Potency Testing of Swine Erysipelas Vaccines by Serology Results of a Pre-validation Study

The European Pharmacopoeia (Ph. Eur.) monograph on Swine Erysipelas Vaccine (inactivated) (Ph. Eur., 1997) requires the potency of each batch to be demonstrated in a mouse protection test. In this parallel-line bioassay, mice are challenged with a virulent strain of Erysipelothrix (E.) rhusiopathiae after immunisation with different doses of either the standard preparation or of the test vaccine. More than one hundred animals are necessary for the routine testing of a single batch. In previous studies (Beckmann und Cubetaler, 1994; Rosskopf-Streicher et al., 1998), we have shown that an indirect enzyme-linked immunosorbent assay (ELISA) may be used to quantify the humoral response of mice. This method can replace the challenge model for the purposes of potency testing in the following manner: Ten mice are immunised subcutaneously with 1/10 of the vaccine dose required for pig vaccination. After three weeks, the mice are bled under anaesthesia. Serum samples are pooled and the antibody content is compared to that of a reference serum. In view of animal welfare the advantages of the alternative model are obvious: A highly reduced number of animals and the replacement of challenge exposure. This includes the discontinuation of the control group with a mortality rate of 100%. A pre-validation study was initiated to evaluate the performance of the serological method. Eight laboratories used the test kits to evaluate pooled serum samples from vaccinated mice. Both the reagents and the test protocol were shown to be satisfactory. The intra- and inter-laboratory reproducibility that was achieved indicates that the method is a strong candidate for validation.