicine, Environmental Health Institute (ISAMB) at the University of Lisbon, and ASTRE, CIRAD, INRAE, based in La Réunion, France.

Link to the paper: Balatsos, G., Blanco-Sierra, L., Karras, V., Puggioli, A., Costa Osório, H., Bellini, R., Papachristos, D.P., Bouyer, J., Bartumeus, F., Papadopoulos, N.T., & Michaelakis, A. 2024. Residual Longevity of Recaptured Sterile Mosquitoes as a Tool to Understand Field Performance and Reveal Quality. Insects 15, no. 11: 826. https://doi.org/10.3390/insects15110826

You can find other scientific papers produced by E4Warning in our “Publication website”: https://www.e4warning.eu/outputs/publications/