title: Genetic evidence for the origins of Venezuelan equine encephalitis virus subtype IAB outbreaks.
abstract: Epizootics of Venezuelan equine encephalitis (VEE) involving subtype IAB viruses occurred sporadically in South, Central and North America from 1938 to 1973. Incompletely inactivated vaccines have long been suspected as a source of the later epizootics. We tested this hypothesis by sequencing the PE2 glycoprotein precursor (1,677 nucleotides) or 26S/nonstructural protein 4 (nsP4) genome regions (4,490 nucleotides) for isolates representing most major outbreaks. Two distinct IAB genotypes were identified: 1) 1940s Peruvian strains and 2) 1938-1973 isolates from South, Central, and North America. Nucleotide sequences of these two genotypes differed by 1.1%, while the latter group showed only 0.6% sequence diversity. Early VEE virus IAB strains that were used for inactivated vaccine preparation had sequences identical to those predicted by phylogenetic analyses to be ancestors of the 1960s-1970s outbreaks. These data support the hypothesis of a vaccine origin for many VEE outbreaks. However, continuous, cryptic circulation of IAB viruses cannot be ruled out as a source of epizootic emergence.
authors.affiliation: Center for Tropical Diseases and Department of Pathology, University of Texas Medical Branch, Galveston 77555-0609, USA.
authors.forename: S C
authors.initials: SC
authors.lastname: Weaver
authors.forename: M
authors.initials: M
authors.lastname: Pfeffer
authors.forename: K
authors.initials: K
authors.lastname: Marriott
authors.forename: W
authors.initials: W
authors.lastname: Kang
authors.forename: R M
authors.initials: RM
authors.lastname: Kinney
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002489:Central America / Q000453:epidemiology; D017931:DNA Primers / Q000737:chemistry; D004196:Disease Outbreaks; D004666:Encephalitis Virus, Venezuelan Equine / Q000145:classification / Q000235:genetics*; D004683:Encephalomyelitis, Equine / Q000453:epidemiology* / Q000821:virology; D008969:Molecular Sequence Data; D009656:North America / Q000453:epidemiology; D010802:Phylogeny; D012367:RNA, Viral / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D013020:South America / Q000453:epidemiology; D014765:Viral Vaccines / Q000009:adverse effects
chemical_list: D017931:DNA Primers; D012367:RNA, Viral; D014765:Viral Vaccines