Researchers from the Carlos III Health Institute (ISCIII) and the Doñana Biological Station (EBD-CSIC) have detected the Sindbis virus for the first time in the Iberian Peninsula, specifically in mosquitoes captured in different locations in the provinces of Málaga, Seville, Huelva, and Cádiz.
According to Jordi Figuerola, a researcher at the Doñana Biological Station and leader of the Zoonosis Ecology and Evolution Group at the CIBER of Epidemiology and Public Health, this virus belonging to the Alphavirus genus mainly circulates among birds and "can sporadically affect people" if a mosquito that has previously bitten an infected bird subsequently feeds on a person's blood.
The infection is usually asymptomatic, although it can cause symptoms such as fever, skin irritations, joint pain, or headache.
"This is the first time it has been detected in the Iberian Peninsula, but we knew it circulated in other areas, such as Scandinavia or Algeria, where it caused an outbreak a few years ago," explains Figuerola. According to the researchers' hypothesis, the virus was likely introduced to Spain in 2017 by migratory birds from North or Central Africa.
Nevertheless, the scientist points out that although this is the first time the virus has been detected in Spain, there may have been previous circulation. "We had old serology data indicating that there could be people with antibodies to this virus, but the virus had never actually been detected," he clarifies.
Figuerola explains that the virus's discovery occurred initially by chance in one of the routine analyses the team conducts to monitor the circulation of the West Nile Fever virus, endemic on the peninsula and which has caused several outbreaks in recent years. In 2024, the pathogen caused 115 symptomatic infections and 10 deaths.
It is common that when mosquitoes with the presence of the West Nile virus are detected, a sample is sent to the National Center for Microbiology for genomic analysis. It was in this study that the presence of another virus, Sindbis, was detected.
With this information in hand, the researchers then began a study to search for and locate the presence of the pathogen. For this, they carried out a study of 31,920 mosquitoes, grouped into 1,149 batches, captured in 2022 in western Andalusia. The Sindbis virus was detected in 137 batches (11.92%) and in five different mosquito species, with the Culex perexiguus species showing the highest infection rate.
Genomic analysis of the strains detected on the peninsula revealed that all belong to genotype I, previously detected in other areas of Europe and Africa. All the details of the study have been published in the One Health journal.
"The study demonstrates the circulation of a virus with potential public health importance long before cases have been detected in humans, so it is crucial to understand the possible spread of this virus in Spain and establish its real impact on the population's health," Figuerola points out.
"This finding is another reason to protect oneself from mosquitoes," the scientist continues.
In this regard, he emphasizes that in areas where there is transmission of viruses like West Nile or this newly detected one, it is important to prepare homes to prevent the presence of mosquitoes, for example, by installing mosquito nets on windows and ensuring that water does not accumulate around the house. A poorly draining drain, plant pot saucers, children's toys, or any object that allows water accumulation can lead to mosquito proliferation. Pools, of course, should be treated, and any container or well should be protected with mosquito netting to prevent the breeding of these insects.
At the institutional level, it is essential for vulnerable municipalities to have mosquito control programs in both urban areas and places like rice fields, where specific biocide treatments can eliminate mosquitoes in the larval stage without affecting the environment and other species.