Improvement of Commercial Swine Erysipelas ELISA Test Applicability for Vaccination Compliance Purpose11 September 2015
The utility of serologic tests for evaluation of Erysipelas infection and protection conferred by vaccines has been a controversial issue, writes A. Callen, I. Lazaro and S. Carceles, Merial.
Furthermore, the variability and validity of current commercial ELISA tests makes difficult its interpretation and limits its applicability in the field.
However, they might be of interest to detect the eventual serological response to vaccination in order to determine the vaccination compliance.
Indeed, vets usually check sera from vaccinated animals in order to test vaccination compliance or immunological response.
Therefore, the aim of this trial was to assess the serological response to PARVORUVAX, a PPV and Erysipelas combo vaccine, with an Erysipelothrix rhusiopathiae (E.r.) ELISA test and to evaluate its reliability according to the interpretation criteria.
Material and methods
Twenty nine gilts and sows of a farrow-to-finish farm were selected and classified according to its age and vaccination status in three groups: 10 randomly selected unvaccinated gilts (NV group) from the gilt pool, 10 pregnant gilts that had been vaccinated twice with PARVORUVAX before mating (BV), and 9 pregnant multiparous (4th to 6th parity) sows that have received several vaccinations with the same vaccine (MV).
Blood samples were taken and tested for E.r. antibodies by an indirect ELISA (Ingezim Mal Rojo, Ingenasa).
The optical density readings were statistically analysed by logistic regression (LR) to evaluate the sensitivity (Se) and specificity (Sp) of the test according to two criteria: known vaccination status or classification according to the test interpretation guidelines. ROC curves were designed for each model.
Results and discussion
The Se and Sp for detection of seroconversion after vaccination following the guidelines of the test were 52.6% and 100% resp. whereas they were 100% and 100% when the test recommended threshold limit (0.294) was corrected to 0.100 according to our LR model.
As a consequence, the area under the curve (AUC) changed from 0.763 to 1.0. Furthermore, our data indicate the variance increased according to the number of vaccinations received: nil, 2 or >2, indicating the need to take parity into consideration for a correct interpretation of test results.
Erysipelas serological tests have been developped to evaluate infection. According to our results, it is advisable to reconsider the threshold of positivity recommended for this test in order to maximize its sensitivity and specificity for compliance purposes.
Presented at the 2015 European Symposium of Porcine Health Management