Changes

=====Transmission=====

=====Transmission=====

Transfer is '''vector'''-mediated, primarily via '''[[Culicidae|mosquito salivary transfer]]'''.  Western EEV and Venezuelan EEV may also be transmitted through nasal secretions but this is less likely.  Disease amplification occurs during the viraemic phase which lasts until nervous signs develop.  Amplification from horses is unlikely with EEE and WEE but occurs with VEE in association with a relatively high viraemia.  Ocular and nasal discharges from infected horses cotnain high concentrations of VEE.  Zoonotic spread has been noted with VEE but is unlikely for the other two serotypes.  Horse to horse spread of EEE is possible.  Humans and horses are terminal hosts for WEE.  Horses with WEE are sentinels for humans in a given area.WEE virus infection in horses is often observed over a wide geographical area, e.g. sporadic cases over 1000 square miles. EEE virus infections are usually observed in limited geographical areas. Highlands J virus, antigenically related to WEE virus, has been isolated from the brain of a horse dying of encephalitis in Florida (4).

Transfer is '''vector'''-mediated, primarily via '''[[Culicidae|mosquito salivary transfer]]'''.  Western EEV and Venezuelan EEV may also be transmitted horse to horse through nasal secretions.  This mode of transmission is less likely, despite the fact that high concentrations of Venezuelan EEV are found in ocular and nasal discharges from infected horses.  The viraemic phase ends when nervous signs develop and is important for disease amplification.  Amplification from horses is likely only with Venezuelan EEV, in association with a relatively high viraemia.  Similarly, zoonotic spread is unlikely for Eastern and Western EEV, but has been noted with Venezuelan EEV.  Humans and horses are terminal hosts for WEE.  Horses with WEE are sentinels for humans in a given area. Highlands J virus, antigenically related to WEE virus, has been isolated from the brain of a horse dying of encephalitis in Florida (4).

=====Seasonal Incidence=====

=====Seasonal Incidence=====