January 10, 2024
Summary of the situation: On 19 Dec 2023, the Pan American Health Organization/World Health Organization (PAHO/WHO) warned about the risk to human health associated with the circulation of the western equine encephalitis virus (WEE). From that date until 9 Jan 2024, 374 additional outbreaks (equine outbreak: occurrence of one or more cases of WEE in equines) in animals were reported (338 in Argentina and 36 in Uruguay) and 21 human cases, all of them in Argentina. Note: Human cases of WEEV have been absent from Argentina for more than 2 decades, similar to the long time absence of WEEV from California. We should remember that the SLEV strains now circulating in the SW USA [including California] were most closely aligned with strains previously isolated from Argentina, perhaps establishing a route/corridor for introduction by migrant birds? Testing Culex mosquitoes by triplex during 2024 would again seem prudent.