| Porcine circovirus type2(PCV2) is the aetiological agent of postweaning multisystemic wasting syndrome (PMWS). Previously, phylogenetic analyses have shown that PCV2isolates can be further divided into three main genotypes as PCV2a, PCV2b and PCV2c. Prior to2004, PCV2a was the main dominant genotype. To date, a shift from PCV2a to PCV2b has been recognized and PCV2b was generally considerd as the dominant genotype prevailed in the swine herds. In this study, cross-protection was used to valuate on the mouse and the pig model. It facilitaes further studies on epidemiology as well as vaccination control of PCV2.Two inactivated vaccines based on PCV2a-LG and PCV2b-YJ strains and two subunit vaccines based on PCV2a-LG-rCap and PCV2b-YJ-rCap which were expressed by recombinant baculovirus system were prepared respectively. Eight-week-old female BALB/c mice (n=165) were randomly divided into eleven groups (15mice each) as follows:eight groups were immunized with four vaccines, and then half of animals were challenged with either PCV2a or PCV2b, other three groups as challenge or mock control. The antibody titers were from1:200to1:800at5weeks post-immunization (p.i.), and the highest titers were present in PCV2a-LG-rCap subunit vaccination groups. The two inactivated vaccines and one PCV2a-rCap subunit vaccine showed100%protection after challenge with either PCV2a or PCV2b. The results of neutralization test showed high level cross-reactivity between the two genotype strains of PCV2. Microscopic damages of the mice lung tissue after the two viruses challenge were developed to some extent, and however, no obvious pathological changes were present in mice from all of vaccination groups. This study suggested that even though there were a certain degree of antigenic differences between two genotypes of PCV2strains, the cross-immunization protection could be provided by both inactivated vaccines and one PCV2a-rCap protein subunit vaccines.In order to further evaluate the immune efficacies and cross-protection of inactivated vaccines between different PCV2genotypes, three virus inactivated vaccines were prepared, including PCV2a-rCL, PCV2b-rYJ and a recombinant vaccine PCV2ab-rJF with the PCV2a capsid gene cloned into the backbone of PCV2b. Fourty-five35-day-old pigs (n=45) were randomly assigned to nine groups (5pigs each). Pigs in2groups (n=10) were immunized with each vaccine and5pigs were subsequently challenged with PCV2a-rCL or PCV2b-rYJ, pigs in the two challenge control groups were inoculated with MEM, pigs in another group were raised as blank control. The antibody titers were from1:400to1:1600in PCV2ab-rJF and PCV2a-rCL immunized groups at5weeks p.i. detected by IPMA. However, the lowest titers were1:200, which was found in the PCV2b-rYJ immunization groups. No clinical signs were observed in PCV2immunized pigs, which have the advantages of improving the relative daily weight gain rate from18.22to20.18%with statistically significant difference, compared with the challenge control pigs. No viremia was detected post-challenge in the vaccinated pigs, in contrast, viremia was present21d～28d post challenge in some challenge control pigs. A significant difference was found in gross and histopathological lesion of lymphoid tissues between PCV2challenge groups and PCV2inactivated vaccine groups (p<0.05). In addition, the viral loads reached up to7.08×1010genomic copies per gram in inguinal lymph node of the challenge control groups. By contrast, the viral loads were all less than4.51×105genomic copies per gram in PCV2inactivated immunity groups. Taken together, this study demonstrated cross-protection between PCV2a and PCV2b. Especially, the recombinant inactivated vaccine PCV2ab-rJF provided the best protection against either PCV2a or PCV2b infection. |
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