La Crosse virus
Image of La Crosse encephalitis virus

La Crosse virus (LACV) is a California (CAL) serogroup virus, in the genus Bunyavirus, family Bunyaviridae.  Members of the family Bunyaviridae have three segments of single-stranded RNA; the virus particles are spherical or oval, enveloped, and are 90-100 nm in diameter.

Other CAL serogroup viruses found in the United States include California encephalitis virus, Jamestown Canyon virus, Snowshoe hare virus, and Trivitattus virus. Because almost all recognized CAL serogroup virus disease cases are caused by LACV, and other CAL serogroup viruses rarely cause recognized human illness, the information on this website emphasizes LACV.