The Molecular Epidemiology Research On Infectious Bursal Disease In Parts Of China

To study the molecular epidemiology of infectious bursal disease (IBDV), 68 edematous and hemorrhagic bursal tissues were collected from parts of China, and 21 IBDV strains were isolated from these bursal tissues. The full-length of VP2 gene (about 1300 bp) were amplified by RT-PCR and sequenced. The deduced amino acid (aa) analysis of VP2 indicated that all the isolates except SH-h strain were characterized by the very virulent IBDV (vvIBDV) conserved aa residues: 222A, 256I, 294I and 299S. Compared to UK661 and Gx, the nt homologous rate was 97.5% to 99.4%, and the aa, 98.9% to 100%. Of all the isolates, the nt homologous rate was 96.7% to 99.9%, and the aa, 98.2% to 100%. Selecting UK661 as the concensus strain, HLJ-1, HLJ-2, HLJ-3 and HLJ-4 had one amino acid substitution (D→N) at position 212 in VP2 major hydrophilic peak A, and HLJ-3 and HLJ-4 had another one (A→V) at position 321 in major hydrophilic peak B. Using serotype II of IBDVs as the out-group, a phylogenetic tree based on the nt sequence of the hypervariable region of VP2 gene was constructed. Our findings demonstrates that all the serotype I viruses could be evoluted from a common ancestor. All isolates were located in vvIBDV group. The other isolates were scattered in the vvIBDV group. The genetic distance indicated that the classical IBDVs were firstly divided from the ancestor, then the variant straians and finally the vvIBDVs.To analyze the antigenic difference between HLJ-2, HLJ-4 and Gx, indirect ELISA was used based on 7 strains of monoclonal antibody. The data were analyzed by one-way analysis of Variance (ANOVA) using the statistical software SPSS 13.0, and the Duncan's was used in the multiple comparisons. The result showed that the difference between HLJ-2, HLJ-4 and Gx were very significant. On this result, Infectious Bursal Disease Vaccine(Gt Strain) was tested against HLJ-4 and Gx. The results suggested that the vaccine could protect chickens from the attack of HLJ-4 and Gx though HLJ-4 and Gx had the different antigenicity.349 serum were collected to idenify the antibodies against Chicken Anemia Virus (CAV), Subgroup J Avian Leukosis (ALV-J) and Reticuloendotheliosis virus (REV) from seven layer or broiler farms by ELISA kit. The results showed that CAV positive rate was more than 60.0%, while ALV-J and REV positive rates were lower. To study the impact of CAV on Infectious Bursal Disease Vaccine (Gt strain), 80 1-day-old chicks were divided into five groups---A (negative control group), B ( infection group), C (Gt-immunized group), D ( -infected and Gt-immunized group) and E (Blank group), 16 feathers per group , chickens in group B and D were intramuscularly infected CAV strain M9905, and at 7 dpi, the chickens were orally immunized with infectious Bursal Disease Vaccine (Gt strain). The serum were collected at 14, 20 and 28 dpi and the IBDV antibody titers were detected by ELISA kit. At 28 dpi, four groups were challenged with IBDV strain Gx, 0.1ml per chicken. The results showed that the infection by CAV reduced the protctive capacity of Infectious Bursal Disease Vaccine (Gt strain) and the antibody titer went up slowly.