Study On The Pathogenicity Of Duck Circovirus And The Pathway Of Inducing Host Lymphocyte Cell Apoptosis

Duck circovirus(DuCV)is a single stranded circular envelopless DNA virus with a genome size of about 2 kb,which is the smallest known animal virus.Duck circovirus disease is an immunosuppressive disease caused by DuCV,characterized by delayed growth and development,disordered feathers,and weight loss in infected ducks.Although ducklings infected with DuCV alone rarely cause death,their risk of infection with other pathogens increases and their harm increases due to a decrease in the body’s immune system.Vaccine immunization is an effective means of preventing infectious diseases,but as of now,there are no commercial vaccines available for the prevention of duck circovirus disease,and no specific drugs have been developed to prevent and control the disease,thereby increasing the difficulty of prevention and control of the disease.The cell apoptosis induced by viral infection is an important pathway for viruses to evade host immune mechanisms and achieve the release and transmission of offspring viruses,it is also often one of the important reasons for host immune suppression.Studying the pathways of cell apoptosis induced by viral infection helps to enhance understanding of the pathogenic mechanism of the virus,thus providing a theoretical basis for the prevention and control of viral diseases.Currently,existing studies have shown that DuCV infection can cause cell apoptosis,but there are few reports on the apoptosis pathways it induces.This study used isolated and cultured duck circovirus to inoculate 7-day-old healthy ducklings,while using ducks inoculated with the same dose of PBS as a control,to observe the clinical symptoms and weight changes of two experimental animals on the 1st,7th,14 th,21st,28 th,35th,and 42 nd days after inoculation.Collect tissue samples at the above time points,use probe method fluorescence quantitative PCR to detect the viral load of each organ,immunohistochemistry to detect DuCV antigen in immune organs,and then observe the tissue lesions caused by duck circovirus infection through pathological section HE staining.Finally,in situ end labeling(Tunel),fluorescent quantitative PCR and double antibody sandwich ELISA were used to detect the apoptosis of spleen,thymus and bursa of Fabricius,the differential expression of mRNA transcriptional levels of key apoptosis regulating genes,and the changes of protein levels of apoptosis factors in serum after DuCV infection,so as to determine the main pathway of host lymphocyte apoptosis induced by duck circovirus infection.The results are as follow:1.On 14 days post infection(14 dpi)after the infection of duck circovirus,the ducks in the infection group showed varying degrees of growth retardation and weight loss,on 35 days after the infection,the ducks in the infection group showed significant growth retardation and weight loss.2.The histopathology observation results of spleen,thymus and bursa of Fabricius in the immune organs of the two groups of experimental animals at different time points showed that the pathological changes of the three immune organs were not obvious 1 day to 14 days after the challenge,and the pathological changes of the three immune organs were obvious 14 days after the challenge,including the loss of lymphocytes,nuclear fragmentation and other pathological changes.3.The detection results of tissue viral load showed that the viral load of each organ showed a significant upward trend from 1 day to 14 days after DuCV infection,and the viral load reached the maximum value at 14 dpi,and then from 14 dpi to 42 dpi,except that the viral load of bursal disease did not decrease significantly,the viral load of other organs decreased significantly.4.The immunohistochemical test results showed that 14 days after DuCV infection,the presence of virus antigens could be detected by all three immune organs.5.The Tunel test results of immune organs showed that 14 days after DuCV challenge,the number of apoptotic cells in the challenge group significantly increased,indicating that DuCV infection can significantly induce cell apoptosis.6.The results of fluorescent quantitative PCR detection of the mRNA transcriptional level of apoptosis regulating genes in immune organs showed that after DuCV infection,the expression of apoptosis regulating genes in the three apoptosis pathways had varying degrees of change.Among them,FasL gene in the receptor pathway had the largest upregulated expression in the spleen,thymus and bursa of Fabricius,and the highest up-regulated expression was 195,126 and 218 times,respectively.7.The expression levels of apoptosis related proteins in serum were determined,and the protein expression levels of apoptosis regulatory factors in the three apoptosis pathways were detected to varying degrees,but the differential expression multiples were low,not exceeding 2 times.Conclusion: DuCV infection can cause growth retardation,disordered coat and weight loss in ducks,and also lead to pathological damage such as lymphocyte reduction and nuclear fragmentation in duck immune organs.After DuCV infection in ducks,the replication level of the virus reached its peak at 14 dpi,with the virus load in immune organs significantly higher than other organs,making it the main target organ for virus replication.Ducks infected with DuCV can simultaneously activate apoptosis regulatory genes in three apoptosis pathways to induce cell apoptosis,among which the receptor pathway is the main pathway for duck circovirus to induce host lymphocyte apoptosis.