Genetic evidence for the origins of Venezuelan equine encephalitis virus subtype IAB outbreaks.
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.
Weaver
S C
SC
Center for Tropical Diseases and Department of Pathology, University of Texas Medical Branch, Galveston 77555-0609, USA.
Pfeffer
M
M
Marriott
K
K
Kang
W
W
Kinney
R M
RM
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
D017931:DNA Primers; D012367:RNA, Viral; D014765:Viral Vaccines