Jf. Hedges et al., Genetic divergence with emergence of novel phenotypic variants of equine arteritis virus during persistent infection of stallions, J VIROLOGY, 73(5), 1999, pp. 3672-3681
The persistently infected carrier stallion is the critical natural reservoi
r of equine arteritis virus (EAV), as venereal infection of mares frequentl
y occurs after breeding to such stallions. Two Thoroughbred stallions that
were infected during the 1984 outbreak of equine viral arteritis in central
Kentucky subsequently became long-term EAV carriers. EAV genomes amplified
from the semen of these two stallions were compared by sequence analysis o
f the six 3' open reading frames (ORFs 2 through 7), which encode the four
known structural proteins and two uncharacterized glycoproteins. The major
variants of the EAV population that sequentially arose within the reproduct
ive tract of each carrier stallion varied by approximately 1% per year, and
the heterogeneity of the viral quasispecies increased during the course of
long-term persistent infection. The various ORFs of the dominant EAV varia
nts evolved independently, and there was apparently strong selective pressu
re on the uncharacterized GP3 protein during persistent infection. Amino ac
id changes also occurred in the V1 variable region of the G(L), protein. Th
is region has been previously identified as a crucial neutralization domain
, and selective pressures exerted on the V1 region during persistent EAV in
fection led to the emergence of virus variants with distinct neutralization
properties. Thus, evolution of the EAV quasispecies that occurs during per
sistent infection of the stallion clearly can influence viral phenotypic pr
operties such as neutralization and perhaps virulence.