Pan-Serotype Diagnostic for Foot-and-Mouth Disease Using the Consensus Antigen of Nonstructural Protein 3B

Development of a competitive chemiluminescence immunoassay using a monoclonal antibody recognizing 3B of foot-and-mouth disease virus for the rapid detection of antibodies induced by FMDV infection

Background

Foot-and-mouth disease (FMD) is a devastating animal disease. Anti-non-structural protein (NSP) antibody detection is very important for confirming suspected cases, evaluating the prevalence of infection, certifying animals for trade and controlling the disease.

Methods

In this study, a competitive chemiluminescence immunoassay (3B-cCLIA) was developed for the rapid detection of antibodies against NSPs in different species of livestock animals using the monoclonal antibody (mAb) 9E2 as a competitive antibody that recognizes NSP 3B.

Results

The cut-off value (50%), diagnostic sensitivity (Dsn) (97.20%, 95.71%, and 96.15%) and diagnostic specificity (Dsp) (99.51%, 99.43%, and 98.36) of the assay were estimated by testing a panel of known-background sera from swine, cattle and sheep, respectively. The accuracy rate of the 3B-cCLIA was further validated and subsequently compared with that of two commercial diagnostic kits. The early diagnostic results showed that antibodies recognizing NSPs developed later (approximately 1–2 days) than antibodies recognizing structural proteins. Furthermore, anti-NSP antibody presence in animals vaccinated multiple times (false positives), especially cattle and sheep, was confirmed, and the false-positive rate increased with the number of vaccinations.

Conclusions

These results indicate that the 3B-cCLIA is suitable for the rapid detection of antibodies against FMDV NSP 3B in a wide range of species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-021-01663-4.

Identification of three linear B cell epitopes against non-structural protein 3ABC of FMDV using monoclonal antibodies

Foot-and-mouth disease virus (FMDV) has led to serious losses in the farming industry worldwide, particularly in cattle and swine. In developing countries, the control and eradication of FMD rely upon vaccination, in which the inactivated vaccine is predominant. In the preparation of inactivated vaccine, a series of purification methods were used to remove non-structural proteins (NSPs). It is necessary to develop a quantitative detection method of residual NSP and confirm a threshold value for the evaluation of the vaccine. Meanwhile, it is also important to develop a sensitive and rapid diagnostic method to distinguish infected animals from vaccinated animals (DIVA). In this study, three monoclonal antibodies (MAbs) against NSP 3ABC, designated 2G5, 9E2, and 1E10, were used. Subsequently, a series of overlapping peptides were expressed using a prokaryotic expression system to determine the minimal epitopes identified by the MAbs. Three linear B cell epitopes (BCEs), "⁹²EYIEKA⁹⁷" "²³EGPYAGPLE³¹" and "²⁰⁹EPHH²¹²", were identified by MAbs 2G5, 9E2, and 1E10, respectively. Alanine-scanning mutagenesis analysis confirmed the critical amino acid in these epitopes. The epitope "⁹²EYIEKA⁹⁷" is located in 3A, which is deleted in some natural deletion mutants that result in a change in virus tropism. MAb 9E2 that identified the epitope "²³EGPYAGPLE³¹" reacted with 3B1 and 3B2, but did not react with 3B3. In combination with sequence alignment analysis, the epitope "²³EGPYAGPLE³¹" is highly conserved among different FMDV isolates. Preliminary screening using the known positive and negative sera indicated the MAb 9E2 has the potential for the development of a diagnostic method for DIVA. The residual NSP in inactivated vaccines can be detected using 9E2-HRP, which indicated the MAb 9E2 is able to evaluate inactivated vaccines. The four-amino acid epitope is the first reported to date that is recognized by 1E10. These results provide valuable insight into the diagnosis of DIVA and the NSP residual evaluation in inactivated vaccines.

Recombinant occlusion bodies of baculovirus as carriers of a non-structural protein of foot-and-mouth disease virus

Here, we developed a diagnostic ELISA for foot-and-mouth disease using recombinant occlusion bodies (rOBs) of baculovirus. We fused Δ3AB_1-3, a polypeptide derived from non-structural proteins of foot-and-mouth disease virus, to polyhedrin (POLH), the major constituent of OBs, under polh promoter. To further assess the most convenient strategy to improve yields, we designed two recombinant baculoviruses, vPOLH and vPOLH_E44G. These carried the sequence of the fusion protein POLH-Δ3AB_1-3 with an additional copy in cis of polh or polh _E44G , respectively, under p10 promoter. Our results show that both viruses expressed POLH-Δ3AB_1-3, which was detected by western blot in purified rOBs with anti-POLH and anti-3AB1 antibodies. We also found that vPOLH_E44G produced larger polyhedra and a significant increase of antigen yield (p < 0.01). Furthermore, the chimeric protein POLH-Δ3AB_1-3 was recognized by sera from experimentally infected animals, showing that translational fusion to POLH does not alter the antigenicity of Δ3AB_1-3. Finally, the rOBs were successfully used in an ELISA test to differentiate infected from vaccinated animals. Taken together, these results demonstrate the great potential of rOBs to develop diagnostic schemes adaptable to animal infectious diseases.

