September 29, 2011 07:34
EEE or eastern equine encephalitis is found usually in eastern half of North America. WEE or western equine encephalitis is the form that affects usually the western half of the continent. Both are most often mosquito and biting insect-borne, humans are also occasionally affected with encephalitis through bites from affected mosquitos.
It is a later summer and early fall disease and typically the same species of mosquito, culex tarsalis , carries both "sleeping sickness" and west nile virus.
The core horse vaccines in our area (Western Canada) have always protected horses from tetanus and EEE and WEE. This is the old "3 way" vaccine. For several years now the core vaccine also includes protection from west nile virus. (4 way or combo vaccine).
Vaccines in the south and southeastern states also protect against VEE, or Venezuelan equine encephalitis.
Outbreaks occur when owners fail to vaccinate weanlings in a herd with a series of 3 vaccines or If many horse owners in an area do not vaccinate or boost annually for years and the procedure falls off the horse culture's radar, especially among novice owners. In addition outbreaks are worse in years when there are more insect vectors and birds who amplify the virus (raise the level of infected insects) Typically EEE is more often deadly than WEE. . I saw some cases when I worked in Virginia and it is very sad to see an incapacitated and unreactive horse.
The take home message is that If horse owners in our area vaccinate adult horses in late spring to mid-summer with a core vaccine booster and complete weanlings vaccine series they have protected their horses even in the face of outbreaks. Foals should be vaccinated at 3, 4, and 5 months, If mare was not boosted with vaccine a month before foaling and 4,5 and 6 months, If mare has been vaccinated a month before foaling. Adults not previously vaccinated require 2 Vaccines 4 to 6 wks apart before July. And all horses yearlings and up require annual boosters.
~Dr Lisa Wayman CPVS