Molecular Epidemiology of Western Equine Encephalitis Virus, South America, 2023–2024
Aline Alves Scarpellini Campos, Ana Cláudia Franco, Fernanda Marques de Souza Godinho, Rosana Huff, Darlan S. Candido, Jáder da Cruz Cardoso, Xinyi Hua, Ingra Morales Claro, Paola Morais, Carolina Franceschina, Thales Bermann, Franciellen Machado dos Santos, Laura Bauermann, Tainá Machado Selayaran, Amanda Pellenz Ruivo, Cristiane Krause Santin, Juciane Bonella, Carla Rosane Rodenbusch, José Carlos Ferreira, Scott C. Weaver, Vilar Ricardo Gewehr, Gabriel Luz Wallau, William Marciel de Souza, Richard Steiner Salvato
Abstract
Western equine encephalitis virus (WEEV) is a mosquitoborne virus that reemerged in December 2023 in Argentina and Uruguay, causing a major outbreak. We investigated the outbreak using epidemiologic, entomological, and genomic analyses, focusing on WEEV circulation near the Argentina‒Uruguay border in Rio Grande do Sul state, Brazil. During November 2023‒April 2024, the outbreak in Argentina and Uruguay resulted in 217 human cases, 12 of which were fatal, and 2,548 equine cases. We determined cases on the basis of laboratory and clinical epidemiologic criteria. We characterized 3 fatal equine cases caused by a novel WEEV lineage identified through a nearly complete coding sequence analysis, which we propose as lineage C. Our findings highlight the importance of continued surveillance and equine vaccination to control future WEEV outbreaks in South America.