RFLP ANALYSIS OF ORF5 GENES OF PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS CH-1A STRAIN DUE TO THE PROCESS OF VIRULENCE ATTENUATION Xuehui Cai,

摘要

Porcine reproductive and respiratory syndrome virus (PRRSV) is an enveloped, single-stranded, positive-sense RNA virus (1,2). The genomic RNA of PRRSV is approximately 15 kb in length with 9 open reading frames (ORFs) (3). According to its genetic and antigenic variations, PRRSV can be divided into the European and North American genotypes that exhibit 55-80% nucleotide identity(4). There are numerous PRRSV isolates that exhibit a high degree of variations.