| In recent years,with the rapid development of large-scale pig farming in China,pig viral diseases have become more and more complex,with old diseases not yet removed,new diseas es re-emerging and diseases constantly appearing;the speed of virus mutation has accelerated,and the majority of viral diseases are immunosuppressive diseases,seriously endangering the healthy development of China’s pig farming industry.Among them,Classical swine fever(CSF),Porcine reproductive and respiratory syndrome(PRRS),Porcine epidemic diarrhoea(PED),Porcine pseudorabies(PR)and Porcine circovirus disease(PCVD)are common viral diseases in large-scale pig farms.To further understand the prevalence of common viral diseases in large-scale pig farms in Shandong Province in the past three years and to formulate corresponding preventive and control measures,pathogenic and serological investigations and analyses of common viral diseases in large-scale pig farms in various regions of Shandong were conducted.From 2020 to 2022,2564 pig tissue samples were collected from different large-scale pig farms in Shandong,and pathogenic tests were performed by Polymerase chain reaction(PCR)for Classical Swine fever virus(CSFV),Porcine reproductive and respiratory syndrome virus(PRRSV),Porcine epidemic diarrhoea virus(PEDV),Porcine pseudorabies virus(PRV)and Porcine circovirus type 2(PCV2)From 2020 to 2022,4803 blood samples were collected from pig farms of different sizes in Shandong Province,and antibody levels against four viruses,CSFV-E2,PRRSV-N,PRV-g E and PCV2-Cap,were measured by Enzyme-linked immunosorbent assay(ELISA).The test results showed that the positive detection rates for CSFV,PRRSV,PRV,PCV2 and PEDV pathogens in the samples collected for testing in 2020-2022 were 3.98%(38/954),19.97%(473/2368),2.35%(24/1023),20.93%(233/1113)and 39.32%(138/351).The detection rate of PCV2,PRRSV and PEDV was high in terms of pathogen detection.The results of the serological survey showed that the antibody positivity rates for CSFV,PRRSV,PRV and PCV2 in the samples tested in 2020-2022 were 83.86%(3986/4753),82.05%(3858/4702),27.89%(1008/3614)and 95.96%(2924/3047)respectively.Combining the results of the laboratory’s long-term epidemiological survey on common viral infectious diseases in Shandong Province and literature reports,it was found that since the outbreak of non-fever,large-scale pig farms have strengthened their biosecurity management systems,resulting in a year-on-year decrease in the positive detection rate of common viral diseases and an increase in serum antibody levels in large-scale pig farms in Shandong Province.In this study,the whole genome of 32 PCV2 isolates was cloned and sequenced,and the predominant strain in Shandong was subtype 2.1d,followed by 2.1b and 2.1e.The nucleotide and deduced amino acid homologies between isolates were 90.7%-100% and 85.4%-100%based on the ORF2 gene,respectively,which were comparable to those of other reference strains at home and abroad.The nucleotide and deduced amino acid homologies were 94.4%-100% and 81.2%-100%,respectively,with the ORF2-based nucleotide and deduced amino acid homologies of other reference strains at home and abroad.In this study,the pathological changes of PCV2-infected pigs with typical clinical signs were observed by autopsy and microscopy.The autopsy revealed significant enlargement of lymph nodes throughout the body,grey-white spots on the surface of the kidneys,focal or diffuse dark red solid lesions in the lungs,lattice-like hyperplasia in the interstitial liver lobules and common ulcers in the gastric mucosa.Histological material was subjected to routine paraffin sectioning and HE staining,and microscopic examination revealed lymphocyte deficiency and macrophage hyperplasia in lymph nodes throughout the body;white marrow lymphocyte deficiency in the spleen;focal infiltration and hyperplasia of lymphocytes and macrophages in the renal interstitium;lymphocyte infiltration in the alveolar wall and lobular interstitium,often followed by catarrhal septic pneumonia;and mild viral encephalitis in the brain.In this study,the whole genome of 12 PEDV isolates was cloned and sequenced,and the predominant strain in Shandong was G1.The nucleotide and deduced amino acid homology among the isolates ranged from 97.2% to 99.9% and 95.9% to 99.7%,respectively,and the nucleotide and deduced amino acid homology with other reference strains based on the ORF2 gene at home and abroad ranged from 93% to 99.1% and 90.9% to 99.4%,respectively.In summary,this study further enriches the epidemiological data of common viral diseases in large-scale pig farms in Shandong Province from 2020 to 2022,comparatively analyses the epidemiological trends of common viral infectious diseases in pigs in Shandong Province from2020 to 2022,analyses the causes of occurrence,and formulates corresponding immunization and prevention and control measures based on the test results.It provides reference data for the scientific and precise prevention and control of viral diseases in large-scale pig farms in Shandong Province,which is conducive to the healthy development of the pig farming industry in Shandong. |
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