ABSTRACT
Classication. The family Togaviridae is comprised of four genera, Alphavirus (26 species), Rubivirus (one species), Pestivirus (three species), and Arterivirus (one species) [1,2]. The alphaviruses include at least seven antigenic complexes, two of which are western equine encephalitis virus (WEEV) and eastern equine encephalitis virus (EEEV), which will be reviewed in this chapter; the other ve are Middelburg, Ndumu, Semliki Forest, Venezuelan equine, and Barmah Forest viruses [3]. While EEEV is the sole species in the EEE antigenic complex, North and South American antigenic varieties can be distinguished serologically [4] and ecologically. EEEV strains have been grouped into four subtypes, I-IV. Lineage I is found mainly in the eastern United States, Canada, and the Caribbean Islands [5] and the isolates from North America form a highly conserved lineage. Lineages II-IV have been isolated mainly in Central and South America; that is, lineage II strains are found in Brazil, Guatemala and Peru; lineage III strains have been isolated in Argentina, Brazil, Colombia, Ecuador, Guiana, Panama, Peru, Trinidad, and Venezuela; and lineage IV have been found in Brazil [6]. In addition, there are old reports of EEEV isolations made in the Philippines, Thailand, the Asiatic region of Russia, and the former Czechoslovakia [7]. Antigenic differentiation should be further examined to determine whether viruses in these distinct lineages with separate ecologies represent different species.