An improved, rapid competitive ELISA using a novel conserved 3B epitope for the detection of serum antibodies to foot-and-mouth disease virus

The highly contagious foot-and-mouth disease virus (FMDV) afflicts cloven-hoofed animals, resulting in significant costs because of loss of trade and recovery from disease. We developed a sensitive, specific, and rapid competitive ELISA (cELISA) to detect serum antibodies to FMDV. The cELISA utilized a monoclonal blocking antibody specific for a highly conserved FMDV nonstructural 3B epitope, a recombinant mutant FMDV 3ABC coating protein, and optimized format variables including serum incubation for 90 min at 20-25°C. Samples from 16 animals experimentally infected with one FMDV serotype (A, O, Asia, or SAT-1) demonstrated early detection capacity beginning 7 d post-inoculation. All samples from 55 vesicular stomatitis virus antibody-positive cattle and 44 samples from cloven-hoofed animals affected by non-FMD vesicular diseases were negative in the cELISA, demonstrating 100% analytical specificity. The diagnostic sensitivity was 100% against sera from 128 cattle infected with isolates of all FMDV serotypes, emphasizing serotype-agnostic results. Diagnostic specificities of U.S. cattle ( n = 1135) and swine ( n = 207) sera were 99.4% and 100%, respectively. High repeatability and reproducibility were demonstrated with 3.1% coefficient of variation in percent inhibition data and 100% agreement using 2 kit lots and 400 negative control serum samples, with no difference between bench and biosafety cabinet operation. Negative results from vaccinated, uninfected cattle, pig, and sheep sera confirmed the DIVA (differentiate infected from vaccinated animals) capability. This rapid (<3 h), select agent-free assay with high sensitivity and specificity, DIVA capability, and room temperature processing capability will serve as a useful tool in FMDV surveillance, emergency preparedness, response, and outbreak recovery programs.

Development of a chemiluminescence immunoassay using recombinant non-structural epitope-based proteins to accurately differentiate foot-and-mouth disease virus-infected and vaccinated bovines

The contamination of inactivated vaccine with non-structural proteins (NSPs) leads to a high false-positive rate, which is a substantial barrier to accurately differentiate foot-and-mouth disease virus (FMDV)-infected animals from vaccinated animals. To address this problem, a new chemiluminescence immunoassay (CLIA) method was developed to detect antibodies targeting the two recombinant epitope-based proteins located in 3A and 3B. The 3Aepitp-3Bepitp CLIA exhibited a diagnostic sensitivity of 94.0% and a diagnostic specificity of 97.5% for the detection of serum samples (naïve bovines, n = 52, vaccinated bovines, n = 422, infected bovines, n = 116) from animals with known status. The CLIA method also had a concordance rate of 88.1% with the PrioCHECK FMDV NSP ELISA based on the detection of 270 serum samples from the field. Importantly, the 3Aepitp-3Bepitp CLIA produced no false-positives when used to detect FMDV in samples from bovines that had been vaccinated up to five times, and it was demonstrated a low false-positive rate when the bovines had been vaccinated up to ten (2.15%) and fifteen times (5.93%). Therefore, the 3Aepitp-3Bepitp CLIA detects FMDV in samples from frequently vaccinated bovines with high accuracy and represents an alternative method to differentiate FMDV-infected and vaccinated bovines.

Development of an Enzyme-Linked Immunosorbent Assay Based on Fusion VP2332-452 Antigen for Detecting Antibodies against Aleutian Mink Disease Virus

For detection of Aleutian mink disease virus (AMDV) antibodies, an enzyme-linked immunosorbent assay (ELISA) was developed using the recombinant VP2332-452 protein as an antigen. Counterimmunoelectrophoresis (CIEP) was used as a reference test to compare the results of the ELISA and Western blotting (WB); the specificity and sensitivity of the VP2332-452 ELISA were 97.9% and 97.3%, respectively, which were higher than those of WB. Therefore, this VP2332-452 ELISA may be a preferable method for detecting antibodies against AMDV.