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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.

Vaccination is the most effective prophylaxis against swine erysipelas. Vaccines are usually tested for efficacy by a challenge of vaccinated and untreated pigs. Up to now the efforts to replace the infection test by a serological method have been limited to the potency test in laboratory animals. Here we provide evidence that the measurement of antibodies by an enzyme-linked immunosorbent assay (ELISA) after vaccination and challenge is also possible in the target species. Pig sera were tested for titre development after a single and repeated vaccination in clinical trials. The efficacy of the vaccines was confirmed by a challenge, which demonstrated that all immunized pigs survived with no signs of disease whereas all control animals became severely ill. The ELISA was also used to measure erysipelas antibodies after immunization of pigs with several vaccines in a field trial. The ELISA may be a suitable alternative to replace the challenge methods currently used for testing of erysipelas vaccines.

Vaccines composed of gram-negative bacteria contain endotoxin in considerable amounts. This may result in adverse effects after vaccination of sensitive animals. For reasons of safety and animal welfare the endotoxin level of veterinary vaccines should be limited. The limulus amebocyte lysate test is suitable to check the endotoxin content in most vaccines. Safety tests in animals should only be performed if the results of the limulus test are satisfactory.