Identification of genetically diverse sequences (ORF 5) of porcine reproductive and respiratory syndrome virus in a swine herd

The ability of genetically diverse strains of porcine reproductive and resp iratory syndrome virus (PRRSV) to coexist in a 1750-sow farm was assessed t hrough the case study describing a chronically infected farm, and also by a n animal experiment involving the use of swine bioassay. The case study emp loyed a program of monitoring sera from suckling, nursery, and finishing pi gs for the presence of PRRSV by polymerase chain reaction (PCR) and virus i solation (VI). The swine bioassay tested homogenates, consisting of lymphoi d and pulmonary tissues, collected from 60 breeding animals from the same f arm. The open reading frame (ORF) 5 portion of selected positive PRRSV dete cted from sera or tissues were nucleic acid sequenced and their phylogenies compared. The results indicated the presence of 3 genetically diverse grou ps, designated PRRSV-A, -B, and -C. Sequence heterology ranged from 5.8 to 11% between groups. Sequence homology ranged from 98.7 to 99.8% within grou ps. Swine bioassay verified the presence of PRRSV-A in 1 of 60 animals, and no evidence of strains B or C were detected. This paper indicates that bas ed on the evaluation of ORF 5, genetically diverse strains of PRRSV appear to coexist, although the frequency and significance of this observation is not understood.