S. Wootton et al., Full-length sequence of a Canadian porcine reproductive and respiratory syndrome virus (PRRSV) isolate, ARCH VIROL, 145(11), 2000, pp. 2297-2323
Presently, one of the most economically important pathogens affecting swine
is the porcine reproductive and respiratory syndrome virus (PRRSV). This v
irus is prevalent in herds throughout the world and continues to pose a sig
nificant threat as newer and more virulent disease phenotypes emerge. In th
is report we describe the full-length nucleotide sequence of a Canadian PRR
SV isolate, designated PA8. A consecutive sequence of 15,411 nucleotides wa
s obtained from a set of overlapping cDNA clones. In order to determine the
extent of genetic variation among isolates recovered from swine in Canada
and the US, as well as to understand the molecular mechanisms governing the
evolution of PRRSV, the full-length sequence of PA8 was compared with that
of two US isolates, VR2332 and 16244B. The genomic sequence of PA8 shared
98.2% and 99.2% identity with 16244B and VR2332, respectively. The untransl
ated regions (UTR) at the 5' and 3/ ends of the genome were very well conse
rved. Notable exceptions include an eight nucleotide difference at the 5' e
nd of the 5' UTR of VR2332 relative to PA8 and 16',44B and a two nucleotide
difference in the 3' UTR of PA8 relative to VR2332 and 16244B. In contrast
to PA8 and VR2332, 16244B possessed two nucleotide differences within the
RNA pseudoknot structure of the ribosomal frameshift region between open re
ading frame (ORF)la and ORFlb. Amino acid differences were distributed thro
ughout the genome, however they appeared to be most extensive in Nsp1 beta
and ORF5 of the nonstructural and structural coding regions, respectively,
suggesting that the evolutionary pressure to conserve these viral genes is
somewhat lower.