Jamestown Canyon encephalitis is an infectious disease caused by the Jamestown Canyon virus, an orthobunyavirus of the California serogroup. It is mainly spread during the summer by different mosquito species in the United States and Canada.
The virus is one of a group of mosquito-borne or arthropod-borne viruses, also called arboviruses, that can cause fever and meningitis or meningoencephalitis, mostly in adults. Jamestown Canyon virus disease is relatively rare; in the United States, the CDC found only 31 disease cases from 2000 to 2013, but it is likely under-recognized and probably endemic throughout most of the United States and parts of Canada.