Changes

=====Transmission=====

=====Transmission=====

Transfer is via '''vector''': mostly through '''[[Culicidae|mosquito salivary transfer]]'''.  WEE and VEE may also be transmitted via 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 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).

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

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