• The research focuses on the relationship between two key meteorological factors—weekly average temperature and cumulative precipitation—and human cases of West Nile Neuroinvasive Disease (WNND), the most severe form of West Nile Virus infection. 
• Led by the Barcelona Supercomputing Center, a team of researchers has analysed data from over 3,000 WNND cases across 20 European countries, finding that climate change has directly increased the probability of local circulation of WNV in Europe.

In recent years, Europe has experienced an increasing number of outbreaks of West Nile Virus (WNV), a mosquito-borne pathogen, recording several cases of West Nile Neuroinvasive Disease (WNND), the most severe clinical form of human infection. A study led by the Global Health Resilience (GHR) group of the Earth Sciences Department at the Barcelona Supercomputing Center-Centro Nacional de Supercomputación (BSC-CNS) investigated the role of meteorological factors, specifically temperature and precipitation, in triggering the incidence of WNND cases across 20 European countries from 2014 to 2022. 

In the study, published in The Lancet Regional Health Europe, the researchers analysed  3,437 WNND cases related to weekly mean temperatures and cumulative precipitation preceding symptom onset. State-of-the-art methods were applied to evaluate the delayed and non-direct association between the two meteorological factors and the risk of developing WNND. 

The results indicate that meteorological factors significantly influence the risk of WNND. On the one hand, weekly mean temperatures exceeding 23°C were linked to a peak risk after 2 weeks, while, on the other hand, cumulative precipitation over 40 mm showed a peak effect after 3 weeks. Approximately 33% of WNND cases were attributed to high temperatures and only about 13% to excessive precipitation. These associations varied geographically, with limited temperature heterogeneity but moderate precipitation effects variability.

Dr Giovenale Moirano, from the GHR group and the first author of the research, stated: “Our study underlines that a notable proportion of WNND cases observed in the last years in Europe are attributable to unusually high temperatures and precipitation levels. Our results add to recent evidence that climate change has directly increased the probability of local circulation of WNV in Europe.”

The findings highlight the critical role of temperature and precipitation in WNND transmission. Elevated temperatures likely boost mosquito activity and the pace of virus replication, while precipitation can create mosquito breeding habitats. These insights underscore the potential of integrating meteorological data into public health strategies, particularly early warning systems, to forecast and reduce WNV-related disease burdens amidst climate change.

ICREA Professor Rachel Lowe, leader of the GHR group at BSC, explained: “By estimating the time interval between unusual meteorological conditions and the risk of developing WNND, our results provide useful information for the disease forecasting during the season and a shift towards operational early warning systems based on climate data.”

This is the first study evaluating the short-term effects of meteorological drivers on WNND incidence (i.e. within 2 months preceding reported WNND cases), considering all WNND cases diagnosed across the European continent over 9 years  (2014-2022). This has enhanced the current understanding of how meteorological factors influence WNV transmission in Europe. Moreover, it is the first study to systematically evaluate the exposure-response function between meteorological factors and WNND cases across multiple European countries as well as to quantify the proportion of WNND cases observed in the recent past attributable to unusual temperature and precipitation levels.

The research was funded by the European Union’s Horizon Europe program through the IDAlert and E4Warming projects. It also benefited from collaboration with the European Centre for Disease Prevention and Control (ECDC). The study emphasizes the need for interdisciplinary efforts to address vector-borne diseases in a warming world.

Reference: 

Moirano, G.; Fletcher, C.; Semenza, Jan C.; and Lowe, R.; 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; 4 Dec 2024; DOI: https://doi.org/10.1016/j.lanepe.2024.101149.