부산대학교 도서관

Lineage 3 of porcine reproductive and respiratory syndrome viruses, which belong to North America type 2, has a long epidemic history in China. The novel lineage 3 viruses constantly emerging in recent years are characterized by a high detection rate and significant pathogenicity. In this study, we investigated the prevalence of lineage 3 in southern China and selected two isolated strains for genome and virulence analyses. A cross‐sectional epidemiology investigation indicated that the prevalence of lineage 3 antigens was 35.68% (95% CI: 27.6–44.3%) among 227 samples collected from over 100 infected farms from January 2016 to July 2017 in southern China. Two novel isolates of lineage 3 were selected. After 20 passages, Marc‐145 cells were not susceptible to those viruses. Full‐length genome analysis indicated that the two strains share 95.2% homology with each other and 95.7%–96.2% with highly pathogenic porcine reproductive and respiratory syndrome viruses (HP‐PRRSVs; JXA1‐like strain, lineage 8.7). Phylogenetic and molecular evolutionary results showed that for the two isolates, HP‐PRRSV provides most of the ORF1 gene. Animal experiment revealed discrepancies in virulence between the strains. Although challenge resulted in 100% morbidity, the isolate carrying most of the HP‐PRRSV ORF1 caused severe clinical symptoms and 40% mortality, whereas the other isolate containing part of the ORF1 gene caused no mortality. Overall, these findings suggest that lineage 3 viruses might be commonly circulating in most of southern China. Frequent recombination events within HP‐PRRSVs of this lineage with changing virulence could represent potential threats to the pig industry. [ABSTRACT FROM AUTHOR]