West Nile and Usutu viruses are efficiently inactivated in platelet concentrates by UVC light using the THERAFLEX...

West Nile virus (WNV) and Usutu virus (USUV) are mosquito-borne flaviviruses (Flaviviridae) that originated in Africa, have expanded their geographical range during the last decades and caused documented infections in Europe in the last years. Acute WNV and USUV infections have been detected in asymptomatic blood donors by nucleic acid testing. Thus, inactivation of both viral pathogens before blood transfusion is necessary to ensure blood product safety. This study aimed to investigate the efficacy of the THERAFLEX UV-Platelets system to inactivate WNV and USUV in platelet concentrates (PCs).

Plasma-reduced PCs were spiked with the virus suspension. Spiked PC samples were taken after spiking (load and hold sample) and after UVC illumination on the Macotronic UV illumination machine with different light doses (0.05, 0.1, 0.15 and 0.2 (standard) J/cm²). Virus loads of WNV and USUV before and after illumination were measured by titration.

Infectivity assays showed that UVC illumination inactivated WNV and USUV in a dose-dependent manner. At a UVC dose of 0.2 J/cm², the WNV titre was reduced by a log₁₀ factor of 3.59 ± 0.43 for NY99 (lineage 1) and 4.40 ± 0.29 for strain ED-I-33/18 (lineage 2). USUV titres were reduced at the same UVC dose by a log₁₀ factor of 5.20 ± 0.70.

Our results demonstrate that the THERAFLEX UV-Platelets procedure is an effective technology to inactivate WNV and USUV in contaminated PCs.