传染性法氏囊病超强毒Gx株的致弱研究

本研究成功将鸡传染性法氏囊病超强毒vvIBDVGx株通过SPF鸡胚的快速培育及鸡胚成纤维细胞传代致弱，揭示了vvIBDV从超强毒力向弱毒力转化过程中，其主要结构蛋白VP2基因核苷酸及推导的氨基酸序列的变化规律。对不同代次细胞毒进行了序列分析。发现细胞毒在第7代以前，VP2基因序列没有改变。与欧洲标准超强毒氨基酸同源性达100%；细胞毒第8代，有个别核苷酸发生了改变。但没有影响氨基酸序列；细胞毒第9代是变化复杂的过渡代；10代毒VP2基因与欧洲标准弱毒Cu-1氨基酸序列同源性达97%；以后的细胞适应毒至20代。其VP2基因序列不再改变。致病性实验表明原代毒对4周龄SPF鸡致死率为64%。细胞毒第5代的致死率为60%，而20代毒对鸡无致病性。在鸡体内连续传代6代不返强。

The Attenuation of vvIBDV Gx Strain

Very virulent infectious bursal disease virus (vvIBDV) Gx strain with high pathogenicity was attenuated through replicating in SPF embryo and CEF. The change pattern of VP2 nucleotide and the deduced amino acid sequences were obtained from this strain of vvIBDV,during the process of attenuation. The results of sequencing , analyzing of every generation viruses showed that there was no changes on VP2 gene before 7th generation, there was a few changes in VP2 gene but not on amino acid at 8th generation , the homology of amino acid sequence with European reference vvIBDV strain was up to 100%;The virus of 9th generation was an intermediate with complex changes. 10th generation had become cell_adapted strain, the homology of amino acid sequence with European reference IBDV attenuated strain Cu_1 was up to 97%. VP2 gene did not changed any more from 10th to 20th generation. The results of pathogenicity tests showed that the original (Gx) was typical vvIBDV with the mortality up to 64%, the virus of 5th generation was still vvIBDV with the mortality up to 60% in 4_week_old SPF chickens, while the virus of 20th generation was no pathogenicity and could not atavistic after propagated 6 generation in SPF chickens.