It is transmitted by the Culex taralis mosquito. Its cycle also includes wild birds with occasional spread to horses and man. Children are more often affected than adults. Asymptomatic infections by these viruses are the most common. The second most common manifestation is a mild, nonspecific febrile illness, usually with headache.
Children generally are more often susceptible to severe disease.
Initial symptoms include headache, fever, malaise, and vomiting. Supportive therapy and intensive nursing are required. EEE and WEE viruses are both related and will show cross-reactivity. Initial infection by one of these viruses will show a specific rise in titer that is higher than titers against any other viruses of the group. Single positive antibody titers may represent past or current infection.