| Porcine circovirus 2(PCV2)is the main pathogen causing porcine circovirus disease,which not only causes related diseases,but also causes immunosuppression and makes pigs susceptible to other pathogens,which is a serious threat to the health of pigs.PCV2 is spread in pig herds worldwide,and especially has a high infection rate in China.Shandong province,as a large livestock province,has a large share of pig farming,and the persistent infection of PCV2 in pig herds seriously restricts the healthy development of pig farming in our province.In this study,the pathogenic prevalence and antibody levels of PCV2 in some areas of Shandong Province from 2018 to 2020 were examined,and the results will help to grasp the epidemiological characteristics and immune status of PCV2 in Shandong Province and lay the foundation for the prevention and control of PCV2.In this study,to understand the recent epidemiological and molecular biological characteristics of PCV2 in Shandong Province,230 pig tonsils and 860 lymph nodes,totaling1090 tissue samples,were collected from pig farms and pig slaughterhouses in eight cities of Shandong Province,including Heze,Liaocheng and Jining,during 2018-2020,and 86 PCV2 positive samples were detected by common PCR,with an overall The positive rate was 7.89%,and there were some differences in the PCV2 positive rate of pigs in different localities,with the highest being 14.2% and the lowest being 4.9%.The collected samples were statistically divided according to seasons and it was found that the highest was 8.5% in winter and the lowest was 6.8% in autumn.Thirteen PCV2 strains were selected for genetic sequencing and genetic evolutionary analysis was performed,and the results showed that the prevalent strains were PCV2b(1/13)and PCV2d(12/13)genotypes,with PCV2 d accounting for 92.3%,which indicated that PCV2 d became the dominant genotype in Shandong Province.The nucleotide homology of whole genome sequences among different sequenced strains ranged from 96.2%to 100%,and the nucleotide homology of ORF2 genome sequences ranged from 94.6% to100%,and the nucleotide homology of ORF2 genome sequences of isolated strains and ORF2 genome sequences of 10 PCV2 reference strains ranged from 80.6% to 100%,indicating that the current homology of PCV2 whole genome sequences The sequence homology of the whole PCV2 gene was high and no large degree of variation was observed.Amino acid mutation site analysis of the ORF2 gene revealed only mutations in individual bases,and prediction of selection pressure sites for ORF2 revealed three positive selection sites(63,190,191),all associated with immune-related epitopes.This may contribute to the immune escape of PCV2,leading to immune failure of PCV2 and expanding its transmission in the pig population.This study clarifies the molecular characteristics and evolutionary pattern of PCV2 in Shandong Province,which is an important reference value for the selection and breeding of PCV2 vaccine strains and vaccine development in Shandong Province.To further understand the antibody level of PCV2 in Shandong pig herds during 2018-2020,3982 pig blood samples were collected from 12 large-scale pig farms in Shandong Province,including Heze,Liaocheng and Jining,and the overall positive rate was 74.53%,which was at a high immunization level.The overall positive rate was 74.53%,which was a high level of immunity,and the results indicated that the overall immunity level of PCV2 in large-scale pig herds was good.However,the positive rate varied greatly among the 12 cities,with the highest being 92.79% and the lowest being 50.74%;if divided by pig groups,the highest positive antibody rate was found in boars(81.24%),followed by hind pigs(80.02%),fattening pigs(73.87%),sows(72.18%)and nursery pigs(72.16%),with little difference among various pig groups,and the positive rate was higher than 70%.In conclusion,PCV2 d genotype is mainly used in pig farms in Shandong province at present,and some of the pig farms in some areas have low immunization level.In addition,in the pig farms that were immunized,cases of disease still occurred and caused more serious economic losses;therefore,the continuous monitoring of the prevalence of PCV2 and its pathogenic characteristics should be strengthened. |
PDF Full Text Request