Anti-VP1 and anti-NP IgG levels in sera before and after viral challenge. Determination of total anti-VP1 IgG antibodies (A) and total anti-NP IgG antibodies (B). (C) Purified VP1 or NP proteins were separated on 12% SDS-PAGE gel and electro-transferred onto membranes. Strips of the membranes were incubated with different types of sera. Arrow indicates the expected position for VP1 band. Arrowhead indicates the expected position for NPfl band.