Dynamics and evolution of genotype 1 porcine reproductive and respiratory syndrome virus following its introduction into a herd concurrently infected with genotypes 1 and 2
This study was conducted to investigate the dynamics and evolution of porcine reproductive and respiratory syndrome virus (PRRSV) genotype 1 following its introduction into a herd concurrently infected with both PRRSV genotypes. The results demonstrated that 2 novel genotype 1 groups emerged, termed clusters II and III. The emergence of cluster II suggested that this cluster of genotype 1 virus potentially correlated with the outbreak. Then, cluster III was detected with the disappearance of cluster II. The evolution of the genotype 1 virus from cluster II to cluster III is likely to be associated with immune evasion induced by amino acid substitutions at N-linked glycosylation sites. In contrast, evolution of the genotype 2 isolates was not observed. This result suggests that genotype 2 viruses were not affected by the emergence of the genotype 1 virus and each genotype developed independently.