Animals Involved
Birds are principal reservoir hosts in North America, snakes might have role in overwintering virus; rodents, marsupials might be reservoir hosts in South America; clinical cases seen in equids and occasionally other mammals and birds; mammals are almost always deadend hosts
Known Distributions
Western hemisphere
Probable Means of Spreading
Mosquito bites; Culiseta melanura important in maintenance cycle in birds in North America; various mosquito species (Aedes, Coquillettidia, Culex) can transmit to people
Clinical Manifestations in People
Nonspecific febrile illness may be followed by severe encephalitis, especially with North American lineage; neurologic sequelae common after encephalitis; case fatality rate 30%–70% with North American lineage; more severe in infants and elderly