Vaccines to prevent Post weaning multi systemic wasting syndrome (PMWS) were developed. The efficacy of the protection conferred by the two major PCV2-proteins, Rep and Cap, alone or in combination can be evaluated on the basis of growth retardation and fever parameters presented by piglets in the challenge-control group (CC) in trial No. 1. We used a prime-boost protocol, including a first DNA vaccine followed by a DNA-booster and a subunit vaccine, two weeks later. In this trial, vaccination significantly reduced the duration of the pyrexic phase, more efficiently in the Orf2 and Orf1&Orf2-vaccine groups than in the Orf1-vaccine group. Moreover, during the third week post-infection, only the Orf2 and Orf1&Orf2 groups showed significantly reduced growth retardation compared to the CC group, which was more pronounced in the Orf2 group. No difference was observed between the Orf2 group and the C group (non-challenged control group), while the Orf1&Orf2 group showed a significant difference with the C group (p<0.01) during the third week. These results were confirmed by a higher /GW3 index in the Orf2 group than in the Orf1&Orf2 group (1.09 vs 0.6) during the third week post-challenge. No clinical symptoms were observed in these two groups, while pigs in the Orf1 group presented typical PMWS symptoms (ataxia, rough hair-coat, wasting). We therefore showed that the Orf2-encoded capsid protein, used in a preparation-based DNA and subunit vaccine, constitutes the major immunogen to induce protection of piglets against a PCV2 challenge. In contrast, the Orf1-encoded replication protein appears to be only weakly immunogenic.
In our trial No. 2, we focused on the vaccine composition to compare the efficacy of the protection conferred by either a DNA vaccine or a subunit vaccine. Independently of the previous results, we decided to use the two associated major PCV2-proteins (Rep and Cap), in two injections. As in the first trial, on the basis of growth retardation and fever parameters presented by piglets in the challenge-control group, we observed that the subunit vaccine significantly reduced the duration of the pyrexic phase (p<0.05) during the third week post-infection, while the DNA vaccine did not have any effect on the duration of the pyrexic phase. All piglets of the DNA group presented hyperthermia higher than 40.5 XC for one to five days versus three piglets of the subunit group for one to three days. In contrast, the two vaccinated groups (DNA and SU) showed a better growth, compared to the CC group. These results were confirmed by a high /GW3 index, 1.20 and 1.54, respectively. The /GW3 index obtained in trial No. 2 was higher than that obtained in trial No. 1. However, we cannot consider so significant the difference in /GW3 obtained in the various groups of animals (Orf2, Orf1&Orf2, DNA, Subunit groups). In the case of conventional commercial vaccines against Aujeszkys disease virus (ADV), the official requirement is a minimum /G7 index of 1.5. Although these two diseases are not comparable, the /GW3 index obtained in the present study indicates a useful protection performance for the production of vaccines against a PCV2 challenge.
We obtained earlier seroconversion with the subunit vaccine two weeks after the first injection, at the time of the second injection, while seroconversion was only observed after challenge with the DNA vaccine. Different antibody titers were elicited in the groups and were higher for DNA and CC groups after challenge, while the antibody titer of the subunit group remained lower, suggesting the absence of PCV2 replication and boosting effect after challenge.