Epidemiology, surveillance and diagnosis of Usutu virus infection in the EU/EEA, 2012 to 2021

Background: Usutu virus (USUV) is a flavivirus with an enzootic cycle between birds and mosquitoes; humans are incidental dead-end hosts. In Europe, the virus was first detected in Italy in 1996; since then, it has spread to many European countries. Aim: We aimed to report on the epidemiology, surveillance, diagnosis and prevention of USUV infection in humans, mosquitoes and other animals in the European Union/ European Economic Area (EU/EEA) from 2012 to 2021. Methods: We collected information through a literature review, an online survey and an expert meeting. Results: Eight countries reported USUV infection in humans (105 cases, including 12* with neurological symptoms), 15 countries in birds and seven in mosquitoes. Infected animals were also found among pets, wild and zoo animals. Usutu virus was detected primarily in Culex pipiens but also in six other mosquito species. Detection of USUV infection in humans is notifiable only in Italy, where it is under surveillance since 2017 and now integrated with surveillance in animals in a One Health approach. Several countries include USUV infection in the differential diagnosis of viral encephalitis and arbovirus infections. Animal USUV infection is not notifiable in any EU/EEA country. Conclusion: Human USUV infections, mainly asymptomatic and, less frequently, with a febrile illness or a neuroinvasive disease, have been reported in several EU/EEA countries, where the virus is endemic. Climate and environmental changes are expected to affect the epidemiology of USUV. A One Health approach could improve the monitoring of its evolution in Europe.