Development of an epitope-blocking-enzyme-linked immunosorbent assay to differentiate between animals infected with and vaccinated against foot-and-mouth disease virus.

An epitope-blocking ELISA (EB-ELISA) was developed to distinguish animals infected with foot-and-mouth-disease (FMDV) from those immunized with commercial vaccines. The assay used monoclonal antibodies to target the 3B core repeat motif (QKPLK) and purified recombinant 3AB proteins from the major B cell line epitopes of FMDV. Sera from uninfected and regularly vaccinated cattle, pigs, goats, and sheep (raised in FMDV free areas) were screened to evaluate the specificity of the EB-ELISA. The specificity scores of the assays were 99.8-100% and 100%, respectively. Reference sera from cattle, pigs, goats, and sheep experimentally infected with FMDV tested positive, with only a single exception. Antibodies formed in response to FMDV 3B appeared 1 week after infection and persisted at high levels for more than 8 weeks within the sera collected from serial bleeding of animals infected with FMDV O/SKR/2000. The EB-ELISA was used to differentiate between farms vaccinated against and those infected with FMDV (FMDV Asia serotype) during the 2005 epidemic in Mongolia by detecting antibodies against the FMDV Asia serotype in outbreak farms. This EB-ELISA method shows promise as an effective tool for FMDV control and eradication.