Association of Venezuelan equine encephalitis virus subtype IE with two equine epizootics in Mexico.

Abstract

Two outbreaks of encephalitis consistent with an etiology of Venezuelan equine encephalitis (VEE) virus occurred in equines on the Pacific coast of southern Mexico in 1993 (Chiapas State) and in 1996 (Oaxaca State). In Chiapas, there were 125 cases, of which 63 were fatal and in Oaxaca, there were 32 cases and 12 fatalities. Virus was isolated from two horses from each outbreak, including three brain isolates and one from blood. Virus isolates (93-42124, ISET-Chi93, Oax131, and Oax142) were shown by indirect immunofluorescence, hemagglutination inhibition, monoclonal antibody ELISA, and nucleotide sequencing to be VEE virus, subtype IE, a type previously thought to be equine-avirulent. Genetic characterization and phylogenetic analysis indicated that the outbreak viruses were identical or nearly identical to one another and that they were closely related to equine-avirulent IE strains from Guatemala and the Gulf coast of Mexico. In a plaque-reduction neutralization test, sera collected from healthy horses in Chiapas and Oaxaca reacted significantly better with isolate 93-42124 than with Guatemala IE isolate 68U201, suggesting that subtle genetic changes may have resulted in alteration of neutralization domains. It is not clear whether these differences may also influence equine virulence. However, renewed VEE virus subtype IE activity in Mexico, and its apparent conversion to equine virulence, underscores the need for increased surveillance, additional laboratory and epidemiologic studies in VEE-endemic regions, and possibly new vaccines.

Venezuelan equine encephalitis emergence: Enhanced vector infection from a single amino acid substitution in the envelope glycoprotein

“…It is now clear that subtype IE VEEV, previously believed not to have epizootic potential, can cause equine disease as witnessed by outbreaks in 1993 and 1996 involving Ͼ160 documented equine cases and probably many additional unconfirmed cases (14). Human serosurveys also indicate that many human infections probably occurred (J.G.E.-F. and S.C.W., unpublished work).…”

“…In 1993 and 1996, outbreaks of equine encephalitis occurred in Mexican Pacific coastal regions of Chiapas and Oaxaca states, respectively (14). Several strains of VEEV subtype IE were isolated from horse brains and sera and were shown to be closely related to enzootic subtype IE strains isolated in nearby coastal Guatemala from 1968 to 1980 (15).…”

Ecological studies of enzootic Venezuelan equine encephalitis in north-central Venezuela, 1997-1998.

“…[1][2][3]5 Venezuelan equine encephalitis epidemics and epizootics were not reported between 1973 and December 1992, when a small human and equine outbreak occurred in the Trujillo and Zulia States of Venezuela. 6 Subsequent outbreaks have been reported during the 1990s in Mexico 7 and Peru, but the largest epidemic/epizootic occurred between April and December 1995, affecting hundreds of thousands of equines and humans in northern Venezuela and Colombia. 9,10 The 1995 outbreak had many similarities to the one that occurred from 1962-1964: first, cases occurred in the same regions of Venezuela and Colombia, and the epicenter was in the Guajira peninsula; second, the VEE virus subtype IC strains isolated in both outbreaks are nearly identical genetically.…”

Experimental Infection of Potential Reservoir Hosts with Venezuelan Equine Encephalitis Virus, Mexico

“…VEE virus (VEEV; Togaviridae: Alphavirus) strains are categorized as either epizootic (associated with equine disease and major epidemics of human disease through equine amplifi cation), or enzootic (not known to cause equine disease). Most VEEV strains, both epizootic and enzootic, have been associated with human disease (1). VEEV is also of biodefense importance; it has been developed as a biological weapon, mainly because it is highly infectious by aerosol transmission and can infect humans with a relatively low dose (2).…”