1. The overall goal of this project is to test the hypothesis that, “The critical virulence determinant of swine-virulent PCV2 resides in a linear 3-4 amino acid region in the center of the second immunogenic epitope of PCV2 nucleocapsid protein.”
2. There are two reasons (academic and practical) that the data generated by this NPB grant are important to producers and the swine industry:
Firstly, a successful outcome (i.e. archival PCV2 recovered from swine tissues 25-years prior to the first reported cases of postweaning multi-systemic wasting syndrome is avirulent for pigs) provides a credible explanation for the historical presence of avirulent PCV2 in swine and also provides a molecular explanation for the sudden emergence of the porcine circovirus diseases (PCVDs) in global swine populations.
Secondly, development of an avirulent yet immunogenic and genomically stable PCV2 (i. e. archival PCV2) will provide the industry with a potential candidate modified-live PCV2 for protection of swine against the PCVDs.
3. We have conclusively demonstrated that a PCV2 virus, reconstructed from archival PCV2 DNA sequences recovered from swine in 1970-71 is avirulent for swine, either alone or in gnotobiotic swine infected with this virus and subsequently immune stimulated. This virus is easily propagated in cell culture and is pig-infectious, stable and has a cell target tropism identical to pig-virulent PCV2s.
4. We have also conducted “proof of concept” experiments wherein we have shown that the archival virus does not potentiate PCVD in dually-infected piglets and also can function as a modified-live virus vaccine for prevention of PCVDs in virulent PCV2-challenged piglets.