How do mosquito-borne diseases spread? Scientific research for public health

11/05/2025

Sampling at the Parc Natural dels Aiguamolls de l’Empordà

A team from CEAB-CSIC is studying the interactions between birds, mosquitoes, humans, and the environment in the Aiguamolls de l’Empordà Natural Park to understand how infections transmitted by dipterans spread. Providing scientific knowledge on this issue is key to designing effective strategies to prevent outbreaks of emerging diseases.

Some migratory birds that stop in wetland areas like the wetlands can carry viruses such as West Nile virus. The infection can be transmitted from bird to bird through mosquito bites, and jump to other animals —including humans— via the Culex pipiens mosquitoes, which feeds on both birds and mammals.

Gaining detailed and scientifically validated knowledge about how this virus spreads is essential to anticipate risk, as it can cause severe symptoms in both animals and people. Moreover, it has been shown that the context of globalization and climate change favors its spread, positioning it as an emerging disease.

A research team from the Centre for Advanced Studies of Blanes (CEAB-CSIC) is studying how West Nile virus spreads as part of the European project E4Warning, which aims to develop early warning systems for mosquito-borne diseases in both endemic and emerging areas. To do so, the team works in areas like the Aiguamolls de l’Empordà, in collaboration with the Natural Park and the Mosquito Control Service of the Bay of Roses and Lower Ter.

One part of their work involves monitoring and studying mosquitoes present in the area throughout the season. Using traps to catch adult mosquitoes, resting traps, and aspirators specially designed by a University of Florida researcher, they identify the species present and their abundance. From the collected mosquitoes, they determine how many are females and how many have ingested blood. In the laboratory, they genetically analyze the blood to find out what animal the mosquito fed on. This step helps reconstruct the network of interactions through which the virus might be circulating and provides a crucial first indicator for assessing the risk of spread at that time based on the species of mosquitoes and birds present.

Another aspect involves linking information on mosquitoes that can act as West Nile virus vectors with a key factor: the reservoir species. The team uses devices placed throughout the Park that record bird calls, allowing them to estimate which species are present and in what numbers, depending on the environment and time of year. This is important because not all bird species are potential virus carriers. Understanding the composition of the bird community at any given time is essential for assessing pathogen circulation risk. Equally important is knowing where and how birds move. For this, certain individuals are fitted with GPS devices to track their daily movements.

These biological data are complemented by environmental data, such as temperature and humidity measurements, water usage in the area, and information on human presence and movement —factors that can help explain the emergence of rural diseases in urban areas. Altogether, this allows researchers to analyze the ecological relationships involved in virus transmission and develop risk prediction maps and models.

The project involves research institutions from several countries, each focusing on a specific aspect of vector-borne diseases. In addition, E4Warning integrates other efforts like Mosquito Alert, which is included in the project to combine citizen science data with research center data. With the knowledge being generated, E4Warning aims to improve risk prediction capacity and contribute to the development of tools to prevent outbreaks of vector-borne diseases.