Comparative evaluation of serological assays for detecting antibodies against structural proteins elicited by foot-and-mouth disease virus vaccines of serotypes O, A, Asia 1 and SAT 2.

Vaccination is the most effective strategy to control and prevent foot-and-mouth disease (FMD). Its effectiveness may be influenced by factors like vaccine formulation, vaccine potency, vaccination strategies, and by circulating variants, which may lead to changes in vaccine requirements and in their control. Serological assays detecting antibodies against structural proteins, such as virus neutralization test (VNT) and structural-protein ELISAs, are widely used to monitor vaccine effectiveness. In overall, serotype-specific tests are required, which should include antigens capable of detecting all variants within a given serotype, particularly those included in the vaccines. This study evaluates the performance of four commercial ELISA kits to detect FMD virus-specific antibody responses in vaccinated cattle and pigs. ELISA results were compared to VNT considered the reference standard. A total of 417 cattle and 189 pig serum samples from animals vaccinated with various formulations, containing O1 Campos, A24 Cruzeiro, A2001, Asia 1 2015 and SAT 2 2015 strains, were analyzed, along with 50 bovine and 47 pig sera from unvaccinated animals. Analysis of 4170 assays revealed varying ELISA sensitivities across different test formats, influenced by both host species and serotype. Kits demonstrating satisfactory performance and strong correlation with VNT, as measured by Cohen´s kappa coefficient, were identified as potential alternatives to VNT. As expected, tests with antigens homologous to the vaccine strain demonstrated almost perfect agreement with VNT. Nevertheless, some kits which use heterologous, or presumably heterologous, antigens also exhibited very good performances, with kappa values indicating almost perfect to substantial agreement with VNT. All assays showed high specificity, opening the possibility of improving the performance of low-sensitivity kits by adjusting cutoff values. It is highlighted the relevance of using kits with proper validation to ensure the ability to recognize antibodies generated by the vaccines in use.