Early seasonal detection of Usutu virus in April 2026

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

Usutu virus is a Flavivirus closely related to West Nile virus. It is mainly transmitted between wild birds by Culex mosquitoes, but is also occasionally transmitted to humans. The virus was first detected in Luxembourg in 2020. After intensifying the surveillance efforts, Usutu virus was again detected during summer and early fall in 2024 and 2025, coinciding with higher vector activity.

Interestingly, the first Usutu virus case for 2026 was already detected in a black bird at the end of April. This marks the earliest seasonal detection of the virus in Luxembourg. For the current season, this signals an earlier and potentially more intense transmission cycle. It also highlights that vector-borne disease surveillance should be carried out over extended periods, if not year-round, to avoid bias and provide early warning.

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 in Dudelange, the Parc Merveilleux and the Nature and Forest Agency.