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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:
** The existence of natural foci where viral infection persists in wild reservoirs. The
reservoirs include rodents: wild birds and bats.
** An increase in the population of mosquito vectors. Stagnant waters in flooded
lands favors an increase in mosquito breeding sites, and consequently, the growth of their
population and a greater exposure of the domestic animals and humans to mosquito bites and
infections carried by them.
** A susceptible equine population. With the exception of a few areas in Guatemala
and Belize, registries of horse vaccinations against EEV and/or EEE in the last four years
are non-existent in the countries affected by Hurricane Mitch. This can translate
into a population that is entirely susceptible to the infection can be implied. The
displacement of humans and this congregation in vulnerable areas, such as overcrowded
refugee camps, surrounded by infected domestic animals, stagnant waters, and poor hygienic
conditions, will be part of the scenario of a possible epidemic.
We are alerting the health authorities in these areas to improve surveillance of
neurological syndromes compatible with equine encephalomyelitis in equines and to
strengthen coordination among sectors for this purpose. Special consideration should be
given to high-risk areas where there are larger numbers of horses, mules and donkeys (late
predictors of equine encephalitides epidemics) and no history of vaccination against EEE
and/or VEE exists in order to take timely and adequate preventive and control measures
such as:
1. Immediate vaccination of horses mules, and donkeys.
2. Detection and treatment of mosquito breeding sites, especially
those close to permanent and temporary human settlements (refugees).
3. Equine case monitoring and reporting, characterized by:
-- Fever, anorexia and depression accompanied by nervous signs such as: deep
depression, difficulties with equilibrium, resting the head on objects, insomnia. Several
animals might show hypersensitivity to touch and sound, excitation, walk in circles,
blindness and bumping into obstacles. They often fall and are unable to get up.
4. Monitoring of probable human cases, characterized by:
-- Fever headache, nausea, vomiting, muscular and pains in the
joints, chills, photophobia and prostration, convulsions or alteration of the state of
conscience, somnolence, hyperacusia and coma.
In people under three years of age:
Fever, alterations of the state of conscience or convulsions.
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.
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