A new porcine reproductive and respiratory syndrome virus strain with highly conserved molecular characteristics in its parental and attenuated strains

Porcine reproductive and respiratory syndrome virus (PRRSV) causes substantial economic losses to many swine-producing regions. In this study, PRRSV strain NT0801-F80 was derived from its parental isolate NT0801 by 80 passages in Marc-145 cells. Experimental infection of piglets clearly demonstrated that strain NT0801-F80 is less virulent than NT0801. However, whole genome sequencing showed that the genomes of the parental and attenuated strains are highly conserved compared with those of four other pairs of virulent parental/attenuated vaccine strains (VR2332 and RespPRRS MLV, JA142 and Ingelvac^® ATP MLV, CH-1a and CH-1R, and JXA1 and JXAR). The attenuated strain NT0801-F80 has only 21 nucleotide changes, producing only 14 amino acid changes in NSP2, GP2, GP3, and GP5, compared with those aa sequences of the virulent parental strain. These mutated aa in the attenuated virus may be involved in virulence. These data provide valuable information on the attenuation mechanism of PRRSV that should be useful in future research.