Identification of Usutu virus in blood donors as part of molecular screening for West Nile virus, France, 2023

BACKGROUNDWest Nile Virus (WNV) can be transmitted via blood transfusion and lead to neuroinvasive forms in recipients of blood products.AIMWe aimed to investigate WNV and Usutu virus (USUV) infections among blood donors in France.METHODSBlood donations in 18 of 96 departments of metropolitan France and from travellers returning from affected areas were screened prospectively for WNV using a commercial nucleic acid test (NAT). In addition, stored samples from blood donations in the affected departments were retrospectively tested with RT-qPCR. Differentiation between WNV and USUV infections in NAT-positive samples was done with a RT-qPCR or by seroneutralisation after seroconversion.RESULTSBetween 18 July and 1 December 2023, 34 (0.018%) of 185,965 blood donation samples were initially positive for WNV. After investigations, 20 donors with USUV infections (16 confirmed, four probable) and five with WNV infections (three confirmed, two probable) were identified. In samples from four donors, WNV and USUV could not be differentiated, and five samples remained indeterminate. Seventeen USUV infections were considered autochthonous: nine departments in the southern and central parts of France, including two departments where WNV was also detected. Infections with USUV were detected between 21 July and 17 October and WNV between 23 August and 20 September.CONCLUSIONVia screening of blood donations, we could identify the circulation of USUV in 2023 in large parts of metropolitan France. A One Health approach is required to better understand the determinants of USUV circulation in France and the clinical consequences of USUV infections in humans.