The rest of the cases are aseptic meningitis and fever. Sequelae occur in a large percentage of infants and young children. The risk factors for acquiring arboviral encephalitis appear to be involvement in outdoor activities, lack of air conditioning, and travel to endemic areas. The life cycle of the virus involves man and mosquitoes, but horses can serve as another dead end host for the virus. EEE can cause fatal disease in horses, however, the horse usually serves as a means for amplifying the virus burden in the environment.
Mosquitos tend to feed on avian species in early summer and on mammals in late summer.
These species serve to amplify some of the arboviruses in addition to transovarial transmission in mosquitos during the winter. Cool, wet weather enhances infection for Culex mosquitoes whereas hot temperatures decrease transmission. The immune response serves an important role in controlling arboviral disease. The duration of the prodrome for alphaviruses is correlated with a better prognosis suggesting that the antibody or cell mediated responses to the virus moderate disease. This is the opposite of the California encephalitis group of bunyaviruses.