Isolation And Identification Of Bovine Viral Diarrhea Virus And Evaluation Of The Inhibitory Effect Of Interferon On It

Bovine viral diarrhea virus(BVDV)is one of the main pathogens of bovine respiratory disease syndrome(BRDC),which can infect a variety of economic animals,including cattle.In addition to respiratory symptoms,BVDV infection can also cause immunosuppression,exacerbating BRDC in collaboration with other respiratory pathogens,causing significant economic losses.Currently,it has been found that BVDV includes genotype 1(BVDV-1)including at least 22 subtypes and genotype 2(BVDV-2)including at least 3 subtypes.The pathogenicity of BVDV and the cross protection between different genotypes are different.This experiment collected bovine nose swabs,throat swabs,and lung samples from sick and dead cattle in Hebei Province.RT-PCR was used to investigate the infection and prevalence of BVDV in cattle farms in Hebei Province.By sequencing the 5 ’-UTR of BVDV,the prevalent subtypes of BVDV in Hebei Province were identified.A total of 63 samples were collected from 4 cattle farms in Hebei Province,with a total positive rate of 38.1%.During the same period,one lung sample from sick and dead cattle in Jiangsu Province was collected,with a positive rate of 100%.Cell culture technology was used to isolate viruses from nucleic acid amplification positive samples.One cytopathogenic strain JS2201 was isolated from dead cattle in Jiangsu(Gen Bank: OP856581),and four cytopathogenic strains were isolated from clinical samples from cattle farms in Hebei.The isolate was sequenced and the virus strain isolated from the lungs of sick and dead cattle in Jiangsu Province was of BVDV1 type.To understand the molecular characteristics of BVDV strains in some areas of Hebei Province,the 5 ’-UTR fragment of the BVDV isolate from Hebei Province was analyzed using MEGA analysis software and the Neighbor Joining method was selected for genetic evolution analysis.The genetic evolution tree was drawn.The results showed that the isolate had 92.3%to 97.0% homology with the BVDV strain reported in Gen Bank,Two of them are the same subtype.The four strains belong to subtypes 1o,1q,and 1b on the same evolutionary branch as MF-3(KY865371),T4-23(MN417855),and Shihezi08132(HQ015423),respectively.The overall testing results confirm that the prevalence of BVDV in Hebei Province is serious.In order to evaluate the virulence and pathogenicity of BVDV isolates isolated in our laboratory,models of BALB/c mice infected with BVDV were established respectively by isolate and reference strains BVDV1 type Oregon C24 V strain and BVDV2 type C1602 strain.By monitoring the clinical symptoms,changes in body weight,viremia,changes in white blood cells and lymphocytes in the blood,histopathological changes in various tissues and organs,and viral load in different groups of mice after the virus attack,The pathogenicity differences between the isolated strain JS2201 and the reference strains of type 1 and type 2 were compared.The results showed that both the BVDV isolate JS2201 and the reference strain were able to successfully infect Balb/c mice,and both the challenged Balb/c mice developed viremia,resulting in a temporary decrease in the number of white blood cells,lymphocytes,and lymphocyte percentage in the blood.This study successfully established a model of acute infection of Balb/c mice with different subtypes of BVDV,and compared and analyzed the pathogenicity differences between the isolated strain and the reference strain,laying a foundation for the development of BVDV vaccine and the study of pathogenesis.Interferon(IFN)is an important antiviral factor secreted by cells.In this study,IFN was selected-α,τ,γ Three kinds of interferon were tested for anti BVDV proliferation.Result display,IFN-αThe strongest antiviral activity against different genotypes of BVDV,IFN-αAfter incubation for 1 day,the BVDV genome RNA was significantly downregulated,and the results were consistent with the trend of virus titer change,confirming IFN-α It has the ability to inhibit BVDV replication.This study systematically studied the prevalence of BVDV in cattle farms in Hebei Province,the identification of BVDV isolates,the pathogenicity study of different genotypes of BVDV,including BVDV isolates,and the evaluation of the inhibitory effect of interferon on BVDV.This study laid a foundation for the screening of recent BVDV epidemic strains,the establishment of animal infection models,and the screening of BVDV therapeutic agents.