Genetic analysis of ORF5 of recent Korean porcine reproductive and respiratory syndrome viruses (PRRSVs) in viremic sera collected from MLV-vaccinating or non-vaccinating farms

Abstract

The 23 open reading frame (ORF) 5 sequences of Korean type II porcine reproductive and respiratory syndrome virus (PRRSV) were collected from viremic sera from the (modified live vaccine) MLV-vaccinating and non-vaccinating farms from 2007 to 2008. The samples were phylogenetically analyzed with previous ORF5 sequences, including type I Korean PRRSV, and previously reported or collected sequences from 1997 to 2008. A MN184-like subgroup of type II Korean PRRSV was newly identified in the viremic sera collected from 2007 to 2008. And of the type I PRRSVs, one subgroup had 87.2 approximately 88.9% similarity with the Lelystad virus, showing a close relationship with the 27 approximately 2003 strain of Spain. The maximum parsimony tree of type II PRRSV from 1997 to 2008 showed that they had evolved to four lineages, subgroups 1, 2, 3 and 4. Most of the recently collected type II PRRSVs belonged to subgroup 4 (48%). The region of three B-cell epitopes and two T-cell epitopes of ORF5 amino acids sequences was considerably different from the MLV in subgroups 3 and 4. In conclusion, the existence of type I PRRSV, which was genetically different from Lelystad virus (Prototype of type I PRRSV), and heterologous type II PRRSVs of viremic pigs detected even in the MLV-vaccinating farms indicated the need for new vaccine approaches for the control of PRRSV in Korea.

Fig. 1

The neighbor-joining (N-J) tree of open reading frame (ORF) 5 sequences of porcine reproductive and respiratory syndrome virus (PRRSV) in viremic pigs from 2007 to 2008. The name of viremic sera sequences were presented as 'I.D-V (or not)-Year', where the 'V' means the PRRSV ORF5 sequences were from a vaccinating farm. Korean specific subgroup (Ksg)-1, 2, 3 and 4 indicates the phylogenetic groups which were grouped as Korean PRRSV-specific subgroup when compared with Asian isolates in the N-J method of a previous paper [7].

Fig. 2

Maximum parsimony tree of type II Korean PRRSV ORF5 from 1997 to 2008. The Lelystad virus, which was a prototype of type I PRRSV, was used as an outgroup. In the maximum parsimony tree, type II Korean PRRSV were mainly divided into four subgroups, subgroup 1, 2, 3 and 4. Ksg-1 and 2 were in the same group, subgroup 1, in this study. Subgroup 2 only contained samples from 2000 to 2003. The MN184-like subgroup was shown to belong to the subgroup 3 which had not been classified before in Korea.

Fig. 3

Amino acid sequences of two type II PRRSV isolates and 23 type II PRRSV ORF5 in the viremic sera from 2007 to 2008. The amino acid sequences were compared with the sequence of MLV. The known B-cell epitopes, epitope A (decoying epitope, 27~30), epitope B (neutralizing epitope, 37~45) and recently identified region (187~200) were indicated by small, medium and large boxes, respectively. Furthermore, the two T-cell epitope regions of GP5 were also indicated by grey backgrounds.