Changes

====Epidemiology====

====Epidemiology====

=====Distribution=====

=====Distribution=====

Disease associated with EEE, WEE and VEE is largely restricted to the Western Hemisphere, ranging from temperate to desert climates.  EEE in the United States is mainly seen in the Southeastern United States but has been detected in all states east of the Mississippi River and some Western states.  Large outbreaks of WEE have been described in California and other Western states but the incidence of clinical disease in these areas has experienced a dramatic decrease. The reason for this unknown but may be due to geographical variation in virulence. Equine disease associated with WEE is rare on the Eastern seaboard ofthe United States. VEE  virus is a very important human andveterinary pathogen in the Western Hemipshoere that can cause large outbreaks of disease in humans and horses over large geopgrahic areas.  VEE has spread into Central America, causing devastating epidemics as far north as Texas. The disease distribution is determined by climatic conditions as well as agricultural practices, such as irrigation, which favour the life cycle and spread of mosquitoes.

Togaviral encephalitis in equids is largely confined to the Western Hemisphere, ranging from temperate to desert climates.  Venezuelan EEV can cause large outbreaks of disease over extensive geographical areas in both humans and horses.  Spread of this virus into Central America has had disasterous consequences with epidemics as far north as Texas. Climatic conditions and interventions that support vector populations, such as irrigation, greatly influence the geographical spread of the disease. 

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

 

Humans and horses are terminal hosts for Western EEV and in a given location, horses with the disease act as sentinels for human infection. Highlands J virus, a subtype of Western EEV, has been isolated from the brain of a horse dying of encephalitis in Florida (Karabatsos ''et.al'', 1988).

EEE in the United States is mainly seen in the Southeastern United States but has been detected in all states east of the Mississippi River and some Western states.  Large outbreaks of WEE have been described in California and other Western states but the incidence of clinical disease in these areas has experienced a dramatic decrease. The reason for this unknown but may be due to geographical variation in virulence. Humans and horses are terminal hosts for Western EEV and in a given location, horses with the disease act as sentinels for human infection. WEE virus infection in horses is often observed sporadically over a wide geographical area, whereas EEE virus infections are usually observed in limited geographical areas. Highlands J virus, a subtype of Western EEV, has been isolated from the brain of a horse dying of encephalitis in Florida (Karabatsos ''et.al'', 1988).

=====Transmission=====

=====Transmission=====