Abstract
BackgroundPorcine reproductive and respiratory syndrome virus (PRRSV) causes devastating disease characterized by reproductive failure and respiratory problems in the swine industry. To understand the recent prevalence and genetic diversity of field PRRSVs in the Republic of Korea, open reading frames (ORFs) 5 and 7 of PRRSV field isolates from 631 PRRS-affected swine farms nationwide in 2013–2016 were analyzed along with 200 Korean field viruses isolated in 2003–2010, and 113 foreign field and vaccine strains.ResultsKorean swine farms were widely infected with PRRSVs of a single type (38.4 and 37.4% for Type 1 and Type 2 PRRSV, respectively) or both types (24.2%) with up to approximately 83% nucleotide sequence similarity to prototype PRRSVs (Lelystad or VR2332). Phylogenetic analysis based on the ORF5 nucleotide sequence revealed that Korean Type 1 field isolates were classified as subgroups A, B, and C under subtype 1, while Korean Type 2 field isolates were classified as lineages 1 and 5 as well as three Korean lineages (kor A, B, and C) with the highest infection prevalence in subgroup A (50.5%) and lineage 5 (15.3%) for Type 1 and Type 2 PRRSV, respectively, among ORF5-positive farms. In particular, the lineages kor B and C were identified as novel lineages in this study, and lineage kor B comprised only the field viruses isolated from Gyeongnam Province in 2014–2015, establishing regionally unique genetic characteristics. It has also recently been confirmed that commercialized vaccine-like viruses (subgroup C) of Type 1 PRRSV and NADC30-like viruses of Type 2 PRRSV (lineage 1) are spreading rapidly in Korean swine farms. The Korean field viruses were also expected to be antigenically variable as shown in the high diversity of neutralizing epitopes and N-glycosylation sites.ConclusionsThis up-to-date information regarding recent field PRRSVs should be taken into consideration when creating strategies for the application of PRRS control measures, including vaccination in the field.
Highlights
Porcine reproductive and respiratory syndrome virus (PRRSV) causes devastating disease characterized by reproductive failure and respiratory problems in the swine industry
Selected viral isolates were sequenced for Open reading frame 5 (ORF5), and further subjected to genetic analysis and compared with Korean field viruses isolated in 2003–2010, commercial vaccine strains (DV of Porcilis® PRRS, VP-046 of UNISTRAIN® PRRS, Ingelvac PRRS MLV of Ingelvac PRRS® MLV, and P129 of Fostera® PRRS) commonly used in the Republic of Korea, PRRSV prototype strains (VR2332 and Lelystad), and field isolates previously reported from other countries
Prevalence of PRRSVs in the Republic of Korea from 2013 to 2016 Among the 631 clinical samples subjected to ORF7 RTPCR, 38.4% (242/631) were positive for Type 1 PRRSV, 37.4% (236/631) were positive for Type 2 PRRSV, and 24.2% (153/631) were positive for both PRRSV genotypes (Fig. 1)
Summary
Porcine reproductive and respiratory syndrome virus (PRRSV) causes devastating disease characterized by reproductive failure and respiratory problems in the swine industry. Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most common and economically significant infectious diseases in the pig industry worldwide [1, 2]. This virus causes clinical disease characterized by reproductive failure in pregnant sows and acute respiratory illness in growing pigs, causing increased preweaning mortality [3, 4]. Owing to its high degree of genetic diversity, the ORF5 sequence has been used for diagnostic identification and classification of PRRS field viruses [4, 24,25,26]
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