Diagnostic application of recombinant non-structural protein 3A to detect antibodies induced by foot-and-mouth disease virus infection

• A recombinant non-structural protein (NSP) 3A (r3A) of FMDV was expressed in E. coli.
• r3A used as an antigen in I-ELISA for detection of FMD infection specific antibodies.
• The diagnostic sensitivity and specificity of 3A indirect-ELISA (I-ELISA) were found to be 95.7% and 96.3%, respectively.
• The performance of the 3A I-ELISA was comparable to that of the earlier validated 3AB3 I-ELISA.

Detection of antibodies to the non-structural proteins (NSPs) of FMD virus (FMDV) is the preferred differential diagnostic method for identification of FMD-infected animals in the vaccinated population. Nevertheless, due to the observed variability in the antibody response to NSPs, the likelihood of screening or confirming the FMD infection status in animals is increased if an antibody profile to multiple NSPs is considered for diagnosis. In order to develop and evaluate an additional NSP-based diagnostic assay, in this study, the recombinant 3A protein of FMDV was expressed in Escherichia coli and used as an antigen for detection of FMD infection specific antibodies. At the fixed cut-off value of 45 percentage of positivity, the diagnostic sensitivity and specificity of 3A indirect-ELISA (I-ELISA) were found to be 95.7% and 96.3%, respectively. In FMD naturally infected cattle, about 85% of clinically infected and 75% of asymptomatic in-contact populations were found positive at 13 months post-outbreak. The 3A I-ELISA was further evaluated with the bovine serum samples collected randomly from different parts of the country. Furthermore, the performance of newly developed 3A I-ELISA was compared with the extensively used in-house r3AB3 I-ELISA, and the overall concordance in test results was found to be 93.62%. The r3A I-ELISA could be useful as a screening or confirmatory assay in the sero-surveillance of FMD in India irrespective of extensive bi-annual vaccination.