Research On Etiology Of Highly-pathogenic Porcine Reproductive And Respiratory Syndrome Virus About Major Pathogen Of Swine High Fever

Porcine reproductive and respiratory syndrome virus(PRRSV) was the causative agent of PRRS,which caused reproductive failure in sows and respiratory problems in piglets.It has caused great damages since its being recognized.In recent,some pig farms in China occured swine high fever in summer or autumn.In 2007,Chinese Agricμlture Department announce that PRRSV was the main antigen in high fever.On the aim of studying epidemiology survery of high fever,we mainly researched on etiology of highly-pathogenic porcine reproductive and respiratory,syndrome virus about Major pathogen of Swine high fever and the below were what we had done:many serum and suspicious samples from forty-one farms by being collected and being attended in JiangSu,BeiJing,HeBei,YunNan,AnHui,HuBei province from May in 2006 to October in 2007,RT-PCR and ELISA were used to detect antibodies and antigens,and the results were analyzed.Clinical diagnose showed that the pigs had fewer neural symptoms and some pigs had hemorrhage phenomena on stomach or bladder in recent years,they could be caused by variants of porcine reproductive and respiratory syndrome virus.209 cases of suspicious samples were detected 120 positive samples by RT-PCR with the positive rate 57.42%.615 cases of secrum samples from 18 farms were detected by ELISA with the positive rate from 80.26%to 87.50%and the average positive rat 84.39%.The average positive rat with sow was up to 83.51%.The average positive rat with hogs was 84.38%.Positive rat of preweaning piglets was 83.51%and nursey pigs was lower than other pigs with the average rate 71.03%.835 cases of secrum samples from 23 nonimmuned hogpens were detected by ELISA with the positive rate from 68.86%to 82.78%.The average positive rat with sow was up to 80%.The average positive rat with hogs was 72.65%.Positive rat of preweaning piglets was 76.98%and nursey pigs was lower than other pigs with the average rate 68.86%.As a whole,positive rat was very high in all hogens and PRRS will be major disease in our country Four strains of porcine reproductive and respiratory syndrome virus were isolated from pathogenic tissue of obvious respiratory syndrome and high fever on some farms in Jiangsu Province in July,2007.They were identified as strains of American type PRRSV by TCID₅₀ detection,sero-logical test and gene sequencing.The menstruation of the virus biological characteristic showed that the four isolated strains all could not resist alkalescence and acidity.Sequence comparison of partial Nsp2 and ORF5 indicated that four strains had no changes in ORF5 region;sequence distance to the standard strain VR-2332 based on the ORF5 genomic amino acid sequence was100%.Genomic amino acid sequence identities showed that.they shared a common feature of thirty deletions in Nsp2 region.four strains had lowly related to vaccine strains RespPRRSReproMLV,CH-1a,RespPRRSMLV which used in China exhibited 57.4%to 82.4%;they closely related to the variation about JXAI,HB-1(sh)/2002,HUN4,hunan-1,YS0608,YNYXI,YNYX3,ZJCJ,exhibited 88.2%～98.5%;they had closely related to each other and exhibited 99.3%to 100%. Phylogenetic tree among 4 strains and other14 PRRSVs trains published were obtained by analyzing genomic amino acid sequence of Nsp2 gene.All the strains were individed into two embranchments,and every embranchment had several small embranchment.Four strains we isolated and vaccine strains VR2332,CH-1a,RespPRRS Repro MLV,RespPRRS MLV fall into different embranchment and they fall into same embranchment with variants(HUN4,JAXI,jiangxi-2,YS0608,ZJCJ),all indicated that four strains weren't from vaccine strains,and they perhaps were variants.The animal test about Fatal Variants of porine reproductive and respiratory syndrome virus was processed in order to copy the typical symptom of PRRSV.The infected piglets were identified by clinical diagnose,pathological diversification,antibody or antigen detection,virus isolation,but the nosogenesis and invasiveness should be further studied.