| Porcine reproductive and respiratory syndrome (PRRS) is characterized by late-term reproductive failure in pregnant sows and respiratory distress in young pigs. The disease was first recognized in the United States in 1987 and has since had devastating effects on the swine industry. PRRS has now been recognized in many countries and considered globally as one of the most economically important diseases of swine. The etiologic agent for PRRS, porcine reproductive and respiratory syndrome virus (PRRSV) is a member of the Arteriviridae. PRRSV is an enveloped, positive-sense single stranded RNA virus with a genome of approximately 15 kb. The genome contains 8 distinct open reading frames (ORFs 1a, 1b, and 2--7). ORFs 1a and 1b encode the viral replicase while ORFs 2-7 encode the viral structural proteins.; Swine herds in the United States have experience outbreaks of a severe form of PRRS starting in 1996. This form of PRRS, referred to as acute or atypical PRRS, has occurred in herds that were vaccinated with commercial modified live viruses (MLVs). The emergence of acute disease-causing strains in vaccinated herds suggests that alternative immunization strategies are needed.; In these studies we have examined the ability of a subunit vaccine to provide immunity to PRRSV. The structural ORFs 2 through 5 from an atypical North Carolina strain of PRRSV were expressed in a baculovirus expression vector, the proteins were purified and tested individually using an aluminum based adjuvant. We found that pigs vaccinated with some of the recombinant structural proteins had significantly reduced temperatures, reduced levels of infectious virus in serum, and displayed no abnormal clinical signs when compared to unvaccinated controls. Recombinant GP4 and GPS proteins were especially effective at stimulating protective immunity to PRRSV. We also examined the effects of vaccination on humoral and cell-mediated immune responses to the PRRSV isolate. We saw no apparent differences in antibody responses to PRRSV in control and vaccinated pigs. However, pigs vaccinated with recombinant GP4 and GP5 displayed significant delayed-type hypersensitivity responses. Results from our experiments suggest that vaccination with purified recombinant structural proteins may be an effective strategy for preventing PRRS. |
