Isolation And Identification Of Infectious Bursal Virus Isolated From Shandong Province And Immune Efficacity Of Its Embryo-adapted Virus

Infectious bursal disease (IBD) is an acute and highly contagious chicken and turkey infectious disease, which was caused by infectious bursal disease virus (IBDV). The disease mainly damages young chickens of 3-6 weeks. It often causes great death and makes production decrease, as well as leading to serious immunosuppression. Variant IBDV and very virulent IBDV (wIBDV) can break through the protection of maternally derived antibody (MDA) even if the titer of MDA is high in young chicken, w IBDV has a trend to infect young chicken less than 3 weeks old, which result in worse economic lose.Based on the prevalence condition of IBDV, it's important to develop an attenuated vaccine that can break through high-titer MDA.Four experiments ware carried out to obtain the attenuated vaccine.Experiment 1, a strain of IBDV was isolated from IBDV-suspected chickens in Shandong province and the pathogenicity on specific pathogen free (SPF) chicken was studied. The result of pathogenicity test showed that the isolated strain could cause 40% of 4-week-old SPF chickens to death when the chickens were inoculated with 0.05mL suspension of bursa of Fabricius diluted with four times of normal saline. It should be a strain of acute IBDV and then was named as IBDV SD0306 temporarily according the time when it was isolated.Experiment 2, in order to confirm the isolated virus was a strain IBDV,the sequence of VP2 hypervariable gene was analyzed. When RNA of IBDV was extracted and and its cDNA was obtained by reverse transcription polymerase chain reaction (RT-PCR) amplification. The cDNA was cloned to pMD18-T for sequence. Sequence comparison of field strain and other ones showed it is highly homologous with wIBDV HK46.Experiment 3, the pathogenicity of embryo-adapted viruses to 28-day-old SPF chickens was test and VP2 hypervariable region gene sequences of them were obtained. IBDV SD0306 was propagated on SPF embryos for 15 generations. The 11th embryo virus (Ell) and 15th embryo virus (E15) were selected to test their pathogenicity to SPF chicken respectively. The animal test showed that they didn't cause obvious clinic symptom except for lymphoid depletion of bursa of Fabricius of E11.The sequences of VP2 between 11th generation and 15 one were conservative. The homology is 100%.Experiment 4, the immune effect of E15 on commercial chicklings was compared with vaccine strain of B87. The inoculation was carried out in 7days and 14 days with different doses .The results showed that E15 didn't cause commercial chickens' disease. It only caused lymphoid depletion of bursa of Fabricius by the inoculation doses of 60 EID50 and 300 EID50. The capacity of breaking through high-titer MDA is high than B87. E15 could offer high protection against the challenge of w IBDV GX 8/99 with temporaryimmunosuppression to immune responsion of NDV.