Highlands J virus (HJV) is a rare zoonotic mosquito-transmitted alphavirus. HJV is transmitted from Culiseta melanura mosquitoes to songbirds in freshwater swamps. HJV is a member of the western equine encephalitis (WEE) complex. Other members of this complex found in the United States include WEE virus (WEEV) and Fort Morgan virus (FMV).
HJV, unlike EEEV, has not been shown to be pathogenic to humans or horses, with the exception of a single report of the virus being isolated from the brain of a horse that died with encephalitis in Florida in 1964 and four human encephalitis cases that were co-infected with St. Louis Encephalitis virus (SLEV).