Porcine reproductive and respiratory syndrome virus: genetic diversity, pathogenesis and modified-live vaccines

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) is a causative agent of PRRS that reproductive failure in sows and respiratory problems in piglets is the hallmark of the disease. Recently, several PRRSV modified live vaccines (MLV) are available, and vaccine selection is a concern. Therefore, the objectives of this study were: 1) to investigate the genetic diversity of Thai PRRSV isolates during 2001-2017; 2) to evaluate the pathogenicity of Thai PRRSV isolates; 3) to determine the efficacy of PRRSV MLV against Thai field PRRSV infection and 4) to investigate the effectiveness of PRRSV MLV when administered via intramuscular (IM) and intradermal (ID) routes against Thai field PRRSV infection. Our results showed that all Thai PRRSV-1 isolates were in subtype 1, which clade A was a dominant strain of PRRSV-1. Meanwhile, Thai PRRSV-2 in lineage 8, sublineage 8.7/HP-PRRSV-2, was the dominant strain of Thai PRRSV-2. When compared the pathogenicity, we noticed that either Thai field PRRSV-1 or PRRSV-2 isolates induced similar clinical disease, and co-infection with both PRRSV species able to cause more severity than those of single infection. For the study of vaccine efficacy, all commercially available PRRSV MLV induce similar humoral- and cell-mediated immune responses with partial cross-protection against Thai field PRRSV infection. Besides, vaccination via IM and ID able to activate an immune response in pigs with partial cross-protection against PRRSV infection. ID vaccination induces more interferon-gamma secreting groups and provide lower interleukin-10 (IL-10) than the IM vaccination. In conclusion, the Thai field PRRSV evolved separately and developed their clusters with higher genetic diversity, and the severity of the co-infection of both PRRSV species is remark. Regardless of vaccine species, all commercial PRRSV MLV provides partial protection against heterologous PRRSV infection, and the ID route might be a choice for PRRSV MLV vaccination in the future.