Worldwide, there are several thousand recognized arboviruses. The term arbovirus was coined many years ago to include viruses that were transmitted to vertebrate animals by arthropods. Mosquitoes, ticks, and biting flies of various kinds are all vectors. In California, the most important viruses transmitted to humans and other vertebrates are mosquitoborne. Western equine encephalomyelitis virus (abbreviated WEE) is one of the important mosquitoborne viral diseases in California. For information on specific California mosquitoborne viruses, select the name of the virus from the menu at the right.