Detection of porcine reproductive and respiratory syndrome virus in oral fluid from naturally infected pigs in a breeding herd

The objectives of the present study were to evaluate the anatomic localization of porcine reproductive and respiratory syndrome virus (PRRSV) in naturally infected pigs and to determine whether oral fluid could be used to detect the virus in infected animals. Two sows, seven 2-month-old grower pigs, and 70 6-month-old gilts were included in this study. PRRSV in sera and oral fluid were identified by nested reverse transcription PCR (nRT-PCR) while lung, tonsil, and tissue associated with oral cavity were subjected to nRT-PCR, immunohistochemistry, and in situ hybridization. In sows, PRRSV was identified in oral fluid and tonsils. PRRSV was also detected in oral fluid, tonsils, salivary glands, oral mucosa, and lungs of all seven grower pigs. However, viremia was observed in only two grower pigs. Double staining revealed that PRRSV was distributed in macrophages within and adjacent to the tonsillar crypt epithelium. In gilts, the North American type PRRSV field strain was detected 3 to 8 weeks after introducing these animals onto the farm. These results confirm previous findings that PRRSV primarily replicates in tonsils and is then shed into oral fluid. Therefore, oral fluid sampling may be effective for the surveillance of PRRSV in breeding herds.

Genetic diversity of porcine reproductive and respiratory syndrome virus in Korea

The high genetic diversity of porcine reproductive and respiratory syndrome virus (PRRSV) has been an obstacle to developing an effective vaccine for porcine reproductive and respiratory syndrome (PRRS). This study was performed to assess the degree of genetic diversity among PRRSVs from Korean pig farms where wasting and respiratory syndrome was observed from 2005 to 2009. Samples from 786 farms were tested for the presence of PRRSV using reverse transcription PCR protocol. A total of 117 farms were positive for type 1 PRRSV while 198 farms were positive for type 2. Nucleotide sequences encoding the open reading frame (ORF) 5 were analyzed and compared to those of various published PRRSV isolates obtained worldwide. Sequence identity of the ORF 5 in the isolates was 81.6~100% for type 1 viruses and 81.4~100% for type 2 viruses. Phylogenetic analysis of the ORF 5 sequences showed that types 1 and 2 PRRSVs from Korea were mainly classified into three and four clusters, respectively. The analyzed isolates were distributed throughout the clusters independent of the isolation year or geographical origin. In conclusion, our results indicated that the genetic diversity of PRRSVs from Korean pig farms is high and has been increasing over time.