Epidemiological Investigation And Eradication Of Bovine Viral Diarrhea For The Cattle Farm

Bovine viral diarrhea（BVD）,also known as mucosal disease（MD）,is an important infectious disease caused by bovine viral diarrhea virus（BVDV）that seriously endangers the development of cattle industry in China.With a wide host spectrum of infection and a large epidemic range,BVD was first reported by Li et al in China in the 1980s and followed by many other reports.With the rapid development of domestic cattle breeding industry,the country pays more and more attention to the prevention and control of BVD,and gradually incorporates epidemiological investigation and decontamination to the comprehensive prevention and control of the disease.Epidemiological investigation is the key and prerequisite for the prevention,control and decontamination of bovine viral diarrhea,while decontamination is one of the important means for the prevention,control and elimination of BVD,as well as the ultimate goal for the prevention and control of the disease.This study aims to understand the epidemiology of bovine viral diarrhea in Jilin Province in recent years,to control and purify the epidemic of the disease by detecting and culling persistently infected cattle with BVDV in the herd,and to provide a demonstration for the prevention and control of BVD in Jilin Province and even nationwide.This study includes the following.A double antibody sandwich ELISA kit for detecting BVDV antigen was used to investigate the epidemiology of BVD in 796 fecal samples collected from cattle farms in some areas of Jilin Province.Detection results showed that BVDV infection was present in cattle in different areas with the infection rate ranging from 3.45%to42.65%,which provides a basis for the selection of target cattle farms for BVD decontamination.Detection of 7645 serum samples from the selected target cattle farms collected from cattle of different seasons and ages were conducted and analyzed.The results showed that the average rate of BVDV infection in the target cattle farms was 12.22%（934/7645）,with 4.73%,8.35%,9.38%and 17.29%for calves,mature cattle,young cattle and adult cattle,respectively.BVDV infection rate in Winter is the highest,up to 14.06%.These results indicated that there was variability in BVDV infection among cattle of different seasons and ages.The cattle tested positive for BVDV were kept in quarantine,and the test was repeated twice after an interval of 21 days.Cattle tested positive three times were judged as persistently infected with BVDV（PI）and culled,while cattle turned from positive to negative during quarantine were judged as recovered cattle.After a year-long monitoring and culling of PI animals,the BVDV infection rate of this target cattle farm gradually decreased from 12.22%to 0.22%,with a total of 514 infected animals eliminated.Meanwhile,MDBK cells were applied to isolate BVDV from 73 positive samples.The immunological characteristics,biotype and genetic variation of the isolated strains were investigated.10 new BVDV strains were successfully isolated from BVDV-infected cattle.Biological characterization showed that 4 of the 10BVDV strains were CP-biotype and 6 were NCP-biotype strains.IPMA assay showed that there was immune cross-reactivity between the isolated strains and BVDV CC13B strain.Sequence alignment analysis showed that the 5’UTR gene of the isolates had 96.8%-97.6%homology with strain 2019BVDO4882（Gen Bank:MW528231.）,while the N^pro gene had 93.39%-95.8%homology with strain 2019BVDO4882.Phylogenetic tree analysis using the 5’UTR sequence revealed that the BVDV strains infecting the target cattle farm belonged to BVDV-1d genotype.These results demonstrated that the nucleotide sequences of the BVDV strains in the target cattle farms were highly homologous and probably originated from the same BVDV strain.In addition,the mixed infection of bovine viral diarrhea virus and bovine enterovirus was also examined for the target cattle farms.The results showed that the single infection rate of BVDV was 10.12%,and the mixed infection rate of BVDV and BEV was 2.10%,which demonstrated the existence of mixed infection of BVDV and BEV in cattle farms and laid the foundation for the prevention,control and decontamination of bovine diarrheal disease in the future.