Ongoing Usutu virus circulation, July 2026

• Clinical and Applied Virology
• Department of Infection and Immunity
• Zoonotic project

After a first single case detected in April 2026, new Usutu virus infections have been confirmed in blackbirds over the 2 last weeks. The recent Usutu virus detections likely mark the beginning of the main transmission period. Indeed, Usutu virus is primarily transmitted between birds by bites from Culex mosquitoes. Higher mosquito activity during summer and early fall thus promotes Usutu virus circulation. Such patterns were already observed in Luxembourg in 2024 and 2025 with the first cases detected at the end of July, followed by cases until September or October.

Usutu virus can be transmitted to a large spectrum of bird species, acting as an additional stressor on bird populations for highly susceptible species. It can also be a health threat to precious birds kept in zoological gardens. The virus can occasionally be transmitted to mammals, including humans. Fortunately, the vast majority of human infections remain asymptomatic or result in mild disease. More severe cases are rarely observed, mainly affecting immune-compromised individuals. In the absence of specific treatment or vaccine, avoiding mosquito bites remains the best prevention measure.

Acknowledgments

Usutu virus surveillance is funded by the Ministry of Agriculture, Food and Viticulture and is carried out in collaboration with the Luxembourg Veterinary and Food Administration (ALVA), the Centre de Soins pour la Faune Sauvage and the Centrale Ornithologique of natur&ëmwelt, the Parc Merveilleux and the Nature and Forest Agency.