PRRSV genetic variation after the 2010 HP-PRRSV introduction in Thailand

Abstract

After the first introduction of porcine reproductive and respiratory syndrome virus (PRRSV) into Thailand, Thai type 1 PRRSV has existed in the Thai swine population and caused subclinical diseases while type 2 PRRSV, which most PRRSV isolates belong to, has caused moderate to severe diseases. Highly pathogenic-PRRSV (HP-PRRSV) has recently emerged in Thailand, causing significant damages since its first introduction in 2010. Genetic characterization of Thai PRRSV isolates collected from several clinically affected swine herds distributed in different geographical locations in 2012 was analyzed using a comparative analysis between 2 hyper-variable regions, NSP2 and ORF5. Eleven selected PRRSV clinical samples collected from 11 clinically affected swine herds distributed in 10 provinces located in 4 regions of Thailand were sequenced. Partial NSP2 and ORF5 sequences of the virus revealed that the studied isolates were Thai type 2 PRRSV and could be separated into 2 groups, Thai HP-PRRSV and previous Thai type 2 PRRSV which had been circulating before the HP-PRRSV introduction in 2010. The Thai HP-PRRSV contained 30 deduced amino acids in 2 positions, which is the genetic characteristic of HP-PRRSV prototypes, and might be derived from the isolates introduced in 2010 or introduced later from neighboring countries based on a phylogenetic analysis. However, the classical Thai type 2 PRRSV isolate found in this study was also able to cause severe clinical diseases in the Thai swine herds. Mutations in some positions of both NSP2 and ORF5 genes naturally occurred; NSP2 and ORF5 are often used as genetic markers in terms of PRRSV evolution. In conclusion, after the introduction of HP-PRRSV, major PRRSV outbreaks in Thailand were mostly caused by HP-PRRSV.