West Nile virus, chikungunya, dengue: Tracking mosquito-borne illnesses across Europe

Mosquito season is in full swing in Europe, and with it, mosquito-borne virus season.

More than 1,000 cases of West Nile virus, chikungunya, and dengue have been reported so far this year, according to the European Centre for Disease Prevention and Control (ECDC), which tracks cases in the European Union and a few other countries in the region.

These viral diseases, which usually occur when an infected mosquito bites someone, are becoming more common in Europe due to increased travel and warmer summer temperatures driven by climate change.

Here’s what you need to know about these illnesses and where cases have been detected so far this summer, as of early September.

West Nile virus

Nine European countries have reported a total of 652 West Nile virus infections this year: Italy (500), Greece (69), Serbia (33), France (20), Romania (15), Hungary (six), Spain (five), Albania (three), and Bulgaria (one).

Those counts include both probable and confirmed cases in people. 

Across Europe, 38 people have died from West Nile virus this year, the ECDC said. Most of these deaths have been in Italy.

Overall, most cases have been among men aged 65 and older, and 91 per cent of infected people have been hospitalised.

About 1 in 150 people who are infected with the virus will develop severe illness, such as encephalitis, which is inflammation of the brain, or meningitis, which is inflammation of the protective membranes around the brain and spinal cord.

These complications can be fatal, according to the World Health Organization (WHO).

Chikungunya

France has reported 301 chikungunya cases this summer, amid an uptick in cases in recent weeks. There have been 34 clusters of chikungunya infections this summer, including 25 that are still active.

Italy, meanwhile, has recorded 107 cases of chikungunya.

Chikungunya is not endemic in the EU, but warmer weather during the summer months makes it easier for mosquitoes to spread the virus. Most cases are typically reported in July or August, the ECDC said.

There are two chikungunya vaccines approved in the EU, but there are no specific treatments.

Chikungunya can cause fever, nausea, headache, fatigue, rash, muscle aches, joint swelling, and joint pain, which can be debilitating and long-lasting. Severe symptoms and death are rare consequences, though babies and older adults are at higher risk.

Dengue

France has seen 19 dengue cases this year, while Italy has seen four and Portugal has reported two cases.

EU health authorities believe the Portuguese infections, which were reported in Madeira in January, were likely contracted last year.

The ECDC said one type of mosquito that spreads dengue has been “established in a large part of Europe” and that another is fairly common around Madeira, Cyprus, and the Black Sea.

Globally, there are 100 million to 400 million dengue infections per year, according to the WHO.

Most people who are infected with dengue have no or mild symptoms, but the virus can cause fever, headache, body aches, nausea, and a rash. In extreme cases, dengue can be fatal.

There is no specific medication to treat dengue, and the best way to avoid infection is to take steps to prevent mosquito bites.

This article was updated on 10 Sept. 2025 with the latest data.