Molecular Epidemiology Investigation Of Porcine Reproductive And Respiratory Syndrome In Chongqing And Its Surrounding Regions

Porcine reproductive and respiratory syndrome ,which is characterized by abortion , prematurity and fetal death of sows and respiratory distress disease of piglets and growing pigs ,is a highly infectious disease caused by porcine reproductive and respiratory syndrome virus (PRRSV) .'high fever'disease outbreaks in many farms in china , causing great economic loses to swine raising ,2006 . It is verified that the main pathogen is highly pathogenic PRRSV (HP-PRRSV) . HP-PRRSV is grouped into typeⅡand have a discontinuous deletion of 30 amino acids in nonstructural protein 2 (NSP2) .PRRS occurred frequently in Chongqing and its surrounding regions ,causing tremendous loss ,2007 . In this study , samples were collected from 9 pig farms 7 counties in Chongqing and its surroundings from June to December 2007 .The objective of our study is to understand the epidemiology regularity and genetic variation of PRRSV in this regions ,and supply potent breadboard evidence to monitoring PRRS .PRRSV is detected through a reverse transcription-polymerase chain reaction (RT-PCR) .The result showed that 52 samples are positive in 187 samples .According to the discontinuous deletion of 30 amino acids of NSP2 in the reported complete sequence of JXA1(the strain of inactivate vaccine ) compared with CH-1a (the strain of attenuated vaccine ) ,a pair of primers P3/P4 were designed by Primer Premier 5.0 through the deletion to detect HP-PRRSV , the result showed that 29 samples were positive .The RT-PCR products of positive samples BQ2,LK,LC,DA3,LK2 and DZ were purified by gel recovery , they were cloned into PUCm-T vector ,the ligation production were transferred it into DH5αand the obtained clones were amplified and cultured ,then sent them to Sangon to sequence determination .Compared with JXA1 ,the sequence homologous rates of nucleotide were 98.4%-99.1% .The secondary structure of deduced amino acide sequences of these samples compared with JXA1 ,BJsy06 ,NX06 and Henan-1 ,the result showed that the secondary structure of these sequence were basically in accordance by the methods of Alpha regions ,Chou-Fasman ,Beta regions ,Chou-Fasman ,Flexible Regions- Karplus- Schulz , Hydrophilicity Plot-Kyte-Doolittle ,Antigentic Index-Jameson-Wolf and Surface Probability Plot-Emini .In this study ,samples with porcine reproductive and respiratory syndrome virus (PRRSV ) were detected from 7 regions in Chongqing and its surroundings .The total infection rate of PRRSV is 27.81% (52/187) .In which the infection rate of HP-PRRSV is 15.51% (29/187) ,55.77% (29/52) of all the PRRSV positive samples .and the infection rate of classical PRRSV is 12.3% (23/187), 44.23% (23/52) of all the PRRSV positive samples .During the investigation ,the epidemiological of HP-PRRSV and classical PRRSV presented the trend of alternation : the infection rate of HP-PRRSV was 80%-100% of 23 PRRSV positive samples among June to August in 2007 ; 12.82% of 39 samples in September ,negative during October to September ,while 28.56% in November .The infection rate of classical PRRSV was low in the early time of investigation , then rose gradually ,57.14% till November .