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Bulletin No. 20 - Winter 2004
VirologyPorcine Reproductive and Respiratory Syndrome (PRRS)
BARFOED AM, BLIXENKRONE-MØLLER M, JENSEN MH, BØTNER A, KAMSTRUP S
DNA vaccination of pigs with open reading frame 1-7 of PRRS virus.
Vaccine, 2004, Volume 22, Nº27-28, 3628-3641
All seven open reading frames (ORF1-7) of a Danish PRRSV isolate were cloned in DNA vaccination vectors. Piglets originating from four litters of a SPF herd were controlled for their PRRSV-negative status by ELISA and randomly distributed into 10 groups of three pigs regardless of sex and size. Pigs were vaccinated six times with 3-week interval using a gene gun system. Seven groups received one recombinant plasmid expressing a single ORF (ORF1-7). One group received all seven recombinant plasmids and one group received the recombinant plasmids expressing the major glycoproteins (ORF3-5). Another group received a plasmid without any ORF and served as control. Blood samples were collected weekly and tested for the presence of specific antibodies. Three weeks after the last vaccination, pigs were challenged intranasally with the same isolate. At that time, they were 27-week-old. The contribution of the individual viral proteins to development of protective immunity was investigated in terms of viremia and virus excretion. The results demonstrated that following three vaccinations, pigs vaccinated with ORF7 alone had a consistent and high antibody response which was not the case in any of the other groups. This supports the idea that the N-protein is particularly immunogenic. Following challenge, high titers of virus neutralizing antibodies were observed in the majority of pigs in all groups. However, the levels of viremia after challenge were similar in all groups indicating that no positive effect on protective immunity was achieved with DNA ORF vaccination.
