Maternal antibody titers in white leghorn chicks against infectious bursal disease virus (IBDV) were measured by a computer-assisted, single-serum-dilution, indirect kinetic-based enzyme-linked immunosorbent assay (KELISA) and by a virus-neutralization (VN) test in order to predict the timing of initial vaccination. Day-old white leghorns were from unvaccinated pullets or from pullets vaccinated either four times or twice with IBDV commercial vaccines. The chicks were immunized once via the drinking water with a commercial "intermediate" live IBDV vaccine at 1, 15, or 28 days of age. Effective initial immunization was confirmed by an increase in antibody to IBDV (serologic conversion) that occurred when maternal antibody decreased to 8 and 9 on a log2 scale. This concentration of antibody was detected between 24 and 28 days of age. The computer-assisted IBDV-KELISA increased the sample processing speed for detecting IBDV antibody, and it was as sensitive as the VN test for predicting the timing of initial IBDV vaccination.
Clostridium septicum and its associated cytolytic α toxin, along with several other clostridial species, has been implicated as the causative agent of gangrenous dermatitis. A recombinant noncytolytic C. septicum α toxin (NCAT) peptide was developed for use as a vaccine and demonstrated to be safe at concentrations as high as 1 mg/ml. NCAT, used as a purified antigen, partially purified antigen, or in combination with native antigens, was compared to salt-fractionated α toxin combined with denatured C septicum bacteria (native) in a vaccination trial. Three-day-old poults were placed into one of five groups and received two, 0.2-ml vaccinations 5 wk apart. Subcutaneous challenge with 3.2 x 10(7) log phase C. septicum resulted in 78% to 95% of the vaccinated birds surviving challenge compared to 48% of sham-injected controls. By ELISA analysis on NCAT-coated plates, birds receiving vaccines containing the recombinant NCAT peptide showed significantly higher blood serum antibody concentrations than did birds receiving vaccines containing native antigens or alum controls. Additionally, high levels of maternally transferred antibodies reactive to NCAT-purified antigens found in the pre-immune sera from naive 3-day-old poults suggest that the tertiary structure of the NCAT peptide has a high homology to the native protein structure. In conclusion, our study showed that the use of a vaccine comprised of a noncytolytic recombinant α toxin peptide antigen provided clinical protection equal to the use of vaccines formulated with inactivated native proteins at a reduced overall cost.
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