Mosquitoes, heat, and tourists: Health Department warns that dengue fever has an easy time spreading through Catalonia.

Barcelona"When we detect cases in humans, we see the tip of the iceberg. We may have many more circulating that we haven't identified," warns Jacobo Mendioroz, Deputy Director General of Surveillance and Emergency Response at Public Health, regarding mosquito-borne diseases. He is referring primarily to dengue, West Nile virus, and chikungunya.

Rising temperatures due to the climate crisis and the increase in international travelers, both Catalans who go on vacation and those who visit the country throughout the summer, combined with the proliferation of mosquitoes, create a breeding ground for these diseases to become increasingly common in Catalonia.

While other areas of the Mediterranean are already seeing a surge in cases, in our country the impact has so far been slowed, but experts admit that they are "buying time" and that the incidence is likely to increase over the years, and that some of these diseases may even become endemic, and each of them.

"Thinking that we'll give up in Catalonia is naive," Mendioroz acknowledges, because the climate crisis is advancing relentlessly and every year thousands of people travel to areas where these diseases are circulating intensely. To curb this scenario and prevent an increase in cases this summer, the Department of Health has stepped up mosquito prevention and control and has its circuits ready to act quickly if cases are detected.

11 autochthonous cases

Despite efforts in epidemiological surveillance, between 2022 and 2024 there has been an increase in cases of mosquito-borne diseases in Catalonia, which have doubled in two years. However, of the 564 positive cases recorded, only 11 were infections of autochthonous origin, that is, in people who had not traveled to countries where dengue is endemic.

Last year, a native outbreak of dengue was detected in Vila-seca, affecting eight people, the largest outbreak in Spain to date. The rapid response of Public Health professionals prevented its spread, but sources within the department acknowledge that there is a risk that not all mosquitoes or infected people will be detected and that the outbreak could continue to grow.

However, the Secretary of Public Health, Esteve Fernández, rules out making predictions about how many cases there will be this summer and whether more local outbreaks will be detected: "Cases may rise, but it's difficult to know right now. We don't know if the incidence will double or triple; it will depend on the weather conditions. It's complex."

Control and surveillance

According to Fernández, surveillance is essential at the local level. Public Health explains that it is important for all municipalities to have a mosquito prevention and control plan, which includes actions to identify and periodically review potential breeding sites, raise public awareness, and provide the necessary treatments, prioritizing larvicides.

When a positive case of one of these diseases is detected that is not associated with international travel, mosquito control centers are activated, deploying to the area and identifying existing mosquito larvae and species to determine the risk of spread. Once the assessment is complete, the larvae and even some mosquitoes are eradicated, and the action is then monitored to ensure no further measures are necessary.

In Catalonia, the tiger mosquito can transmit dengue, chikungunya, and Zika, and the common mosquito can transmit the West Nile virus. For this reason, the Health Department emphasizes the importance of controlling these two species. A West Nile virus surveillance program also exists to detect early transmission in birds and horses and identify risk areas.