The primary viremia seeds target organs which replicate virus and serve as a source of virus for release in the circulation. Virus can then enter the neural tissue causing encephalitis. The symptoms of arbovirus infection usually have an abrupt onset. The incubation period can vary from 3 to 21 days. Sequelae of encephalitis can be severe.
Most arbovirus infections are inapparent and immunity is life-long.
The virus replicates in the cytoplasm with the genomic RNA translating nonstructural proteins and a subgenomic RNA from the 3' end encoding structural polypeptides. The arboviruses reside within the alphavirus family. Their are three major alphaviruses which are arthropod borne. The virus was first isolated in the U.S. in 1933 and is maintained in an enzootic cycle involving wild birds and mosquitoes in fresh water swamps. The vector involved is Culiseta melanura which rarely bites mammals, explaining the rare transmission to humans and equines.