Pathogenic Characteristics of Five Different Lineage of Korean PRRSV-2 Isolates (NADC30-Like, VR2332-Like, LKA, LKB, and LKC)

Porcine reproductive and respiratory syndrome virus (PRRSV) is a significant pathogen in the worldwide swine industry. The virus shows high genetic variation coupled with a broad range of virulence in pigs. Although multiple lineages of the virus have been prevalent throughout in Korea, the characteristics of lineage-wise pathogenicity are largely unknown. Therefore, this study was designed to analyze and compare the pathogenicity of 11 representative Korean PRRSV-2 isolates selected from PRRSV-2 lineages circulating in Korea, NADC30-like, VR2332-like, and three nation-specific lineages (lineage KOR A (LKA), lineage KOR B (LKB), and lineage KOR C (LKC)), which have been continuously prevalent in the nation. Eleven groups of pigs were experimentally infected with one Korean PRRSV-2 isolate through four consecutive animal experiments. Body weight and body temperature were recorded during each 4-week challenge experiment period, and virological, serological, and histopathological tests were performed on the collected samples. The data from the animal experiments were integrated into two indicators-excretion and clinical signs-through correlation and principal component analysis (PCA). Meta-analysis was used to compare PRRSV-2 isolates using each indicator. Based on these analyses, while L1C viruses used in this study (JB15-N-P31-GB and JB15-N-PJ73-GN, similar to NADC30-like strains) exhibited low or moderate levels of excretion and clinical signs, lineage 5 (L5) or modified live vaccine (MLV)-variant strains exhibited high levels of excretion compared to other PRRSV-2 isolates. However, the L5 variants all caused mild clinical signs, except for JB15-N-PJ4-GN, which showed the 4th highest clinical sign indicator. Among the Korean lineages (LKA, LKB, and LKC), two LKB strains (GGYC45 and JB15-N-PJ10-GN) were the most virulent as they showed the highest mortality after the challenge. On the other hand, the LKA and LKC viruses displayed lower excretion indicators than L5 strains, but they had higher-ranked clinical sign indicators than low-virulence L5 MLV variants. In conclusion, PRRSV prevalent in Korea has diverse excretion and clinical characteristics, and certain lineage is highly pathogenic. These results will offer useful insights to prevent spread of PRRSV and improve the efficacy of vaccines in the future.