Molecular identification and phylogenetic analysis of NSP2 and ORF5 genes of PRRSV in China 2012-2015

Porcine reproductive and respiratory syndrome (PRRS), caused by PRRS virus (PRRSV), is a major threat to the swine industry worldwide. The genome of PRRSV is characteristic of its extensive genetic variation, resulting in the complexity of not only genotype but strain diversity. In China, the distribution and ranks of the different PRRSV strains remain unknown in the swine herds although classical, high pathogenic (HP-) and novel variant PRRSVs co-exist. This study revealed the temporal distribution and ranks of PRRSV strains in Henan province of China during 2012-2015 based on the molecular epidemiology and evolutionary characteristics of PRRSV.

Initially, total 468 tissue samples were collected from diseased pigs at different ages from 165 herds in Henan province, China, during 2012-2015.Full-length ORF5 gene and truncated NSP2 gene of PRRSV were amplified by RT-PCR with sero-/geno-type-specific primers and PCR products were sequenced and analyzed by DNAstar, and phylogenetic trees were constructed by MEGA5.

Of 468 samples, 141 (30.1%) were positive for PRRSV. In 2012, 80% of samples detected were HP-PRRSV positive, and 10% of samples were NADC30-Like positive. Notably, however, NADC30-Like positive samples increased to 78.2% (68/87) in 2015, showing a much higher incidence than that in 2012. In contrast, the incidence of HP-PRRSV positive samples decreased from 80% in 2012 to 18.4% in 2015.Meanwhile 65 NSP2 and 79 ORF5 sequences were obtained from a total of 79 filed strains. Phylogenetic trees revealed that all 79 strains belonged to genotype 2 of PRRSV and were clustered into Subgroup 2 represented by JXA1 (HP-PRRSV) and Subgroup 4 represented by NADC30, respectively, indicating that NADC30-Like and HPPRRSV strains were the dominant strains in Henan province.

Since the first report in China, PRRS has been existed and evolved for 20 years and caused severe economic losses. Since 2011,HP-PRRSVderived live vaccines have been commercially launched for compulsory immunization against PRRS in China, and then such vaccine-related PRRS cases increased during 2012-2014 followed by a decrease in 2015 with a less use of the vaccine. In addition, PRRSV strain NADC30 was isolated in U.S.A in 2008, and then the clinical cases remarkably increased over the following years. In China, a historical import amount of sows from U.S.A reached the peak in 2012 and from then on NADC30-Like strains have been increasingly identified from the herds following the distribution of the sows and their offspring. This study warns that people should pay more attention to the use of HP-PRRSV live vaccines and to the quarantine when importing animals.

Disclosure of Interest: None Declared.