Foot-and-mouth disease virus-infected but not vaccinated cattle develop antibodies against recombinant 3AB1 nonstructural protein

Foot-and-mouth disease (FMD) vaccines induce antibodies against structural and some nonstructural proteins present in vaccine preparations. To differentiate between FMDV-infected and vaccinated animals, we developed immunochemical assays capable of detecting antibodies against a FMDV nonstructural protein. Recombinant nonstructural 3AB1 protein was expressed in E. coli and in insect cells and used to detect anti-3AB1 antibodies. ELISA and Western blot analysis showed that sera fi-om cattle infected with FMDV reacted with recombinant 3AB1 protein whereas sera from cattle which had been vaccinated against FMDV, mock-infected, or infected with different bovine viruses did not recognize the 3AB1 protein. In contrast, anti-virus infection associated antigen (VIAA) antibodies were present in both FMDV-infected and vaccinated animals. Detection of anti-3AB1 antibodies in sera of experimentally infected cattle obtained between 7 and 560 days postinfection indicated that immunological tests based on the detection of recombinant 3AB1 protein could be used for the diagnosis of FMDV infection.