| Porcine reproductive and respiratory syndrome(PRRS)is caused by porcine reproductive and respiratory syndrome virus(PRRSV)to failure in reproduction of sows and in respiratory of piglets characterized by acute viral Infectious diseases.It makes more difficult to provide effective protection because of intricate recombination between genes and caused severe economic losses to the current breeding industry in China.Therefore,it is of great significance to explore the molecular epidemiology investigation of PRRSV and the mechanism of genetic evolution.In this study,the enzyme-linked immunosorbent assay(ELISA)was used to detected PRRSV antibody level of 8 large-scale pig farms in Shuozhou A and B,Luliang A,B,and C pig farms,Jinzhong A pig farm and Linfen A and B pig farms Which have been immunized by inactivated vaccines from 2019 to2020 in Shanxi Province.A total of 4384 serum samples were collected in 2019,of which 3426 met the standard,with an antibody positive rate of 78.15%,and the positive rate ranged from the lowest Shuozhou B pig farm(38.60%)to the highest Shuozhou A pig farm(92.20%),analysis of different time found that the antibody positive rate from 49.00% to 85.42%,and the antibody level fluctuated greatly in each time period.In 2020,a total of 6559 serum samples were collected,of which 5594 were positive samples,and the overall positive rate was 85.29%.In different pig farms,the positive rate of Shuozhou A pig farm(94.64%)was highest,positive rate of Linfen A pig farms(68.42%)is the lowest.According to the analysis of different periods,the positive rate of antibodies in each period ranges from the lowest level in June(73.66%)to the highest level in February(96.72%),which are all higher than the national immunization standards,the overall level is relatively stable.From 2019 to 2020,the overall antibody level is on the rise.In order to further study the prevalence of PRRSV strains in Shanxi Province,a total of 251 tissue samples including lungs,lymph nodes,tonsils,spleens,were collected from slaughterhouses in different regions of Shanxi Province for RT-PCR etiological testing.The results showed that the number of positive samples was 15,there are 9 NADC30-like strains among them.It is speculated that the current PRRS strains in Shanxi Province are mainly NADC30-like strains of line I.One of the strains was successfully for isolated on Marc-145 cells,and named SXht2012.The genome-wide amino acid and nucleotide homology analysis of this strain showed that its 5’UTR and Nsp1,Nsp4-6 have the highest homology with the highly pathogenic strain JXA1(line 8),while the rest are with the NADC-30 strain(line 1)has high homology.It’s showed that the SXht2012 is a recombinant strain of H-PRRSV and NADC-30.In summary,the PRRSV antibody level in Shanxi Province from 2019 to 2020 is on the rise.The pathogen isolation of PRRS shows that the current main epidemic line I(NADC30-like strain),and the recombinant virus strains in Shanxi Province have begun to appear.This study will put forward a new theoretical reference for the prevention and control of PRRS in Shanxi Province. |
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