Pathogenicity of three genetically diverse strains of PRRSV Type 1 in specific pathogen free pigs

Abstract

Studies from Eastern European countries proved that porcine reproductive and respiratory syndrome virus Type 1 (PRRSV-1) harbours high genetic diversity and that genetically divergent subtypes 2-4 circulate in this area. In the present study, we compared the pathogenicity of two different PRRSV-1 subtype 2 strains and a strain representing PRRSV-1 subtype 1. Four groups of 8-week-old specific pathogen free pigs were either infected with subtype 2 strain ILI6, subtype 2 strain or BOR59, subtype 1 strain 18794, or mock inoculated. The most pronounced clinical signs were observed in pigs infected with BOR59. Pigs from both subtype 2 strain infected groups exhibited significantly elevated mean body temperatures on DPI 2 compared to the other two groups, the difference remaining significant up to DPI 13 for the BOR59 group, only. The pigs in the latter group also displayed significantly highest levels of early viremia together with the most rapid APP response. Overall, the results indicated that BOR59 strain can be considered a highly pathogenic strain, similarly to subtype 3 strains Lena and SU1-bel, while the virulence of the other subtype 2 strain ILI6 was intermediate between BOR59 and subtype 1 strain.

Efficacy and safety of simultaneous vaccination with two modified live virus vaccines against porcine reproductive and respiratory syndrome virus types 1 and 2 in pigs

“…an animal that become positive after being tested negative. The duration of nasal excretion of PRRSV was in line with the previous studies quoted above (7)(8)(9)(10)(11)(12)(13)(14). There is probably a limited risk that these weakly positive animals would transmit the virus horizontally to naïve animals [21], but the persistence of vaccine virus for two-three months after vaccination emphasize the importance of keeping vaccinated animals isolated from naïve animals for a sustained time period prior to mingling.…”

“…Only few studies have been performed with these diverse East-European strains, but a series of studies have revealed that at least some subtype 3 strains are more virulent than typical subtype 1 strains [35][36][37][38]. Recently, we have shown that some subtype 2 strains seem to be more virulent than subtype 1 strains [10] and in both the previous and the present study ILI6 induced more severe clinical signs and more pronounced viremia than the PRRSV-1, subtype 1 strains. Nevertheless, the clinical signs were much less severe than seen following challenge with the two subtype 3 strains SU-1 and Lena [35,36].…”

“…Nine weeks after vaccination (DPV 62), all pigs were moved to new separated groups according to the PRRSV strain they were planned to be challenged with ( Table 1). The challenge was done with either PRRSV-1, subtype 1 (strain 18794 [10]), PRRSV-2 (strain 19407b) or PRRSV-1 subtype 2 (strain ILI6 [10]) according to Table 1. The PRRS-19407B had been isolated in January 1997 from the lungs of a stillborn pig.…”

“…Total RNA was extracted from serum, nasal swabs and lung samples as previously described [10]. Known PRRSV positive samples and negative controls were included for at least each batch of 10 samples.…”

“…A recent designed assay was used for the real-time RT-qPCR analyses [10]. The assay was designed specifically to detect PRRSV-1 subtype 1 and subtype 2 strains used in this study.…”