Improvement Porcine Parvovirus (PPV) ELISA Test Reliability04 September 2015
Porcine Parvovirus (PPV) vaccines have been widely used in the field to prevent PPV induced reproductive problems since the early 80’s with a high level of satisfaction. However, the pattern of seroconversion after vaccination is often lower and more irregular than after field virus infection, write A. Callen, I. Lazaro and S. Carceles, Merial.
Indeed, it may eventually cause some concern about the level of protection induced by vaccination in spite of the lack of correlation between the test results and the degree of protection (Edwards et al. 1986 Efficacy of porcine parvovirus vaccines, Vet. Rec., 119, 203-205).
Moreover, farmers and vets usually check sera from vaccinated animals for antibodies in order to test vaccination compliance or immunological response.
Therefore, the aim of this trial was to assess the serological response to PARVORUVAX® with a commercial 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 their age and their vaccination status in three groups: 10 randomly selected unvaccinated gilts 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 (twice as gilt and every lactation).
Blood samples were taken and tested for PPV antibodies by an indirect ELISA (Ingezim PPV, Ingenasa).
The optical density readings were statistically analysed by logistic regression 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. Receiver Operating Characteristic curves were designed for each model.
Results and discussion
The Se and Sp following the guidelines of the test were 47% and 100% respectively. whereas they were 94.7% and 100% when the threshold limit was corrected to 0.100 instead of 0.300 according to our logistic regression model.
As a consequence the area under the curve changed from 0.763 to 0.989. Furthermore, our data indicate heteroscedasticity because 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.
PPV serological tests have been developed to evaluate infection. According to our results, when using serological tests to evaluate PPV vaccination compliance, it is advisable to reconsider the threshold of positivity recommended for this test in order to maximize its sensitivity and specificity.
Presented at the 2015 European Symposium of Porcine Health Management