Arthropod-borne viruses, or arboviruses, pose an increasing risk to public health within the WHO European Region. The rise in ambient temperatures, among other factors, has created favourable conditions for native vectors and facilitated the establishment of invasive vector species capable of transmitting viruses previously unknown to the Region.
Of particular concern are mosquito-borne viruses, including dengue virus and West Nile virus.
Dengue
In December 2023, WHO declared a Grade 3 global emergency for dengue because of a 30-fold global increase in reported dengue in recent decades. Dengue virus is a flavivirus, transmitted by certain species of Aedes mosquitoes.
The past decade has seen an expansion in the establishment of invasive Aedes mosquito species across the Region. In 2017, Aedes albopictus (Asian tiger mosquito) was known to be established in 17 countries in the Region. As of June 2025, this Aedes species is reported to be established in 30 countries across the Region. Aedes aegypti (yellow fever mosquito) was known to be established in 4 countries in the Region in 2017, which has increased to 5 countries as of 2025.
Although dengue is not endemic in the Region, locally-acquired cases have previously been reported in Croatia, France, Italy, Madeira (Portugal) and Spain. In 2023, the Region reported 130 locally-acquired cases. In 2024, this number increased to 304, the highest number ever recorded since surveillance began.
WHO/Europe has identified countries that have potential for autochthonous transmission of dengue based on the presence of competent vectors, climate suitability, historical and recent autochthonous cases and other factors. In response, seasonal surveillance for autochthonous cases of dengue virus (and, simultaneously, chikungunya virus and zika virus) has been reinitiated in the Region for the second season in 2025.
West Nile virus
West Nile virus (WNV), also a flavivirus, is a mosquito-borne zoonosis. WNV is mainly transmitted by certain species of Culex mosquitoes, which are considered native to many countries in the Region. WNV is endemic in many countries in the Region.
Over the past 2 decades, the Region has experienced an upsurge in the frequency of WNV outbreaks, an expansion of the affected geographical area and extended transmission seasons. It is likely there will be a further spread of the disease in the coming summer period due to the favourable conditions for vector and virus activity.
Purpose of the webinar
On 17 July 2025, Member State representatives and external stakeholders will join this webinar to discuss regional updates on dengue and West Nile virus, challenges in surveillance and control from Member State perspectives, recent actions taken by WHO/Europe to better understand the situation through surveillance and the responses now needed.
A key part of this will be the presentation of WHO/Europe’s surveillance initiatives for arboviruses in the Region. The webinar will be held in English with simultaneous interpretation into Russian available.