| Porcine reproductive and respiratory syndrome virus(PRRSV) is classified in the family Arteriviridae in the newly created order Nidovirales. Typical clinical signs of PRRSV infection in susceptible animals include inappetence, fever and respiratory disease in pigs of any age and abortion or increased proportions of stillborn and weak-born pigs in pregnant animals. Although porcine reproductive and respiratory syndrome(PRRS) was first reported in swine herds in the United States in 1987, it spread rapidly and became endemic in most of the major swine-producing areas throughout the world during the 1980s. Today, it is one of the most economically important diseases of the global pork-producing community. Although it was firstly reported in 1995, it spread rapidly all over the country and become epidemic in recently years.Porcine reproductive and respiratory syndrome virus(PRRSV), the causative agent of PRRS, is a small-enveloped virus containing a single positive-stranded RNA genome. And the virus is genetically, antigenically, and pathogenically heterogenic. Substantial sequence divergence exists between the European and North American genotypes of the virus, showing only about 70％nucleotide sequence identity. Among the North American isolates, PRRSV genomic sequences also vary significantly.In the present study, we have done some work such as isolation of PRRSV, cloning of its structural protein genes and analysis of its sequence. The results are useful in revealing the genetic relationships between the different strains. The main projects are:1. Isolation and identification of PRRSVOne doubted PRRSV srain were isolated and identified from visceral organs of piglets from the farms in Huangshi. The cytopathogenic effect(CPE) observed on MARC-145 consists of the appearance of small rounded clumps of cellsraised above the remainder of the infected monolayer. And then infected cells become progressively pycnotic and death from the monolayer gradually. After the isolate was inoculated on MARC-145 for several generations, the result of it's TCID50 test was 10-361/0.1 mL. The diameter of virus particle was about 50～65nm. The isolated virus was spherical and has envelope. Virus neutralization test showed that the isolate was neutralized by the serum to American genotype of PRRSV, not by the sera agaist HCV,PPV,PRV,JEV respectively. According to the above results, the isolated virus was identificated as PRRSV and named PRRSV HS strain. 2. Cloning and sequence analysis of construction protein genes of PRRSV strain HSORF2a-ORF7 genes of PRRSV HS strain were obtained by RT-PCR and sequenced after being cloned directly into the pMD 18-T. The sequences of ORF2a-ORF7 genes of the isolate were compared with the sequences of other PRRSV strains in GenBank by DNAMAN software. The results showed that the ORF2a-ORF7 of the PRRSV HS strain shared 83.6％-99.7％of nucleotide homology and 86.6％-99.6％of amino acid identity with that of North American genotype(VR-2332,Resp MLV,16244B,HN1,BJ-4,CH1-a,HB-1,HB-2), respectively. And they shared only 38.9％-49％of nucleotide homology and 54.2％-78.2％of amino acid homology with that of LV, respectively. The phylogenetic trees revealed that the PRRSV HS strain was clustered within North American genotype and had close relationship with HN1,VR-2332,RespMLV,16244B,BJ-4. And there are a limited number of unique mutations in the structural proteins of ORFs 2a to5 in the PRRSV HS stain which are different that of other PRRSV strains.
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