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Bulletin No. 22 - Summer 2005
VirologyPorcine Reproductive and Respiratory Syndrome (PRRS)
KIM WI, KIM JJ, YOON KJ
Immunological significance of PRRSV genetic variation.
American Association of Swine Veterinarians - Proceedings, 2005, 379
Seventy PRRSV field isolates were sequenced for the major envelope protein (GP5) gene and compared to the North American PRRSV reference strain (VR-2332) in order to assess their genetic variability. The neutralizing activity of sera collected from pigs experimentally infected with VR-2332 was evaluated towards each of the field isolates which were classified into susceptible and resistant groups. Cross-protection against viruses from each group was then evaluated in pigs passively immunized with salt-precipitated immunoglobulins on the base of the level of viremia measured by PCR and the presence of viral antigens by immunohistochemistry. Most field isolates (59/70) were classified as resistant and shared 86.1-95.5% ORF5 sequence homology with VR-2332. All resistant viruses achieved infection. The remaining field isolates (10/70), classified as susceptible by in vitro neutralization, shared 95-99.5% homology with VR-2332. Seven of them were partially or completely blocked by cross-preotection while viremia was detected with the other three. The results of serum neutralization suggest that changes in the amino acid sequence of ORF5 give rise to no or suboptimal protection. Serum-virus neutralization test could be a more reliable tool to assess the level of cross-protection among PRRS viruses than sequence homolgy.
