在对国内某地区7个患病猪群流行病学调查的基础上，用Marc2.45细胞培养从4个猪群流产胎儿分离到3株导致细胞病变的病毒--J1、J2和J3株。它们对氯仿和热（56℃，1h）、甲醛、酸、碱均敏感。病毒粒子呈球状，直径30～80nm，负染后病毒粒子大小80～100nm，在Marc2145细胞质内增殖，52溴22'2脱氧尿核苷（BUDR）对其无抑制作用。结合血清学试验，鉴定3个毒株均为猪繁殖和呼吸综合征病毒（PRRSV），可能为美洲型PRRSV。

应用RT-PCR技术，从我国东北和华北地区分离的2个猪繁殖和呼吸综合征病毒（PRRSV）毒株中扩增获得部分核衣壳蛋白基因。该基因片段长度与美洲型野毒株VR2332 RT-PCR扩增片段相同，均为433bp，长于欧洲型Lelystad毒株扩增片段长度（395bp）。此外，用另1对引物，从这2个分离毒株及VR2332毒株扩增获得部分GP5蛋白基因，其限制性酶切片段长度多态性分析结果相同或相似。该结果表明，我国不同地区流行的PRRSV可能属于同一毒株，并且来源于美洲。

To elucidate the characteristics of molecular epidemiology of PRRSV in China, the nucleotide sequence of open reading frame 5 (ORF5) coding regions from two wild PRRSV strains, J 1 and S1, isolated in northern and mid-eastern regions of China was determined by RT-PCR. Comparison showed that only 4 different bases between J 1 and S1 strains resulted in 3 amino acid (aa.) changes in their deduced proteins. There were 3 and 2 different aa. between the deduced aa. sequences of J 1, S1 strains and the American prototype ATCC virus VR2332 respectively, while there existed 16 and 15 aa. changes between the 2 isolates and the modified live vaccine strains derived from VR2332. The putative protein molecular weight, isoelect ric point, signal region, glycosylation site and possible transmembrane helices of ORF5 of each strains were similar to that of VR2332 strain. These result s showed that the two isolates belong to the same genotype and they may come from USA.

上海地区6个规模化猪场断奶后仔猪出现全身消耗性综合征，剖检的18头病仔猪都表现肺脏严重病变和淋巴结肿大出血。分别设计针对猪繁殖与呼吸综合征病毒（porcine reproductive and respiratory syndrome virus，PRRSV）N蛋白和2型猪圆环病毒（porcine circovirustype2，PCV-2）部分基因的特异性PCR引物，通过RT2PCR和PCR技术从患病猪肺脏组织均扩增出PRRSV和PCV-2的特异基因片段。结合临床症状和流行病学调查，证实上海地区出现PRRSV和PCV-2的混合感染。

The VP3 structural protein gene fragment of chinese IBDV was amplified by RT-PCR, and inserted into the expression vector p GEX-2TK. Restriction enzyme analysis and partial sequence analysis showed that the sequence of foreign gene cloned was the same as that of VP3 gene reported before. On the other hand, the gene was located in the BamHI/EcoRI site of this vector in the corrected open reading frame. The recombinant plasmid, p GETVP33, could stably express VP3 as glutathione s-tranferase (GST) fusion protein with high efficiency (up to 34% of the total bacterial soluble protein) in E. coli BL21 through IPTG induction. Chicken incoulatad with the total bacterial protein in oil adjuvant at 14 days of age could produce IBDV-specific antibody as measured by EL ISA and were partially protected against challenge with virulent IBDV.