Enhancement of equine infectious anemia virus virulence by identification and removal of suboptimal nucleotides

Pathogenicity was reportedly restored to an a virulent molecular clone of equine infectious anemia virus (EIAV) by substitution of 3' sequences from the pathogenic variant strain (EIAV(PV)). However, the incidence of disease in horses/ponies was found to be significantly lower (P = 0.016) with the chimeric clone (EIAV(UK)) than with EIAV(PV). This was attributable to 3' rather than 5' regions of the proviral genome, where EIAV(UK) differs from the consensus EIAV(PV) sequence by having a 68-bp duplication in the 3' LTR and arginine (R, 03) rather than tryptophan (W-103) at position 103 in the second exon of rev. In EIAV(UK) recipients the duplication was rapidly eliminated and R-103 replaced by W-103 in the viral population. Furthermore, removal of the 3' variant sequences from EIAV(UK) (EIAV(UK3)) resulted in an equivalent (P = 0.013) disease potential in Equus caballus to EIAV(PV). The 68-bp duplication and/or R-103 may limit peak viral RNA accumulation during acute infection. (C) 2003 Elsevier Science (USA). All rights reserved.