Western Equine Encephalitis Virus in Blood Donors during Outbreak, Argentina, 2023-2024.

Western equine encephalitis virus (WEEV) reemerged in Argentina during 2023-2024, raising public health concerns and posing a potential threat to blood transfusion safety. We assessed the effect of WEEV circulation on the blood supply by implementing responsive, community-informed interventions within a regional hemovigilance system, including epidemiologic mapping, enhanced donor selection criteria, and alphavirus-specific nucleic acid testing. Among 637 donors residing in outbreak-affected areas, we detected 1 asymptomatic viremic donor. Phylogenetic analysis showed that the viral sequence clustered within the contemporary South American outbreak lineage, consistent with ongoing regional transmission. Those findings demonstrate silent WEEV circulation among blood donors and highlight the critical role of donor surveillance as a sentinel system for emerging arboviruses. Hemovigilance provides valuable insights into viral circulation in the broader population, underscoring the need to integrate molecular surveillance into routine blood bank practices to strengthen transfusion safety and public health preparedness.