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Vaccination has been one of the most important interventions in disease prevention and control. The impact of vaccination largely depends on the quality and suitability of the chosen vaccine. To determine the suitability of a vaccine strain, antigenic matching is usually studied by in vitro analysis. In this study, we performed three in vitro test methods to determine which one gives the lowest variability and the highest discriminatory capacity. Binary ethylenimine inactivated vaccines, prepared from 10 different foot-and-mouth disease (FMD) virus serotype A strains, were used to vaccinate cattle (5 animals for each strain). The antibody titers in blood serum samples 3 weeks postvaccination (w.p.v.) were determined by a virus neutralization test, neutralization index test, and liquid-phase blocking enzyme-linked immunosorbent assay (ELISA). The titers were then used to calculate relationship coefficient (r 1 ) values. These r 1 values were compared to the genetic lineage using receiver operating characteristic (ROC) analysis. In the two neutralization test methods, the median titers observed against the test strains differed considerably, and the sera of the vaccinated animals did not always show the highest titers against their respective homologous virus strains. When the titers were corrected for test strain effect (scaling), the variability (standard error of the mean per vaccinated group) increased because the results were on a different scale, but the discriminatory capacity improved. An ROC analysis of the r 1 value calculated on both observed and scaled titers showed that only r 1 values of the liquid-phase blocking ELISA gave a consistent statistically significant result. Under the conditions of the present study, the liquid-phase blocking ELISA showed less variation and still had a higher discriminatory capacity than the other tests.

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Isotype specific ELISAs to detect antibodies against swine vesicular disease, which may help to estimate the moment of infection, were developed and validated on sera from pigs experimentally infected with four different isolates of swine vesicular disease virus. Virus specific IgM antibodies could be detected from days 3–49 and occasionally up to day 91 after infection. IgG1 antibodies were first detected at day 8 and IgG2 at day 11. IgA antibodies coincided with IgG1 antibodies, but antibody titres varied widely. From the results obtained with the sera from the experimentally infected pigs, we calculated the day at which 50% of the pigs had become positive (D50). A D50 of 5, 4, 12, 12 and 24 days was calculated, respectively, for the appearance of antibodies in the virus neutralization test, the IgM, total IgG, IgG1 and IgG2 ELISA. A D50 of 49 days was calculated for the disappearance of IgM antibodies. The isotype specific ELISAs proved to be valuable tools to study the epidemiology of the disease.