The Usutu virus is detected for the first time in mosquitoes in Cádiz

A study by the Carlos III Health Institute and the Higher Council for Scientific Research (CSIC) has detected for the first time the presence of the Usutu virus in mosquitoes in the province of Cádiz, in addition to confirming that human exposure to the West Nile virus has multiplied by four in seven years, going from 0.2% in 2015 to 0.9% in 2022.

As reported by the CSIC in a note, the discovery of the Usutu virus, belonging to the Africa-3 lineage, has occurred in specimens of the Culex perexiguus species captured in the province of Cádiz within an entomological surveillance program developed between 2022 and 2024 in collaboration with the Junta de Andalucía.

This zoonotic pathogen can generate symptoms similar to those of the West Nile virus in humans and, as warned by CSIC research professor at the Doñana Biological Station Jordi Figuerola, the results confirm that the virus "is present", so "it is necessary to determine to what extent it may be causing cases of infection in humans."

The research, led by Ciberinfec staff at the National Microbiology Center with the participation of the Doñana-CSIC Biological Station and Ciberesp, thus documents for the first time the simultaneous circulation of both orthoflaviviruses in the province, where there are still "gaps" regarding the diversity of these pathogens and the real exposure of the population.

Given this scenario, Figuerola has stressed that "mosquito control and virus surveillance programs should be reinforced" to know which pathogens circulate, where they do so with greater intensity and what environmental and climatic factors influence their expansion, in addition to insisting on the need to reduce the abundance of insects in inhabited areas and raise awareness among the population to protect themselves from their bites.

Regarding the West Nile virus, serological analyzes carried out on serum samples from ten municipalities in the province show that seroprevalence, the percentage of people with antibodies in the blood, grew from 0.2% to 0.9% between 2015 and 2022, also expanding its territorial scope from three to nine locations.

The RT-PCR analyzes on the captured mosquitoes also confirmed the circulation of the West Nile virus in different areas of the province, some with human and animal cases already reported previously, which supports the "endemic" nature of this virus in Cádiz.

Figuerola recalled that the Nile virus is "a re-emerging virus in Europe" that has increased its cases in Spain in recent years, an extreme confirmed by these data.

For her part, the first author of the study and Ciberinfec researcher, Laura Guillén-Calvo, has highlighted the relevance of the One Health approach, pointing out that "the combination of entomological surveillance and serological studies allows us to better understand the circulation of these viruses and the transmission dynamics of orthoflaviviruses in endemic areas."