中文摘要：

从具有新的流行病学特征的传染性法氏囊病（IBD）发病鸡群中分离到2株传染性法氏囊病病毒（IBDV），分别命名为QL和ZZ—ll，对4周龄SPF鸡的致死率分别为94％和86％。为分析该毒株的分子生物学特征，对其全基因组序列进行了测定，2个病毒株基因组A节段长度为3260bp、B节段长度2827bp。病毒演化分析结果显示2个病毒基因组A节段的核苷酸序列与已发表的强毒株序列的同源性分别为96．8％～98．1％和96．9％～98．4％，处在IB—DV超强毒株分支上；而B节段与已发表的弱毒株序列的同源性分别为89．7％～90．4％和90．0％～90．7％，位于弱毒株分支上。IBDV超强毒株和弱毒株序列特征氨基酸残基与基序分析表明，QL和ZZ—11两个病毒株的A节段VP2基因的氨基酸残基为222A、249Q、253Q、254G、256I、294I和299S，七肽基序为SWSASGS，均符合超强毒株的分子特征；而B节段777～782位核苷酸序列为GGTGCC，没有KpnI酶切位点，具有弱毒株的序列特点。以上分析结果表明，QL和ZZ—11为IBDV自然重配株，A节段源于超强毒株，而B节段源于弱毒株。

英文摘要：

Two isolates of infectious bursal disease virus （IBDV） with new epidemiological charac teristics in China were acquired and named as QL and ZZ-11. The mortality rate of specific patho-gen free （SPF） chickens inoculated with the isolate QL was 94% ,and ZZ-11 was 86%. By sequen cing,the genomes of QL and ZZ-11 were the same in size,and segment A and B were 3 260 bp and 2 827 bp,respectively. The phylogenetic analysis showed that segment-A of the two isolates were 96.8%o to 98.1% and 96.9% to 98.4 % homology to that of the published strains belonging to the very virulent strain branch;while segment-B was in the branch of the attenuated strains,the ho- mologies were from 89.7% to 90.4% and from 90.0% to 90.7%. Segment A of the two isolates had molecular characteristics of very virulent strains with 222A, 249Q, 253Q, 254G, 256I, 294I, 299S and heptapeptide motif SWSASGS in VP2 gene; While segment B owned the sequencecharacteristics of attenuated strains which did not have Kpn I restriction sites at their 777-782 nu cleotides （GGTGCC）. It indicated that QL and ZZ-11 might be the natural reassortment viruses with segment A derived from the very virulent strains and segment B from the attenuated strains, separately. The discovery of reassortment viruses in nature suggests an additional risk of using live IBDV vaccines,which could act as genetic donors for genome reassortment.