| Summary: | 碩士 === 國立中興大學 === 獸醫微生物學研究所 === 91 === Infectious bursal disease is a highly contagious disease caused by infectious bursal disease virus (IBDV). The infection of IBDV often causes the atrophy in the bursa, and leads to an immune suppression of affected chickens. IBDV might also cause a high mortality of infected chickens and therefore lead to an economic loss of the poultry producer. The goal of this study is to compare the nucleotide difference between field viruses and vaccine strains of IBV, and to examine the possible virulence of IBDV live vaccine, and to express the recombinant VP2 protein that could be used in the serology of IBDV. Sequence analysis of VP2 gene of 22 live vaccine strains of IBDV showed that there were 11 attenuated strains, 7 classical strains, 1 Australian strain, 1 vv-IBDV-like strain, and 2 unclassified strains. Filed isolates of IBDV have sequences very similar to those of vv-IBDV isolated in China. These results showed that live vaccine strains of IBDV used in Taiwan could be classified into several categories, including the attenuated, classical, Australian and vv-IBDV-like strains, but no antigen variant strain has been found. To examine the possible virulence of these vaccine viruses, 3 vaccine strains (bursine 2, D78 strain and MB71) were used to infect 2-week-old SPF chickens, and results showed that the MB71 strain could produce the highest antibody titer against IBDV, but also caused the atrophy in bursa and the lowest bursa/body weight ratio of infected chickens. It is therefore possible that incorrect use of MB71 might lead to an outbreak of IBDV. Finally, we produced recombinant VP2 proteins of IBDV in E. coli host, and used Western blot assay to test the antigenicity of these recombinant proteins. We hope that these recombinant VP2 proteins could be used to differentiate sera of vaccinated chickens from those of filed infected chickens.
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