West Nile Fever in Brazil in 2026: Emergence of Human Cases and Implications for Integrated Surveillance

West Nile fever (WNF) is a zoonotic arboviral disease caused by West Nile virus (WNV), maintained primarily in an enzootic cycle involving birds and mosquitoes, particularly species of the genus Culex. Although evidence of viral circulation has previously been documented in Brazil, human disease remains infrequently recognized. This study aimed to describe the human cases of WNF identified in Brazil in 2026 and to interpret their epidemiological significance within an integrated One Health surveillance framework. A descriptive retrospective study was conducted using secondary information from the Ministry of Health, state and municipal health authorities, scientific literature, and official technical documents, incorporating information available through 28 August 2026. Four human cases were confirmed—two in Santa Catarina and two in São Paulo—and one probable/under-investigation case was identified in Piauí. The confirmed cases showed heterogeneous clinical presentations, including neuroinvasive manifestations, hospitalization, and one death; the latter was recorded as associated with stroke, with its relationship to WNV infection remaining under investigation. One confirmed case had recent travel to the Amazon region, while other probable sites of infection remained under investigation. The available public sources did not provide concurrent entomological or animal surveillance results sufficient to establish a local transmission chain. The 2026 events therefore constitute a sentinel epidemiological signal that supports intensification of integrated human, laboratory, entomological, animal, and environmental surveillance rather than inference of sustained autochthonous transmission.