Record outbreaks of mosquito-borne West Nile and chikungunya viruses in Europe

The European Centre for Disease Prevention and Control (ECDC) warned on Wednesday, ahead of World Mosquito Day, of record outbreaks of West Nile virus (WNV) and chikungunya virus infection that point to a new normal in Europe.

The old continent is experiencing longer and more intense transmission seasons for mosquito-borne diseases , including WNV infection and chikungunya virus disease. This shift is due to climatic and environmental factors such as rising temperatures, longer summers, milder winters, and changes in rainfall patterns; conditions that combine to create a favorable environment for mosquitoes to thrive and transmit viruses.

As of 13 August 2025, eight European countries had reported 335 locally transmitted human cases of WNV infection and 19 deaths. Italy remains the most affected country, with 274 confirmed infections, followed by Greece (35), Serbia (9), France (7), Romania (6), Hungary (2), Bulgaria (1) and Spain (1).

France has reported 111 cases of chikungunya virus disease, and Italy has reported seven, mainly associated with outbreaks in the southern and southeastern regions. No deaths have been reported in continental Europe, but worldwide, 240,000 cases of the disease and 90 deaths have been recorded so far in 2025.

"Europe is entering a new phase, where more prolonged, widespread, and intense transmission of mosquito-borne diseases is becoming the new normal. ECDC is working closely with all Member States to provide tailored support and timely public health guidance to strengthen the European response," said Dr. Pamela Rendi-Wagner, Director of ECDC.

The tiger mosquito , which transmits the chikungunya virus ( Aedes albopictus ), has established itself in 16 European countries and 369 regions , compared to just 114 regions a decade ago. Combined with increased international travel, this spread increases the likelihood of local outbreaks.

Europe has recorded 27 chikungunya outbreaks so far in 2025 , a new record for the continent. For the first time, a locally transmitted case of chikungunya virus disease has been reported in the French region of Alsace , an exceptional occurrence at this latitude, highlighting the continued expansion of the risk of transmission northward.

Regarding West Nile virus in Europe , the highest number of cases in three years has been recorded. The ECDC expects infections to continue to rise, likely reaching a seasonal peak in August or September. Over the past decade, the infection has been detected in new areas each season. This year, for the first time, cases have been reported in the Italian provinces of Latina and Frosinone , and in Sălaj County in Romania.

"There have been small outbreaks of the chikungunya virus in France, in certain areas very close to Spain, such as the French Riviera and the Basque Country, but no local cases have been detected in our country so far. Although, due to the proximity of France and the number of cases, it could happen. It's true that we have a significant national vector control plan that is currently working very well," Dr. Gema Fernández Rivas, spokesperson for the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC), told ABC. The expert believes that this increase in cases in Europe could continue over the years. "Perhaps not an alarming situation, not a pandemic, but it's likely that these cases and small local outbreaks will appear in some European countries over the years, and we may see them appear in more countries or more frequently," she concludes.

The new ECDC guidelines outline practical surveillance, prevention, and control measures for chikungunya virus disease, dengue , and Zika virus , with recommendations tailored to European countries, including those with little experience or that have not previously faced the threat of these mosquito-borne diseases. “As the mosquito-borne disease landscape evolves, more people in Europe will be at risk in the future. This makes prevention more important than ever, both through coordinated public health actions and personal protective measures,” said Dr. Céline Gossner, Head of the Foodborne, Waterborne, Vector-borne and Zoonotic Diseases Section at ECDC. “There is an urgent need to strengthen and scale up efficient and environmentally friendly mosquito control interventions,” she added.

The ECDC recommends that people living in affected areas and visitors, especially the elderly, children, and those with weakened immune systems, protect themselves from mosquito bites by using repellent, long sleeves and long pants, especially at dawn and dusk; and using mosquito nets on windows and beds, and using air conditioning/fans.