Validation of a screening liquid phase blocking ELISA for swine vesicular disease.

A direct liquid-phase blocking ELISA (LPBE) was developed for serological examination of swine vesicular disease (SVD). The sensitivity and specificity of the test were assessed on 272 and 365 sera collected on two farms where an outbreak had occurred. The specificity of the direct LPBE was higher than the specificity of the indirect LPBE. The European Community reference serum for SVD (RS 01-04-93), which has been adopted as the threshold for SVD serological examination in the European Community, had a mean titre of 2.19 in the neutralisation test. At a cut-off level of 2.0 in the neutralisation test, the sensitivity of the direct LPBE (screening at 1:432 final dilution) on the two farms was 90% and 99%, respectively. Based on these results, the screening dilution of the direct LPBE was adjusted to 1:160 final dilution, to obtain a sensitivity > or = 98% on both farms. Regression analyses showed a good correlation between the virus neutralisation test and the direct LPBE (r = 0.87). Compared to the indirect LPBE described before, the direct LPBE correlates better with the neutralisation test, has a higher specificity, and is more rapid. Because sera are tested in only one dilution, the test is highly suitable for the examination of large numbers of serum samples.