Changes

====Epidemiology====

====Epidemiology====

=====Distribution=====

=====Distribution=====

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.   

Togaviral encephalitis in equids is largely confined to the Western Hemisphere.  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.  EEE has been recorded across the United States, but mostly in the Southeastern States. As its names suggests, WEE has a predilection for the Western states which have been subject to significant outbreaks in the past.  A regional alteration in virulence has been proposed for the steep decline in clinical case numbers observed in this area. A lag phase of 2-5weeks is commonly observed between horse and human cases of WEE in a given locus.  Both are dead-end hosts for the virus.   A subtype of Western EEV, Highlands J virus, was isolated from the brain of a horse with 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=====