Equine encephalitides are viral zoonoses that occur episodically and cause outbreaks in equines and, less frequently, in humans. The ethiological agents are viruses belonging to the genus Alphavirus in the Togaviridae family. Infection is maintained in natural foci between wild reservoirs anD mosquitoes. Three viruses are important: Western equine (WEE), eastern equine (EEE) and Venezuelan equine encephalomyelitis (VEE). A fourth member, Higlands J virus, occurs in the eastern United States, primarily in Florida.
In Central America, a growing activity of syndromes compatible with equine encephalitis has been observed in horses during the last three years, particularly in Belize, Guatemala,Honduras and Panama. Laboratory isolations of the virus and/or serological typing have shown EEE and VEE viral infection. These two agents are known to cause high morbidity and mortality among horses, donkeys and mules that, in turn, become amplifiers of the infection that eventually spreads to human by mosquito bites.
The VEE virus has caused major epidemics in the Americas. In 1969, an outbreak started in Ecuador and spread through Peru, Colombia, Venezuela, Central America and Mexico reaching finally Texas in 1971. Close to 50,000 equines died. In Ecuador, alone, 31,000 human cases were reported and 310 deaths.
In 1995, an outbreak occurred in Venezuela and Colombia that affected seven States in Venezuela and the Department of La Guajira in Colombia. This outbreak registered more than 40,000 human cases and 46 deaths. The outbreak was associated with one period of unusually intense rain with a subsequent increase of mosquito populations, vectors of VEE virus and the lack of vaccination among the equine population.
The current situation in Central America is similar:
For more information, you can consult the Manual "Bases for Epidemiological Surveillance of Venezuelan equine encephalitis in the Region of the Americas", which includes definition of concepts, guidelines for the establishment and development of programs for epidemiological surveillance and examples of formats for the management of the information system during normal conditions and in case of outbreaks or epidemics.
Albino J. Belotto
Veterinary Public Health Program
División of Disease Prevention and Control
PAHO/WHO, Washington, D.C.