| As one of the five major pastoral areas in China,Xinjiang accounts for one-sixth of the country’s area,the cattle and sheep industry is a household name and the pig industry has development prospects.Swine infectious diseases affect the development of the pig industry,among which porcine reproductive and respiratory syndrome as an important disease affecting the respiratory problems of pigs should attract the attention of farmers.Objective: To investigate the serology and virus molecular biology of porcine reproductive and respiratory syndrome(PRRS)in large-scale pig farms in some areas of Xinjiang to understand the prevalence of PRRS disease in some pig farms in Xinjiang.Based on the positive results of PRRSV nucleic acid test,representatives from different regions were selected to construct a PRRSV GP5 gene evolution tree to understand the genetic evolution of PRRSV in Xinjiang to grasp the epidemic strain of PRRSV in the region.Pathological histological observation of diseased tissues and organs was performed to further understand the impact of PRRSV on tissues and organs and to provide scientific basis for clinical judgment.Methods: Clinical incidence cases were investigated in five regional large-scale pig farms in Kuitun,Shihezi,Changji,Shawan,and Urumqi during 2020-2021 using on-site epidemiological surveys and pathological anatomical methods.1.Blood and diseased pig tissues and organs were collected using serological ELISA;2.Molecular biology RT-PCR techniques were used for detection,and the detected pathogen sequences were compared with domestic and foreign pig PRRSV GP5 fragments were compared;3.The collected tissues and organs of the dead pigs were fixed,section production of paraffin,HE staining,and microscopic observation.Results: 1.During 2020-2021,a total of 1028 blood samples were collected from large-scale pig farms in five regions of Xinjiang,including Kuitun,Shihezi,Changji,Shawan,and Urumqi,by mandatory immunization against PRRS,and the serological test results were 90.6%(931/1028)of total antibody positivity;among them,374 cases met the requirements in 2020,and the antibody detection rate The antibody detection rate was 94.0%(374/398);557 cases met the requirements in 2021,and the antibody detection rate was 88.4%(557/630).From the perspective of each regional large-scale pig farm,the best immunization effect was found in Shawan in 2020 and Kuitun in 2021,with 100% immunization effect.The neatness of antibodies varied among regional pig farms.The results indicated that the vaccine achieved certain protective effect in different regions,among which the differences in antibody positivity rate might be due to feeding management and implementation of immunization programs at different times.2.On-site epidemiological survey of large-scale pig farms in some regions of Xinjiang from 2020 to 2021 Nucleic acid testing was conducted on 174 samples collected with suspected PRRSV infection,and the total nucleic acid testing positivity rate was 43.1%(75/174),of which 45.2%(47/104)were positive in 2020 and 40%(28/70)in 2021.The highest positive rate of nucleic acid test was 82.6%(19/23)in Urumqi in 2020,and the lowest positive rate was in Changji with 20%(5/25);the highest positive rate was 60%(15/25)in Kuitun in 2021,and the lowest positive rate was in Shawan with 20%(2/10),the results indicated that all five regional large-scale pig farms had different degrees of PRRSV infection in all five regional large-scale pig farms.According to the evolutionary tree and similarity analysis,all samples in this survey belonged to PRRSV type II,among which sample No.6(Changji area)had affinity with Hu N4 and JXA1,and the remaining samples had affinity with NADC30 strain.Similarity analysis showed that sample 6 detected in Changji area had 93.5% homology with Hu N4 and JXA1,samples 1,3,4,7,8,11,12,13,14,15,16,17 had the highest homology with NADC30 strain GP5 gene sequence of 79.7% to 89.7%,samples 2,5,9 had the highest homology with JL580 strain GP5 gene sequence The highest sequence homology was77.3%-89%,and the highest sequence homology was 80.7% between sample 10 and the GP5 gene of strain HNjz15.This indicates that there is an epidemic of NADC30-like and HP-PRRSV-like strains in Xinjiang.3.The clinical signs and pathological sections of pigs with confirmed PRRSV infection are complex.Usually PRRSV attacked the respiratory and reproductive systems,and clinical cases showed different degrees of damage to various tissues and organs in PRRSV-infected pigs.The clinical visual signs were redness of skin and mental lethargy,etc.;the autopsy revealed foamy fluid in trachea,fleshy lung,brittle liver to touch,hyperplasia in spleen and hemorrhage in brain,etc.;the pathological sections showed that besides interstitial pneumonia of different degrees,other tissues and organs also had pathological damage such as spleen and lymph node hyperplasia.Conclusion: The rate of antibody protection against PRRSV in some areas of Xinjiang investigated in this study has some positive significance.The results of the molecular biology of the virus showed that there were different degrees of PRRSV infection in some areas of Xinjiang,and there were NADC30-like strains and HP-PRRS-like strains prevalent in this survey.microscopic pathological sections of PRRSV-positive pigs showed that in addition to different degrees of interstitial pneumonia,other histological organs also had pathological damage such as spleen and lymph node hyperplastic inflammation. |
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